Ocean Currents

Real time sea surface height observations and explanations at SEACOOS.org

Currents can be classified based on where we find them. Those we can measure at the ocean surface extend down into the ocean interior, most often confined to the upper 400 meters of the ocean, though some of the strongest ocean currents can go much deeper. Deep currents found well below the ocean surface are very important in defining climate change over hundreds of thousands of years, and yet we know very little about them. The ocean is very big, and to describe the circulation requires current information at many locations and through time.

Real coastal wind observations and explanations at SEACOOS.org

Two major forces drive ocean currents: pressure gradients and wind stress. Pressure gradients can be caused by differences in sea surface height, similar to water piling up on one side of a bucket. They can also be caused by density differences. These gradients have many causes, such as wind blowing over water near a boundary, density differences based on temperature and salinity changes, or changing water surface slopes due to tides or waves. Wind-generated currents are the result of friction between the water surface and the overlying atmosphere. When the wind flows, it drags surface waters along with it. As surface waters move in response to the wind stress, energy is transferred to greater ocean depths, creating motion well below the ocean surface.

Real time sea surface temperature observations and explanations at SEACOOS.org

Ocean currents are important because they provide an efficient way to move ocean water and anything planktonic from one place to another. Accurate estimates of oceanic flow paths bring economic benefits and increase human safety. For example, understanding current patterns improves search and rescue operations, helps to track oil spills and other pollutants, aids in ship routing to save fuel, and provides important information for fishery management. Currents also transport nutrients, organisms, and other biological and chemical components that are important for sustaining ocean life. A reliable base of information on currents is also critical for weather prediction, such as hurricane forecasting. Large ocean currents such as the Gulf Stream transport tremendous amounts of heat toward higher, more temperate latitudes. Monitoring ocean heat transport is critical for understanding the earth’s heat budget and associated global climate change.