|
The global oceanic conveyer belt (shown above in a simplified illustration), is a unifying concept that connects the ocean's surface and thermohaline (deep mass) circulation regimes, transporting heat and salt on a planetary scale. The conveyor belt system can be thought of as beginning near Greenland and Iceland in the North Atlantic where dry, cold winds blowing from northern Canada chill surface waters. The combined chilling of surface waters, evaporation, and sea-ice formation produces cold, salty North Atlantic Deep Water (NADW). The newly formed NADW sinks and flows southward along the continental slope of North and South America toward Antarctica where the water mass then flows eastward around the Antarctic continent (in the Antarctic Circumpolar Current). There the NADW mixes with Antarctic waters (i.e., AABW and AADW). The resulting Common Water, also called Antarctic Circumpolar water, flows northward at depth into the three ocean basins (primarily the Pacific and Indian Oceans).
|
These bottom waters gradually warm and mix with overlying waters as they flow northward. They move to the surface at a rate of only a few meters per year. After rising to the surface in the Pacific, the surface waters flow through the many passages between the Indonesian islands into the Indian Ocean. Eventually they flow into the Agulhas Current, the Indian Ocean boundary current that flows around southern Africa. After entering the Atlantic Ocean, the surface waters join the wind-driven currents in the Atlantic, becoming saltier by evaporation under the intense tropical sun. Trade winds transport some of this water vapor out of the Atlantic Ocean basin, across the Isthmus of Panama, and into the Pacific Ocean basin. Atlantic surface waters eventually return northward to the Labrador and Greenland seas in the North Atlantic. Continued operation of the oceanic conveyor belt is important to northern Europe's moderate climate because of northward transport of heat in the Gulf Stream and North Atlantic Current. The system can weaken or shut down entirely if the North Atlantic surface-water salinity somehow drops too low to allow the formation of deep-ocean water masses. This apparently happened during the Little Ice Age (about 1400 to 1850 AD). The conveyer system shut down and northern Europe's climate became markedly colder. Old paintings from this era show Dutch skaters on frozen canals-something that would not occur during today's climatic regime. Cores extracted from deep-sea sediment deposits contain evidence of earlier cold periods. Adapted from DataStreme Ocean and |
