Upwelling and DownwellingThe Ekman Transport SystemKella Randolph, M. Ed.

Upwelling and downwelling

• 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).

• Coastal upwelling and downwelling also influence weather and climate

About 71% of our planet is covered with oceans. About 97% of all Earth’s water is in the oceans.

We depend on the oceans for food, transportation, minerals, and recreation.

We now understand that the world’s climates are determined by the heat exchange caused by ocean currents.

Ocean Currents Map

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The Ekman spiral is one of the oldest results in dynamical oceanography. It was first proposed (conceptually) by the great Norwegian explorer Fridtjof Nansen. As part of a polar expedition in the late 1890s, Nansen froze his ship Fram into the ice north of Spitzbergen Island and allowed it to drift for more than two years. During the expedition he noticed that the drift of the boat was generally to the right of the wind. Nansen proposed that this motion was the result of the Coriolis force, which causes objects to veer to the right in the northern hemisphere and to the left in the southern hemisphere. He supposed further that as the ice pushed on the water immediately below it, that water would move still further to the right of the wind, though a little more slowly. Extended down through the water column, the result would be a spiral structure. The mathematics behind this spiral were formalized by V. Walfrid Ekman in 1905, the spiral itself was not seen in the open ocean until 1986, by Jim Price, Robert Weller, and Becky Schudlich of the Woods Hole Oceanographic Institution ." (above article was published by http://www.gfdl.gov/~a1g/Ekman_spiral.html )

Currents flow in complex patterns.

Currents flow in complex patterns affected by wind, the water's salinity and heat content, bottom topography, and the earth's rotation. Upwelling brings cold, nutrient-rich water from the depths up to the surface. The earth's rotation and strong seasonal winds push surface water away from some western coasts, so water rises on the western edges of continents to replace it, which is why the ocean is so much colder on the east coast than the west coast. Marine life thrives in these nutrient-rich waters. Colder or saltier water tends to sink, so you can imagine that the waters off the coast of Antarctica are really cold. A global "conveyor belt" sets in motion when deep water forms in the North Atlantic, sinks, moves south, and circulates around Antarctica, and then moves northward to the Indian, Pacific, and Atlantic basins. It can take a thousand years for water from the North Atlantic to find its way into the North Pacific.

Oceans store a large amount of heat, so small changes in ocean currents can have a large effect on coastal and global climate as they carry enormous amounts of heat north and south.

Salinity and temperature are two factors that affect the density of sea water.

Upwelling brings nutrient rich water to the surface along with fish.

Where Ekman transport moves surface waters away from the coast, surface waters are replaced by water that wells up from below in the process known as upwelling. This example is from the Northern 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.

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.

Where Ekman transport moves surface waters away from the coast, surface waters are replaced by water that wells up from below in the process known as upwelling. This example is from the Northern Hemisphere.

Where Ekman transport moves surface waters toward the coast, the water piles up and sinks in the process known as downwelling. This example is from the Northern Hemisphere.

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).

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.

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The Thermohaline Circulation systemOceans play a HUGE role in redistributing heat around the globe. Ocean surface water that is heated by the sun near the equator eventually makes its way to the high latitudes where it cools off. When it is cooled, it sinks. Eventually, that cooled water makes its way back to the equator where it wells up and becomes surface water again. The whole cycle then repeats itself. This system of upwelling, heating, cooling, and downwelling is called the global thermohaline circulation system. Its primary influence is to transfer heat from the equator to the high latitudes.

http://www.ncdc.noaa.gov/paleo/ctl/thc.html Downloaded Thursday, 10-Jul-2014 05:09:07 EDT Last Updated Wednesday, 20-Aug-2008 11:22:39 EDT by paleo@noaa.gov

The giant oceanic salt and heat pump known as the Thermohaline Circulation. Too much fresh water in the North Atlantic and Arctic Oceans might slow down or stop the pump, which could cause a sudden climate cooling for the residents of the United Kingdom, Germany, Sweden, Norway, and eastern North America.Source: Intergovernmental Panel on Climate Change (IPCC) 2001 Report

Marine Biological Laboratory

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Poleward-moving currents are warm, and equatorward-moving currents are cold. Surface ocean currents are driven by global winds and play an important role in redistributing heat around the globe.

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Library of California Current Large Marine Ecosystem Law and Regulation. Free to use; Customizable Searching

The California currentThe California current, which flows southward along the California coastline is located 40 to 100 miles off the west coast of North America, may be found above, in a range of red and orange colors. The image is made from Sea Surface Temperature (SST) data from the MODIS instrument carried on Aqua, a NASA satellite. Compare this image to the western boundary current image, notice that the California current has cooler water temperatures than the Gulf Stream Current. The image also shows upwelling and eddies in the California Current system.

Credit: Image provided by Norman Kuring, NASA/GSFC

The Gulf Stream is a powerful western boundary current in the North AtlanticOriginating in the Gulf of Mexico, waters in the Gulf Stream travel at speeds of about one to three knots (1.15-3.45 miles per hour or 1.85-5.55 kilometers per hour). The Gulf Stream influences the climate of the east coast of Florida, keeping temperatures warmer in the winter and cooler than the other southeastern states in the summer. Since it also extends toward Europe, it warms western European countries as well.

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NOAA Ocean Explorer: Investigating the Charleston Bump The path of the Gulf Stream (shown with white arrows) is easily identified on this sea surface temperature satellite image, where warm waters appear as oranges and reds, and cooler waters as yellows, greens and blues. The deflection of the Gulf Stream by the Charleston Bump results in the development of a counterclockwise rotating eddy, called the Charleston Gyre.

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This single-beam bathymetric map of the Charleston Bump (courtesy NOAA Ship Whiting) shows its major features. The ramp is formed by the tilted pavement of Maganese-Phosphorite rock.

Sea-viewing Wide Field-of-view Sensor (SeaWiFS) image of the Charleston Gyre and regional coastline. The gyre is generated by the interaction of the Gulf Stream with the Charleston Bump, which is located just southwest of the gyre. The background SeaWifs image was produced by Norman Kuring of the SeaWiFS Project, NASA GSFC, and is available on the Internet at:NASA GSFC

The Charleston Bump exerts a profound influence on the Gulf Stream’s path.

As the Gulf Stream passes over the Bump, it is deflected seaward, generating a string of meanders similar to a lazy river passing through hilly terrain. On the Gulf Stream’s western edge, these meanders produce swirling centers of counterclockwise flow, known as cyclonic eddies. As these eddies spin, the sea surface tends to "bulge up" in their center, causing deeper, colder water to move upwards. This slow lifting of bottom waters is known as upwelling. The upwelling pumps nutrient-rich bottom waters toward the surface, resulting in high levels of ocean productivity. This is well demonstrated in the seasonal variability in primary productivity, as inferred from satellite imagery.

Movements of warm and cold ocean waters regulate climate.A map of Nordic seas and subpolar basins shows the circulation of surface currents (solid curves) and deep currents (dashed curves) that form a portion of the Atlantic Meridional Overturning Circulation. Much like a conveyor belt, the climate-regulating ocean pattern transports warm surface waters toward the north and cool, deep waters toward the south. Credit: Jack Cook, Woods Hole Oceanographic Institution

The continental shelf

Wind driven circulation on the North Carolina shelf resembles the coastal upwelling observed off the west coast of North America, but with some important differences. First, the North Carolina shelf is quite shallow; depths are consistent with the the inner shelf off California. Second, winds in the CoOP study area reverse weekly, and drive upwelling and downwelling circulation in rapid alternation. This contrasts with the seasonal upwelling observed on the west coast. Downwelling circulation is further complicated by the presence of the Chesapeake Bay plume, which drives a coastal jet of faster currents. By contrast, during upwelling, along-shelf currents are strongest near the upwelling front, about 10 km offshore.

http://cynthiacudaback.org/Science/NC.html

The Continental Shelf.

Most continents extend far beyond the point where ocean meets land. Their extended perimeter is referred to as the continental shelf.

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Additional Background:

• MBL Ecosystems Center

• Pan Arctic River Transport of Nutrients, Organic Matter and Suspended Sediments (PARTNERS) Project Press Release

• PARTNERS Project Website

• Marine Science Institute, University of Texas at Austin

• Woods Hole Oceanographic Institution

• Woods Hole Research Center

• International Arctic Research Center

• Applied Physics Laboratory - University of Washington

Find out more by looking at these sites. Find a searchable list by clicking below.

http://hermes.mbl.edu/news/press_releases/2006/2006_pr_08_24.html