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upwelling
Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water towards the ocean surface, replacing the warmer, usually nutrient-depleted surface water. The nutrient-rich upwelled water stimulates the growth and reproduction of primary producers such as phytoplankton. Due to the biomass of phytoplankton and presence of cool water in these regions, upwelling zones can be identified by cool sea surface temperatures (SST) and high concentrations of chlorophyll-a.〔Anderson DM, Prell WL. (1993). A 300 KYR record of upwelling off Oman during the late quaternary: evidence of the Asian southwest monsoon. Paleoceanography, 8(2): 193-208.〕〔Sarhan T, Lafuente JG, Vargas M, Vargas JM, Plaza F. (1999). Upwelling mechanisms in the northwestern Alboran Sea. Journal of Marine Systems, 23: 317-331.〕
The increased availability in upwelling regions results in high levels of primary productivity and thus fishery production. Approximately 25% of the total global marine fish catches come from five upwellings that occupy only 5% of the total ocean area.〔Jennings, S., Kaiser, M.J., Reynolds, J.D. (2001) "Marine Fisheries Ecology." Oxford: Blackwell Science Ltd. ISBN 0-632-05098-5〕 Upwellings that are driven by coastal currents or diverging open ocean have the greatest impact on nutrient-enriched waters and global fishery yields.〔〔Mann, K.H., Lazier, J.R.N. (2006) ''Dynamics of Marine Ecosystems: Biological-Physical Interactions in the Oceans''. Oxford: Blackwell Publishing Ltd. ISBN 1-4051-1118-6〕
==Mechanisms==
The three main drivers that work together to cause upwelling are wind, Coriolis effects, and Ekman transport. They operate differently for different types of upwelling, but the general effects are the same.〔Bakun A. (1990). Global climate change and intensification of coastal ocean upwelling. Science, 247: 198-201.〕 In the overall process of upwelling, winds blow across the sea surface at a particular direction, which causes a wind-water interaction. As a result of the wind, the water is transported a net of 90 degrees from the direction of the wind due to Coriolis forces and Ekman transport. Ekman transport causes the surface layer of water to move at about a 45 degree angle from the direction of the wind, and the friction between that layer and the layer beneath it causes the successive layers to move in the same direction. This results in a spiral of water movement down the water column. Then, it is the Coriolis forces that dictate which way the water will move; in the Northern hemisphere, the water is transported to the right of the direction of the wind. In the Southern Hemisphere, the water is transported to the left of the wind.〔Chelton DB, Schlax MG, Freilich MH, Milliff RF. (2004). Satellite measurements reveal persistent small-scale features in ocean winds. Science, 303:978-983.〕 If this net movement of water is divergent, then upwelling of deep water occurs to replace the water that was lost.〔〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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