The Ocean Currents of the Indian Ocean Explained

Ocean currents are the large, steady flows of seawater that carry heat, salt, nutrients and drifting life across the world’s seas, and the northern Indian Ocean around India is the only major ocean basin where they reverse direction twice a year with the monsoon winds. Where the Atlantic and Pacific keep their great circulations turning the same way all year, the Arabian Sea and the Bay of Bengal flip between an eastward-flowing summer system and a westward-flowing winter system. This explainer, last updated 4 November 2026, describes how the currents of the Indian Ocean work, what they do to India’s weather, fisheries and coasts, and why scientists watch them so closely.

These flows are easy to overlook from the shore, yet they shape the heat that feeds the monsoon, the nutrients that feed sardines and mackerel, the saltiness that helps cyclones strengthen, and the routes that ancient sailors used to cross to Arabia and East Africa. To understand India’s climate and coastal economy, it helps to understand the sea currents around it.

Key Takeaways

• Ocean currents are persistent flows of seawater driven mainly by winds, with help from Earth’s rotation, temperature and salinity differences, and the shape of the coastlines.
• The northern Indian Ocean is unique because the monsoon reverses the winds, and the surface currents reverse with them, between a summer and a winter pattern.
• In summer the Somali Current races northward and the Southwest Monsoon Current crosses the Arabian Sea and Bay of Bengal eastward, driving strong upwelling off Somalia, Arabia and India’s southwest coast.
• Upwelling brings cold, nutrient-rich water to the surface and supports some of India’s most productive fisheries, including oil sardine and mackerel off Kerala and Karnataka.
• The Bay of Bengal’s freshwater inflow creates a warm, stratified surface that helps cyclones draw heat, while the Arabian Sea is saltier and more strongly mixed.
• Large-scale patterns such as El Nino and the Indian Ocean Dipole alter ocean heat and currents and can strengthen or weaken the monsoon.

What are ocean currents?

Ocean currents are continuous, directed movements of seawater generated by wind, differences in water density, tides and the rotation of the Earth. They can be thought of as rivers within the sea, some flowing at the surface for thousands of kilometres and others creeping along the deep ocean floor over centuries.

Two main types are usually recognised. Surface currents are driven mostly by winds and occupy the upper few hundred metres. They are bent by the Coriolis effect, which turns moving water to the right in the Northern Hemisphere and to the left in the Southern Hemisphere, and they are steered by continents. Deep currents form part of the thermohaline circulation, driven by differences in temperature and salinity that make water sink in some places and rise in others, and they move far more slowly. Together they transport heat from the tropics towards higher latitudes and help set regional climates.

In most oceans the surface currents arrange themselves into huge gyres, circular loops around the subtropical high-pressure zones, with strong, narrow currents along the western edges and weak, broad flows along the eastern edges. The Indian Ocean follows this pattern in the Southern Hemisphere, but its northern half behaves differently.

Why are the Indian Ocean’s currents different from those of other oceans?

The Indian Ocean’s currents are different because the northern part of the ocean is closed off by the Asian landmass at about 25 degrees North, and the monsoon reverses the winds across it every year. The Pacific and Atlantic extend into the Arctic and have steady trade-wind belts that feed permanent northern gyres. The Indian Ocean has no ocean to its north, and the intense heating of Asia in summer and cooling in winter flips the wind direction between southwest and northeast.

As a result, the northern Indian Ocean does not form a permanent circulation loop north of the equator. Instead it carries a seasonal system that follows the winds with a delay of weeks. This reversal has been known to sailors for over two thousand years: Arab, Indian and African traders crossed the sea in dhows on the summer monsoon and returned with the winter monsoon, using wind and current together. The whole system is part of what scientists call the monsoon-ocean coupled system.

South of the equator the picture is more conventional, with a subtropical gyre made up of the westward South Equatorial Current, the southward Agulhas Current off Africa, the eastward flow in the Southern Ocean and the northward flow off Western Australia. Even so, the connection between the two halves, along the equator and through the Indonesian archipelago, makes the whole basin unusually dynamic.

What are the main ocean currents of the Indian Ocean?

The main ocean currents of the Indian Ocean are the Somali Current, the Southwest Monsoon Current and Northeast Monsoon Current, the Equatorial Counter Current, the South Equatorial Current, the Agulhas Current, the Leeuwin Current and the coastal currents along India’s shores. Some are seasonal and others are permanent.

Along the equator, narrow eastward jets known as Wyrtki Jets appear twice a year, in spring and again in autumn, and move warm water across the ocean. These jets are an important part of the seasonal heat balance and of the Indian Ocean Dipole.

How do the currents flow in summer during the southwest monsoon?

In summer, during the southwest monsoon from roughly June to September, the Southwest Monsoon Current flows eastward across the Arabian Sea and the Bay of Bengal while the Somali Current surges northward along the African coast. The strong southwesterly winds push surface water toward the east and the northeast, and they set up a remarkable circulation on the western side.

The Somali Current in this season is among the fastest on the planet, reaching speeds of several metres per second at its peak. It turns offshore near the Horn of Africa and forms large rotating eddies, including a feature called the Great Whirl. Winds parallel to the coasts of Somalia and Oman push surface water away from land, and cold water rises from below to replace it, a process called upwelling. This creates cold, productive waters and cools the surface of the Arabian Sea, which in turn affects the monsoon.

Closer to India, the West India Coastal Current flows southward along the Konkan, Karnataka and Kerala coast, and upwelling off the southwest coast brings cooler, nutrient-rich water to the surface. The East India Coastal Current meanwhile tends to flow northward. The Southwest Monsoon Current carries Arabian Sea water around the southern tip of India and Sri Lanka and into the Bay of Bengal, linking the two basins.

How do the currents reverse in winter during the northeast monsoon?

In winter, during the northeast monsoon from roughly November to February, the Northeast Monsoon Current flows westward across the Bay of Bengal and Arabian Sea, and the Somali Current weakens and turns to flow southward along the African coast. The winds now blow from the northeast, so surface water is pushed in the opposite direction from summer.

The West India Coastal Current reverses and flows northward along India’s west coast, carrying warmer, lower-salinity water, and the East India Coastal Current flows southward along the east coast in the northeast monsoon season, bringing fresh river water from the Bay of Bengal southward. Winter upwelling also occurs in some parts of the northern Arabian Sea, driven by cooling and mixing rather than wind alone, which feeds seasonal plankton blooms.

The transitions between seasons in April to May and October to November are particularly interesting. The equatorial jets pump warm water eastwards, and the changing winds shape the timing of the monsoon’s onset and withdrawal. These are also the periods when cyclones are most common in the Bay of Bengal and Arabian Sea.

What is upwelling and why does it matter for Indian fisheries?

Upwelling is the rise of cold, nutrient-rich deep water to the sunlit surface, and it matters for Indian fisheries because it fuels plankton blooms that feed some of the country’s biggest fish catches. When currents and winds push surface water away from a coast or divert it offshore, deeper water rises to take its place, bringing nitrate and phosphate that phytoplankton, the tiny drifting plants at the base of the food chain, use to grow.

Along India’s southwest coast, summer upwelling coincides with the monsoon and supports large shoals of oil sardine and Indian mackerel, which are caught in huge numbers off Kerala, Karnataka and Goa. Fishing communities have long observed that catches and migrations follow the seasons, and their calendars match the current system. The same upwelling off Somalia and Oman sustains the rich Arabian Sea fishery and is a reason for the intense plankton blooms visible from space.

The system is sensitive. Years in which the monsoon is weak, or the Indian Ocean is unusually warm, can reduce upwelling and affect catches. Scientists have linked changes in sardine landings to variations in monsoon winds, ocean temperature and currents. India’s ocean agency, INCOIS in Hyderabad, uses satellite data on sea surface temperature and chlorophyll to issue Potential Fishing Zone advisories, helping fishers find fish and save fuel.

How do ocean currents affect India’s monsoon and climate?

Ocean currents affect India’s monsoon and climate by moving heat and moisture, which sets the temperature of the sea surface from which monsoon rain draws its energy. Warm seas supply water vapour and heat to the air, while cooler upwelled waters can reduce evaporation and alter wind patterns.

The Arabian Sea and Bay of Bengal act as heat reservoirs and moisture sources. During the summer, the Somali Current and upwelling cool parts of the Arabian Sea, while the Equatorial Indian Ocean and the Bay of Bengal remain very warm. These contrasts influence where the monsoon winds are strongest and where rain bands form. The warm waters south of India and in the western Pacific warm pool are part of the broader tropical heat engine behind the monsoon.

Ocean currents also help carry the memory of the climate. Heat stored in the upper ocean takes weeks to months to change, so ocean conditions in spring can influence monsoon rainfall in summer. The Indian Ocean Dipole is a key example. In a positive phase, the western Indian Ocean is warmer and the eastern part cooler, with stronger winds along the equator and changed currents. A positive dipole often supports a stronger Indian monsoon and can offset a weakening caused by El Nino, while a negative phase tends to do the opposite. These are tendencies, not guarantees.

How do the Bay of Bengal and Arabian Sea currents differ?

The Bay of Bengal is fresher and more layered than the Arabian Sea, because huge rivers such as the Ganga, Brahmaputra, Irrawaddy and Godavari pour fresh water into it, while the Arabian Sea loses more water by evaporation and is saltier. This difference shapes their circulation, productivity and weather.

The fresh water in the Bay of Bengal forms a barrier layer, a thin low-salinity cap that stops warm surface water mixing with the cooler layers below. This keeps the surface warm and gives passing cyclones more energy to draw upon, one reason the Bay produces many strong storms. The Arabian Sea has historically had fewer cyclones, though warming there has been linked to more intense recent storms.

Do ocean currents influence cyclones near India?

Ocean currents influence cyclones near India mainly by shaping where warm water sits and how much heat is available, rather than by steering the storms themselves, which are guided by winds in the atmosphere. Cyclones draw energy from warm sea surfaces, typically above about 26 to 27 degrees Celsius, and they weaken when they pass over cooler or well-mixed water.

Warm eddies and pools of deep warm water in the Bay of Bengal and the Arabian Sea can let a storm rapidly intensify, while cold-water patches created by upwelling and by the storm’s own stirring can slow it. Salinity layering in the Bay of Bengal helps keep the surface warm. Ocean heat content, measured by satellites and Argo floats, is now a standard input in cyclone intensity forecasts by the India Meteorological Department.

How are ocean currents changing with climate change?

Ocean currents are changing with climate change mainly because the Indian Ocean is warming rapidly and winds and stratification are shifting, though the exact effects on individual currents are still being studied. The tropical Indian Ocean has warmed faster than many other basins, and it holds more heat in its upper layers than before. Warmer water increases evaporation, sea level rise and the energy available to cyclones.

Researchers have reported more frequent marine heatwaves, changes in the strength of the Somali Current and upwelling, and possible shifts in the Indian Ocean Dipole, but the evidence is evolving and models do not always agree. Warming also tends to strengthen stratification, which can reduce the mixing that brings nutrients up, with possible effects on plankton and fish stocks. Deoxygenation is a concern in the Arabian Sea, which already has one of the world’s largest low-oxygen zones.

These changes make monitoring essential. Networks of Argo floats, moored buoys such as the Research Moored Array for African-Asian-Australian Monsoon Analysis and Prediction, ships and satellites give scientists a near-real-time view, improving monsoon, cyclone and fishing forecasts.

Bottom Line

The ocean currents around India are not fixed rivers but a seasonal machine that follows the monsoon. In summer they drive upwelling and fisheries, in winter they reverse and bring river water south and warm water north, and all year they store and move the heat that powers the monsoon and cyclones. As the Indian Ocean warms, better observation of these currents is becoming a practical necessity for fishers, forecasters and coastal planners.

Frequently Asked Questions

Why do ocean currents reverse in the northern Indian Ocean?

They reverse because the monsoon winds reverse. Southwesterly winds in summer and northeasterly winds in winter push the surface water in opposite directions, and the currents follow the winds with a delay of some weeks.

What is the Somali Current?

The Somali Current is a western boundary current along the coast of Somalia that flows strongly northward in the summer monsoon and weakly southward in winter. In summer it is one of the fastest ocean currents on Earth and drives intense upwelling.

How do ocean currents affect Indian fisheries?

They drive upwelling, which brings nutrient-rich water to the surface and fuels plankton blooms that support fish such as oil sardine and mackerel. Catch patterns along the west coast follow the seasonal currents and monsoon.

What is the Indian Ocean Dipole?

The Indian Ocean Dipole is a climate pattern in which the western Indian Ocean becomes warmer or cooler than the eastern part. A positive phase often supports a stronger Indian monsoon, while a negative phase tends to weaken it.

Do ocean currents steer cyclones?

Not directly, since cyclones are steered mainly by atmospheric winds. Currents and warm eddies influence how much heat is available, which affects how strong a cyclone can become.

Which currents flow along India’s coasts?

The West India Coastal Current runs along the west coast and the East India Coastal Current along the east coast. Both change direction with the seasons, flowing in opposite directions in the summer and winter monsoons.

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