Nutrient Exchange Fluxes between Aegean and Black Seas through The Marmara Sea

Long-term data obtained in the Turkish Strait System (TSS) including the Sea of Marmara, the Dardanelles and Bosphorus straits, during 1990-2000, have permitted us to calculate seasonal and annual fluxes of water and nutrients (nitrate, phosphate) exchanged between the Aegean and Black Seas through the TSS. Two-layer flow regimes in the TSS introduce the brackish waters of the Black Sea into the Aegean basin of the northeastern Mediterranean throughout the year. A counter flow in the TSS carries the salty Mediterranean water into the Black Sea via the Marmara deep basin. The annual volume influx from the Black Sea to the Marmara upper layer is nearly two-fold the salty water exported from the Marmara to the Black Sea via the Bosphorus underflow. The brackish Black Sea inflow is relatively rich in nitrate and phosphate in winter, decreasing to the lowest levels in late summer and autumn. Biologically labile nutrients of Black Sea origin are utilized in photosynthetic processes in the Marmara Sea and are partly exported to the Marmara lower layer. Eventually, the brackish Black Sea waters reach the Dardanelles Strait, with modified bio-chemical properties. On the other hand, the salty Mediterranean waters with low concentrations of nutrients enter the Marmara deep basin. During threir 6-7 year sojourn in the Marmara basin, the salty waters become enriched in nitrate (DIN) and phosphate (DIP), due to oxidation of planktonic particles sinking from the Marmara surface layer. The annual nutrient inputs from the Black Sea to the Marmara basin were estimated as 8.17x108 moles of DIN and 4.25x107 moles of DIP, which are much less than the importation from the Marmara lower layer via the Bosphorus undercurrent. The salty Aegean water introduces nearly 6.13x108 moles of DIN and 2.79x107 moles of DIP into the Marmara lower layer. The estimated DIP outflux from the Aegean Sea is nearly 2 times less than the importation from the Marmara Sea via the Dardanelles Strait

Elemental composition of seston and nutrient dynamics in the Sea of Marmara

The Sea of Marmara, an intercontinental basin with shallow and narrow straits, connects the Black and Mediterranean Seas. Data obtained during 1991-1996 have permitted the determination of the elemental composition of seston in the euphotic zone and the N:P ratio of the subhalocline waters of the Marmara Sea. Since primary production is always limited to the less saline upper layer (15-20 m), of the Marmara Sea, the subhalocline waters of Mediteranean origin are always rich in nutrients (NO3 + NO2 = 8-10 mu m, PO4 = 0.8-1.2 mu m) but depleted in dissolved oxygen (30-50 mu m) throughout the basin, yielding an -O-2:N:P ratio of 178.9:1. Pollution of the surface waters since the 60s has modified the subhalocline nutrient chemistry slightly. In the euphotic zone, the N:P ratio of the seston changes from 5.9 to 9.5 between the less and more productive periods. Though the biology of the Marmara has changed significantly during the previous two decades, the close relationship observed between the elemental composition of the surface seston and the NO3:PO4 ratio of the subhalocline waters strongly suggests that during the whole year primary production throughout the basin and POM export to the lower layer remain nitrogen-limited. This suggestion needs to be confirmed by bio-assays, biological studies and sediment trap data from the upper subhalocline depths. Nonetheless, the counterflows in the Marmara basin possess relatively low N:P ratios in both dissolved and particulate nutrients and extend as far as the adjacent sea

Variations in the vertical structure of water chemistry within the three hydrodynamically different regions of the Black Sea

High-resolution, basin-wide chemical data reveal that the Black Sea upper layer possesses distinct chemical features at specific density surfaces, but with some noticeable regional differences in their positions and magnitudes. The nitracline, is consistently established at smaller density surface relative to the phosphocline over the basin; thus, N:P molar ratios appear to be unexpectedly high (40-80) within the upper nutricline, especially in the anticyclonic regions (ACR). The ratio drops to levels of 4-8 at the nitrate mar;ima formed within the base of the main oxycline. Phosphate profiles display a prominent minimum within the suboxic zone of tl le cyclonic regions (CR), which weakens markedly within the coastal regions and rim current. Vertical distributions of chemical ratios have led to valuable information on the relative fluxes in the oxic/anoxic transition zone as well as the quality of data sets from different years

Spatial Isopycnal Analysis of the Main Pycnocline Chemistry of the Black Sea: seasonal and interannual variations

The results of 1991-1994 basin-wide investigations have been analysed using the method of spatial isopycnal analysis. Seasonal and interannual variations of phosphates, nitrates, dissolved oxygen and the suboxic zoneare revised. The range and possible reasons of spatial and temporal variations in the density-dependent vertical profiles of nutrients and oxygen in the layer of the main pycnocline, in the thickness and the position of suboxic zone of the Black Sea are discussed

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TÜBİTAK YDABÇAG Proje15.04.199