Levantine intermediate water

The concentration of dissolved nutrients in the deep waters of the Eastern Mediterranean is much lower than those in other oceans of the world, and when these are mixed into the surface waters they support very low primary productivity. The basic reason for this ultra-oligotrophic status is that the Mediterranean has an anti-estuarine (reverse thermohaline) circulation in which nutrient-depleted surface waters flow into the western basin at the Straits of Gibraltar and then on into the eastern basin at the Straits of Sicily. The deeper counter current consists of Levantine Intermediate Water (LIW) which contains a significant amount of dissolved nutrients. 

Figure 4.2 shows a typical vertical temperature and salinity profile from the eastern Levantine Basin in May. Beneath a shallow mixed layer and sharp seasonal thermocline, there is a modified Atlantic water, which has a characteristic low salinity. As the surface water flows to the east the modified Atlantic water becomes progressively more saline. Eventually it is converted into LIW and Levantine Deep Water (LDW). The transformation occurs in rather limited areas within the eastern basin where the oceanographic and climatic conditions combine to cause downward flow of water in winter. As occurs in all parts of the ocean, it results in the downward flow of biogeochemically active chemical substances such as oxygen, carbon dioxide and nutrients from the surface into intermediate and deep water. 

Morcos, S.A. (1972) Sources of Mediterranean intermediate water in the Levantine Sea, in Studies in Physical oceanography, vol 2, (ed. A.L. Gordon), New York, Gordon and Breach, pp. 185-206. 

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