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Seasonal variation of the cold intermediate water in the Southwestern Black Sea and its interaction with the Sea of Marmara during the period of 1996-1998

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Seasonal variations of the cold intermediate water (CIW) in the southwestern Black Sea and its entrance into the Strait of Istanbul (Bosphorus) within the upper layer flow have been studied by using monthly oceanographic data sets collected in 1996-1998 period. In addition, the advection of the CIW via Strait Of Istanbul to the Sea of Marmara has been investigated.

The CIW is a permanent and characteristic water mass of the Black Sea, markedly observed in the northwestern Black Sea. It is transported with the Rim Current along the boundary of the basin. The average temperature of the CIW is about 6o C. The 8oC isotherms defines its upper and lower boundaries. The upper boundary of CIW rises up to the 20 m depth in the shelf and coastal upwelling regions with a thickness of 40 m. On the other hand, the depth of the upper boundary may decrease down to 40 m with a thickness of 120 m in the anticyclonic regions.

The CIW, located between 30 and 65m depths, was observed from April to September at the northern approaches of the Strait of Istanbul in the Black Sea. However, the CIW, within the Black Sea's upper layer flow, does not enter into the strait in the beginning (April, May) and at the end (September) of this period. The CIW between 20 and 50m water depths was observed in the northern entrance of the strait in summer (June, July and August) and it was carried into the strait by the southbound surface current. Its temperature increases southwards along the strait, due to the mixing with the warmer surface and bottom layers. This increment ranges between 2 and 4oC depending on the rate of mixing. The physically altered waters enter the Sea of Marmara with temperature of 11-14oC.

In the Sea of Marmara, a residual cold intermediate layer (CIL) is observed in summer, it is just placed on top of the halocline. The average temperature of the upper layer increases from spring to autumn. In some months, however, there is a decrement in the average temperature of the upper layer. The altered CIW waters entering the Sea of Marmara may be responsible for this cooling.

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