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national oceanic and atmospheric administration

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Winds blowing across the ocean surface push water away. Water then rises up from beneath the surface to replace the water that was pushed away. This process is known as upwelling.

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Encyclopedic entry. Upwelling is a process in which currents bring deep, cold water to the surface of the ocean. Upwelling is a result of winds and the rotation of the Earth.

Subjects

Biology, Geography, Physical Geography

Upwelling is a process in which currents bring deep, cold water to the surface of the ocean. Upwelling is a result of winds and the rotation of the Earth.

The Earth rotates on its axis from west to east. Because of this rotation, winds tend to veer right in the northern hemisphere and left in the southern hemisphere. This is known as the Coriolis effect and is largely responsible for upwelling in coastal regions.

The Coriolis effect also causes upwelling in the open ocean near the Equator. Trade winds at the Equator blow surface water both north and south, allowing upwelling of deeper water.

The wind patterns generated during slow-moving cyclones can also blow surface water aside, causing upwelling directly beneath the eye of the cyclone. The colder water eventually helps to weaken the cyclone.

Effects of Upwelling
Biodiversity and productivity
Because the deep water brought to the surface is often rich in nutrients, coastal upwelling supports the growth of seaweed and plankton. These, in turn, provide food for fish, marine mammals, and birds.

Upwelling generates some of the world's most fertile ecosystems. A 25,900-square-kilometer (10,000-square-mile) region off the west coast of Peru, for example, undergoes continual coastal upwelling and is among the richest fishing grounds in the world. Overall, coastal upwelling regions only cover 1 percent of the total area of the world's oceans, but they provide about 50 percent of the fish harvest brought back to shore by the world's fisheries.

During El Niño, a weather phenomenon that typically occurs every three to seven years, the Pacific Ocean's climate changes dramatically. The transition zone between warm surface water and cold deep water deepens. Trade winds are also weak during El Niño. The combination of weak winds and deeper water limits upwelling. The reduction in nutrient-rich water leads to a lower fish population in the area, and therefore to a smaller fish crop.

Animal movement
Upwelling affects the movement of animal life in the area. Tiny larvae-the developing forms of many fish and invertebrates-can drift around in ocean currents for long periods of time. A strong upwelling event can wash the larvae far offshore, endangering their survival.

Coastal climate
The cold water welling up to the surface cools the air in the region. This promotes the development of sea fog. The city of San Francisco, California, is famous for its chilly, foggy summers, brought on by seasonal upwelling in the area.

Downwelling is a kind of reverse upwelling. Instead of deeper water rising up, warm surface water sinks down. Upwelling and downwelling patterns often alternate seasonally. The West Coast of the United States, for example, experiences summer upwelling and winter downwelling, as the winds change directions with the seasons. Downwelling

Fast Fact

Artificial Upwelling
Scientists and businesses are working to create areas of "artificial upwelling" to pump cold water to the surface. Researchers hope artificial upwelling will increase fish crops from the Gulf of Mexico to southwest Australia.

Artificial upwelling involves complex technology using the motion of waves to bring cold, nutrient-rich water from the deep ocean to the surface. Experiments in artificial upwelling have been tried in the Pacific Ocean near the Hawaiian Islands.

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Encyclopedic entry. Upwelling is a process in which currents bring deep, cold water to the surface of the ocean. Upwelling is a result of winds and the rotation of the Earth. Biology, Geography, Physical Geography Upwelling is a process in which currents bring deep, cold water to the surface of the ocean.

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In some coastal areas of the ocean (and large lakes such as the North American Great Lakes), the combination of persistent winds, Earth's rotation (the Coriolis effect), and restrictions on lateral movements of water caused by shorelines and shallow bottoms induces upward and downward water movements. As explained above, the Coriolis effect plus the frictional coupling of wind and water (Ekman transport) cause net movement of surface water at about 90 degrees to the right of the wind direction in the Northern Hemisphere and to the left of the wind direction in the Southern Hemisphere. Coastal upwelling occurs where Ekman transport moves surface waters away from the coast; surface waters are replaced by water that wells up from below.

Where Ekman transport moves surface waters toward the coast, the water piles up and sinks in the process known as coastal downwelling. Upwelling and downwelling illustrate mass continuity in the ocean; that is, water is a continuous fluid so that a change in distribution of water in one area is accompanied by a compensating change in water distribution in another area.

Upwelling is most common along the west coast of continents (eastern sides of ocean basins). In the Northern Hemisphere, upwelling occurs along west coasts (e.g., coasts of California, Northwest Africa) when winds blow from the north (causing Ekman transport of surface water away from the shore). Winds blowing from the south cause upwelling along continents' eastern coasts in the Northern Hemisphere, although it is not as noticeable because of the western boundary currents. Upwelling also occurs along the west coasts in the Southern Hemisphere (e.g., coasts of Chile, Peru, and southwest Africa) when the wind direction is from the south because the net transport of surface water is westward away from the shoreline. Winds blowing from the north cause upwelling along the continents' eastern coasts in the Southern Hemisphere.

Upwelling and downwelling also occur in the open ocean where winds cause surface waters to diverge (move away) from a region (causing upwelling) or to converge toward some region (causing downwelling). For example, upwelling takes place along much of the equator. Recall that the deflection due to the Coriolis effect reverses direction on either side of the equator. Hence, westward-flowing, wind-driven surface currents near the equator turn northward on the north side of the equator and southward on the south side. Surface waters are moved away from the equator and replaced by upwelling waters.

Upwelling and downwelling influence sea-surface temperature and biological productivity. Upwelling waters may originate below the pycnocline and are therefore colder than the surface waters they replace. Sometimes upwelling waters are confined to the mixed layer depending on the thickness of the warm layer. You may have experienced upwelling at the beach on a windy day when the warm surface water was blown offshore and replaced by chilly water from below. Where the thermocline is shallow, the upwelling waters are usually rich in the dissolved nutrients (e.g., nitrogen and phosphate compounds) required for phytoplankton growth. This nutrient transport into the surface waters where sunlight, also required for phytoplankton growth (photic zone), is present, results in rapid growth of phytoplankton populations. Since phytoplankton form the base of marine food webs, the world's most productive fisheries are located in areas of coastal upwelling that bring cold nutrient rich waters to the surface (especially in the eastern boundary regions of the subtropical gyres); about half the world's total fish catch comes from upwelling zones. On the other hand, in zones of coastal downwelling, the surface layer of warm, nutrient-deficient water thickens as water sinks. Downwelling reduces biological productivity and transports heat, dissolved materials, and surface waters rich in dissolved oxygen to greater depths. This occurs along the west coast of Alaska in the eastern boundary region of the Gulf of Alaska gyre (driven by winds in the Aleutian low).

Alternate upwelling of nutrient poor and nutrient rich waters off the coast of Ecuador and Peru are associated with El Niño and La Niña episodes in the tropical Pacific. During El Niño the pycnocline is so deep that the upwelled waters come from the nutrient poor waters above the pycnocline. In extreme cases, nutrient-deficient waters coupled with over-fishing cause fisheries to collapse bringing about severe, extended economic impacts.

Coastal upwelling and downwelling also influence weather and climate. Along the northern and central California coast, upwelling lowers sea surface temperatures and increases the frequency of summer fogs. Relatively cold surface waters chill the overlying humid marine air to saturation so that thick fog develops. Upwelling cold water inhibits formation of tropical cyclones (e.g., hurricanes), because tropical cyclones derive their energy from warm surface waters. During El Niño and La Niña, changes in sea-surface temperature patterns associated with warm and cold-water upwelling off the northwest coast of South America and along the equator in the tropical Pacific affect the inter-annual distribution of precipitation around the globe (see soon to be listed websites for more on the effects of these changes).

Adapted from DataStreme Ocean and
used with permission of the
American Meteorological Society.

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Ocean Motion : Definition : Wind Driven Surface Currents - Upwelling and Downwelling

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Learn about the ocean in motion and how ocean surface currents play a role in navigation, global pollution, and Earth's climate. Also discover how observations of these currents are crucial in making climate predictions.

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How do ocean currents work? - Jennifer Verduin

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Winds drive ocean currents in the upper 100 meters of the ocean's surface. However, ocean currents also flow thousands of meters below the surface. These deep-ocean currents are driven by differences in the water's density, which is controlled by temperature ( thermo) and salinity ( haline). This process is known as thermohaline circulation.

In the Earth's polar regions ocean water gets very cold, forming sea ice. As a consequence the surrounding seawater gets saltier, because when sea ice forms, the salt is left behind. As the seawater gets saltier, its density increases, and it starts to sink. Surface water is pulled in to replace the sinking water, which in turn eventually becomes cold and salty enough to sink. This initiates the deep-ocean currents driving the global conveyer belt.

# data[].attributes.attachment_link.keywords[]
national oceanic and atmospheric administration

# data[].attributes.attachment_link.description
Winds drive ocean currents in the upper 100 meters of the ocean's surface. However, ocean currents also flow thousands of meters below the surface. These deep-ocean currents are driven by differences in the water's density, which is controlled by temperature ( thermo) and salinity ( haline). This process is known as thermohaline circulation.

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5.1 Properties of Water – Introduction to Oceanography

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The most obvious feature of the oceans is that they contain water. Water is so ubiquitous that it may not seem like a very interesting substance, but it has many unique properties that impact global oceanographic and climatological processes. Many of these processes are due to hydrogen bonds forming between water molecules.

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Gulf Stream Atlantic oceanic currents could collapse as early as 2025: Study | WION Climate Tracker

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