Climate Fact: Strengthening Upwelling Patterns

Ocean currents transport heat from the Equator to the higher latitudes, as well as nutrient rich water from the depths of the ocean to the surface. The transport of cooler, nutrient rich water upward is a process known as upwelling. Upwelling feeds much of the life at the ocean’s surface, and 20 percent of the World’s fish catch occurs in areas where the upwelling is strong, although these areas account for only about one percent of the Planet’s ocean surface area. The Canaries Current, a southward moving current that brings cold, nutrient rich water up to the Moroccan Coastline, feeds a valuable fishery there. In the past century, the Sahara Desert Region has warmed faster than the adjacent ocean waters. This means that the low pressure zone over the Sahara desert has become lower and the high pressure zone that sits over the ocean has not changed that much, which has increased the pressure difference between these zones. Because the difference in pressure between the land and the ocean drives the winds that "pull" cold waters from the depths of the ocean to the surface, the winds have strengthened, and the upwelling has also strengthened. Over the Twentieth Century, the surface waters off the Moroccan coast have cooled by about 2.2 degrees Fahrenheit. Although other warm periods over the past 2,500 years have also corresponded to a strengthening of this current, the cooling that has happened over the past century is unprecedented.

(Source: McGregor, H.V. et at. "Rapid 20th-Century Increase in Coastal Upwelling off Northwest Africa." Science 315 (2007) 637-639.)