Nutrient and organic carbon exchanges between the Black and Marmara Seas through the Bosphorus Strait

Recent systematic chemical data, together with a new estimate of the water fluxes, permit the calculation of the total phosphorus (TP), nitrogen (TN) and organic carbon (TOC) exchanged between the Black and the Marmara Seas through the Bosphorus. Assuming the chemical concentrations of the exchanging waters to be constant on a yearly time scale, the estimated total annual fluxes are as follows. inly river-borne annual flows of TN and TOC into the Sea of Marmara from the Black Sea are about three times those from the Marmara Sea into the Black Sea whereas the TP exchanges are comparable. The large TN export by Black Sea waters relative to the TP outflux is the result of the high N:P ratio of nutrients [primarily in the forms of nitrate, less labile dissolved organic nitrogen (DON) and ortho-phosphate] introduced by the polluted rivers to the northwestern Black Sea. The DON comprises about 75% of the TN inflow into the Marmara Sea whereas nearly 50% of the TP inflow is composed of dissolved inorganic phosphorus. Biologically labile nutrients exported from the Black Sea, corresponding to a new production of (3.5–4.9) × 105 tons C y−1 in the Marmara Sea, are almost compensated by the Bosphorus underflow as nitrate and phosphate primarily of biogenic origin.