South Equatorial Current

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.

South America to about the date line (180 ). These trade winds also drive near-equatorial surface flow westward as the South Equatorial Current (SEC). This piles up warm surface water in the western Pacific to create a deep warm pool and results in depression of the depth of the thermocline from east to west. The westward flow in the surface SEC is partly compensated by a return flow to the east in the thermocline ( 150m) called the Equatorial Undercurrent (EUC). 

Figure 3 shows the ethylene concentrations reported by Lamontagne et al. (7) for the cruise in 1972 which intersects the 1974 cruise track. At that time, an average maximum value for ethylene of 5.3 X ml/l, and an average low value of 2.6 X 10 ml/l was found. This broad 1972 maximum and the 1974 maximum fit the geographic location of the South Equatorial current relatively well. No chlorophyll a data were obtained in 1972. 

There is a broad but significant increase for ethylene between 5°N and 10 °S which corresponds to the position of the South Equatorial Current (S.E.C.). The data reported by Lamontagne et aL (7, Figmre 3) shows this maximum for ethylene in the same area. A similar but smaller maximum was found for propylene in 1972, and this is also the case for the 1974 cruise. It is likely that these broad gentle increases for ethylene and propylene result from the S.E.C. sweeping biologically rich upwelled water away from the South American coast. Chlorophyll a data follow the general pattern set forth by ethylene and support this speculation. 

Once in the ocean, the tides and currents driven by wind control the circulation of shallow water. Seven major currents, shown in Figure 2.1 [27], move water around the globe the West Wind Drift (or the Antarctic Circumpolar Current), East Wind Drift, the North and South Equatorial currents, the Peru Current, the Kuroshio Current, and the Gulf Stream. These currents can move quickly. The Gulf Stream, for example, usually travels at a speed of 3 or 4 knots, which is equivalent to 5.6 to 7.4 kilometers per hour [27]. As these currents spiral through the ocean they form five major gyres the North Atlantic, South Atlantic, North Pacific, South Pacific, and Indian Ocean gyres. 

Fig. 6.1 Major features of surface circulation in the NW Indian Ocean during (a) Northeast monsoon, and (b) Southwest monsoon (EACC - East African Coast Current SECC - South Equatorial Countercurrent SC - Somali Current WICC - West Indian Coast Current NMC - Northeast Monsoon Current LH - Lakshadweep High SG - Southern Gyre GW - Great Whirl SE - Socotra Eddy RHJ -Ras-al-Hadd Jet LL - Lakshadweep Low SMC - Southwest Monsoon Current). Redrawn from Schott and McCreary (2001) with permission from Elsevier Science.

There are substantial differences between glaciation of the southern and the northern polar regions. In the south, Antarctica is a sole continent in polar position. It is surrounded by large oceans, and is screened from warm equatorial currents at about 60 S by the Antarctic Convergence. In the north, a relatively small but deep Arctic Ocean is surrounded by continents, its waters coihmimicating with the Atlantic and the Pacific oceans by narrow straits, the Nansen Strait and the Bering Strait, respectively. 

A phenomenon reoccurring every few years in the equatorial part of the Pacific ocean, characterized by movement of a mass of warm water eastward towards the west coast of South America. This change in ocean conditions has long been recognized in Peru, where sailors noticed that an unusual counter-current appeared in certain years around the area of the port of Paita. They named this current El Nino - the Christ Child - because it usually appeared immediately after Christmas. It was also known that the appearance of this current coincided with different weather conditions, particularly increased rainfall and sometimes flooding. 

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