essay on ocean currents

Ocean Currents Map

Why are ocean currents important, types of ocean currents.

Ocean currents are driven by a variety of factors, including tides, winds, and changes in water density. These factors work together to create a complex system that has a significant impact on our weather, marine travel, and oceanic ecosystems. Tides, which are caused by the gravitational pull of the moon and the sun, play a role in driving ocean currents. The rising and falling of tides create a rhythmic movement of water, contributing to the flow of currents. Winds also have a strong influence on ocean currents. Global wind systems, driven by the uneven heating of the Earth's surface, transfer heat from the tropics to the polar regions. This heat transfer creates pressure differences in the atmosphere, which in turn generate winds. These winds, known as surface winds, push the surface waters of the ocean, creating surface currents. In addition to tides and winds, changes in water density contribute to the formation of ocean currents. Variations in temperature and salinity, both of which affect water density, play a crucial role. This process, known as thermohaline circulation, drives deep ocean currents. In cold regions like the North Atlantic Ocean, differences in water density caused by variations in temperature and salinity are particularly important. It is important to note that ocean currents are not solely influenced by abiotic factors. Biological factors also come into play. The distribution of food and nutrients in the ocean can be influenced by ocean currents, which in turn affects marine ecosystems. In conclusion, the driving forces behind ocean currents are diverse and interconnected. Tides, winds, and changes in water density all contribute to the complex system of currents that shape our planet's climate system and support marine ecosystems.

Surface Currents

Deep ocean currents, tidal currents.

Ocean Currents Map PDF

The Great Pacific Garbage Patch

This collection of litter (composed mostly of tiny pieces of plastic) is located in the north pacific. the trash is collecting in the calm center of the north pacific subtropical gyre. a gyre is a large system of swirling ocean currents. the north pacific subtropical gyre is made of four separate currents: the california current, the north equatorial current, the kuroshio current, and the north pacific current. these four currents are moving large amounts of trash towards the great pacific garbage patch — helping it grow ever larger., to understand ocean currents, it's best to start with understanding the waves. and how it plays a large role in creating energy..

The five major oceans wide gyres are the North Atlantic, South Atlantic North Pacific South Pacific, Indian Ocean, Ocean gyres and world map pacific of plastic pollution. The currents we see at the beach are called coastal currents that can affect land and wave formations. Currents travel around 5.6 miles per hour in warmer waters of the northern hemisphere and in the North Pacific moves much slower in cold water at 0.03 to 0.06 miles per hour.

Connected One World Ocean

Currents & marine organisms.

Ocean currents exist both on and below the surface. Some currents are local to specific areas, while others are global. And they move a lot of water. The largest current in the world, the Antarctic Circumpolar Current, is estimated to be 100 times larger than all the water flowing in all the world’s rivers! All of this moving water helps more stationary species get the food and nutrients they need. Instead of going looking for food, these creatures wait for the currents to bring a fresh supply to them. Currents also play a major role in reproduction. The currents spread larvae and other reproductive cells. Without currents many of the ocean’s ecosystems would collapse.

What Can You Do?

Cleaning up the Great Pacific Garbage Patch is a challenge. It is not close to any coastline, which means no one country or organization has stepped up to take responsibility for its cleanup. However, many ocean conservation organizations, such as Ocean Blue Project, one of the best Ocean cleanup organizations removing 1 million pounds of plastic by 2025. Help save our blue economy by making a one time donation to help remove plastic pollution from a beach near you.  

The best way to support this effort — reduce your use of single-use plastics. If less plastic is being used, then less of it will end up in our oceans.

What are the Five Oceans of the World?

"the five bodies of water and the global ocean produces more then half oxygen humans breath.", historically the ocean was thought of having 4 oceans the pacific, atlantic, indian, and arctic. today we have five bodies of water and our one world ocean or five oceans aka ocean 5, and two seas covering over 71 percent of the earths surface and over 97 percent of the earth’s water. only 1% of earths water is freshwater and percent or two is part of our ice glaciers. with sea level rise just think of our ice melting and how a percent of earth would so be under water. the oceans of the world host over 230,000 marine animals species and more could be discovered as humans learn ways to explore the deepest sections of the ocean. we all share the same ocean our one world ocean, learn more about how we can protect the microplastics that are harming fish and how we can support the ocean cleanup..

The Southern Ocean also known as the antarctic area.

The Antarctic ocean is the smallest of our oceans and the fourth largest and is full of wildlife and mountains of ice lastly throughout the year. Although this area is so cold humans have managed to live here. One of the largest setbacks is with global warming most of the ice mountains is expected to melt by 2040. The depth of The Antarctic Ocean is 23,740′ in depth. The Southern Ocean also known as the Antarctic Area: 7.849 million mi².  How many people live in the Antarctic? No humans  live in Antarctica  permanently, but around 1,000 to 5,000  people live  through the year at the science stations in  Antarctica . The only plants and animals that can  live  in cold  live  there. The animals include penguins, seals, nematodes, tardigrades and mites.

Fun facts: Between Africa and Austral

Indian Ocean is located between Africa and Austral-Asia and the Southern Ocean. is the third largest of our oceans and covers a fifth ( 20%) of our earths surface. Until the mid 1800s the Indian Ocean was called the Eastern Oceans. The Indian Ocean is around 5.5 times the size of United States and is a warm body of water depending on the Ocean Currents of the Equator to help stabilize the temperatures. 

Atlantic Ocean ​boards North America, Africa, South America, and Europe. This Ocean is the second largest of our five oceans and home of the largest islands in the world. The Atlantic Ocean covers 1/5 of the earths surface and 29% of the waters surface area.

The  Atlantic Ocean  ranks the second for the most  dangerous ocean  waters in the world. This  ocean  water is usually affected by coastal winds, temperature of the water surface currents maps. 

6 Types of Plants That Live in the Atlantic Ocean

• Kelp. Kelp grows in cold coastal waters. …
• Seagrass. …
• Red Algae. …
• Coral and Algae. …
• Coralline Algae.

Pacific Ocean Temperatures or conditions are split:  cold  in east, and warmer in west. In Oregon the body of water is average 54 degrees. Winter has huge Oregon King Tides leaving the norther waters super rough seas. 

Fun Facts For Youth: Atolls are in the warmer conditions of the Pacific Ocean and are the Coral Sea Islands West of the Barrier Reef in Australia. Atolls are only found in the warm ocean waters, located in the southern water bodies of our ocean. 

Ocean Plastic The Pacific Ocean is also the home for the most  micro plastics  floating in our oceans. The plastic are caused by humans littering by accident or just littering. Plastic pollution makes its way to the ocean in many directions by getting into street drains, rivers, blowing in the wind, or from fishing boats. learn about how some animals help lower plastic pollution.

6 Types of Plants That Live in the Pacific Ocean

• Kelp. Kelp grows in cold coastal water bodies.
• Coral and Algae
• Coralline Algae

How do Ocean Currents affect Climate

Ocean currents move warm and cold water, to polar regions and tropical regions influencing both weather and climate and changing the regions temperatures. Learn more about Ocean Blue nonprofit working to remove plastic from our Ocean. 

Ocean currents, also known as continuous and directed movements of ocean water, play a crucial role in shaping our climate, local ecosystems, and even the seafood we enjoy.

These currents are a result of various factors, including tides, winds, and changes in the water’s density. They can be categorized into two types: surface currents and deep ocean currents, which together create a complex system with far-reaching effects on our environment. Surface currents, influenced by tides and winds, occur on the ocean’s surface and have a significant impact on weather patterns and marine travel.

Prevailing Winds – Wind Currents of The World

They can create favorable conditions for sailing or hinder maritime transportation, influencing trade routes and travel times.

These currents also have a direct influence on coastal ecosystems, affecting the distribution of nutrients and the migration patterns of marine species.

What Causes Deep Ocean Currents

Deep ocean currents, on the other hand, are driven by changes in water density, caused by variations in temperature and salinity. These currents flow in the depths of the ocean, and their slow but steady movement plays a critical role in regulating Earth’s climate.

They help distribute heat around the globe, influencing regional and global temperature patterns. Deep ocean currents also play a crucial role in the transport of nutrients and oxygen to deep-sea ecosystems, supporting a diverse array of marine life. It is important to note that ocean currents are not solely influenced by natural factors.

Coastal and sea floor features, such as underwater mountains or canyons, can alter the direction, speed, and location of these currents.

Additionally, the Coriolis effect, a result of Earth’s rotation, also contributes to the complex movement of ocean currents. In summary, ocean currents are dynamic and intricate systems that are driven by tides, winds, water density, and influenced by coastal and sea floor features.

How Does The Ocean Affect Climate and Weather on Land

Their impact extends beyond the surface of the ocean, affecting weather patterns, marine travel, and the delicate balance of marine ecosystems. Understanding these currents is crucial for comprehending the interconnectedness of our planet’s climate and ecosystems.

Why Is The Ocean Blue

Clean water is blue because water absorbs and reflects the blue sky as light bounces red light, red orange yellow, light spectrum of reflections of light as a significant to lowering sediments as for taking care of our wild rivers protective sediments runoff destroying our ocean., clean water is blue because water absorbs and reflects the blue sky as light bounces red light, red orange yellow, light spectrum of reflections of light as a significant to lowering sediments as for taking care of our wild rivers protective sediments runoff destroying our ocean. ocean blue feels beach cleanups conjointly facilitate the long wavelength of the blue color by lowering floating ocean plastics have to be compelled to facilitate keep our ocean blue by protecting clean water. because the ocean absorbs the red yellowness wavelength of light as the aspect of the white lightweight you’ll usually see a glimpse of reminder red etc once viewing the blue ocean reflections we tend to see most frequently. the blue color lower floating sediments that may lower the short wavelengths of lightweight of sunshine spectrum that permits our ocean blue wavelengths reflections of sunshine to be the blue light color. therefore removing plastic floating in our ocean helps permit blue ocean water and our water molecules of safe of blue water., ways to contribute to the ocean.

Ocean Activities for Kindergarten to 2nd Grade

Save the Whales Graphic Hoody

Save the Whale Graphic T-Shirt

Save The Ocean Shirt Microplastics Bird T-shirt (Unisex)

Eco Friendly Reusable Water Bottle

Ocean Themed Clothing Save The Ocean Birds Shirt (Unisex)

Seastar Save The Ocean T-Shirt (Unisex)

Sea the Change Microplastic Turtle Graphic T-Shirt (Unisex)

Marine Biology for Kids Science Kit — Marine Science Ocean Debris STEM Kit

Pride for the Ocean Trucker Hat

Ocean Blue Logo Trucker Hat (Adult)

STEM Activities for Preschoolers

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Ocean water is on the move, affecting your climate, your local ecosystem, and the seafood that you eat. Ocean currents , abiotic features of the environment, are continuous and directed movements of ocean water. These currents are on the ocean’s surface and in its depths, flowing both locally and globally.

Map of temperature of the North Atlantic Ocean shows the warm Gulf Stream current along the East Coast of the United States transporting heat northward towards the cooler high latitudes. (Image credit: NOAA)

Winds, water density, and tides all drive ocean currents. Coastal and sea floor features influence their location, direction, and speed. Earth’s rotation results in the Coriolis effect which also influences ocean currents. Similar to a person trying to walk in a straight line across a spinning merry-go-round, winds and ocean waters get deflected from a straight line path as they travel across the rotating Earth. This phenomenon causes ocean currents in the Northern Hemisphere to veer to the right and in the Southern Hemisphere to the left.

Drifters, buoys, Argo floats and more help scientists monitor the global ocean, including areas that are difficult to travel to via research ship.

Surface currents

Differences in water density, resulting from the variability of water temperature ( thermo ) and salinity ( haline ), also cause ocean currents. This process is known as thermohaline circulation. In cold regions, such as the North Atlantic Ocean, ocean water loses heat to the atmosphere and becomes cold and dense. When ocean water freezes, forming sea ice, salt is left behind causing surrounding seawater to become saltier and denser. Dense-cold-salty water sinks to the ocean bottom. Surface water flows in to replace the sinking water, which in turn becomes cold and salty enough to sink. This "starts" the  global conveyer belt , a connected system of deep and surface currents that circulate around the globe on a 1000 year time span. This global set of ocean currents is a critical part of Earth’s climate system as well as the ocean nutrient and carbon dioxide cycles.

Biological influence

Ocean currents are an important abiotic factor that significantly influences food webs and reproduction of marine organisms and the marine ecosystems that they inhabit. Many species with limited mobility are dependent on this "liquid wind" to bring food and nutrients to them and to distribute larvae and reproductive cells. Even fish and mammals living in the ocean may have their destinations and food supply affected by currents.

Upwelling currents bring cold nutrient-rich waters from the ocean bottom to the surface, supporting many of the most important fisheries and ecosystems in the world. These currents support the growth of phytoplankton and seaweed which provide the energy base for consumers higher in the food chain, including fish, marine mammals, and humans.

EDUCATION CONNECTION

Educators can use ocean currents to help students learn and appreciate the interaction of Earth's systems and how scientists study these processes with drifting buoys,  sound monitors , and other methods. The lesson plans, labs, and other resources in this collection can help students understand how distant abiotic factors, such as water density, Earth’s rotation, and ocean currents can impact local climate and biomes, the beaches we visit, and the seafood that we eat.

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8.4: Ocean Currents

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Ocean water is constantly in motion (Figure 14.7). From north to south, east to west, and up and down the shore, ocean water moves all over the place. These movements can be explained as the result of many separate forces, including local conditions of wind, water, the position of the moon and Sun, the rotation of the Earth, and the position of land formations.

Figure 14.7 : Ocean waves transfer energy through the water over great distances.

Lesson Objectives

• Describe how surface currents form and how they affect the world’s climate.
• Describe the causes of deep currents.
• Relate upwelling areas to their impact on the food chain.

Surface Currents

Wind that blows over the ocean water creates waves. It also creates surface currents , which are horizontal streams of water that can flow for thousands of kilometers and can reach depths of hundreds of meters. Surface currents are an important factor in the ocean because they are a major factor in determining climate around the globe.

Causes of Surface Currents

Currents on the surface are determined by three major factors: the major overall global wind patterns, the rotation of the Earth, and the shape of ocean basins.

When you blow across a cup of hot chocolate, you create tiny ripples on its surface that continue to move after you’ve stopped blowing. The ripples in the cup are tiny waves, just like the waves that wind forms on the ocean surface. The movement of hot chocolate throughout the cup forms a stream or current, just as oceanic water moves when wind blows across it.

But what makes the wind start to blow? When sunshine heats up air, the air expands, which means the density of the air decreases and it becomes lighter. Like a balloon, the light warm air floats upward, leaving a slight vacuum below, which pulls in cooler, denser air from the sides. The cooler air coming into the space left by the warm air is wind.

Because the Earth’s equator is warmed by the most direct rays of the Sun, air at the equator is hotter than air further north or south. This hotter air rises up at the equator and as colder air moves in to take its place, winds begin to blow and push the ocean into waves and currents.

Wind is not the only factor that affects ocean currents. The ‘Coriolis Effect’ describes how Earth’s rotation steers winds and surface currents (Figure 14.14). The Earth is a sphere that spins on its axis in a counterclockwise direction when seen from the North Pole. The further towards one of the poles you move from the equator, the shorter the distance around the Earth. This means that objects on the equator move faster than objects further from the equator. While wind or an ocean current moves, the Earth is spinning underneath it. As a result, an object moving north or south along the Earth will appear to move in a curve, instead of in a straight line. Wind or water that travels toward the poles from the equator is deflected to the east, while wind or water that travels toward the equator from the poles gets bent to the west. The Coriolis Effect bends the direction of surface currents.

The third major factor that determines the direction of surface currents is the shape of ocean basins (Figure 14.15). When a surface current collides with land, it changes the direction of the currents. Imagine pushing the water in a bathtub towards the end of the tub. When the water reaches the edge, it has to change direction.

Figure 14.15 : This map shows the major surface currents at sea. Currents are created by wind, and their directions are determined by the Coriolis effect and the shape of ocean basins.

Effect on Global Climate

Surface currents play a large role in determining climate. These currents bring warm water from the equator to cooler parts of the ocean; they transfer heat energy. Let’s take the Gulf Stream as an example; you can find the Gulf Stream in the North Atlantic Ocean in Figure 14.15. The Gulf Stream is an ocean current that transports warm water from the equator past the east coast of North America and across the Atlantic to Europe. The volume of water it transports is more than 25 times that of all of the rivers in the world combined, and the energy it transfers is more than 100 times the world’s energy demand. It is about 160 kilometers wide and about a kilometer deep. The Gulf Stream’s warm waters give Europe a much warmer climate than other places at the same latitude. If the Gulf Stream were severely disrupted, temperatures would plunge in Europe.

Deep Currents

Surface currents occur close to the surface of the ocean and mostly affect the photic zone. Deep within the ocean, equally important currents exist that are called deep currents . These currents are not created by wind, but instead by differences in density of masses of water. Density is the amount of mass in a given volume. For example, if you take two full one liter bottles of liquid, one might weigh more, that is it would have greater mass than the other. Because the bottles are both of equal volume, the liquid in the heavier bottle is denser. If you put the two liquids together, the one with greater density would sink and the one with lower density would rise.

Two major factors determine the density of ocean water: salinity (the amount of salt dissolved in the water) and temperature (Figure 14.16). The more salt that is dissolved in the water, the greater its density will be. Temperature also affects density: the colder the temperature, the greater the density. This is because temperature affects volume but not mass. Colder water takes up less space than warmer water (except when it freezes). So, cold water has greater density than warm water.

Figure 14.16 : Thermohaline currents are created by differences in density due to temperature (thermo) and salinity (haline). The blue arrows are deep currents and the red ones are surface currents.

Figure 14.17 : Surface and deep currents together form convection currents that circulate water from one place to another and back again. A water particle in the convection cycle can take 1600 years to complete the cycle.

More dense water masses will sink towards the ocean floor. Just like convection in air, when denser water sinks, its space is filled by less dense water moving in. This creates convection currents that move enormous amounts of water in the depths of the ocean. Why is the water temperature cooler in some places? Water cools as it moves from the equator to the poles via surface currents. Cooler water is more dense so it begins to sink. As a result, the surface currents and the deep currents are linked. Wind causes surface currents to transport water around the oceans, while density differences cause deep currents to return that water back around the globe (Figure 14.17).

As you have seen, water that has greater density usually sinks to the bottom. However, in the right conditions, this process can be reversed. Denser water from the deep ocean can come up to the surface in an upwelling (Figure 14.18). Generally, an upwelling occurs along the coast when wind blows water strongly away from the shore. As the surface water is blown away from the shore, colder water from below comes up to take its place. This is an important process in places like California, South America, South Africa, and the Arabian Sea because the nutrients brought up from the deep ocean water support the growth of plankton which, in turn, supports other members in the ecosystem. Upwelling also takes place along the equator between the North and South Equatorial Currents.

Figure 14.18 : An upwelling forces denser water from below to take the place of less dense water at the surface that is pushed away by the wind.

Lesson Summary

• Ocean waves are energy traveling through the water.
• The highest portion of a wave is the crest and the lowest is the trough.
• The horizontal distance between two wave crests is the wave’s length.
• Most waves in the ocean are wind generated waves.
• Ocean surface currents are produced by major overall patterns of atmospheric circulation, the Coriolis Effect and the shape of each ocean basin.
• Ocean surface circulation brings warm equatorial waters towards the poles and cooler polar water towards the equator.
• Deep ocean circulation is density driven circulation produced by differences in salinity and temperature of water masses.
• Upwelling areas are biologically important areas that form as ocean surface waters are blown away from a shore, causing cold, nutrient rich waters to rise to the surface.

Review Questions

• What factors of wind determine the size of a wave?
• Define the crest and trough of a wave.
• What is the most significant cause of the surface currents in the ocean?
• How do ocean surface currents affect climate?
• What is the Coriolis Effect?
• Some scientists have hypothesized that if enough ice in Greenland melts, the Gulf Stream might be shut down. Without the Gulf Stream to bring warm water northward, Europe would become much colder. Explain why melting ice in Greenland might affect the Gulf Stream.
• What process can make denser water rise to the top?
• Why are upwelling areas important to marine life?
• Provided by : Wikibooks. Located at : http://en.wikibooks.org/wiki/High_School_Earth_Science/Ocean_Movements . License : CC BY-SA: Attribution-ShareAlike

Ocean Currents: The Driving Forces and Implications for Earth’s Climate | Sociology UPSC | Triumph IAS

Table of Contents

Ocean Currents

(relevant for geography section of general   studies paper prelims/mains).

Ocean currents represent the perpetual flow of water within the ocean, akin to aquatic counterparts of rivers. These currents adhere to established trajectories, mirroring the presence of rivers within the oceanic expanse. Oceanic currents are classified into two well-defined systems—the surface circulation, which agitates the upper stratum of the ocean, and the deep circulation, which courses through the depths of the sea floor.

Ocean Currents and Their Causes:

Ocean currents are instigated by a confluence of factors, including wind patterns, disparities in water density due to temperature and salinity discrepancies, gravitational forces, and occurrences like earthquakes or storms.

• Influence of Gravity: Surface currents within the ocean are primarily driven by global wind systems powered by solar energy. Additionally, Coriolis forces resulting from the Earth’s rotation intersect with these currents. Role of
• Planetary Winds: The arrangement of surface currents is dictated by the prevailing wind directions. The interaction of surface wind-driven currents with geographic features also produces upwelling currents, which then give rise to deepwater currents.
• Density Variation: Another determinant of ocean currents is the variance in water density due to temperature and salinity differences, leading to thermohaline circulation. This mechanism propels water masses through the ocean’s depths, carrying essential elements like nutrients, oxygen, and heat.
• Unforeseen Events: Geophysical incidents such as powerful storms and underwater earthquakes possess the capacity to initiate significant ocean currents , causing the movement of water masses toward shorelines and shallower areas. Earthquakes may also trigger rapid downslope shifts of water-soaked sediments, creating potent turbidity currents.
• Influential Topography: When a wide-ranging current is funnelled into a confined space, its strength can intensify markedly. On the ocean floor, water masses channelled through narrow gaps in ridge systems or around seamounts can give rise to currents of greater magnitude than those found in the surrounding waters. This phenomenon has implications for the distribution and abundance of marine organisms and for the endeavours of scientists studying them, along with their equipment.

The ocean currents act as the global conveyor belt and thus play a dominant role in determining the climate of many of Earth’s regions.

Sample Question for UPSC Sociology Optional Paper:

Q 1: “How do ocean currents impact the social and economic activities of coastal communities?” Answer: Ocean currents influence fish migration patterns, which directly affect the livelihoods of fishermen. They also play a role in the climate of coastal regions, thereby affecting agriculture and tourism.

Q 2: “What role do ocean currents play in global inequality?” Answer: Ocean currents can have varying effects on different regions, influencing climate and therefore agricultural productivity, which can contribute to economic disparities between nations.

Q 3: “Discuss the sociological implications of thermohaline circulation.” Answer: Thermohaline circulation affects global climate, which in turn impacts food security, migration patterns, and economic stability, thereby having broader sociological implications.

Related Blogs …

To master these intricacies and fare well in the Sociology Optional Syllabus , aspiring sociologists might benefit from guidance by the Best Sociology Optional Teacher and participation in the Best Sociology Optional Coaching . These avenues provide comprehensive assistance, ensuring a solid understanding of sociology’s diverse methodologies and techniques.

Ocean currents, surface currents, deep circulation, thermohaline circulation, wind patterns, water density, temperature, salinity, gravitational forces, climate change, marine ecology, Coriolis forces, Ocean currrents

Choose T he Best Sociology Optional Teacher for IAS Preparation?

At the beginning of the journey for Civil Services Examination preparation, many students face a pivotal decision – selecting their optional subject. Questions such as “ which optional subject is the best? ” and “ which optional subject is the most scoring? ” frequently come to mind. Choosing the right optional subject, like choosing the best sociology optional teacher , is a subjective yet vital step that requires a thoughtful decision based on facts. A misstep in this crucial decision can indeed prove disastrous.

Ever since the exam pattern was revamped in 2013, the UPSC has eliminated the need for a second optional subject. Now, candidates have to choose only one optional subject for the UPSC Mains , which has two papers of 250 marks each. One of the compelling choices for many has been the sociology optional. However, it’s strongly advised to decide on your optional subject for mains well ahead of time to get sufficient time to complete the syllabus. After all, most students score similarly in General Studies Papers; it’s the score in the optional subject & essay that contributes significantly to the final selection.

“ A sound strategy does not rely solely on the popular Opinion of toppers or famous YouTubers cum teachers. ”

It requires understanding one’s ability, interest, and the relevance of the subject, not just for the exam but also for life in general. Hence, when selecting the best sociology teacher, one must consider the usefulness of sociology optional coaching in General Studies, Essay, and Personality Test.

The choice of the optional subject should be based on objective criteria, such as the nature, scope, and size of the syllabus, uniformity and stability in the question pattern, relevance of the syllabic content in daily life in society, and the availability of study material and guidance. For example, choosing the best sociology optional coaching can ensure access to top-quality study materials and experienced teachers. Always remember, the approach of the UPSC optional subject differs from your academic studies of subjects. Therefore, before settling for sociology optional , you need to analyze the syllabus, previous years’ pattern, subject requirements (be it ideal, visionary, numerical, conceptual theoretical), and your comfort level with the subject.

This decision marks a critical point in your UPSC – CSE journey , potentially determining your success in a career in IAS/Civil Services. Therefore, it’s crucial to choose wisely, whether it’s the optional subject or the best sociology optional teacher . Always base your decision on accurate facts, and never let your emotional biases guide your choices. After all, the search for the best sociology optional coaching is about finding the perfect fit for your unique academic needs and aspirations.

To master these intricacies and fare well in the Sociology Optional Syllabus , aspiring sociologists might benefit from guidance by the Best Sociology Optional Teacher and participation in the Best Sociology Optional Coaching . These avenues provide comprehensive assistance, ensuring a solid understanding of sociology’s diverse methodologies and techniques. Sociology, Social theory, Best Sociology Optional Teacher, Best Sociology Optional Coaching, Sociology Optional Syllabus. Best Sociology Optional Teacher, Sociology Syllabus, Sociology Optional, Sociology Optional Coaching, Best Sociology Optional Coaching, Best Sociology Teacher, Sociology Course, Sociology Teacher, Sociology Foundation, Sociology Foundation Course, Sociology Optional UPSC, Sociology for IAS,

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The Role of Ocean Currents in Climate

ThinkTV, Teachers' Domain

This video segment uses data-based visual NOAA representations to trace the path of surface ocean currents around the globe and explore their role in creating climate zones. Ocean surface currents have a major impact on regional climate around the world, bringing coastal fog to San Francisco and comfortable temperatures to the British Isles.

Notes from our reviewers

The CLEAN collection is hand-picked and rigorously reviewed for scientific accuracy and classroom effectiveness. Read what our review team had to say about this resource below or learn more about how CLEAN reviews teaching materials .

• Teaching Tips This video provides some useful visuals for a unit on global ocean currents. There is a very nice research project in the teaching tips section asking students to research a coastal city to determine how ocean currents determine its climate.
• About the Science Video focuses on role of surface ocean currents in global climate. Comment from expert scientist: Asks students to think on both global and local scales. Includes (though necessarily briefly) both major processes that move ocean water: wind forcing and density. Relates the oceans to climate processes on large scales (e.g. heat uptake by the ocean) and smaller scales (e.g. El Niño, local coastal climates).
• About the Pedagogy This video includes a background essay and teaching tips. Links to other videos and resources are included, making it easy to build a more comprehensive unit on ocean currents.
• Technical Details/Ease of Use The quality of the streaming video is likely not suitable for classroom projection. The download versions are of higher quality.

How the Ocean Current Affect Animals’ Life in the Sea Essay

Introduction, ocean currents and marine turtles, nekton’s (fishes), sea urchins, works cited.

An ocean current refers to a continuous water flow in the ocean following a defined path. This occurs either at the surface of the ocean or below the surface, it also may be parallel or vertical to the surface. These currents are either caused by wind or changes in density (Thermohaline currents). Ocean currents affect the climate, temperatures, and biotic systems especially the fisheries but also those plants and animals on the seashore (Gray et al. 1).

Ocean currents affect marine life in different ways some of these include; as water flows along a given path, there are many sea animals along the same path. Depending on the strength of the ocean current, sea animals along the path are flown along with the water, and the animals are moved to new regions that are sometimes thousands of kilometers away causing redistribution of marine life. During the flow, nutrients are also moved from the bottom of the sea and exposed to sunlight in the process called upwelling. This increases marine nutrients leading to the increased nutrient provision to marine life.

Ocean currents sometimes cause the movement of warmer water to colder regions or cold water to water regions. This interferes with the temperature of the water and may affect sensitive marine life in the region like it may end up freezing some marine animals to death. This paper discusses how the ocean currents affect marine animals with particular reference to turtles, sea urchins, and Nektones

Marine turtles rely entirely on ocean currents for their movements. Young marine turtles especially are moved to their pelagic nurseries by ocean currents and these serve as their habitats. The hatching of turtle eggs relies on oceanic tides and more especially on the frontal tides. This reduces the risk of exposing these eggs to predators. The fertilization of the turtle eggs also depends on ocean waves that transport the larvae to allow for fertilization to occur.

During the development of these turtles, their movement is still aided by ocean currents like in the case of searching for food they flow along with the currents to newer regions that could have food to keep them alive. The turtles are cauterized by two major directional movements where one is usually to the feeding area and the other to the nesting area; both two movements are aided by oceanic currents (Luschi, HAys, and Papi 294).

These are families of sea animals that are strong swimmers and large enough to have the strength to propel against ocean currents. Their bodies are streamlined such that they move swiftly. These include fishes, whales, and Dolphins. Ocean currents have such effects on these sea animals as they bring food to them from the shores and other places so the animals can feed on it. Besides the food, they cause the animals to move about and this allows the animals to be away from predators for their survival. During winter, ocean currents cause oceans waters to swirl around which causes a warming effect on the water and this allows the animals to survive the cold weather.

During summers, cold water from the Polar Regions is flown causing a cooling effect in the warmer regions. The currents also allow the animals to migrate or relocate to more accommodating weather conditions. Animals play in water and ocean current give the animals the whirling effect that gives the sea animals especially the large sea animals like Dolphins to whirl out and enjoy the changing weather.

Sea urchins and the starfish are greatly affected by ocean currents just like the other sea animals. Their larvae are transported over long distances to allow for fertilization to occur anywhere in the sea. These currents also aid the movement of these sea urchins. This allows them to have easy access to food, to redistribute to regions that are unoccupied and maybe unexploited. However, it should be noted that sometimes very strong oceanic currents can cause the death of sea urchins (Gray et al. 7)

Ocean currents are water movements in large volumes along a given path in the oceans, seas, or any large water bodies. These movements are usually caused by wind or the upwelling movement in the water bodies. It is important for the sea animals as it causes their movement to food-rich areas or brings feed to the animals. Food is the most essential part of the survival of any creature including those in large water bodies. Ocean currents are therefore inevitable to the survival of sea animals as they cause the flow of food nutrients within the sea.

Gray Eileen, Alexander Ann, Darling Tina, and Sharkey Nelda. “Moving water-Ocean currents and winds.” Drifters , 1998. Web.

Luschi Paolo, HAys Graeme, and Papi Florian. A review of long-distance movement by marine turtles and possible role of ocean currents . Cesenatico: Oikos, 2003.

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1. IvyPanda . "How the Ocean Current Affect Animals’ Life in the Sea." September 5, 2022. https://ivypanda.com/essays/how-the-ocean-current-affect-animals-life-in-the-sea/.

Bibliography

IvyPanda . "How the Ocean Current Affect Animals’ Life in the Sea." September 5, 2022. https://ivypanda.com/essays/how-the-ocean-current-affect-animals-life-in-the-sea/.

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An essay on the winds and the currents of the ocean

Introduction. - The earth is surrounded on all sides by an exceedingly rare and elastic body, called the atmosphere, extending with a diminishing density to an unknown distance into space, but pressing upon the earth with a force equal to that of a homogenous atmosphere five and a half miles high. It is also partially surrounded by the ocean, which is of a very variable depth, and known to be, in many places, more than four miles. If the specific gravity of the atmosphere and of the ocean were everywhere the same, all the forces of gravity and of pressure which act upon any part of them, would be in exact equilibrium, and they would forever remain at rest. But as some parts of the earth are much warmer than others, and air and water expand and become rare as their temperature is increased, their specific gravities are not the same in all parts of the earth, and hence the equillibrium is destroyed, and a system of winds and currents is produced. It is proposed in this essay to inquire into the effects which are produced, both in the atmosphere and in the ocean, by this disturbance of equilibrium, and by means of a new force which has never been taken into account in any theory of winds and currents, to endeavor to account for certain phenomena in their motions, which have been a puzzle to meteorology and hydrology. As there are some uncertain data connected with the subject, such as the amount of the disturbing force, the effects of continents, friction, etc, which render a complete solution of the problem impractible, we shall aim at giving a popular explanation of observed phenomena rather than a complete solution of the problem; yet we shall give the result of some calculations, based upon known date, or at least upon very reasonable hypothesis, which will show that the causes which we have given are adequate to the effects which are attributed to them. We shall divide the subject into two parts, and treat, first, of the winds, and secondly, of the currents of the ocean.

The motions of the atmosphere. - From about the parallel of 28° on each side of the equator the winds on the ocean, where they are not influenced by any local causes, blow steadily towards the equator, having also a western motion, producing what are called the north-east and south-east trades. At the meeting of these currents near the equator there is a calm called the equatorial calm-belt, or the doldrums, where the air rises up and flows in the upper regions towards the poles, until it arrives near the 28°, where it is met by an upper current flowing from the poles. The meeting of these upper currents produces an accumulation of atmosphere from under which the air flows out in both directions on account of the increased pressure; a strong and steady current, as we have seen, towards the equator, and another not so strong and somewhat variable over the middle latitudes, towardg the poles, having at the same time an eastern motion, and producing what are called the passage-winds. As this current flows at the surface towards the poles, it gradually rises up and returns in the upper regions towards the equator, meeting the upper current from the equator near the tropics as has been stated.

Such are the general motions of the atmosphere, as laid down by Lieutenant Maury, and as represented in his diagram of the winds. [1] But there are numerous observations which have been made in very high latitudes both in the north and the south, which show that the currents flowing over the middle latitude towards the poles, do not extend to the poles, but that the atmosphere above a certain latitude, has a tendency to flow from the poles, producing another meeting of the air at the surface near the polar circles similar to the one at the equator, except that the currents are comparatively feeble and consequently the belt of meeting not so well defined, and that here also air rises up and flows each way in the upper regions towards the equator and the poles. "Sir J. Ross has shown that there is a large prevalence of north winds over the southern ones in the middle of North America as low down as latitude 70° and longitude 91°58' west, not merely in winter, but in every month in the year. The northern winds were not only more than double as frequent as the southern, but more than double as strong; and he also found southern winds largely to predominate in latitude 77° south." [2] If then there were no continents, or other local causes of disturbance, the motions of the atmosphere would be as represented in the following diagram, in which the direction of the wind is represented by the arrows, and the external part of which represents the motion of the air in the plane of the meridan. This system, however, is found to prevail on the ocean only, and is very much interfered with in other parts on account of local causes of disturbance, especially in the northern hemisphere, where the uniformity of the earth's surface is most interrupted by land.

The pressure of the atmosphere - The atmospere everywhere presses upon the surface of the earth with a force equal to the pressure of a column of mercury of nearly thirty inches in height. This pressure, however, is not the same in all parts of the earth, but varies in different latitudes as well as from an inch lower at the equator, and seems to stand the lowest about the polar circle, where a very remarkable depression has been observed in many places. "It is a singular fact," says Mrs. Somervill, (page 268) "discovered by our navigators, that the mean height of the barometer is an inch lower throughout the Antarctic ocean at Cape Horn, than it is at the Cape of Good Hope, or at Valparaiso." A similar depression has likewise been observed near the sea of Okhotsk in eastern Siberia. It also appears from the tables of the South Sea Exploring Expedition, by Captain Wilkes, that the barometer stands lowest near the polar circle, where it stands at a mean of about twentynine inches, and higher both north and south of it. After examining various authorities and all the circumstances connected with this subject, Professor Espy comes to the conclusion, that "there are three belts where the barometer stands below the mean, with almost constant rain and snow - one near the equator, one near the arctic circle, and one near the antarctic circle, and also that there are, certainly two belts in the outer borders of the trade-winds, where the barometer stands above the mean, and almost certainly two regions more - one around the north pole and the other around the south pole - where the barometer stands above the mean." It also appears for a great many observations made at different places on the Atlantic, at the level of the ocean, that the barometer stands more than half an inch lower at the arctic circle, than it does at the outer limit of the trade winds, and that there is also a considerable depression at the equator. [3]

The forces concerned in producing the motions of the atmosphere. - There are four principal forces which must be taken into account in a correct theory of the winds. The first arises from a greater specific gravity of the atmosphere in some places than others, on account of a difference of temperature and of the dew-point; for, when it becomes heated or charged with vapor in any place to a greater degree than at others, it becomes specifically lighter, and hence, the equilibrium is destroyed. There is a flowing together, then, of the heavier air on all sides, which displaces the lighter air, and causes it to rise up and flow out in a contrary direction. This is the primum mobile of the winds, and all the other forces concerned are dependent on it for their efficiency. A second force arises from the tendency which the atmosphere has, when, from any cause, it has risen above the general level, to flow to places of a lower level. These two preceding forces generally produce counter-currents. Again, when, from any cause, a particle of air has been put in motion toward the north or south, the combination of this motion with the rotatory motion of the earth produces a third force, which causes a deflection of the motion to the east when the motion is to the north, and a deflection to the west when it is toward the south. This is the same as one of the forces contained in La Place's general equations of the tides, the analytical expression of which is 2 n u r sin. l cos. l ; l being the latitude; n , the motion of the earth at the equator; u , the velocity of the particle north or south; and r , the radius of the earth. The fourth and last force arises from the combination of a relative east or west motion of the atmosphere with the rotatory motion of the earth. In consequence of the atmosphere's revolving on a common axis with that of the earth, each particle is impressed with a centrifugal force, which, being resolved into a vertical and a horizontal force, the latter causes it to assume a spheroidal form conforming to the figure of the earth. But, if the rotatory motion of any part of the atmosphere is greater than that of the surface of the earth, or, in other words, if any part of the atmosphere has a relative eastern motion with regard to the earth's surface, this force is increased, and if it has a relative western motion, it is diminished, and this difference gives rise to a disturbing force which prevents the atmosphere being in a state of equilibrium, with a figure conforming to that of the earth's surface, but causes an accumulation of the atmosphere at certain latitudes and a depression at others, and the consequent difference in the pressure of the atmosphere at these latitudes very materially influences its motions. This force is also expressed by one of the terms of La Place's equations, the analytical expression of which is 2 n v r sin. l ; v being the relative eastern or western velocity of the atmosphere.

Hadley's theory This theory, which is the commonly received theory of the trade-winds, and with which the reader is no doubt familiar, is based upon the first three forces only given above, no account being taken of the fourth. But as it may be seen from the analytical expressions of the last two forces given above, that the latter is greater than the former, and the east and west motion of the atmosphere depends upon the former, we have reason to suppose that the latter also may have a considerable effect, and that it should be taken into account in a correct theory of the winds. Accordingly we see that although Hadley's theory furnishes an explanation of the trade-winds, yet it does not account for many other remarkable phenomena in the motions of the atmosphere, but even requires motions to satisfy it entirely at variance with them. According to this theory, there should be a current on the surface of the earth from the pole to the equator in a kind of loxodromic spiral, and a similar counter-current in the upper regions from the equator towards the poles. The barometer also should stand highest at the poles where the air is coldest and most dense, and gradually fall as it is brought nearer the equator. But both of these, as we have shown, are contrary to observation. The position also of the exterior limits of the trade-winds near the parallels of 28°, the flowing of the atmosphere in the upper regions from both sides towards these parallels, and a low barometer near the polar circles, cannot be explained by this theory, and have not been satisfactorily explained by meteorologists. It is true Professor Espy says the highness of the barometer near the parallels of 28° is owing to the flowing over of the atmosphere which rises up at the equator; but this overflow of atmosphere could have no tendency to accumulate at these parallels, since it evidently would flow on gradually towards the poles to supply the draught caused by the flow towards the equator, as this theory requires. He also assigns as a cause of the low barometer about Cape Horn and the antarctic circle, the abundant rains which prevail there and the consequent disengagement of caloric, which rarefies the atmosphere there. But, if the belt of calms and rains near the equator is caused by the barometer standing lower there then at the outer limit of the trade-winds, which causes a flow of atmosphere there at the surface, and, if rains generally in any region, according to Professor Espy's own theory of clouds and rains, is caused by a low barometer there, and a consequent flowing in from all sides and a rising up of the atmosphere, then the lowness of the barometer in those regions must be the cause of the rains, and not the rain the cause of the lowness of the barometer, as will appear for other reasons.

We shall now undertake to show, that all these phenomena, and others connected with storms, which have never been accounted for by any theory, may be satisfactorily accounted for by taking into account the fourth force given above.

Why the outer limits of the trade-winds are near the parallels of 28°. - If from any cause the atmosphere receives a motion either towards or from the poles, the action of the third force above, causes a deflection of it towards the east, as it moves towards the poles, and towards the west as it moves towards the equator; and as the prime moving cause of the principal currents of the atmosphere has a tendency to cause it to flow towards and from the poles, the general result is, that towards the poles the atmosphere has a motion towards the east, but near the equator towards the west. But from the principle of the preservation of areas, the sum of the products of all the particles of the atmosphere, multiplied into their velocities and their distances from the axis of revolution, cannot be changed be the action of a central force, or by the mutual action of the particles upon each other; hence the sum of the products of each particle into its distance from the axis, and into its relative eastern velocity, must be equal to the sum of similar products, taken with regards to the particles having a relative western motion. But, as the portion of the atmosphere having a relative eastern motion, is nearer the axis than that which has a relative western motion, and as the part having a western motion, inasmuch as it is further from the axis, must be somewhat less than the part comprised between these parallels, in order to make the products equal, unless the relative velocity of the part having an easterly motion is very much greater. Hence, the dividing lines between the portions of the atmosphere having a relative east and west motion, must be within these parallels; and, as the outer limits of the trade-winds depend upon those lines, they must also fall within these parallels; and they are accordingly found to be about the parallels of 28°.

The cause of high barometer about the parallels of 28°, and the low barometer at the polar circles. - The greater pressure of the atmosphere at the parallels of 28° than at the equator and the polar circles can only be caused by an accumulation of atmosphere there. This accumulation results, necessarily, from the action of the new force which we have introduced into the theory of the winds. For, as we have seen, all the atmosphere between the parallels of 28° and the poles has, and, according to theory, must have, a general eastern motion; and this gives such a value to the analytical expression of the fourth force, enumerated above, as to cause the atmosphere to recede from the poles toward the equator. But the western motion of the atmosphere between the parallels of 28° gives that expression a negative value there; and, hence, this force causes the atmosphere to recede from the equator, also. This force then, has a tendency to cause the atmosphere in the upper regions to recede from both the poles and the equator, and to accumulate about the parallels of 28°, and, as it may seem by merely inspecting the expression of this force given above, that for the same value of v , or motion of the atmosphere east or west, this force is much greater toward the poles than it is near the equator, it causes a considerable depression of the atmosphere at the poles, and only a slight one at the equator, as represented in the diagram. The amount of this elevation and depression is not indicated entirely by the barometer, for the height of the barometer depends upon both the height of the atmosphere and its density. Therefore, as the atmosphere is much denser at the polar circles than at the parallels of 28°, on account of its being much colder, the accumulation of atmosphere at these parallels and its depression towards the poles, must be considerable to cause the barometer to stand higher at these parallels than the polar circles.

We shall now give the results of some calculations, based upon a reasonable hypothesis, which show that this new force introduced is entirely adequate to produce an accumulation of atmosphere at the parallels of 28°, and a depression of it at the poles to such an amount, that the difference in the height of the barometer at the parallels of 28°, and a depression of it at the polar circles, may correspond with observations. As friction is a very important element in calculations of the motion of the atmosphere, and its effect cannot be determined, it would be impossible to calculate the motion of the atmosphere from the forces which act upon it, if they were even accurately known. We will therefore assume certain motions of the atmosphere, which are known not to vary much from observation, upon which we will base our calculations. If we assume that the east and west motions of the atmosphere may be represented by the expression 2sin 3/2 p cos. 3/2 p v , p being the polar distance of the place, it would make these motions vanish at the poles and at the parallels of 30°, and we have reason to think, would pretty well represent the motions of the atmosphere east and west at all latitudes except near the equator, where it would make it a little too great. Upon this assumption it may be shown by calculations, the results of which only can be given here, that if v , or the maximum east or west motion of the atmosphere, were only ten miles per hour, it would cause a heaping up of the atmosphere near the parallels of 28° which would make the barometer, if the atmosphere were everywhere of the same density, stand two inches higer here than at the poles. The same hypothesis would also make the depression at the equator only one-ninth that at the poles. If we now suppose that the greater specific gravity alone of the atmosphere at the poles, is sufficient to cause the barometer to stand one inch higher there than at the equator, which would only require a difference of temperature of about 16°, it would still leave a difference in the height of the barometer between the poles and the equator about equal to the observed difference in the southern hemisphere. It would also add a little to the depression of the baromter at the equator, which would make it a little more than one-ninth of that at the poles, and consequently make it correspond with observation. We think therefore it is evident that the observed difference in the height of the barometer in difference latitudes, is owing to the joint effect of a gradual increase of specific gravity from the equator to the poles, and of a heaping up of the atmosphere near the parallels of 28°, caused by the action of this new force that we have taken into account.

Explanation of the passage-winds and calm-belts at the limits of the trade-winds. - As the pressure of the atmosphere, on account of its accumulation there, is greatest about the parallel of 28°, this pressure has a tendency to cause it to rush out from beneath both, towards the poles and the equator. If the motions of the atmosphere were as great at the surface of the earth as in the upper regions, the force which causes a heaping up of the atmosphere about the parallels of 28°, would be as great below as in the upper regions, and would prevent the flowing out of the air below towards the poles. But, on account of friction, the eastern motion of the atmosphere cannot be so great at the surface of the Earth as above, and consequently the accumulation of atmopshere mentioned above, is caused principally by the upper currents, and the pressure wich causes it to flow out below towards the poles, where the barometer, as we have seen, stands much lower, is greater than the force below which causes the accumulation of atmosphere. The lateral pressure then of the atmosphere, and its horizontal motion which has a tendency to cause it to flow at the surface of the Earth, from the poles towards the equator; and secondly, the heaping up of the atmosphere at the outer limits of the trade-winds, which causes it to rush out below, both towards the equator and the poles; thirdly the action of the force depending upon the east or west motion of the atmposphere, wich we have seen, must be greater above than at the surface of the Earth. Between the parallels of 28° and the equator, the first two forces combine against the latter, which is small near the equator, and produce a strong and steady current at the surface of the Earth towards the equator, which, being combined with the rotatory motion of the Earth, gives rise to the tradewinds. Beyond these parallels, the first and third forces are opposed to the second, but it may be seen from the analytical expression of this second force, obtained from our preceding assumption, and which cannot be given here, that this force is very great in the middle latitudes, and consequently it prevails over the two, causing a current towards the poles, which combined with the rotatory motion of the Earth, produces the southwest winds in the northern hemisphere, and northwest winds in the southern hemisphere, called passage-winds. This force has its maximum about the parallels of 48°, and above these decreases rapidly, so that at the polar circles the other two forces begin to prevail over it, and cause a current from the poles. The forces then acting upon the atmosphere at the surface of the earth, causes it to flow in opposite directions, from the parallels of 28° and the poles, and to flow together near the equator and the polar circles. Hence, there is a rising up of the atmosphere at the latter places, and a flowing thence in the upper regions to the former places, where it descends, and thus a system of current is produced as represented by the arrows in the external part of the diagram, which represents a meridional vertical section of the atmosphere. It was shown that about the parallel of 28°, the atmosphere can have no motion east or west, and it has now been shown that these are the parallels also of greatest pressure, whence the currents flow both towards the equator and the poles, consequently there must necessarily be here calm-belts, such as are well-known from observation to exist.

We think now, it is manifest, that the introduction of our new force into the theory of the winds, exactly accounts for all the principal motions of the atmosphere, and clears up the difficulties which have heretofore puzzled meteorologists.

Maury's theory of the crossing of the winds. In order to account for the motions of the winds and other phenomena, Lieutenant Maury advances the theory that there is a crossing of the winds or currents at the calm-belts of the equator and the parallels of 28°; that the currents flowing at the surface towards the equator, cross there, each becoming the upper current in the other hemisphere after it crosses the calm-belt at the equator, and then flowing towards the poles until it meets the upper current flowing toward the equator about the parallel of 28°, where there is supposed to be another crossing, each current then becoming again the surface current, and flowing in the same direction as before. [4] He also makes, by his arrangement, the rains in each temperate zone depend upon the vapor received by the winds in their passage to the equator as a trade-wind in the opposite hemisphere. We think there is no necessity for resorting to such an argument to account for the phenomena of the winds, but that they all are satisfactorily accounted for, as above, by tracing out the effects of well known forces without resorting to the mysterious agents of magnetism and electricity. Besides, there is no known principle by which two currents can interpenetrate and cross each other without mingling together, and, especially, is there none by which a current saturated with vapor can pass through a dry current and each one after afterwards retain its distinctive character of a moist or dry current, which this theory requires.

The fact that Ehrenberg has discovered South American infusoria in the blood-rains and "sea-dust" of the Cape Verde Islands and other places, does not prove the crossing of the winds; for, according to the explanation of the winds given above, there are two curents flowing into each calm-belt, and also two flowing out in opposite directions, as it were from a common reservoir, and, consequently, whatever is carried into these belts from either side down flow out again in each direction; and so infusoria in one hemisphere can easily pass to the other without a distinct crossing of the currents. And it even the moist current of the torrid zone could pass though the dry ones to the temperate zones, they could not produce rain there; for Professor Espy has conclusively shown that no descending current, however saturated with moisture, can ever produce rain. [5]

Explanation of the winds at the peak of Tenerife. - We have stated that the greatest atmospheric pressure is about the parallels of 28°, but these cannot be accurately the parallels of the greatest accumulation, for this pressure depends both upon the height of the atmosphere and its density, and, as the density increases gradually with the latitude, there must be an increase of pressure beyond the parallel of greatest accumulation, until the decrease of pressure from the one cause equals the increase from the other. But, as the calm-belts in the upper regions must be where the currents meet, and consequently where there is the greatest accumulation of atmosphere, it follows that the calm-belts are not exactly at the same parallels at the surface of the Earth as in the upper regions, but that they incline above toward the equator, as represented in the diagram. And this explains the peculiarity in the winds at the Peak of Tenerife. This peak stands near the outer limits of the trade-winds, and, as this limit moves north an south with the seasons, the northeast and southwest winds are found to prevail at the base alternatively. But at the top of the peak the southwest winds always prevail, because, when the calm-belt is furthest north, it still leaves the top of the peak north of it, where the southwest winds prevail, where the northwest trades are blowing below. When this belt occupies its most southern position, it leaves both at the top and the bottom of the peak north of it, and, consequently, the southwest wind blows both at the top and the bottom. In the fall, as the calm-belt moves south, more of the peak gradually becomes north of the calm-belt, and hence the southwest winds, which always prevail at the top, should gradually descend lower on the peak until they reach the base, which is exactly in accordance with observation.

The effect of continents - If the surface of the earth were all covered by the sea, uninterrupted by continents, the tradewinds and passage-winds, and also the calm-belts, would extend, without any interruption, entirely round the earth. But continents, and especially high mountain ranges, seem to have a very material effect in changing this regular system of winds. Thus the high table-lands and mountain ranges in Mexico and the western part of the United states, seem to turn the westward current of the trade-winds on the Caribbean sea and the Gulf of Mexico northward over the parallel of the calm-belt into the Unites States, where it arrives at the latitudes where the atmosphere has a general tendency to flow eastward, and thus a kind of aerial gulf-stream is produced. This is evident not only from observations on the general directions of the winds in the Guld of Mexico and the United States, but also from the observed routes of storms, which must be governed very much by the general movements of the part of the atmosphere in which they occur. Instead of the regular trade-winds from the northeast in the Caribbean sea, the prevailing cours of the lower current, is from a point south of east instead of north of east. [6] It is also found from observations at Barbedoes that, while the eastern winds are most prevalent, the southeast winds greatly predominate over the northeast ones. Of a great many hurricanes, also, which had their origin in the Atlantic, east of the Caribbean sea, and whose routes have been determined, by Mr. Redfield, nearly all moved in a direction north of west, until they arrived at the longitude of Florida or the Gulf of Mexico, where they curved around towards the north, and after passing the parallel of the calm-belt, towards the northeast, in the direction of Newfoundland and the northern part of the Atlantic. And this is exactly the route we would suppose the westward currents of the lower part of the atmosphere, interrupted by the high mountain ranges of Mexico, would take. But on the west coast of North America, the eastward current of the northern part of the Pacific, impinging against the range of the Rocky mountains, is turned down towards the equator, and hence the prevailing direction of the wind on the Pacific, west of Mexico, is from the northwest. The eastern coast of Africa also seems to have a similar effect upon the westward current of air in the Indian ocean; for the hurricanes which orginate in that ocean, on approaching that coast, are turned southward and finally towards the southeast into the southern ocean. The typhoons, also, of the China sea seem to be influenced in a similar manner by the eastern part of Asia. These changes of the general direction of the wind which prevail on the open ocean must be caused by the continents.

Hurricanes and storms. - Hurricanes are generally supposed to be produced by the meeting of adverse currents, which produce gyratory motions of the atmosphere at the place of meeting. That they may receive their origin and first impulse in this way, we think is very probable; but that violent hurricanes, extending over a circular area nearly one thousand miles in diameter, and continuing for ten days, and proceeding with increasing violence from the torrid zone to high northern latitudes, depends upon any primitive impuls alone, we think is very improbable. For if even any part of the atmosphere should receive such an impulse as to pruduce a most violent hurricane, friction would soon destroy all motion and bring the atmosphere to rest. Besides, no gradually accelerated motion can depend upon a primitive impulse alone, even where there is no friction. Hurricanes then, and all ordinary storms, must begin and gradually increase in violence by the action of some constantly acting force, and when this force subsides, friction brings the atmospher to a state of rest. This force may be furnished by the condensation of vapor ascending in the upward current in the middle of the hurricane, in accordance with Professor Espy's theory of storms and rains. According to this theory, all storms are produced by an ascending current of warmer atmosphere above by means of the caloric given out of the vapor which is condensed as it ascends to colder regions above. Therefore, as long as this ascending current can be supplied with air saturated with vapor this continual rarefaction must take place, and also the ascent of the air from all sides to supply its place. If, then, all the lower stratum of atmosphere over a large district were saturated with vapor, without some disturbing cause, it might remain undisturbed; but if from any cause an ascending current is produced, either by local rarefaction of air my means of heat, or by the meeting of two adverse currents, which produces a gyratory motion and consequent rarefaction in the middle on account of the pressures being taken away by the centrifugal force, as soon as the air below, saturated with vapor, ascends to the colder regions above, the vapor is condensed and the caloric given out continues to rarefy it so long as the ascending column is supplied with moist air, and consequently the surrounding colder air presses in below from all sides, and thus a hurricane of more or less violence is produced and kept up for ten or twelve days, moving with the general direction of the motion of the atmosphere where it occurs. The violence then of the hurricane, and also its duration, depends upon the quality of vapor supplied by the currents flowing in below. Hence, it is, that the tropical hurricanes which originate in the Atlantic, east of the Caribbean sea, do not abate their violence until they reach a high northern latitude where the atmosphere is cold and dry.

The cause of the gyratory motions of hurricanes. - It has been established by Redfield, Reid, Piddington, and others, that all hurricanes and ordinary storms have a gyroatory motion around a center, and that these gyrations in the northern hemisphere, ar from right to left against the hands of a watch, but in the southern hemisphere from left to right with the hands of a watch. There are some however, amongst whom is Professor Espy, who deny the gyratory character of storm entirely, and contend that there is only a rushing of the air from all sides below towards a centre, without any gyration. We think this gyratory character of storms has been too well established to admit of any doubt. No one, however, has ever given any satisfactory reason why these gyrations in the one hemisphere are always sinistrorsal and in the other dectrorsal. It is true, Mr Redfield [7] endeavors to account for the sinistrorsal gyrations of the hurricanes and storms which proceed from the Gulf of Mexico towards Newfoundland, by means of the pecularities of the aerial currents in the region of the Gulf and the adjacent coast of the Pacific. But if there are the same kind of gyrations over the whole hemisphere, it is evident that the cause which produces them must be as extended as the hemisphere itself. It has also been suggested that this tendency to a distinct kind of gyration in each hemisphere, may be owing to the magnetism of the air. [8]

We shall now undertake to show that there cannot be a rushing of air from all sides towards a center, on any part of the earth except at the equator, without producing a gyration, and that the tendency to a distinct kind of gyration in each hemisphere, is owing, neither to any pecularities of the winds or aerial currents, nor to the mysterious agent of magnetism, bu that it results, as a necessary consequence, form the action, upon the atmosphere, of the four forces which we have taken into consideration in the first part of this essay.

It has been shown that when a particle of air receives a motion toward the poles it is deflected toward the east, as in the passage-winds, but when it revieves a motion toward the south, there is a force which also turns it toward the west, as in the tradewinds. It has likewise been shown that when the air has a relative motion east, it has a tendency, on account of the greater centrifugal force, to move also towards the south, but that when it has a relative motion west, it has a tendency, on account of the diminished centrifugal force, to move also towards the north. If, then, we suppose that the air at M , N , O and P on the diagram (page 8), has a tendency, on account of rarefaction or for any other reason, to flow towards c , from what has been stated, the air at M would not move equally towards c , but would be deflected northward a little towards m . In like manner the air at N when there is any force which tends to make the surrounding air flow towards a center, the resultants of all the forces which act upon it must cause it to receive a gyratory motion, and that this motion in the northern hemisphere must be sinistrorsal, but in the southern hemisphere the contrary.

It may be observed here that these gyrations are not cucular but spiral, gradually approaching the center; for the forces which tend to produce these gyrations depend for their efficacy upon a motion from all sides towards the center. First, the force of which we have already treated tends to give the atmosphere a gyratory motion, as soon as it begins to converge towards a center; and secondly, these gyrations, however slight, being once produced, the centripetal force, which causes the air to flow towards the center, accelerates these gyrations as they approach the center, upon the principle by means of a string, are rapidly accelerated as the string becomes shorter. Hence if the first of these forces be only sufficient to produce a very slight gyration, the latter or centripetal force may cause very rapid gyrations near the center. And it is only upon this principle that the rapid motion of the air in a hurricane can be produced, and any theory which does not take this principle into account is defective. This centripetal force is caused by the superior pressure of the denser atmosphere on the borders of the hurricane or storm, and consequently prevails only in the lower part of the atmosphere. In the upper regions it has a tendency to recede from the center for two reasons; first, on account of the gyratory motion wich it has received below in appraoching the center, which it still, in some measure, retains after ascending to the regions above, where the surrounding pressure does not prevail, and consequently the centrifugal force resulting from the gyrations, causes it to recede from the center; secondly, because the ascending current causes an accumulation of atmosphere above the general level, which gives it a tendency also to flow out in all directions form the center. These motions however, are not distinctly towards and from the center, but in spirals, so that the currents below may be at right angles with the currents above; and hence it is that in our ordinary storms attended with rain, the clouds in the lower part of the atmosphere frequently move in a direction at right angles with the direction of those above.

It has been stated that the gyrations below approach the center in a spiral, but this approach must be slow towards the center; for, at a certain distance from the center, the gyrations becoms so rapid that the centrifugal force nearly equals the centripetal, produced by the external pressure of the atmosphere, and then the further appoach towards the center in a great measure ceases,and consequently the force which produces the gyrations. Hence, at a certain distance from the center the hurricane has the greatest violence, and within this circumference, friction in a great measure destroys the gyrations, so that the middle of our most violent hurrianes is a calm. The extent of this calm is a circle, varying generally from five to thirty miles in diameter.

If we examine the analytical expressions of the forces which produce these gyrations, we will see that at the equator they have no value, and hence no hurricane can have its origin exactly on the equator. Accordingly, of all the hurricanes which have originated within the tropics, none have been traced back to the equator, but always to some region from 10° to 20° from it.

The reason why the hurricanes which originate east of the Caribbean sea pass northward to the east of the United States, may be owing to the direction of the wind here and on the Caribbean sea, which generally blows north of west, as has been observed in the former part of this essay. If the general direction of the trade-winds prevailed here, they would be carried on towards the equator, as those without doubt are which originate at other places in the same latitude.

We come now ot the second part of our subject, the currents of the ocean.

The general motions of the ocean. - Inasmuch as the atmosphere and the ocean are both fluids somewhat similarly situated, except that there is a similarity of their general motions. This is known from observation to be the case, except that the continents interfere more with the motion of the ocean than with those of the atmosphere. The general motion of the ocean in the torrid zone, where it is not interrupted by continents, is toward the west with an average velocity of about ten miles in twenty-four hours. Towards the poles the motion, in general, is towards the east, which is a necessary consequence of the preservation of areas; for if one part have a western motion, another part must have an eastern one, as was shown with regard to the atmosphere. If, then, there were no continents, there would be a general flowing of all the tropical parts of the ocean westward, and of the remaining parts toward the east. But when the tropical or equatorial current impinges agains the eastern sides of the continents as in the Atlantic, a part is turned along the eastern side towards each pole. Likewise, when the eastern flow towards the poles, strikes against the western sides of a continent, it is deflected towards the equator. Hence the northern parts of both the Atlantic and Pacific, have a tendency to a vortical motion, their tropical parts moving westward, and then turning northward on the eastern sides of the continents and joining the eastern flow, and south again towards the equator on the western sides of the continents. And it is evident from observation, that the southern parts of these oceans, and also the Indian ocean, have a tendency, in some measure, to the same kind of motions, except that the continents do not extend so far south, and consequently only a part of the eastern flow is turned towards the equator, the rest flowing on and producing the general eastern motion of the waters observed in the southern ocean.

The forces which produce the motions of the ocean - The primum mobile of the motions of the ocean, as of the atmosphere, depends principally upon the difference of temperature between the equatorial and polar regions. The temperature of the ocean, on the surface at the equator, is about 80°, and it has a temperature above the mean temperature of the earth, which is 39°.5, to the depth of 7200 feet. Towards the poles it is below the freezing point, and continues below the mean temperature at the parallel of 70°, to the depth of 4500 feet.* As water expands about 0.000455 of its bulk for every degree of increasing tempeature, and sea-water contracts down to the temperature of 28°, calculations based upon these data, supposing the temperature to increase or decrease in proportion to the depth, make the specific gravity of the part at the equator, so much less than that at the poles, that it would have to rise about ten feet above the general level of the equator to be in equilibrium at the bottom of the sea, with the part at the poles. But then the equilibrium at the surface would be destroyed, and the waters would flow there towards the poles, where the superior pressure at the bottom over that of the equator, would cause a current to flow back at the bottom of the sea, towards the equator. Hence, if this cause of disturbance existed alone, ther would be a current at the bottom of the sea from the poles to the equator, moved by a force equal to the pressure of a stratum of water of about five feet, and one at the surface from the equator towards the poles, moved by an equal force. But this motion, combined with the rotatory motion of the earth, gives rise to other forces, just as in the case of the atmosphere, which greatly modify these motions, as will be shown hereafter.

The preceding are the principle forces concerned in giving motion ot the waters of the ocean. Lieutenant Maury, however, lays little stress upon these, and seems to think that the principle agencies concerned in these motions, arise from evaporation, the saltness of the ocean, galvanism, &c.* But we think it may be shown that these agencies can have no perceptible effect.

First, Lieutenant Maury supposes excessive evaporation to take place within the tropics and this vapor to be carried away and precipitated in extra-tropical regions, and infers that this would have, at least, a very sensible effect in producing the currents of the ocean. He puts the amount of evaporation of a stratum of one-half of an inch per day. Now if a stratum of water one-half of an inch in thickness is evaporated in twenty-four hours in one place and precipitated in another, it produces a difference of level of one inch between the two places, and the currents which it produces must be such as are sufficient to restore this level in the same space of time. Now we may judge how exceedingly small a current this would produce when we consider that there is a rise of about two feet in the open ocean at one place and a fall of the same amount at another every six hours, caused by the tides, and yet the flowing of the water from the one place to the other place to produce this rise at one place, and fall at the other, it is well known does not produce any sensible currents in the open sea. Again, this matter can be easily reproduced by calculation. If a stratum of water, one-half of an inch in thickness were taken up by evaporation from the torrid zone, and none of it precipitated there but all conveyed to the temperate and polar zones, it may be demonstrated upon the supposition that the ocean is four miles in depth, that the flow of water towards the equator to restore the equilibrium in the same time would not amount to a velocity of one foot per hour.

We think it may be likewise shown by calculations based upon reasonable hypothesis, if not entirely upon well-known data, that the salts of the sea also can have but little influence in producing currents. Lieutenant Maury makes a similar hypothesis in treating of the influence of the salt of the ocean, which he does in treating of the influence of evaporation, and supposes that the excess of salt left in the torrid zone by the excess of evaporation there, and the great precipitation in the temperate and polar regions produces such a difference in the specific gravity as to destroy the equilibrium of the sea, and to have a very sensible influence in producing current, and especially the Gulf-stream.

With regard to the latter, he supposes that the water of the Gulf of Mexico has a much greater specific gravity than the water in the Atlantic, on account of the great evaporation to which it has been exposed in its passage from the coast of Africa across the Atlantic ocean and through the Caribbean sea, and that, consequently, it is forced out into the Atlantic by its greater pressure. Now, suppose it takes the water a year, which is about the actual time, to pass from the coast of Africa to the Gulf of Mexico; in this time, according to the hypothesis, there is evaporated a stratum of water fifteen feet in depth, and, as the salt contained in this stratum cannot be evaporated, it remains in the part left, and increases it saltness. But sea-water contains only about three per cent of saline matter, and consequently the amount of salt contained in this stratum of fifteen feet only increases the weight of the rest to an amount equal to the weight of a stratum of water about six inches deep. Hence, it only gives the water of the Gulf a tendency to flow out into the Atlantic with a force equal to the force with which a homogenous fluid would flow out with its surface six inches above the general level of the Atlantic. This is much less than the opposing force arising from the great specific gravity of the water in the northern part of the Atlantic on account of its lower temperature, as we have shown by calculations. The same reasoning may be applied to any other part of the ocean; for, if the salt of the ocean has any influence in producing currents, it must be to produce an undercurrent from the torrid zone, where evaporation is supposed to be in excess, toward the poles, and consequently, a counter-current at the surface from the poles toward the equator. But, upon any reasonable hypothesis, the water at the surface cannot lose by evaporation in passing from the poles to the equator, a stratum of water of such a depth, that the amount of salt contained in it can increase the specific gravity at the equator as much as the lower temperature increases it toward the poles; hence, if the salt of the sea has any sensible influence, it is only in opposition to a greater influence, and, consequently, it has a tendency to diminish, rather than increase, the currents of the ocean. We think it, therefore, manifest that neither evaporation nor the salts of the sea can have much influence in producing currents, even upon Lieutenants Maury's hypothesis, that evaprotation is greatly in excess of precipitation in the torrid zone. But is this a true hypothesis? Although there is a great evaporation in the torrid zone, there is also great precipitation; for, with few exception, more rain falls at the equator than in any other part of the earth, and it is only the amount of evaporation over precipitation that should be taken into account, which we have reason to think is very small, and, if professor Espy's theory is correct, it can not be anything; for, according to this theory, no vapor can pass from the torrid to the temperate zones and produce rain, since the current bearing it there would be a descending current, and consequently could not produce it.

The ocean not level. - As it has been shown in the case of the atmosphere, that the resultant of the forces causes an accumulation about the parallels of 28°, so as the motions of the ocean are somewhat similar, and it is acted upon by the same forces, it may be shown that there must be a slight accumulation about those parallels in the ocean also. Whatever may be the causes of the motion of the ocean, we know that in the torrid zone it has a small western motion, and in the other parts a slight motion towards the east. The great equatorial current of the Atlantic moves about ten miles in twenty-four hours, but if we suppose that the average motion of the water in the torrid zone is five miles only per day, and that the mximum velocity of the water eastward in the extra-tropical regions is the same, using the same hypothesis we did with regard to the atmosphere, the forces which result from these motions must cause an accumulation of more than forty feet about the parallel of 28°, above the level of the sea at the poles, and about five feet above the level of the equator. This however, would be the amount of accumulation to produce an equilibrium of the forces at the surface, but as this accumulation would then produce greater pressure there upon the bottom than towards the poles and at the equator, it would produce, as in the case of the atmosphere, a flowing out from beneath this accumulation towards the poles and the equator, and settling down of the surface above, below the state of equilibrium, sufficient to cause a counter-current at the surface from the poles and the equator to supply the currents below. The accumulation there would be only about one-half that stated above, and there would be a flowing of water at the surface from both sides towards the parallel of 28°, and below a current in both directions from these parallels, similare to the motions in the atmosphere.

That the water of the ocean has such a motion as has been stated, appears from observations of its motions and other circumstances. Says Lieutenant Maury, "There seems to be a larger flow of polar water into the Atlantic than of waters from it, and I cannot account for the preservation of the equilibrium of this ocean by any other hypothesis than that which calls in the aid of undercurrents." It is well-known that in Baffin's bay there is a strong surface-current running south, and a strong counter-current beneath running north. Another evidence of this general tendency of the waters, is, that icebergs, in both hemispheres, are drifted from the poles towards the equator, and in the south Atlantic and Pacific oceans,there are large collections of drift and sea-weed about the parallels of 28°, so thickly matted that vessels are retarded in passing through them. [9]

These collections can only be formed by the flowing of the water at the surface from both sides to these parallels. It has been supposed that these collections are owing to the slight vortical motion of these oceans, it being supposed that any floating substances on the surface would have a tendency to collect at the vortex. This, however, would not be the case, for on account of friction at the bottom, the surface would have a greater vortical motion than the bottom, and consequently the water would be driven very slowly at the surface by the centrifugal force towards the sides, where it would cause a slight elevation and increase of pressure, which would cause the water to return towards the vortex at the bottom and not at the top; and hence floating substances at the surface could have no tendency to collect at the vortex.

We have corroborated these deductions from theory by numerous experiments made with a vessel of water with light substances on the surface. When the vessel is first receiving a vortical motion, the substances collect in the middle; for, as it is the vessel which gives motion to the water by means of the friction, the vessel, and consequently the bottom of the water, has then a greater motion than the top; and hence the reverse of what is stated above takes place; but, if the vessel is now stopped, and the water within allowed to continue its motion, the vortical motion at the bottom is retarded faster than at the top, and soon has a slower motion there, when the light substances on the surface are seen to recede from the vortex towards the sides, and if there are any light substances on the bottom they collect in the centre, all of which proves, that the water recedes from the middle at the surface, and returns to it at the bottom, and exactly agrees with the deductions from theory. These collections of sea-weed, then, cannot be caused by the vortical motions of the ocean, but must be the result of a general tendency of the surface water, to flow from both the equator and the poles towards these parallels; and, as it is prevented from collecting on these parallels near either side, on account of the slight vortical motion of the ocean, it collects only in the middle.

Explanation of the Gulf-stream - We come now to the Gulf-stream, which has been a puzzle to philosophers ever since it was discovered. Many explanations have been given, and all known forces which can have any influence, have been brought in to account for this wonderful phenomenon. The most usual explanation is, that it is the escaping of the waters which have been forced into the Caribbean sea and the Gulf of Mexico by the trade-winds, which have been supposed to raise their surface above the general level, and thus afford a head as it were for the stream. This, without doubt, has a very considerable effect, but it has not generally been deemed adequate alone to account for the phenomenon, nor does it, in connection with all other known influences, afford a satisfactory explanation. "What is the cause of the Gulf-stream." says Lieutenant Maury, "has always puzzled philosophers. Modern investigations are beginning to throw some light upon the subject, though still all is not yet clear."

We shall now endeavor to show that the additional force which we have taken into account in explaining both the winds and the currents of the ocean, and which seems to have been overlooked heretofore, will at least throw much additional light upon the subject, if not afford a complete explanation. We have shown that this force, which results form the eastward flow of the water in extra-tropical regions, and from the western motion within the tropics, has a tendency to drive the water from the poles towards the equator, and also slightly from the equator towards the poles, and to produce an accumulation of at least twenty feet on the parallel of 28° above the level at the poles, upon the supposition that the maximum of this east and west flow is only five miles per day. But if, from any cause, the force which results from this eastward flow should be cut off at any place, the water would flow northward at that place with a force equal to that which would result from a head on the parallels of 28°, at least twenty feet above the level towards the poles. Now, it may be seen from the configuration of the coast of the United States, that this force is actually cut off along that coast; for this force depends upon the eastward flow of the water there, which it cannot have, inasmuch as it must flow in both ways along the coast to fill up the vacuum which such a motion would produce. As the Gulf of Mexico, therefore, and the adjacent parts of the Atlantic, lie in the parallel of greatest accumulation, the water must flow from these parts along the coast with a force equal to that stated above. In addition to this, the momentum of the water flowing westward in the torrid zone, with a motion depending upon the prime moving course, due to a difference of specific gravity between the poles and the equator, in connection with the rotatory motion of the earth, and being independent of the effect of the trade-winds, must force the water in the Caribbean sea and the Gulf of Mexico considerably above the general level and add to the preceeding force. When we consider that the motion of the water which produces tides on our coasts, is in general imperceptible in the open ocean, and yet, on account of the sloping bottom of the ocean, which causes a smaller volume of water to receive the momentum of a larger one, it causes considerable rise of the water along the coast, we have reason to think that the general tendency of water westward in the torrid zone may keep the water in the Gulf considerably above the general level, since its water and that in the Caribbean sea, if the bottom of the ocean be sloping, must in great measure receive the momentum of the whole body of the water moving westward in the adjacent part of the Atlantic. The eastern tendency of the water in the northen part of the north Atlantic, due to the prime moving force mentioned above and independent of the winds which prevail there, causes the surface of the ocean in the latitude of Newfoundland to be somewhat depressed below the general level next to the coast, which also adds to the force of the Gulf-stream. All these forces, taken in connection withthe influence of the trade-windst, to which this phenomenon has been mainy attributed, we think, furnish a complete and satisfactory explanation of that great wonder and mystery of the ocean, the Gulf-stream.

The Greenland and other currents. - The general eastward motion of the waters of the ocean in the northern part of the Atlantic, and consequent depression next the coast of North America, also furnish an explanation of the cold current of water flowing between the Gulf-stream and the coast of the United States, called the Greenland current. On account of the rotatory motion of the earth, the water of the Gulf-stream in flowing northward, tends to the east, and for the same reason the water flowing from Greenland and Baffin's bay to supply the eastern flow, tends towards the west, and consequently flows in between the Gulf-stream and the coast of the United States.

There must be a motion of the waters somewhat similar to that of the Gulf-stream and the Greenland current, wherever the great equatorial current impinges against a continent, and the eastward flow towards the poles is cut off. Hence, on the eastern coast of South America, there is a warm Brazilian current towards Cape Horn, and on the eastern coast of Africa, the Mozambique current which at the Cape of Good Hope is called the Agulhas current. Also, on the eastern coast of Asia, there is the warm China current, flowing towards the north, similar to the Gulf-stream, and the cold Asiatic current, insinuating itself between it and the coast, like the Greenland current.

On the western side of the continents a motion somewhat the reverse of this must take place. Hence, instead of a warm stream flowing towards the north, there is a cold current flowing towards the equator. On the west of Portugal, and the northern part of Africa, there is a flow of colder water towards the equator, both to join the great equatorial current flowing across the Atlantic. On the west coast of South America, is Humboldt's current, 8° or 10° colder than the rest of the ocean in the same latitude, both tending towards the equator to there join the great western current across the Pacific, and to fill up, as it were, the vacuum which this current has a tendency to leave about the equator, on the western coast of America.

NASHVILLE, October 4, 1856.

• ↑ Physical Geography of the sea, page 70.
• ↑ Professor Espy's Third Report on Meterology, § 101.
• ↑ See Kaenitz' Meteorology. by C. Walker, page 277.
• ↑ See "Physical geography of the Sea" § 106.
• ↑ Third report on Meteorology §§ 68, 69.
• ↑ See W. C. Redfield Esq. on three several hurricanes, etc., in Silliman's Journal, second series, vol. I., page 13.
• ↑ Silliman's Journal, second series, Vol II., page 325.
• ↑ Maury's Physical Geography of the Sea § 224.
• ↑ Humbold's Cosmos, Vol. 2 page 278

This work was published before January 1, 1929, and is in the public domain worldwide because the author died at least 100 years ago.

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Ocean Currents

What is Ocean Current? It is a horizontal movement of seawater that is produced by gravity, wind, and water density. Ocean currents play an important role in the determination of climates of coastal regions.

As an important topic of Geography (Oceanography), questions could be framed either in Prelims or Mains (GS 1) papers of the IAS Exam .

Candidates can check previous years’ Geography Questions in UPSC Prelims in the linked article.

Understand the basics of ocean currents in this article.

Ocean Water and Ocean Currents

The movement of ocean water is continuous. This movement of ocean water is broadly categorized into three types:

The streams of water that flow constantly on the ocean surface in definite directions are called ocean currents.

Ocean currents are one of the factors that affect the temperature of ocean water.

• Warm ocean currents raise the temperature in cold areas
• Cold ocean currents decrease the temperature in warmer areas.

To understand the ocean waves and related concepts, check the links below:

Relevant Facts about Ocean Currents for UPSC

• The magnitude of the ocean currents ranges from a few centimetres per second to as much as 4 metres (about 13 feet) per second.
• The intensity of the ocean currents generally decreases with increasing depth.
• The speed of ocean currents is more than that of upwelling or downwelling which are the vertical movements of ocean water.
• Warm Ocean Currents
• Cold Ocean Currents

What causes ocean currents?

Horizontal pressure-gradient forces, Coriolis forces, and frictional forces are important forces that cause and affect ocean currents. NCERT Notes on Factors Affecting Wind mention Coriolis Force that one can read in the linked article.

Rise and fall of the tide

Tides give rise to tidal currents. Near the shore, tidal currents are the strongest. The change in tidal currents is periodical in nature and can be predicted for the near future. The speed of tidal currents at some places can be around 8 knots or more.

The ocean currents at or near the ocean surface are driven by wind forces.

Thermohaline Circulation

‘Thermo’ stands for temperature and ‘Haline’ stands for salinity. The variations in temperature and salinity at different parts of the oceans create density differences which in turn affect the ocean currents.

What is a Frictional Force?

The movement of water through the oceans is slowed by friction, with surrounding fluid moving at a different velocity. A faster-moving layer of water and a slower-moving layer of water would impact each other. This causes momentum transfer between both layers producing frictional forces.

What are geostrophic currents?

When the pressure gradient force on the ocean current is balanced by the Coriolis forces, it results in the geostrophic currents.

• The direction of geostrophic flow is parallel to an isobar.
• The high pressure is to the right of the flow in the Northern Hemisphere, and the high pressure to the left is found in the Southern Hemisphere.

North and South Equatorial Currents

North Equatorial Current

• North Equatorial Current flows from east to west in the Pacific and the Atlantic Ocean.
• North Equatorial Current flows between the latitudes of 10 degrees and 20 degrees north.
• It is not connected to the equator.
• Equatorial circulation separates this current between the Pacific and Atlantic oceans.

South Equatorial Current

• It flows in the Pacific, Atlantic, and Indian oceans.
• The direction of the south equatorial current is east to west.
• The latitudes in which the current flows are between the equator and 20 degrees south.
• It flows across the equator to 5 degrees north latitudes in the Pacific and Atlantic Oceans.

What is the Equatorial Counter Current?

It is found in the following three oceans:

• Indian Ocean
• Atlantic Ocean
• Pacific Ocean

It is found between north and south equatorial currents at about 3-10 degrees north latitude.

What is Antarctic Circumpolar Current?

The ocean current that flows clockwise around the Antarctic is called the Antarctic Circumpolar Current. It is also called West Wind Drift. It is a feature of ocean circulation of the Southern Ocean.

• It does not have a well-defined axis
• It consists of a series of individual currents which are separated by frontal zones.

What is a Global Conveyor Belt?

A system of ocean currents that helps in the transportation of water around the world is called a global conveyor belt. As per National Geographic, “Along this conveyor belt, heat and nutrients are moved around the world in a leisurely 1000-year cycle.”

Distribution of Ocean Currents

The ocean currents are distributed across five oceans. The list of important ocean-wise currents is given below:

Download the  UPSC syllabus from the linked article as it will help candidates to remain on track while they prepare for any topic.

Frequently Asked Questions on Ocean Currents

Q 1. what is meant by ocean current, q 2. what are tidal currents.

For Geography preparation, check the links below:

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Ocean Currents: Factors Affecting, Types & Effects

An ocean current is a continuous movement of s breakwater caused by various forces like wind, the Coriolis effect, waves, temperature, and salinity differences. These currents flow horizontally and can travel long distances. They created a global conveyor belt that greatly impacts the climate of different regions on Earth. Warm currents along coasts increase temperatures by warming the sea breezes. For instance, the Gulf Stream makes northwest Europe more temperate.

Ocean currents are driven by winds and water density, while factors like the shape of the ocean basin also influence them. There are two main types: surface currents and deep-water currents, which play a crucial role in shaping ocean waters worldwide.

Factors Acting on the Ocean Currents

Ocean currents are caused by various forces acting on seawater.

Pressure Gradient: These forces result from differences in water density due to temperature and salinity changes. The Coriolis Effect: – It is caused by Earth’s rotation and also plays a significant role in determining the direction of ocean currents. It causes moving objects to appear deflected in a particular direction, resulting in clockwise currents in the Northern Hemisphere and counterclockwise currents in the Southern Hemisphere. – The Coriolis force always acts perpendicular to motion and is influenced by the geographic latitude and the speed of the moving water. These forces, along with others, work together to create the complex patterns of ocean currents observed worldwide. Frictional Forces: When water moves through the oceans, it encounters friction, which slows it down. Imagine a faster-moving layer of water dragging along a slower-moving layer, causing a transfer of momentum between them. This is called frictional forces. The movement of water is affected by turbulence, transferring energy to smaller scales until it dissipates heat. Wind blowing over the sea surface also transfers momentum, creating wind-driven circulation. Ocean currents along the ocean floor and sides are also influenced by friction with the motionless ocean floor removing momentum from the water circulation. Geostrophic Currents: – In most of the ocean away from the boundary layers, frictional forces have less impact. The equation of motion for horizontal forces is a simple balance between the horizontal pressure gradient and the Coriolis force. This balance is called geostrophic balance. – On a non-rotating Earth, water would flow from high to low pressure due to a horizontal pressure gradient. – But since Earth rotates, the Coriolis force deflects the motion. The geostrophic balance is achieved when the Coriolis force exactly balances the pressure-gradient force. This results in currents called geostrophic currents. – The direction of these currents is perpendicular to the pressure gradient, with clockwise rotation in the Northern Hemisphere (anticyclonic motion) and counterclockwise rotation in the Southern Hemisphere (cyclonic motion). The relief of the sea surface also plays a role in defining the flow of geostrophic currents.

Two Types of Ocean Circulation

Ocean circulation is driven by two main factors: (1) wind-driven circulation , influenced by the wind’s force on the sea surface (2) thermohaline circulation , affected by changes in water density caused by heat and water exchange with the atmosphere. These two types of circulation are interconnected because wind speed affects both buoyancy and momentum exchange between the sea and air. The wind-driven circulation is stronger and forms circular patterns known as gyres, dominating different ocean regions. On the other hand, thermohaline circulation is slower, extending from the surface to the seafloor and covering the entire global ocean.

Wind-Driven Circulation

• Wind stress creates a similar circulation pattern in each ocean, forming gyres that span the whole ocean. Subtropical gyres stretch from the equator to the westerlies around 50° latitude, while subpolar gyres extend poleward from the westerlies.
• The depth of wind-driven currents depends on ocean stratification, with tropical regions having strong stratification and currents reaching less than 1,000 meters (about 3,300 feet) deep, while low-stratification polar regions have currents reaching the seafloor.

Equatorial Currents

• At the Equator, there are westward currents, called the North Equatorial Current in the Northern Hemisphere and the South Equatorial Current in the Southern Hemisphere.
• Near the thermal equator, an eastward-flowing current, the Equatorial Counter Current, is found just north of the geographic Equator.
• An undercurrent, the Equatorial Undercurrent, flows eastward below the surface current.
• These equatorial currents are affected by the Southern Oscillation, causing variations in circulation patterns known as El Niño events.

Effects of Ocean Currents on Climate and Ecology

• Ocean currents have a significant impact on climate and marine ecosystems.
• Influencing Local Temperature : They influence temperatures worldwide and play a role in preventing ice formation along seashores, affecting shipping routes.
• Survival Food Chain: Currents from polar regions carry plankton, essential for the survival of marine creatures.
• Importance for marine life : Ocean currents also help disperse life forms, including the life cycle of the European Eel.
• Shipping Industry: Understanding surface ocean currents is vital for shipping efficiency and has been critical for sailing ships in the past.
• Renewable Power Generation : Ocean currents can be used for marine power generation in certain regions.

What are Ocean Currents and Examples?

Ocean currents are continuous, directed movements of seawater flowing through the global oceans. They are driven by various factors, including wind, temperature, salinity and Earth’s rotation. Ocean currents play a crucial role in redistributing heat, nutrients and marine life across the planet, influencing climates and ecosystems. Examples of major ocean currents include the Gulf Stream, North Atlantic Drift, Antarctic Circumpolar Current, California Current, and the Kuroshio Current.

Why is an Ocean Current?

Ocean currents exist due to the combined effects of various forces acting on seawater. Wind-driven currents are caused by the transfer of momentum from the moving air to the ocean’s surface, creating circular gyres. Additionally, thermohaline circulation arises from variations in water density, influenced by temperature and salinity differences. Both wind-driven and thermohaline currents contribute to the ocean’s dynamic circulation, distributing heat and nutrients and shaping global climates.

What are Ocean Currents Briefly Explain.

Ocean currents refer to the continuous flow of seawater throughout the world’s oceans. They can be wind-driven, influenced by the force of winds on the sea surface, or thermohaline, driven by temperature and salinity variations. These currents play a vital role in redistributing heat, nutrients, and marine life, affecting global climates and ecosystems.

What are the 5 Major Ocean Currents?

The five major ocean currents are: a) Gulf Stream: Located in the North Atlantic, it transports warm water from the tropics to the North Atlantic region, affecting the climate of Western Europe. b) North Atlantic Drift: An extension of the Gulf Stream, it flows towards the northeast, carrying warm water along the western coasts of Europe. c) Antarctic Circumpolar Current: Encircling Antarctica, it connects the Atlantic, Pacific, and Indian Oceans, making it the largest and most important ocean current in the world. d) California Current: Flows southward along the western coast of North America, influencing the region’s climate and marine life. e) Kuroshio Current: Similar to the Gulf Stream, it carries warm water from the tropics to the western Pacific, impacting the climate and marine ecosystems of eastern Asia.

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Evolution of the most powerful ocean current on Earth

Ocean sediment cores reveal climate-related fluctuations in the Antarctic Circumpolar Current in past epochs

Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research

The US drilling vessel JOIDES Resolution carries out expeditions as part of the international Ocean Discovery Programme

Credit: International Ocean Discovery Program / Bill Crawford

The Antarctic Circumpolar Current plays an important part in global overturning circulation, the exchange of heat and CO2 between the ocean and atmosphere, and the stability of Antarctica’s ice sheets. An international research team led by the Alfred Wegener Institute and the Lamont-Doherty Earth Observatory have now used sediments taken from the South Pacific to reconstruct the flow speed in the last 5.3 million years. Their data show that during glacial periods, the current slowed; during interglacials, it accelerated. Consequently, if the current global warming intensifies in the future, it could mean that the Southern Ocean stores less CO2 and that more heat reaches Antarctica. The study was just released in the journal  Nature .

What moves 100 times as much water as all the Earth’s rivers combined, measures 2,000 kilometres across at its widest point, and extends all the way down to the deep sea? The Antarctic Circumpolar Current (ACC). In the past, this ocean current system, the most powerful on Earth, was subject to substantial natural fluctuation, as recent analyses of sediment cores have revealed. Colder phases in the Pliocene and subsequent Pleistocene, during which the ACC slowed, correlate to advances of the West Antarctic Ice Sheet. In warmer phases the ACC accelerated, accompanied by the retreat of the ice sheet. “This loss of ice can be attributed to increased heat transport to the south,” says Dr Frank Lamy, a researcher in the Marine Geology Division of the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) and first author of the  Nature  study. “A stronger ACC means more warm deep water reaches the ice-shelf edge of Antarctica.”

“The ACC has a major influence on heat distribution and CO2 storage in the ocean. Until recently, it remained unclear how the ACC responds to climate fluctuations, and whether changes in the ACC offset or amplify the effects of warming,” says Lamy. “Therefore, to improve forecasts of our future climate and the stability of the Antarctic Ice Sheet using computer simulations, we need paleo-data that can tell us something about the intensity of the ACC in past warm phases in Earth’s history.”

To gather that data, in 2019 an international expedition led by Lamy and geochemist Prof Gisela Winckler from the Lamont-Doherty Earth Observatory, Columbia University (USA) ventured to the central South Pacific on board the drilling ship  JOIDES Resolution . There, in the subantarctic zone, the research team extracted two extensive drill cores, gathered at a depth of 3600 metres. “The drill sites are in the vicinity of Point Nemo, the point on the Earth that is farthest from any landmass or island, where the ACC flows without any influences from continental landmasses,” explains Prof Helge Arz, a marine geologist at the Leibniz Institute for Baltic Sea Research in Warnemünde and one of the study’s main authors. “Using the sediment deposits in this region, we can reconstruct its mean flow speed in the past.”

The 145- and 213-metre-deep drill cores in the South Pacific were part of the International Ocean Discovery Program (IODP), the goal of which is to unlock Earth’s history on the basis of geochemical traces left behind in marine sediments and rock formations under the seafloor. They were preceded by extensive reconnaissance work done on various expeditions with the research vessel Polarstern. The sediment cores date back 5.3 million years and encompass three entire epochs: 

• the Pliocene, during which it was up to three degrees warmer than today and the atmospheric CO2 concentration, at more than 400 ppm, was similar to today’s;
• the Pleistocene, which began 2.6 million years ago and was characterised by alternating ice ages (glacials) and warm periods (interglacials);
• and the Holocene, a warm period that began roughly 12,000 years ago, following the last ice age, and continues up to the present.

Drawing on the layers in the cores, which correspond to different epochs, the experts analysed the size distribution of the sediment particles, which are deposited differently on the seafloor, depending on the water’s flow speed. This allowed them to trace the evolution of the ACC since the early Pliocene, when a prolonged cooling of the climate began. Sediment cores from previous Polarstern cruises to the South Pacific offered additional clues on the dynamics of the ACC.

Their findings show that, up to three million years ago in the Pliocene, the ACC first accelerated as the Earth gradually cooled. This was due to a growing temperature gradient between the Equator and Antarctica, which produced powerful westerly winds – the main motor of the ACC. Despite the prolonged cooling, it then began to slow. “The switch came at a time when the climate and the circulation in the atmosphere and the ocean experienced major changes,” says Frank Lamy. “2.7 million years ago, at the end of the Pliocene, broad expanses of the Northern Hemisphere were covered in ice and the Antarctic ice sheets expanded. This was due to changes in ocean currents, set off by tectonic processes, together with a long-term cooling of the ocean and decreasing atmospheric CO2 levels.”

With regard to the last 800,000 years, in which the atmospheric CO2 levels varied from 170 to 300 ppm, the researchers were able to identify a close connection between ACC strength and glacial cycles: during warm periods, in which the atmospheric CO2 levels rose, the flow speed increased by up to 80 percent compared to the present; during ice ages, it decreased by up to 50 percent. At the same time, during transitions between interglacials and glacials there was a shift in the ACC’s position and therefore in the upwelling of nutrient-rich deep water in the Southern Ocean, as geochemical sediment analyses revealed. They show that the silicate shells of diatoms – the most important phytoplankton in the Southern Ocean – were deposited on the seafloor farther north in ice ages than in warm periods.

“A weaker ACC and lower atmospheric CO2 levels during the ice ages of the Pleistocene indicate less pronounced upwelling and more stratification in the Southern Ocean, that is, more CO2 storage,” says Gisela Winckler. Due to anthropogenic climate change, the study concludes, the ACC could grow stronger in the future. This could impact the CO2 balance of the Southern Ocean and lead to accelerated melting of Antarctic ice.

Background: the Antarctic Circumpolar Current As a circular current flowing clockwise around Antarctica, the Antarctic Circumpolar Current (ACC) connects the Atlantic, Pacific and Indian Oceans. As such, it has a pivotal role in global ocean circulation and, through the Atlantic conveyor belt, ultimately influences the climate in Europe. Driven by the powerful westerly winds of the subantarctic zone, and by temperature and salinity differences between the subtropics and the Southern Ocean, the ACC forms a barrier for the warm surface water of the subtropics on its way to the Antarctic. At the same time, comparatively warm deep water from the Atlantic and Pacific flows into it. Large ocean gyres that are formed in the ACC and wander south, together with the upwelling of deep water, transport heat to the ice shelves on the continental margin, especially in the Pacific sector of the Antarctic. Moreover, the upwelling produced by the ACC brings nutrients to the surface, which drives algal growth while amplifying biological carbon export to the deep sea in the process – but also the transport of CO2, which is released into the atmosphere.

10.1038/s41586-024-07143-3

Method of Research

Observational study

Subject of Research

Not applicable

Article Title

Five million years of Antarctic Circumpolar Current strength variability

Article Publication Date

27-Mar-2024

Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.

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Study documents slowing of Atlantic currents

by Cazzy Medley, University of Maryland

While scientists have observed oceans heating up for decades and theorized that their rising temperatures weaken global currents, a new study led by a University of Maryland researcher documents for the first time a significant slowing of a crucial ocean current system that plays a role in regulating Earth's climate.

Published recently in Frontiers in Marine Science , the paper led by Earth System Science Interdisciplinary Center (ESSIC) scientist Alexey Mishonov examined decades of data on the Atlantic Meridional Overturning Circulation (AMOC) found in the National Oceanic and Atmospheric Administration's (NOAA) World Ocean Atlas.

Mishonov and co-authors Dan Seidov and James Reagan from NOAA discovered that the current system's flow remained stable and consistent from 1955 to 1994. However, in the mid-1990s, AMOC strength began to decline and the current began to move slower, which the scientists attribute to the continued warming of the ocean's surface and the accompanying changes in the salinity of its upper layers.

AMOC, which includes the Gulf Stream, carries warm water toward higher latitudes , releasing heat into the atmosphere and bringing cold waters to the tropics. This forms a continuous loop that redistributes heat across the ocean.

"If AMOC slows down, the heat exchange will be reduced, which in turn will affect the climate, causing hot areas to get hotter and cold areas to get colder," said Mishonov. This could lead to global climate changes, sea level rise, impact on marine ecosystems and other climate feedbacks.

A similar, but highly exaggerated and fictionalized dynamic powered the plot of the 2004 disaster blockbuster "The Day After Tomorrow," in which a flow of fresh water from melting glaciers led to the sudden collapse of North Atlantic Ocean currents, leading to outlandish effects like global superstorms and the sudden appearance of glaciers across much of the northern hemisphere.

"Of course, most climate scientists do not share these Hollywood fantasies, and no one inside scientific communities believes that anything remotely similar can happen," Mishonov said of the film. "However, most do believe that substantial slowing of AMOC might result in significant climate change that cannot be foreseen and predicted. Therefore, increased interest in AMOC functionality is fully warranted."

Mishonov and co-authors believe that the key to understanding the ocean climate trajectory is identifying how the North Atlantic climate responds to ongoing surface warming over decadal timespans.

The researchers used World Ocean Atlas data covering 1955–2017 as well as climate reanalysis data on decadal wind stress and sea surface height fields from UMD's Simple Ocean Data Assimilation project to determine fingerprints of the North Atlantic's circulation and AMOC's dynamics.

The authors found that although the entire North Atlantic is systematically warming, the climate trajectories in its different subregions reveal radically different characteristics of regional decadal variability, reflecting diverse climate patterns. For example, while the temperature has gradually increased from 1955 to 2017, it dropped in the more northern Atlantic from 1955 to 1994, then rose from 1995 to 2017. Similar patterns are also visible in salinity and density.

This variation in climate characteristics indicates that the current situation may not predict what the future may hold, including whether AMOC's slowdown will persist, accelerate or diminish in the next decade. However, the paper suggests that scenarios involving the slowdown or collapse of AMOC cannot be dismissed. Next, the authors plan to explore other regions of the global ocean to look for similar patterns in long-term temperature and salinity variability.

Journal information: Frontiers in Marine Science

Provided by University of Maryland

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News from the Columbia Climate School

Key Ocean Current Contains a Warning on Climate

Kevin Krajick

It carries more than 100 times as much water as all the world’s rivers combined. It reaches from the ocean’s surface to its bottom, and measures as much as 2,000 kilometers across. It connects the Indian, Atlantic and Pacific oceans, and plays a key role in regulating global climate. Continuously swirling around the southernmost continent, the Antarctic Circumpolar Current is by far the world’s most powerful and consequential mover of water. In recent decades it has been speeding up, but scientists have been unsure whether that is connected to human-induced global warming, and whether the current might offset or amplify some of warming’s effects.

In a new study, an international research team used sediment cores from the planet’s roughest and most remote waters to chart the ACC’s relationship to climate over the last 5.3 million years. Their key discovery: During past natural climate swings, the current has moved in tandem with Earth’s temperature, slowing down during cold times and gaining speed in warm ones―speedups that abetted major losses of Antarctica’s ice. This suggests that today’s speedup will continue as human-induced warming proceeds. That could hasten the wasting of Antarctica’s ice, increase sea levels, and possibly affect the ocean’s ability to absorb carbon from the atmosphere.

The findings were just published in the journal Nature.

“This is the mightiest and fastest current on the planet. It is arguably the most important current of the Earth climate system,” said study coauthor Gisela Winckler , a geochemist at Columbia University’s Lamont-Doherty Earth Observatory who co-led the sediment sampling expedition. The study “implies that the retreat or collapse of Antarctic ice is mechanistically linked to enhanced ACC flow, a scenario we are observing today under global warming,” she said.

The conditions for the ACC were set about 34 millions years ago, after tectonic forces separated Antarctica from other continental masses further north and the ice sheets began building up; the current is thought to have started flowing in its modern form 12 million to 14 million years ago. Driven by continuous westerly winds, and with no land in the way, it circles Antarctica clockwise (as seen from the bottom of the Earth) at about 4 kilometers (2.5 miles) per hour, carrying 165 million to 182 million cubic meters of water each second.

Scientists have observed that winds over the Southern Ocean have increased in strength about 40% in past 40 years . Among other things, this has speeded the ACC and energized large-scale eddies within it that move relatively warm waters from the higher latitudes toward Antarctica’s huge floating ice shelves, which hold back the even vaster interior glaciers. In parts of Antarctica, especially in the west, these warm waters are eating the undersides of the ice shelves―the main reason they are wasting, not warming air temperatures.

“If you leave an ice cube out in the air, it takes quite a while to melt,” said Winckler. “If you put it in contact with warm water, it goes rapidly.”

“This loss of ice can be attributed to increased heat transport to the south,” said the study’s lead author, Frank Lamy , of Germany’s Alfred Wegener Institute. “A stronger ACC means more warm, deep water reaches the ice-shelf edge of Antarctica.”

Through a complex set of processes, the ocean waters ringing Antarctica also currently absorb about 40% of the carbon that humans introduce into the atmosphere. It is unclear whether the speedup of the ACC will compromise this, but some scientists fear it will.

The study involved some 40 scientists from a dozen countries. At sea, aboard the drill ship JOIDES Resolution, researchers gathered ocean-floor sediment underlying the ACC near Point Nemo —the spot in the far southwestern Pacific that is farthest from land anywhere, some 2,600 kilometers from even the tiny Pitcairn Islands. The two-month cruise took place from May to July 2019, during the violent austral winter, when there was little daylight and waves as high as 20 meters threatened the ship.

The ship’s crew dropped a drill string some 3,600 meters from the ocean surface to the ocean floor. They then penetrated the floor and removed sediment cores measuring 150 and 200 meters each. Using an advanced X-ray technique, the scientists later analyzed layers built up over millions of years. Since smaller particles tend to settle during times when the current is sluggish and larger ones when it is fast, they were able to chart scores of changes in the ACC’s speed over time. Compared to the mean flow over the last 12,000 years―the period since the last ice age encompassing the development of human civilization―flows dropped by as much half during cold times, and at times nearly doubled during warm ones.

Using previous studies of the West Antarctic Ice Sheet , they correlated fast-flow periods with repeated bouts of ice retreat. These were punctuated by colder times, when glaciers advanced. The warmest extended period of the 5.3-million year record was during the Pliocene, which ended about 2.4 million years ago. After that came a period called the Pleistocene, when dozens of chilly glacial periods alternated with so-called interglacials, when temperatures rose, the current speeded up and the ice pulled back. Currently much of the West Antarctic Ice Sheet is frozen to land that is below sea level, so it is highly susceptible to invasion by warm ocean waters. Were it to melt entirely, it would raise global sea levels by about 190 feet.

“These findings provide geological evidence in support of further increasing ACC flow with continued global warming,” the researchers write in their paper. “If true, a future increase in ACC flow with warming climate would mark a continuation of the pattern observed in instrumental records, with likely negative consequences.”

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Ocean currents and their importance

Updated 22 May 2023

Subject Geography ,  Nature ,  United States

Downloads 41

Category Science ,  Environment ,  World

Topic Ocean ,  Sea ,  California

Ocean currents are vertical or horizontal movements that occur in the world's seas, both on the surface and deep depths. Currents typically move in one direction and aid in the circulation of moisture on the ground as a result of water pollution and weather. The size of ocean currents, which can be found all around the world. The most well-known currents include the California and Humboldt currents in the Pacific, the Atlantic, and the Monsoon Indian currents in the Indian Ocean (Chelton, Schlax, Michael, and Ralph 2004)

Ocean currents are classified into two categories. The sizes and strengths of the various varieties vary. They encompass both surface and deep ocean currents. Surface ocean currents are situated in the upper part of the ocean which is around 400 meters and they are making up around 10% of the total current oceans. Frictions of wind are the major causes of the surface ocean currents because wind creates frictions as it moves across the water. Water then moves in a pattern that is a spiral that is caused by the friction forces hence leading to the creation of gyres. Gyres can move to either clockwise or counterclockwise depending on their location. Those that are located in the Northern Hemisphere moves in the clockwise direction while those in the southern hemisphere moves in counter-clockwise direction (McCullough 1978, 9-33)

Surface currents move at a high speed which decreases at about 100 meters down the ocean. Surface currents usually move to long distances and for this reason, the Coriolis force plays an important role in the movement as it tends to aid them further hence helping them in the creation of circular patterns. Due to the unevenness of the current oceans the gravity plays an important role in the movement. Where the water meets the land mounds are usually made. They can also be formed where the currents merge or where water is warmer. Gravity is the one that leads to the formation of the currents as it pushes water down the slope on the mounds.

Deep water currents

Deep water currents are also known as thermohaline circulation are usually found deeper in the ocean for around 400 meters down. It makes up a larger part of ocean current which is about 90%. Gravity, just like in the surface currents also plays a role in this currents but this is usually created by the difference in the water densities. Salinity and temperature of the water is what creates the density difference in the water (Koblinsky, Niiler, and Schmitz 1989)

Warm water always holds less salt and for this reason, it is less dense than cold water that holds more salt hence the density difference. As the warm water rises it leaves a void that is filled with cold water and as cold water rises it also leaves a space that is filled with warm water. This forms a thermohaline circulation. This thermohaline circulation can be also be referred to as the global conveyor belt because this movement of water forms a circle that acts as a submarine river that moves water all over the ocean (Peplow 2006).

Seafloor topography and the ocean's shape affects both surface and deep water currents because of the restrictions they give concerning where water can move.

Importance of ocean currents

Ocean currents have a significant importance in the movement of energy and moisture throughout the atmosphere. For this reason, they have a positive impact on the weather of the world. For instance, the Gulf Stream originates from the Gulf of Mexico to Europe and has warm currents. This warm current makes the water in the Gulf warm. Since the water is warm, the surface also is warm and this warms keeps Europe warmer than other places with the same latitude as Europe (Scheltema & Rudolf 1968)

The Humboldt currents, just like the Gulf affects the weather. When the currents of Chile and Peru coasts are cold they create productive waters that usually keep the coast cool and arid in the northern Chile. The climate in Chile usually changes when these currents are disrupted and El Nino is believed to be the main cause of the disturbance.

Like the movement of moisture and energy debris can be moved around the world after being trapped by the currents. This can be used in the formation of icebergs and trash islands and it can be created by man.

In the arctic ocean, along with the coasts of Newfoundland and Nova Scotia, the Labrador currents are formed there and it is very famous in the iceberg shipping into lanes in North of the Atlantic.

Navigation can also be assisted by currents plan. Shipping costs and also consumption of fuel can be reduced with the knowledge of the currents by avoiding trash and also icebergs. To reduce the amount of time that is spent on the sea, shipping companies and also sailing races always apply the knowledge of the currents to reduce the amount of time spent on the sea.

Last but not least, the world’s sea life can be distributed by the ocean currents. The movement of the many species always depends on the waves to move them from one location to another. It does not need necessarily be for breeding, it can be a movement over large seas.

Ocean currents as alternative energy

Ocean currents can be used as an alternative to energy in today world. Water carries an enormous amount of energy because of its density. This energy could be captured and used for instance in the driving of water turbines. Some countries like USA, Japan, China, and German are testing this kind of energy.

Ocean currents are also important to geographers, meteorologists and another scientist in the earth atmosphere relation. This is another alternative use besides the energy use.

Vertical stratification of water

The vertical appropriation of water densities in collections of fresh or salt water is known as stratification and is portrayed by the vertical density slope. The more the expansion in density with depth and the greater the vertical slope, the higher the steadiness of the stratification. At the point when the vertical density inclination is small or the density diminishes with depth, the stratification is unsteady. Stable stratification causes a diminishing in the vertical exchange of warmth, mass, and force. Unsteady stratification prompts serious vertical exchange in the body of water (Bianchi, Alejandro, Bianucci, Piola, Pino, Schloss, Poisson, & Balestrini 2005)

In seas and oceans, stratification is represented for the most part by varieties in water temperature and saltiness at the surface and furthermore beneath the surface, where the varieties are because of change in weather conditions and adiabatic procedures.

In bodies of fresh water, the temperature of the water greatest density is 4°C, and the stratification depends exclusively on temperature. For this situation, two sorts of stratification are conceivable: direct and inverse. Direct stratification happens when the temperature of all the water in the lake is not under 4°C. The hottest masses of water at that point lie at the surface; the cooler alternate masses, the greater the depth at which they are found. Inverse stratification happens when the water temperature is under 4°C. The water at the surface is then cooler than in the lower layers (Pollard, Raymond &June 2017, 36-43)

Hydrographic structure, as temperature or saltiness stratification, speed shear, and turbulent blending can make biologically critical highlights with horizontal scales running from 100s to 1000s of meters, and vertical sizes of centimeters to a couple of meters. As of late, the significance of fine-scale vertical structure in the water segment has turned out to be all the more recognized. Thin layers seem to happen in zones of the water segment containing vertical density jumps and speed shear. Where these layers happen they may fill in as habitats for exceptional connections in marine food webs. Gradients may moderate sinking rates and cause the gathering of flocs, marine snow, phytoplankton, and microbial groups in a few layers.

Regularly, these layers create solid optical or acoustic signs proposing expanded phyto-and zooplankton plenitude. Also, the speed shear related with these features may impact the transport of hatchlings and effective conveyance to juvenile nursery regions. Very little is thought about these structures in the New Jersey and Middle Atlantic Bight areas. In the New York Bight Apex, a zone that ensures the results of being almost a vast human populace, thin layers might be instrumental in the cycling of supplements and contaminants through the framework and coordinating them into higher trophic levels. Hence, it is basic for us to comprehend the structure and capacity of these interesting biological communities.

Regional distribution of salinity, temperature, and pressure in the ocean circulation

Temperature

The temperature of seawater is settled at the ocean surface by warm exchange with the air. The normal approaching vitality from the sun at the earth’s surface is about four times higher at the equator than at the poles. The normal infrared radiation heat loss to space is more consistent with latitudes. As a result there is a net contribution of warmth to the earth's surface into the tropical districts, furthermore, this is the place we locate the hottest surface seawater. Warmth is then exchanged from low to high scopes by twists in the wind and by currents in the ocean.

The geothermal heat motion from the inside of the Earth is for the most part inconsequential but in the region of aqueous vents at spreading edges and in generally dormant areas like the deep northern North Pacific. Water is transparent, so the radiation infiltrates some distance beneath the surface; heat is additionally conveyed to further levels by blending. Because of the high specific heat of water, diurnal also seasonal temperature varieties are relatively small compared with the shallow ends of water; maritime temperature varieties are on the request of a couple of degrees, with the exception of an extremely shallow water.

Most solar energy is retained inside a couple of meters of the sea surface, directly warming the surface water and giving the vitality to photosynthesis by marine plants and algae. Shorter wavelengths penetrate further than longer wavelengths. Infrared radiation is the first to be retained, trailed by red, etc. Warmth conduction from itself is extremely slow, so just a little extent of warmth is exchanged downwards by this process. The principal component to exchange warm further is turbulent blending by winds and waves, which sets up a mixed surface layer that can be as thick as 200-300 meters or considerably more at mid-latitudes in the untamed sea in winter or under 10 meters in shielded coastal front waters in summer.

Salinity distribution

The saltiness of surface seawater is controlled basically by the harmony between dissipation and precipitation. Subsequently, the most elevated salinities are found in the purported sub-tropical focal gyre areas focused at around 20° to 30° North and South, where dissipation is broad however precipitation is insignificant. The highest surface salinities, other than evaporating bowls, are found in the Red Sea.

Why is saltiness important?

1. Saltiness, alongside temperature, determines the density of seawater, and subsequently its vertical stream designs in thermohaline flow.

2. Saltiness records the physical procedures influencing a water mass when it was last at the surface.

precipitation/vanishing – salts barred from vapor

solidifying/defrosting – salts avoided from ice

3. Saltiness can be utilized as a moderate (constant) tracer for deciding the birthplace and mixing of water types.

Surface seawater salinities generally measure the local balance between dissipation and precipitation.

Low salinities happen close to the equator because of rain from rising environmental flow.

High salinities are run of the mill of the hot dry gyres flanking the equator (20-30 degrees scope) where climatic flow cells dive.

Saltiness can also be influenced by ocean ice formation/dissolving (e.g. around Antarctica)

Since the seawater marks of temperature and saltiness are obtained by processes at the air-ocean interface, we can also say that the density qualities of a parcel of seawater are resolved when it is at the ocean surface. Temperatures of seawater fluctuate greatly (- 1° to 30°C), though the saltiness run is little (35.0 more or less 2.0). The North Atlantic contains the hottest and saltiest water of the major seas, the Southern Ocean (the district around Antarctica) is the coldest, and the North Pacific has the least normal saltiness.

This densities mark is bolted into the water parcel when it sinks. The densities will be altered by mixing with different parcels of water, however, in the event that the density marks of all the end part water masses are known, this mixing can be disentangled and the extents of the diverse source waters to a given bundle can be resolved. To a first guess, the vertical thickness conveyance of the sea can be portrayed as a three-layered structure. The thickness reliance of seawater on saltiness, temperature, and weight has been resolved and figured, and conditions portraying this connection can be utilized. The densities of seawater is an element of temperature, weight, and saltiness and is a key oceanographic property. The normal density of seawater is close to 1.025gm cm-3.

While considering the solidness of a water section, it is helpful to have the capacity to ascertain the densities of a water relative to its surroundings from consideration just of its temperature and saltiness.

Ocean circulation

The chemistry and biology of the ocean are superimposed on the ocean’s flow, in this way it is vital to oversee briefly the powers driving this flow and give a few estimates of the transport rates. There are many reasons why it is vital to understand the basics of the circulation. For instance;

Poleward streaming, warm, surface, western currents boundaries and flows, for example, the Gulf Stream and the Kuroshio profoundly affect the sea surface temperature (SST) and the atmosphere of land territories flanking the ocean

The El-Nino Southern Oscillation (ENSO) marvel is interannual irritation of the atmosphere framework described by debilitating of the exchange winds also, warming of the surface water in the central and eastern central Pacific Sea. The effects of ENSO are felt worldwide through disturbance of wind movement and weather patterns

Deep Circulation

The flow of the profound sea beneath the thermocline is known to as abyssal circulation. The currents are slow (~ 0.1 m/sec) and hard to quantify, however, the example of circulation can be unmistakably found in the properties of the deep water masses (temperature and saltiness). The geography of the ocean floor assumes a vital part in obliging the circulation and a significant part of the deep stream is channeled through entries, for example, the Denmark Straight, Gibbs Fracture Zone, Vema Channel, Samoan Passage, furthermore, Drake Passage

The Global Conveyor Belt (Rahmstorf & Stefan 2002, 207)

The sea transport line is one of the real components of the present sea dissemination system. A key component is that it conveys a tremendous measure of warmth to the North Atlantic and this has significant ramifications for past, present, and likely future atmospheres. Warm and salty surface streams in the western North Atlantic (e.g. the Gulf Stream) transport heat to the Norwegian-Greenland Seas where the warmth is exchanged to the environment. The cooling increases the density of ocean water bringing about the development of frosty and salty water in the North Atlantic. This water sinks to the depth and forms the North Atlantic Deep Water (NADW).

Thermohaline going round drives a worldwide scale arrangement of currents called the "global conveyor belt." The conveyor belt starts on the surface of the sea close to the pole in the North Atlantic. Here, the water is chilled by cold temperatures. It also gets saltier in light of the fact that when ocean ice shapes, the salt does not solidify and is left in the surrounding water. The chilly water is currently denser, due to the additional salts, and sinks toward the sea base. Surface water moves in to supplant the sinking water, in this manner making an ebb and flow.

This deep water moves south, between the landmasses, past the equator, and down to the closures of Africa and South America. The current flow goes around the edge of Antarctica, where the water cools and sinks once more, as it does in the North Atlantic. In this way, the conveyor belt gets "revived." As it moves around Antarctica, two areas split off the conveyor belt and turn northward. One segment moves into the Indian Ocean, the other into the Pacific Ocean.

These two areas that split off warm up and turn out to be less dense as they travel northward toward the equator, with the goal that they ascend to the surface (upwelling). They at that point circle back southward and westbound toward the South Atlantic, at the end coming back toward the North Atlantic, where the cycle starts once more.

The transport line moves at much slower speeds (a couple of centimeters for each second) than wind-driven or tidal streams (tens of several centimeters for each second). It is assessed that any given cubic meter of water takes around 1,000 years to finish the adventure along the worldwide transport line. Also, the transport moves an enormous volume of water—more than 100 times the stream of the Amazon River (Ross, 1995).

The conveyor belt is likewise a key part of the worldwide sea supplement and carbon dioxide cycles. Warm surface waters are drained of supplements and carbon dioxide, however, they have improved again as they go through the transport line as profound or base layers. The base of the world's natural way of life relies upon the cool, supplement rich waters that help the development growth of algae and seaweed.

Gulf Stream ocean currents

Starting in the Caribbean and ending in the northern North Atlantic, the Gulf Stream System is one of the world's most strongly considered current systems. This broad western limit current assumes an imperative part in the poleward exchange of warmth and salt and serves to warm the European subcontinent. Conventional hydrographic examinations in this district incorporate those of Iselin (1936) and Gulf Stream '60 (Fuglister 1963, 184). The high level of mesoscale action related with this framework additionally has pulled in oceanographers. Research of these marvels have concentrated on the "snapshot" presentation of the region and have included examinations, for example, SYNOP, Gusto, and ABCE/SME. The Gulf Stream system is sufficiently effective to be promptly observed from space and was seen in even the most punctual satellite altimetry studies, for example, Seasat and later Geosat. Strong thermal gradient additionally made it visible to infrared estimations, as VHRR (Very High-Resolution Radiometer) readings utilizing the early NOAA satellites, THIR (Temperature and Humidity Infrared Radiometer) readings from Nimbus satellites, and Advanced VHRR (AVHRR) readings from later NOAA satellites.

The Gulf Stream starts upstream of Cape Hatteras, where the Florida Current stops to take after the mainland rack. The position of the Stream as it leaves the drift changes consistently. In the fall, it moves north, while in the winter and late-winter it moves south. Contrasted and the width of the current (around 100-200 km), the scope of this variety (30-40 km) is moderately small. However, late investigations recommend that the meridional scope of the yearly variation in stream way might be more like 100 km. Different qualities of the current are more factor. Critical changes in its vehicle, wandering, and structure can be seen through many timescales as it voyages upper east.

The transport of the Gulf Stream about copies downstream of Cape Hatteras at a rate of 8 Sv each 100 km (Knauss 1969). It creates the impression that the downstream increment in transport between Cape Hatteras and 55°W is generally because of expanded speeds in the deep waters of the Gulf Stream (Johns et al. 1995). This expansion in speed is believed to be related to profound distribution cells discovered north and south of the present (Hall and Fofonoff 1993). Cases of these distributions incorporate little distributions east of the Bahamas (Olson et al. 1984; Lee et al. 1990), the Worthington Gyre south of the Gulf Stream in the vicinity of 55° and 75°W (Worthington 1976), and the Northern Recirculation Gyre north of the Gulf Stream (Hogg et al. 1986). Late investigations recommend that the distributions relentlessly increment the vehicle in the Gulf Stream from 30 Sv in the Florida Current to a most extreme of 150 Sv at 55°W (Hendry 1982,).

The region of the Gulf Stream's branch point is exceedingly unique and subject to quick change. The high level of mesoscale movement, alongside quick changes in the significant surface streams, make this an extremely troublesome locale to study. Some portion of this inconstancy emerges from the high measure of vortex action. Vortex dynamic vitality along both the Gulf Stream and the North Atlantic Current is at peak value here (Richardson 1983, 19). There is also the presence of elongated, high- pressure cells along the seaward side of the North Atlantic Current. These weight cells might be connected to upheavals of Labrador Current water from the Grand Banks that prompt broad mixing toward the end of the Gulf Stream

Bibliography

Rahmstorf, Stefan. "Ocean circulation and climate during the past 120,000 years." Nature 419, no. 6903 (2002): 207-214.

Pollard, Raymond, and Jane Read. "Circulation, stratification and seamounts in the Southwest Indian Ocean." Deep Sea Research Part II: Topical Studies in Oceanography 136 (2017): 36-43.

Molinari, Robert L., Donald Olson, and Gilles Reverdin. "Surface current distributions in the tropical Indian Ocean derived from compilations of surface buoy trajectories." Journal of Geophysical Research: Oceans 95, no. C5 (1990): 7217-7238.

McCullough, J. "Near-surface ocean current sensors: Problems and performance." In Current Measurement, Proceedings of the 1978 IEEE First Working Conference on, vol. 1, pp. 9- 33. IEEE, 1978.

Ellison, Christopher RW, Mark R. Chapman, and Ian R. Hall. "Surface and deep ocean interactions during the cold climate event 8200 years ago." Science 312, no. 5782 (2006): 1929-1932.

Fuglister, Frederick C. "Gulf stream'60." Progress in oceanography 1 (1963): 265IN9273IN11275-272274IN14373.

Richardson, P. L. "Gulf stream rings." In Eddies in marine science, pp. 19-45. Springer, Berlin, Heidelberg, 1983.

Hendry, R. M. "On the structure of the deep Gulf Stream." Journal of Marine Research (1982).

Knauss, John A. "A note on the transport of the Gulf Stream." Deep-Sea Res. 16 (1969): 117- 123.

Peplow, Mark. "Ocean currents flip out." Nature (2006).

Calsbeek, Ryan, and Thomas B. Smith. "Ocean currents mediate evolution in island lizards." Nature 426, no. 6966 (2003): 552-555.

Chelton, Dudley B., Michael G. Schlax, Michael H. Freilich, and Ralph F. Milliff. "Satellite measurements reveal persistent small-scale features in ocean winds." science 303, no. 5660 (2004): 978-983.

Stramma, Lothar, and Matthew England. "On the water masses and mean circulation of the South Atlantic Ocean." Journal of Geophysical Research: Oceans 104, no. C9 (1999): 20863-20883.

Koblinsky, Cl J., P. P. Niiler, and W. J. Schmitz. "Observations of wind‐forced deep ocean currents in the North Pacific." Journal of Geophysical Research: Oceans 94, no. C8 (1989): 10773-10790.

Scheltema, Rudolf S. "Dispersal of larvae by equatorial ocean currents and its importance to the zoogeography of shoal-water tropical species." Nature 217, no. 5134 (1968): 1159-1162.

Bianchi, Alejandro A., Laura Bianucci, Alberto R. Piola, Diana Ruiz Pino, Irene Schloss, Alain Poisson, and Carlos F. Balestrini. "Vertical stratification and air‐sea CO2 fluxes in the Patagonian shelf." Journal of Geophysical Research: Oceans 110, no. C7 (2005).

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Evolution of the most powerful ocean current on Earth

Ocean sediment cores reveal climate-related fluctuations in the antarctic circumpolar current in past epochs.

The Antarctic Circumpolar Current plays an important part in global overturning circulation, the exchange of heat and CO 2 between the ocean and atmosphere, and the stability of Antarctica’s ice sheets. An international research team led by the Alfred Wegener Institute and the Lamont-Doherty Earth Observatory have now used sediments taken from the South Pacific to reconstruct the flow speed in the last 5.3 million years. Their data show that during glacial periods, the current slowed; during interglacials, it accelerated. Consequently, if the current global warming intensifies in the future, it could mean that the Southern Ocean stores less CO 2 and that more heat reaches Antarctica. The study was just released in the journal  Nature.

What moves 100 times as much water as all the Earth’s rivers combined, measures 2,000 kilometres across at its widest point, and extends all the way down to the deep sea? The Antarctic Circumpolar Current (ACC). In the past, this ocean current system, the most powerful on Earth, was subject to substantial natural fluctuation, as recent analyses of sediment cores have revealed. Colder phases in the Pliocene and subsequent Pleistocene, during which the ACC slowed, correlate to advances of the West Antarctic Ice Sheet. In warmer phases the ACC accelerated, accompanied by the retreat of the ice sheet. “This loss of ice can be attributed to increased heat transport to the south,” says Dr Frank Lamy, a researcher in the Marine Geology Division of the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) and first author of the  Nature  study. “A stronger ACC means more warm deep water reaches the ice-shelf edge of Antarctica.”

“The ACC has a major influence on heat distribution and CO 2 storage in the ocean. Until recently, it remained unclear how the ACC responds to climate fluctuations, and whether changes in the ACC offset or amplify the effects of warming,” says Lamy. “Therefore, to improve forecasts of our future climate and the stability of the Antarctic Ice Sheet using computer simulations, we need paleo-data that can tell us something about the intensity of the ACC in past warm phases in Earth’s history.”

To gather that data, in 2019 an international expedition led by Lamy and geochemist Prof Gisela Winckler from the Lamont-Doherty Earth Observatory, Columbia University (USA) ventured to the central South Pacific on board the drilling ship  JOIDES Resolution . There, in the subantarctic zone, the research team extracted two extensive drill cores, gathered at a depth of 3600 metres. “The drill sites are in the vicinity of Point Nemo, the point on the Earth that is farthest from any landmass or island, where the ACC flows without any influences from continental landmasses,” explains Prof Helge Arz, a marine geologist at the Leibniz Institute for Baltic Sea Research in Warnemünde and one of the study’s main authors. “Using the sediment deposits in this region, we can reconstruct its mean flow speed in the past.”

The 145- and 213-metre-deep drill cores in the South Pacific were part of the International Ocean Discovery Program (IODP), the goal of which is to unlock Earth’s history on the basis of geochemical traces left behind in marine sediments and rock formations under the seafloor. They were preceded by extensive reconnaissance work done on various expeditions with the research vessel Polarstern. The sediment cores date back 5.3 million years and encompass three entire epochs: 

• the Pliocene, during which it was up to three degrees warmer than today and the atmospheric CO 2 concentration, at more than 400 ppm, was similar to today’s;
• the Pleistocene, which began 2.6 million years ago and was characterised by alternating ice ages (glacials) and warm periods (interglacials);
• and the Holocene, a warm period that began roughly 12,000 years ago, following the last ice age, and continues up to the present.

Drawing on the layers in the cores, which correspond to different epochs, the experts analysed the size distribution of the sediment particles, which are deposited differently on the seafloor, depending on the water’s flow speed. This allowed them to trace the evolution of the ACC since the early Pliocene, when a prolonged cooling of the climate began. Sediment cores from previous Polarstern cruises to the South Pacific offered additional clues on the dynamics of the ACC.

Their findings show that, up to three million years ago in the Pliocene, the ACC first accelerated as the Earth gradually cooled. This was due to a growing temperature gradient between the Equator and Antarctica, which produced powerful westerly winds – the main motor of the ACC. Despite the prolonged cooling, it then began to slow. “The switch came at a time when the climate and the circulation in the atmosphere and the ocean experienced major changes,” says Frank Lamy. “2.7 million years ago, at the end of the Pliocene, broad expanses of the Northern Hemisphere were covered in ice and the Antarctic ice sheets expanded. This was due to changes in ocean currents, set off by tectonic processes, together with a long-term cooling of the ocean and decreasing atmospheric CO 2 levels.”

With regard to the last 800,000 years, in which the atmospheric CO 2 levels varied from 170 to 300 ppm, the researchers were able to identify a close connection between ACC strength and glacial cycles: during warm periods, in which the atmospheric CO 2 levels rose, the flow speed increased by up to 80 percent compared to the present; during ice ages, it decreased by up to 50 percent. At the same time, during transitions between interglacials and glacials there was a shift in the ACC’s position and therefore in the upwelling of nutrient-rich deep water in the Southern Ocean, as geochemical sediment analyses revealed. They show that the silicate shells of diatoms – the most important phytoplankton in the Southern Ocean – were deposited on the seafloor farther north in ice ages than in warm periods.

“A weaker ACC and lower atmospheric CO 2 levels during the ice ages of the Pleistocene indicate less pronounced upwelling and more stratification in the Southern Ocean, that is, more CO 2 storage,” says Gisela Winckler. Due to anthropogenic climate change, the study concludes, the ACC could grow stronger in the future. This could impact the CO 2 balance of the Southern Ocean and lead to accelerated melting of Antarctic ice.

Background: the Antarctic Circumpolar Current

As a circular current flowing clockwise around Antarctica, the Antarctic Circumpolar Current (ACC) connects the Atlantic, Pacific and Indian Oceans. As such, it has a pivotal role in global ocean circulation and, through the Atlantic conveyor belt, ultimately influences the climate in Europe. Driven by the powerful westerly winds of the subantarctic zone, and by temperature and salinity differences between the subtropics and the Southern Ocean, the ACC forms a barrier for the warm surface water of the subtropics on its way to the Antarctic. At the same time, comparatively warm deep water from the Atlantic and Pacific flows into it. Large ocean gyres that are formed in the ACC and wander south, together with the upwelling of deep water, transport heat to the ice shelves on the continental margin, especially in the Pacific sector of the Antarctic. Moreover, the upwelling produced by the ACC brings nutrients to the surface, which drives algal growth while amplifying biological carbon export to the deep sea in the process – but also the transport of CO 2 , which is released into the atmosphere.

• Global Warming
• Oceanography
• Early Climate
• Origin of Life
• El Niño-Southern Oscillation
• Ocean current
• Global warming

Story Source:

Materials provided by Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research . Note: Content may be edited for style and length.

Journal Reference :

• Frank Lamy, Gisela Winckler, Helge W. Arz, Jesse R. Farmer, Julia Gottschalk, Lester Lembke-Jene, Jennifer L. Middleton, Michèlle van der Does, Ralf Tiedemann, Carlos Alvarez Zarikian, Chandranath Basak, Anieke Brombacher, Levin Dumm, Oliver M. Esper, Lisa C. Herbert, Shinya Iwasaki, Gaston Kreps, Vera J. Lawson, Li Lo, Elisa Malinverno, Alfredo Martinez-Garcia, Elisabeth Michel, Simone Moretti, Christopher M. Moy, Ana Christina Ravelo, Christina R. Riesselman, Mariem Saavedra-Pellitero, Henrik Sadatzki, Inah Seo, Raj K. Singh, Rebecca A. Smith, Alexandre L. Souza, Joseph S. Stoner, Maria Toyos, Igor M. Venancio P. de Oliveira, Sui Wan, Shuzhuang Wu, Xiangyu Zhao. Five million years of Antarctic Circumpolar Current strength variability . Nature , 2024; 627 (8005): 789 DOI: 10.1038/s41586-024-07143-3

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Strange & offbeat.

Strongest ocean current on Earth is speeding up and causing problems

T he Antarctic Circumpolar Current (ACC) is the most powerful current on Earth, encircling Antarctica and influencing the global climate .

Over the last few decades, observations show that it has been speeding up. Experts were uncertain whether this was a result of human-caused warming or a natural pattern.

However, scientists have discovered that this oceanic powerhouse is getting even stronger. What does this mean for our planet's future?

Ocean depths

An international team of researchers embarked on a daring expedition to remote, turbulent waters. The goal was to recover sediment cores containing millions of years' worth of clues about the ACC's behavior alongside Earth's temperature changes.

Through meticulous analysis, the experts uncovered the secrets held within the layers of sediment.

Current, climate, and ice

The study reveals a strong link between the ACC's speed and Earth's overall temperature, much like a thermostat.

During colder periods, the current slowed down. But when the planet warmed up naturally in the past, the current responded by speeding up.

What's truly alarming is that these past ACC speedups were directly connected to major losses of Antarctic ice . We're observing a similar speedup of the ACC right now , driven by human-caused warming.

This suggests that Antarctica's ice will likely continue to retreat – potentially fueling sea-level rise and even affecting the ocean's ability to soak up carbon from our atmosphere.

Why Antarctic currents matter

"This is the mightiest and fastest current on the planet. It is arguably the most important current of the Earth climate system," said Gisela Winckler, a geochemist at Columbia University's Lamont-Doherty Earth Observatory .

ACC is a major player in Earth's climate system, acting as a global conveyor belt that redistributes heat and nutrients across the world's oceans.

Characteristics of the ACC

Vast scale : The ACC is the largest ocean current, stretching around Antarctica and connecting the Atlantic, Pacific, and Indian Oceans. It's the only ocean current that encircles the globe completely, free from any continental barriers.

Volume and speed : It transports more water than any other current -- approximately 135 million cubic meters per second. Its flow is influenced by wind patterns, the Earth's rotation, and differences in water density.

Depth and width : The ACC extends from the surface to the ocean floor, reaching depths of up to 4,000 meters (about 13,123 feet) and spans widths of up to 2,000 kilometers (about 1,243 miles).

Functions of the ACC

Climate regulation : The ACC plays a crucial role in regulating the global climate. It helps distribute heat around the planet by moving warm water from the equator towards the poles and cold water towards the equator.

Carbon sequestration : The ACC is instrumental in the global carbon cycle. It absorbs significant amounts of carbon dioxide from the atmosphere, transporting it deep into the ocean where it can be stored for centuries.

Nutrient distribution : By stirring up water from different depths (upwelling), the ACC brings nutrients from the deep to the surface, supporting marine ecosystems around Antarctica and beyond.

Importance of the ACC

Biodiversity support : The nutrients brought to the surface by the ACC support phytoplankton blooms, which are the foundation of the Antarctic food web, sustaining a diverse array of marine life from krill to whales.

Impact on global ocean circulation : The ACC influences global ocean circulation patterns, including the formation of deep water masses in the North Atlantic that drive the global conveyor belt, a critical component of Earth's climate system.

Climate change indicator : Changes in the speed or pattern of the ACC can indicate alterations in the global climate system. Its acceleration due to increased westerly winds is a concern, as it could have implications for sea-level rise and global temperature patterns.

The ocean's influence on Antarctic current

How does the speeding up of the ACC affect things directly? Here's how:

Melting Antarctica's ice shelves

Winds over the Southern Ocean have grown about 40% stronger in the past few decades, driving the ACC and pulling warmer waters towards Antarctica's floating ice shelves.

These shelves act like giant plugs holding back huge glaciers. The warmer water erodes them from below, causing melting.

"If you leave an ice cube out in the air, it takes quite a while to melt. If you put it in contact with warm water, it goes rapidly" explains Winckler.

Uncertain carbon sponge

The oceans around Antarctica are a vital component of the Earth's carbon cycle. They absorb a substantial amount of the carbon dioxide (CO2) that humans emit into the atmosphere, roughly 40%, acting as a "carbon sponge."

This process is critical in moderating global warming, as it removes CO2 from the atmosphere, where it would otherwise trap heat, contributing to the greenhouse effect.

Why ocean currents are important

Ocean currents play a crucial role in shaping the Earth's climate and supporting marine ecosystems. These massive, continuous streams of water flow through the world's oceans, transporting heat, nutrients, and organisms across vast distances.

Types of ocean currents

Two primary types of ocean currents exist: surface currents and deep water currents.

Surface currents, driven by wind patterns and the Earth's rotation (Coriolis effect), flow in the upper 400 meters of the ocean.

Deep water currents, on the other hand, are driven by density differences caused by variations in temperature and salinity.

Antarctic and other ocean currents

Several major ocean currents significantly impact the Earth's climate and marine life:

The Gulf Stream : This warm, swift current originates in the Gulf of Mexico and flows along the eastern coast of the United States before crossing the Atlantic Ocean towards Europe.

The Antarctic Circumpolar Current : As discussed in this article, this current connects the Atlantic, Pacific, and Indian Oceans, facilitating the exchange of water and influencing global climate patterns.

The Kuroshio Current : Also known as the Japan Current, this western boundary current in the North Pacific Ocean transports warm, tropical water northward, affecting the climate of Japan and the Korean Peninsula.

Impact on climate and marine life

Ocean currents regulate global climate by redistributing heat from the equator to the poles, moderating temperatures worldwide.

They also transport nutrients, plankton, and other organisms, supporting diverse marine ecosystems and fisheries.

As the Earth's climate continues to change due to global warming, ocean currents may also undergo significant alterations.

Melting ice caps, rising sea levels, and shifting wind patterns can all influence the strength and direction of currents, potentially leading to far-reaching consequences for the planet's climate and marine life.

Future of Antarctic current

"These findings provide geological evidence in support of further increasing ACC flow with continued global warming," noted the researchers.

As humans continue to pump greenhouse gases into the atmosphere, it's almost certain that the ACC will keep speeding up. This is likely to unleash more intense warming around Antarctica, further destabilizing the West Antarctic Ice Sheet.

This vast reservoir of ice, much of it below sea level, holds the potential to raise global sea levels dramatically.

It's time to pay attention to Antarctic current

The ACC isn't getting as much attention as rising temperatures or melting Arctic ice caps, but perhaps it should. This mighty current has a complex relationship with our planet's climate system, and changes to it will have ripple effects worldwide.

Understanding these complex forces, along with reducing greenhouse gas emissions, is essential to prepare for a future where a sped-up ACC, rising seas, and extreme weather might reshape our world.

More about ocean currents

The study is published in the journal Nature .

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