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Ocean Processes in Climate and Climate Change

Author:
[ Harry Leach ] -

Abstract:

mohaline circulation transports heat and freshwater to the Atlantic Ocean from other parts of the globe, yet there is evidence to suggest that this global circulation may change dramatically if quantities of freshwater are released into the North Atlantic. The wind-driven surface circulation depends sensitively on the pattern of troposphere winds, as evidenced by the reversal of the Somali current in the face of the seasonal monsoon change; changes in Ekman suction in, for example, the Southern Ocean, should the winds there strengthen or weaken, will influence the supply of nutrient- and carbon dioxide-rich Deep Water to the surface there. The transport of properties and enhancement of primary productivity by mesoscale eddies depends on their activity, which results from the ambient available potential energy determined by the thermohaline forcing and surface wind-stress. The strength of cooling and mixing at the surface determines the depth of winter mixed layers and the depth from which nutrients can be returned to the euphonic zone instead of being lost to the ocean interior. The ocean can sequester carbon dioxide both physically and biologically. Cold water leaving the surface layer can take dissolved carbon dioxide with it into the interior ofthe ocean; the cold for the water potentially the more carbon dioxide and conversely the warmer the less. Dissolved carbon dioxide will however eventually return to the surface, even if it is a thousand years later, but carbon dioxide converted to organic matter by primary productivity has a chance of being buried in the sediment and sequestered permanently. Primary productivity is limited by nutrients and, while the lack of major nutrients such as nitrate and phosphate may limit productivity in subtropical gyres, the lack of iron in southern Polar Regions may explain the low productivity there. Changing patterns of winds could control productivity by crucially affecting the supply of key minor elements to remote ocean regions. The principal dangers for the ocean in global change can be summarized as the breakdown of thermohaline circulation, changes in the wind-driven flow, changes in nutrient supply and changes in the sequestration of C02, either by the physical pump or by the biological pump.

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