Antarctic currents

Figure 4.13. Elements of the global water balance with the role of the ocean taken into account. Notations wA0L, wA0P, wA0I, wA0P precipitation Hpo, Hop Straits of Gibraltar Rp, Rj, RL rivers EPA, E1A, EPA, ELA evaporation Apl, A1P the Antarctic Current MP1 the Cape Igolny Current CPj the East-Australian Current fiPL Bering Strait 1LP Arctic ice DPP Drake Passage IP Antarctic ice NPI Indonesian seas Slf> Sfl straits.

The total dissolved amount of the metal always presented a surface concentration higher than the minimum observed at a depth of 10-25 m (1.6-2.2 nM) compared with the surface concentration (2.0-3.6 nM) the concentration further increased to values of between 2.2 and 3.7 nM near the bottom. The Cu concentration along a vertical profile in the Ross Sea offshore at Cape Adare, an area affected by the coastal Antarctic current, was reported by Abollino et al. (131). 

Atlantic Ocean Nodule abundance in the Atlantic Ocean appears to be more limited than in the Pacific or Indian Oceans, probably as a result of its relatively high sedimentation rates. Another feature which inhibits nodule abundance in the Atlantic is that much of the seafloor is above the calcium carbonate compensation depth (CCD). The areas of the Atlantic where nodules do occur in appreciable amounts are those where sedimentation is inhibited. The deep water basins on either side of the Mid-Atlantic Ridge which are below the CCD and which accumulate only limited sediment contain nodules in reasonable abundance, particularly in the western Atlantic. Similarly, there is a widespread occurrence of nodules and encrustations in the Drake Passage-Scotia Sea area probably due to the strong bottom currents under the Circum-Antarctic current inhibiting sediment deposition in this region. Abundant nodule deposits on the Blake Plateau can also be related to high bottom currents. 

Fig. 1. Major oceanographic features 1. Canary Current, 2. Gulf Stream, 3. North Atlantic Current, 4. Sargasso Sea, 5. North Atlantic Gyre, 6. Labrador Current, 7. Loop Current, 8. North Pacific Gyre, 9. South Equatorial Current, 10. Benguela Current, 11. Humboldt Current, 12. Antilles Current, 13. Florida Current, 14. Brazil Current, 15. Kuroshio, 16. Antarctic West Wind Drift.

Over the past decade, plastic debris has become a common feature of beaches and coastal waters adjoining populated areas of Europe (36-38), the Mediterranean (39-41), North and Central America (42-44) and New Zealand (45). Plastics are also present in the open ocean both near the major shipping lanes and in the most remote regions of the world (the Arctic (46), the Benguela Current (47), the Cape Basin area of the South Atlantic (48), the Humboldt Current in the South Pacific (49), and the Antarctic (50, 51). 

In the Cape Basin region of the South Atlantic, polyethylene and polypropylene pellets were observed at concentrations of 1333-3600 pellets km (48). Since this area is far from any major shipping lane and is dominated oceanographically by the Antarctic West-Wind Drift with possibly some input from the Brazil Current, the source of the floating plastic was thought to be ships transporting the raw material in the South Atlantic (48). The weathered appearance of the pellets indicated that they had been adrift for an extended period and, therefore, carried long distances by the ocean currents. 

The conveyor belt is shown schematically in Fig. 10-11. Warm and salty surface currents in the western North Atlantic (e.g., the Gulf Stream) transport heat to the Norwegian-Greenland Seas where it is transferred to the atmosphere. This heat helps moderate the climate of northern Europe. The cooling increases the density resulting in formation of the now cold and salty North Atlantic Deep Water (NADW) (Worthington, 1970). The NADW travels south through the North and South Atlantic and then joins the Circumpolar Current that travels virtually unimpeded in a clockwise direction around the Antarctic Continent. 

Deep water also forms along the margins of Antartica and feeds the Circumpolar Current. The Weddell Sea, because of its very low temperature, is the main source of Antarctic Bottom Water (AABW) which flows northward at the very bottom into the South Atlantic, and then through the Verna Channel in the Rio Grande Rise into the North Atlantic. It ultimately returns southward as part of the NADW. 

The Circumpolar Current is a blend of waters of North Atlantic ( 47%) and Antarctic margin ( 53%) origin (Broecker, 1997). This current is referred to as the Pacific Common Water and is the source of deep water to the Indian and... 

Smetacek, V., de Baar, H. J. W., Bathmann, U. V. et al. (eds) (1997). Ecology and biogeochemistry of the Antarctic Circumpolar current during austral spring Southern Ocean JGOFS Cruise ANT X/6 of R.V. Polarstem. Deep-Sea Res. II44,1-519. 

When DDT was widely used, it was released into the environment in a number of different ways. The spraying of crops, and the spraying of water surfaces and land to control insect vectors of diseases, were major sources of environmental contamination. Waterways were sometimes contaminated with effluents from factories where DDT was used. Sheep-dips containing DDT were discharged into water courses. Thus, it is not surprising that DDT residues became so widespread in the years after the war. It should also be remembered that, because of their stability, DDT residues can be circulated by air masses and ocean currents to reach remote parts of the globe. Very low levels have been detected even in Antarctic snow ... 

The continued depletion of Antarctic ozone and the appearance of spring ozone depletion over the Northern hemisphere between the latitudes of 40 and 55 N. detectable by the improved analysis of older data and the development of better ozone observational methods, resulted in a tightening of the CFC phaseout provisions during the 1990 and 1992 reviews,10 held in London and Copenhagen, respectively, and the extension of the restrictions to other, potentially ozone-depleting substances. Table 2 summarizes the current position. 

For methane hydrate, the minimum water depth is 381 m in freshwater and upto 436 m in seawater, respectively, at 277 K. In the world s oceans at water depths greater than 600 m, the temperature is typically uniform at 277 K, due to the density maximum in seawater. Lower bottom water temperature exceptions can be found with strong subbottom currents from Antarctic and Arctic environments such as the north of Norway or Russia. Methane-phase equilibrium data in Chapter 6, indicate that 3.81 MPa are required to stabilize methane hydrates at 277.1 K. Using the rule of thumb 1 MPa = 100 m water, hydrates in pure water would be stable at depths greater than 381 m. 

It has been estimated that one chlorine atom has an atmospheric lifetime of one to two years and may destroy 100,000 ozone molecules, thus contributing to the mysterious ozone hole. The British Antarctic Survey discovered the lowest ozone concentration in Earth s atmosphere ever recorded, in October 1984 nearly 40 percent less than the historical average for Antarctica. Atmospheric currents concentrate CFCs over Antarctica, creating the ozone hole that in 1984 was larger than the United States and taller than Mount Everest. The loss of ozone as a protective layer permits the penetration of increased levels of ultraviolet light to Earth s surface. 

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