. The Composition of sea-water : comparative and descriptive oceanography. Seawater -- Composition. t52 REDFIELD, KETCHUM AND RICHARDS countercurrent mechanism on the distribution of a nonconservative property is found in the strait connecting Lake Maracaibo with the sea. During the rainy season this strait is swept out by water escaping from the lake. The net move- ment is seaward at all depths. Although the deeper layers have lower velocities than the surface the strait is too short to permit any notable change in the concentrations of oxygen to develop along its length. With the advent of t
. The Composition of sea-water : comparative and descriptive oceanography. Seawater -- Composition. t52 REDFIELD, KETCHUM AND RICHARDS countercurrent mechanism on the distribution of a nonconservative property is found in the strait connecting Lake Maracaibo with the sea. During the rainy season this strait is swept out by water escaping from the lake. The net move- ment is seaward at all depths. Although the deeper layers have lower velocities than the surface the strait is too short to permit any notable change in the concentrations of oxygen to develop along its length. With the advent of the dry season the outflow slackens and water of higher salinity crosses the shallow sill separating the strait from the sea, and flows lake ward beneath the outflow of surface water. Within a few months the oxygen content of the deep counter current becomes greatly reduced in the direction of its movement (see Fig. 12).. o 20 40 60 _ ' - 5 - / " —- - -^_ - - " — ^ ~**^C 4 - <l / - MARCH I i i I 1 1 20 50 Fig. 12. Distribution of oxygen in section along Strait of Maracaibo during wet season, May, and dry season, March. Lake Maracaibo lies to the right. Arrows indicate the direction of non-tidal currents. Ordinate, depth in feet; abscissa, scale of miles; contour interval, 1 ml oxygen/m3. (After Redfield, 1955.) Extreme examples of the accumulation of nonconservative elements are provided by fjords. These estuaries are separated from the outer sea by sills which limit the active exchange of water to a relatively shallow layer and thus permit the deep water to stagnate. They thus represent the limiting case of differential advection in which the ratio of the velocities of the upper and lower layers is very large. The sinking of organic matter into the deep basins leads to reduction in oxygen content, the production of hydrogen sulfide and the accumulation of unusual concentrations of phosphate. In a large series of fjords examined by Strom (1936) great variations
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