CHEMICAL PROPERTIES OF THE TWO-LAYER FLOW REGIMES IN THE TURKISH STRAITS

Chemical properties of the two-layer flow regimes in the Turkish Straits

Süleyman Tuğrul, Çolpan Polat, Özden Baştürk, Emin Hatipoğlu, Ayşen Yılmaz, Semal Yemenicioğlu, Cemal Saydam, İlkay Salihoğlu

Middle East Technical University, Institute of Marine Sciences, P.K. 28, Erdemli 33731, lçel, TURKEY

Abstract

Systematic data obtained at the exits of the Bosphorus and Dardanelles straits between 1986 and 1994 permit us to understand the seasonal variations in the nutrient properties of the counter flows in the Turkish Straits. The brackish outflow from the Black Sea enters the Marmara Sea with low levels of inorganic nutrients (PO4-P˂0.1 µM; NO3+NO2-N˂0.1-0.2 µM) from spring to autumn but possesses unexpectedly high concentrations (PO4-P=0.3-0.4 µM; NO3+NO2-N=5-7 µM) in early winter. The calculated annual average concentrations of POand NO3+NO2 are about 0.11 and 1.3 µM, respectively. However, the nutrient properties of the brackish waters of Black Sea origin are modified noticeably as they flow through the Marmara basin and the Dardanelles both by biomediated chemical processes and by the ex-port of biogenic organic particles to the lower layer. The salty Mediterranean inflow to the Marmara deep basin via the Dardanelles Strait contains low nutrient concentrations ( NO3+NO2-N=1.0 µM; PO4-P=0.05 µM on average). However, the salty water, before reaching the Black Sea via the Bosphorus, is much enriched with inorganic nutrients in the Marmara basin by the input from the surface flow; the average concentrations being as high as 9.6 µM for NO3+NO2-N and 1.0 µM for PO4. In other words, the initially nutrient-poor Mediterranean water spreads into the Black Sea with its nitrate+nitrite and phosphate concentrations enriched at least 10-20 fold, which are larger than the biologically labile nutrient content of the Black Sea outflow.

Keywords: Bosphorus, Dardanelles, phosphorus compounds, nitrogen compounds

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