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APPENDIX E 326 Black Sea The Black Sea is the archetypical anoxic basin (Pickard and Emery, 1990). The surface circulation is defined by an anticlockwise gyre in each of the east and west basins (Pickard and Emery, 1990). It receives a volume of fresh water via river runoff and precipitation that far exceeds the amount of evaporation; consequently, its salinity is depressed (Pinet, 1992). A sharp halocline stratifies the water column; additionally, summer heating creates a thermocline that further intensifies vertical stratification. There is a pronounced density discontinuity at about 100 m (Pinet, 1992). Renewal of the deep water of the Black Sea is very slow, because it occurs via water which flows in along the bottom of the Bosporus. This inflow is so small (193 cubic kilometers (km) per year (Dietrich, 1963) in proportion to the total volume of water that renewal below a depth of 30 m is estimated to take about 2,500 years (Sverdrup et al., 1942). Thus, salinity in the deep sea remains low, representing the equilibrium between influx and vertical convection (Dietrich, 1963). Below a depth of about 200 m, the Black Sea contains large amounts of hydrogen sulfide rather than oxygen. With the exception of anaerobic bacteria, water below this depth is inhospitable to life (Pinet, 1992). Although the residence time of water below the halocline is long, mixing occurs at a faster rateâabout once every 100 years, via storm movement of deeper water and surface cooling over the winter, which lessens density stratification (Pinet, 1992). Caribbean Sea The Wider Caribbean special area includes the Caribbean Sea and the Gulf of Mexico. The area consists of a number of deep basins separated by major sills (Clark, 1986). The Caribbean Sea is tropical and experiences little seasonal change. Over much of the area there is a permanent thermocline at about 100 m. Upwelling is not a dominant feature, although there are localized areas where bottom water comes to the surface. Because of the permanent thermocline and lack of upwelling, the Caribbean tends to be nutrient-poor, confining fisheries to the shallow waters (Clark, 1986). There are approximately 60 species of corals in the Caribbean Sea. The second largest coral reef in the world is the 250 km-long barrier reef in the waters off Belize (Pinet, 1992). The greater Caribbean area attracts about 100 million tourists each year (Clark, 1986), with 3 million of those coming on cruise ships (Elder and Pernetta, 1991).
