Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 324
Clean Ships Clean Ports Clean Oceans: Controlling Garbage and Plastic Wastes at Sea APPENDIX E Characteristics of Annex V Special Areas excerpts1 from: An Analysis of Proposed Shipborne Waste Handling Practices Aboard United States Navy Vessels R. L. Swanson, R. R. Young, and S. S. Ross Marine Sciences Research Center State University of New York at Stony Brook Stony Brook, New York CHARACTERISTICS OF SPECIAL AREAS Antarctic Ocean The East Wind Drift (attributed to the prevailing easterly winds) is a westward-flowing coastal current around most of the continent. Further north, the Southern Ocean is dominated by the Antarctic Circumpolar Current. This strong current flows in an eastward direction between about latitude 40°S and latitude 60°S. Surface flow is driven primarily by the frictional stress of the westerly winds in the region. This stress, together with the Coriolis force, contributes a northward component to the surface current, resulting in the formation of fronts. Below the surface layer, the density structure is in geostrophic balance with the circulation (Pickard and Emery, 1990). There are three major basins in the Antarctic Ocean: the Atlantic-Indian-Antarctic Basin, the Eastern Indian-Antarctic Basin (also referred to as the Australian-Antarctic Basin or Knox Basin), and the Pacific Antarctic Basin (or Bellingshausen Basin). There is also a single deep-sea trench, the South Sand- 1 These excerpts have been edited for grammar and style; factual accuracy is the sole responsibility of the authors. Copies of the complete paper may be obtained from the Marine Board, National Research Council, 2101 Constitution Avenue, N.W., Washington, D.C. 20418.
OCR for page 325
Clean Ships Clean Ports Clean Oceans: Controlling Garbage and Plastic Wastes at Sea wich Trench, in the Antarctic Ocean, on the east of the South Sandwich Island and adjoining the Scotia Ridge. The trench extends 600 miles and reaches a maximum depth of 8,260 meters (m), located between latitude 55°S longitude 32°W and latitude 61°S longitude 27°W (Fairbridge, 1966). Two to three thousand tourists each year visit the Antarctic. Palmer Station, a U.S. research base on the peninsula, has become such a popular destination that a quota has been introduced (Elder and Pernetta, 1991). It is estimated that total annual production of plant matter in surface waters south of the Antarctic Convergence is 610 million tonnes. The Baltic Sea The Baltic Sea, including the Gulf of Bothnia and the Gulf of Finland, is the largest area of brackish water in the ocean system (Pickard and Emery, 1990). It is brackish because precipitation and runoff greatly exceed evaporation (Sverdrup et al., 1942). Its bottom topography is irregular, with a mean depth of 57 m and a number of basins, the deepest of which is 459 m deep (Pickard and Emery, 1990). The Baltic is connected to the Atlantic Ocean at its southwest end through intricate passages. Its sill depth in the narrows between Gedser and the Darss is about 18 m, leading to the Kattegat and the North Sea (Pickard and Emery, 1990). Evaporation and precipitation each are estimated at about 47 centimeters (cm) per year, thus canceling one another. Annual river runoff is equivalent to 130 cm of water over the entire sea; however, there are significant year-to-year variations (Pickard and Emery, 1990). Overall general circulation is weak (approximately 1 cm per second) (Pickard and Emery, 1990), as there are no tidal currents to disturb the stratification (Dietrich, 1963). Because of shallow sill depth, a rejuvenation of the deep water occurs only when large-scale meteorological conditions can override the estuarine circulation. These conditions are not rare: Significant vertical mixing can occur because the Baltic basin is so shallow and broad (Gross, 1967). Thus, it is possible for the residence time of the Baltic to be less than one year, although this is variable. The area's humid climate aids the development of a density discontinuity layer, thus greatly Preventing a thermohaline convection. The Baltic is a two-layer system with a well-mixed upper layer 30-50 m deep in the south, increasing to 60-70 m in the central Baltic (Pickard and Emery, 1990). Dissolved oxygen may reach saturation levels in the surface layers but is relatively low in deep water. Changes may occur on a decadal time scale and are related to variations of inflowing water to the south. There has been a general trend toward decreasing dissolved oxygen values since the beginning of the twentieth century (Pickard and Emery, 1990). In many of the deep basins which have a residence time of several years, anoxic conditions occur (Pickard and Emery, 1990).
OCR for page 326
Clean Ships Clean Ports Clean Oceans: Controlling Garbage and Plastic Wastes at Sea 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 rate—about 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).
OCR for page 327
Clean Ships Clean Ports Clean Oceans: Controlling Garbage and Plastic Wastes at Sea Gulf of Mexico The Gulf of Mexico forms the northeastern component of the Wider Caribbean. It is surrounded by the Yucatan Peninsula, Cuba, and the Florida coast and exhibits a wide continental shelf. Its northern shoreline consists mostly of sedimentary material derived from Mississippi River Basin. The western and southern coasts are characterized by large lagoons separated from the sea by barrier beaches. Residence times for water within lagoons varies widely. In the Great Barrier Reef, times of 0.5-4 days have been estimated for lagoons of 2-10 km in diameter; for Bikini Atoll, 40-80 days, and for the very shallow Fanning Atoll (18 km long but only a few meters deep), periods of up to 11 months have been estimated (Pickard and Emery, 1990). The salinity of lagoons varies with tidal action, evaporation, and freshwater input from rain and runoff from land (Elder and Pernetta, 1991). The lagoons serve as an important habitat. The Gulf of Mexico and the Caribbean Sea are connected by the Yucatan Channel (sill depth about 1,600 m). The topography is rugged, with great contrasts between ridges and troughs. This is an area of particular interest for tectonophysical and geophysical studies, due to the presence of pronounced gravity anomalies, volcanism, and strong seismic activity (Neumann and Pierson, 1966). The Gulf of Mexico may be divided into two halves, based on the character of its circulation. The eastern part is dominated by the Loop Current, whose water originates in the northwestern Caribbean Sea as the Yucatan Current and flows into the central eastern gulf. The Yucatan Current flows over a sill between the Yucatan and western Cuba and deepens to 1,800 m in the Gulf (Pinet, 1992). From there, it veers eastward and exits to the south of Florida. (Water in the eastern Gulf that is deeper than 600 m remains in the basin, trapped by a shallow sill south of Florida [Pinet, 1992].) This current rotates clockwise and has surface speeds of 50-200 cm per second (Pinet, 1992). In contrast, circulation is weak and variable in the western half of the Gulf of Mexico where the clockwise surface flow averages less than 50 cm per second (Pinet, 1992). Primary productivity in the Gulf of Mexico is generally low, averaging about 25 grams (g) carbon per m3 per year; however, some areas are much more productive due to upwelling and an inflow of nutrients from the Mississippi River. In the northern Gulf, primary productivity ranges from 250-350 g carbon per m3 per year. Almost two-thirds of the United States contributes to freshwater runoff into the Gulf of Mexico, greatly stressing the environment. Most pollutants discharged by U.S. rivers are dispersed in the western Gulf, where levels may build up due to the weakly circulating water of the area (Pinet, 1992).
OCR for page 328
Clean Ships Clean Ports Clean Oceans: Controlling Garbage and Plastic Wastes at Sea The Mediterranean Sea Mediterranean water forms in the northwestern part of the Mediterranean Sea in winter. Cooler winter temperatures and higher-than-normal evaporation, associated with the cold, dry Mistral winds, increases the surface water density such that vertical mixing occurs all the way to the sea floor (2,000 m). Evaporation (about 100 cm per year) exceeds precipitation plus river runoff, so there is a net loss of volume which is made up by inflow of salt water from the Atlantic Ocean (Pickard and Emery, 1990). The homogeneous Mediterranean water mass has a salinity of more than 38.4 practical salinity units (psu) and a temperature of about 12.8°C (Davis, 1977). Mediterranean water leaves the Straits of Gibraltar at approximately 300-500 m depth, below incoming Atlantic water. Intense mixing occurs at the interface of the Mediterranean and Atlantic waters. The least-mixed Mediterranean water has a salinity of 36.5 psu and a temperature of 11°C (Davis, 1977). Due to its high density, it sinks to about 1,000 m, where it becomes neutrally buoyant and spreads out. This distinctive tongue of mediterranean water can be recognized throughout much of the Atlantic Ocean by its high temperature and salinity profiles. The Mediterranean Sea's relatively long residence time (estimated at 70-100 years) makes it particularly vulnerable to pollution. North Sea The North Sea is broad and shallow; thus, it is subject to storm surges (Gross, 1982). At its southern end the North Sea is constricted at the Straits of Dover; however, there is no geographical northern boundary. The south and southeastern parts are less than 50 m deep, and the northern part is 120-145 m deep. The North Sea is not an homogeneous body of water. The residence time is approximately 0.9 year (Otto, 1983). Overall, there is an excess of precipitation over evaporation. In winter, however, the lee effect of the British Isles produces a net loss by evaporation in the western and southwestern parts of the North Sea. During summer, all parts receive an excess of water due to precipitation. As surface waters become less saline, stratification occurs between the warm, less dense water over the deeper water. During calm weather in the eastern North Sea and German Bight, a thermocline may develop, resulting in reduced oxygen concentrations in the bottom water (Clark, 1986). Persian Gulf The average depth of the Persian Gulf is 30 m, with a maximum depth of 90 m. It is so shallow that there is no significant exchange of water between it and the adjacent Gulf of Oman (Sverdrup et al., 1942), although some water does
OCR for page 329
Clean Ships Clean Ports Clean Oceans: Controlling Garbage and Plastic Wastes at Sea flow into the Arabian Sea (Pickard and Emery, 1990). Because the Persian Gulf is so shallow, it experiences uniformly high levels of salinity (40-70 psu) and wide seasonal changes in sea temperatures (15-38°c). Thorough wind-driven mixing occurs throughout most of the year (International Maritime Organization, 1994). The Persian Gulf experiences high evaporation and low rainfall rates—a contributing factor to the high salinity of the water. These factors work to restrict biological diversity, and many species live at or near their limits of environmental tolerance (International Maritime Organization, 1994). Under these conditions, any added stress, such as an oil spill or other pollution event, can disproportionately influence the area. Red Sea The Red Sea is a rift valley, resulting from the separation Of Africa and the Arabian peninsula (Pickard and Emery, 1990). With the exception of the Suez Canal, it is closed to the north. It opens to the Gulf of Aden, Arabian Sea, and the Indian Ocean to the south, through the narrow strait of the Bah al Mandab. There is a sill of about 110 m at the Bah al Mandab (Pickard and Emery, 1990). There are no rivers flowing into the Sea. Evaporation is high (about 200 cm per year), while precipitation averages about 7 cm per year, making this the most saline large body of ocean water in the world (Pickard and Emery, 1990). The surface layer is saturated with dissolved oxygen; however, absolute values are low (less than 4 milliliters per liter) due to high temperatures and salinities. Red Sea circulation varies seasonally with the winds. In summer (southwest monsoon) the winds are to the south. Surface flow is southward, with outflow through the Bah al Mandab; additionally, there is a subsurface inflow to the north through that strait. In winter (northeast monsoon) the winds over the southern half of the sea change to the north, and there is a northward surface flow over the entire Red Sea, with a subsurface southward flow through the Bah al Mandab. The outflow is from an intermediate layer to about 100 m. This water can be traced through the Arabian Sea and down the west side of the Indian Ocean (Pickard and Emery, 1990). Residence time for the surface layer has been estimated at six years; for the deep water, about 200 years (Pickard and Emery, 1990). A notable feature of the Red Sea are the hot brine pools found in some of the deepest parts. Pickard and Emery offer the explanation with fewest arguments. They assert that ''this is interstitial water from sediments, or solutions in water of crystallization from solid materials in the sea bottom, released from heating from below and forced out through cracks into the deep basins of the Red Sea.''
OCR for page 330
Clean Ships Clean Ports Clean Oceans: Controlling Garbage and Plastic Wastes at Sea TABLE E-1 General Physical Characteristics of MARPOL Special Areas depth (m) mean area (106km2) volume (103km3 surface temp. range (°C) surface salinity range (psu) relative surface water viscositya (%) residence time (years) Antarctic Ocean 4,000 -2/+4 34.6 94-110 100 Baltic Sea 86 0.39 33 -2/+15 6-8 65-107 short Black Sea 1,166 0.46 537 9-5** 18-21** 53-79 2500*-3000§ Caribbean Sea 2,491 2.8 6,860 25-28 36 51-55 Gulf of Mexico 1,512 1.5 2,332 20-29 36 50-61 100* Mediterranean Sea 1,494 2.5 3,758 13-26 37-39 54-73 70-100 North Sea 91 0.60 55 5-16 34-35 67-92 0.9|| Persian Gulf 25* 0.24 10 10-25 38 55-78 long Red Sea 558 0.45 251 18-32 40-41 47-65 6.0§ a Assumes 100% at 0 psu and 0°C. Sources: van der Leeden et al., 1990; *Geyer, 1981; *Sverdrup et al., 1942; **Pinet, 1992; §Pickard and Emery, 1990; ||Otto, 1983
OCR for page 331
Clean Ships Clean Ports Clean Oceans: Controlling Garbage and Plastic Wastes at Sea REFERENCES Clark, R.B. 1986. Marine Pollution. Oxford: Oxford University Press. Davis, R.A., Jr. 1977. Principles of Oceanography. Reading, Mass.: Addison-Wesley Publishing Co., Inc. Dietrich, G. 1963. General Oceanography (translated from German). New York: John Wiley & Sons. Elder, D. and J. Pernetta (eds.). 1991. Random House Atlas of the Oceans. New York: Random House with World Conservation Union. Fairbridge, R.W. (ed.). 1966. The Encyclopedia of Oceanography. New York: Reinhold Publishing Corp. Geyer, R.A. (ed.). 1981. Marine Environmental Pollution, 2. Dumping and Mining. College Station: Texas A&M University. Gross, M.G. 1967. Oceanography: A View of the Earth. Columbus, Ohio: Charles E. Merrill Books. Gross, M.G. 1982. Oceanography: A View of the Earth. Englewood Cliffs, N.J.: Prentice-Hall, Inc. International Maritime Organization (IMO). 1994. Three years on: The Persian Gulf oil spill. IMO News 1:21-24. Neumann, G. and W.J. Pierson, Jr. 1966. Principles of Physical Oceanography. Englewood Cliffs, N.J.: Prentice-Hall. Otto, L. 1983. Currents and water balance in the North Sea. Pp. 26-43 in North Sea Dynamics, J. Sundermann and W. Lenz, eds. Berlin: Springer-Verlag. Pickard, G.L. and W.J. Emery. 1990. Descriptive Physical Oceanography: An Introduction. Oxford: Pergamon Press. Pinet, P.R. 1992. Oceanography: An Introduction to the Planet Oceanus. St. Paul, Minn.: West Publ. Sverdrup, H.U., M.W. Johnson, and R.H. Fleming. 1942. The Oceans: Their Physics, Chemistry, and General Biology. Englewood Cliffs, N.J.: Prentice-Hall. van der Leeden, F., F.L. Troise, and D.K. Todd. 1990. The Water Encyclopedia, 2nd Ed. Chelsea, Mich.: Lewis Publishers.
Representative terms from entire chapter: