Coastal Upwelling

(printable version)

Life Cycle of an Upwelling Event

During the summer months, the surface of the ocean near our coast is heated by the sun. This warming causes stratification (warm surface/cold bottom). Typically, winds during our summer months are from the southwest, bringing all that hot humid air up from the Gulf of Mexico. These winds do not blow that surface layer directly to the northeast, but to the southeast. This 90 degree difference in wind and water current direction is due to the spin put on the water by the earth's coriolis force (earth's spin).

When the warm surface water is blown offshore, the cold bottom water rises, like a conveyor belt, and hits the beach. This cold water also brings sediment up from the bottom. Phytoplankton (microscopic plants) which float along the surface, used this sediment as food and bloom, causing the water to become green and murky. The figure above demonstrates what happens at the surface and below the water when winds blow from the southwest along the New Jersey coast. Now you know why the beaches can be so cold and "dirty" on the warmest days of the year.