. The Composition of sea-water : comparative and descriptive oceanography. Seawater -- Composition. 66 REDFIELD, KETCHUM AND RICHARDS [CHAP. 2 it moves toward the site of upwelling, as the result of the sinking of organized matter from the surface layers as they move offshore. In support of this, the oxygen is diminished in about the proportions required for the decomposition of organic matter. The classic examples of upwelling are found along the eastern boundaries of the oceans in the trade-wind belt. The distribution of total phosphorus in a section crossing the Benguela current off the wes
. The Composition of sea-water : comparative and descriptive oceanography. Seawater -- Composition. 66 REDFIELD, KETCHUM AND RICHARDS [CHAP. 2 it moves toward the site of upwelling, as the result of the sinking of organized matter from the surface layers as they move offshore. In support of this, the oxygen is diminished in about the proportions required for the decomposition of organic matter. The classic examples of upwelling are found along the eastern boundaries of the oceans in the trade-wind belt. The distribution of total phosphorus in a section crossing the Benguela current off the western coast of Africa, where up- welling occurs, is shown in Fig. 15. At all depths the concentrations of phos- 200 400 600 800 — 1000. Fig. 15. Distribution of total phosphorus and salinity in a section along 24th parallel off west coast of Africa. Solid contours, total phosphorus, mg atoms/m3; broken con- tours, salinity, %„. Depths in meters. (Based on Crawford Stations 450-458, October, 1958.) phorus increase markedly as the coast is approached. If this enrichment were due entirely to the movement of deep water into the upper layers, the isohalines should parallel the phosphorus isopleths, which is not the case. The fact that along any isohaline the phosphorus increases markedly toward the coast indicates that some process other than the physical motions of the water leads to an accumulation of this element in the upwelling area. Upwelling can only be maintained by a flow of deep water toward the site of upwelling to replace the surface water moved offshore by the wind. Off the coasts of California (Sverdrup and Fleming, 1941) and Peru (Gunther, 1936) counter currents are present in the sub-surface waters during the periods of upwelling. It seems probable that nutrients accumulate in areas of upwelling because of the differential advection of water at different depths and in ac- cordance with the principles which apply in estuaries. This accumulation must contribute subs
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