Distribution of chemical constituents of sea water in the eastern sea off Philippine and in the Luzon straits.

Abstract

This report is a description of the distribution of chemical constituents of sea water collected by R/V “TAKUYO” in the eastern sea off the Philippines and in the Luzon straits, The cruises of the R/V “TAKUYO” were carried out in the summer of 1965 and 1966 as a part of the Cooperative Study of the Kuroshio and Adjacent Regions, Distributions of phosphate, silicate and dissolved oxygen are illustrated and some relationships between oxygen consumed and phosphate or silicate are shown with figures, Main results are as follows. 1) Salinity minimum layer was seen at the level of 500 to 600 meters deep in the zone about 20°N, This minimum layer becomes shallower towards south gradually to 5°N. Large horizontal gradients of chemical constituents of sea water in the direction across the current were seen in the region of the North Equatorial Current, the Kuroshio off Luzon, the Mindanao Current and Equatorial Counter Current. But the gradient in these current regions was smaller than that of the Kuroshio off the south coast of Japan. 2) The oxygen minimum layer was found 100-200 meters below the salinity minimum layer. The values of oxygen minimum in this whole region are remarkably high(l.8-1.2 ml/l) compared with other area in the Pacific. 3) Almost linear relation between silicate and depth was seen when logarithmic scale was used. 4) The upper layer water between 15° N. and 25° N. is characterized by high salinity, almost saturated dissolved oxygen and low concentration of nutrient matter. The thickness of this water layer is 300 to 400 meters. In the upper layer of the Equatorial Countercurrent region of 5°-7° N, the distribution of some constituents is variable from place to place. In the layer deeper than 200 meters of the same region the distribution is more uniform. In the northern part of the South China Sea, thin surface mixing layer and gentle gradient of vertical distribution of the constituents were observed. This may be due to the smaller relative movement between upper and lower water, 5) An approximately linear relationship between apparent oxygen utilization (A,O.U.) and phosphate concentration was observed. The inclinations of P/A.O.U. on these P-A.O.U. figures were 1. 6 μg-at/l/13 ml. The ratio of Si/P was seen to be comparatively constant at a range of 2 to 3 ml/l of A.O.U. This values lay between 10 to 20 and nearly equal to that obtained by Richards (1958) in the Atlantic ocean.