ON THE OXYGEN SUPPLY OF THE DEEP PACIFIC OCEAN1

The existence of an oxygen minimum layer in the Pacific Ocean precludes vertical diffusion of oxygen from the surface to the deeper water. To maintain the known oxygen content, oxygen used in the deep water must be replenished by an inflow of relatively oxygen-rich water into the Pacific Ocean at high southern latitudes and an outflow of water with lower oxygen concentrations across the oxygen minimunl surface. An estimate of the average rate of oxygen consumption gives a value for this flow of about 3 x 10” m’/sec. In a recent paper, Wooster and Volkmann ( 1960) examined the temperature and oxygen distribution at 5 km depth in the Pacific bcean to obtain indications of the deep circulation. They concluded that the circilation is generally from south to north but did not arrive at -an estimated rate of circulation. The fact that a surface of minimum oxygen concentration exists everywhere in the Pacific Ocean makes it possible to obtain an approximation of the rate of this circulation. Because of the oxygen minimum surface, there can be noSupply of -oxygen to the deep waters by vertical eddy diffusion. The oxygen requirement must be met by waters with relatively high oxygen concentrations flowing into the deeper Pacific Ocean and later leaving across the oxygen minimum surface with a lower concentration. This change in oxygen concentration can be estimated, and a knowledge of the rate of oxygen consumption below the oxygen minimum then leads to a rate of volume transport. The rate of oxygen consumption can at present only be estimated approximately; however, in the absence of other data, this estimate may be useful. The oxygen distribution in the world ocean has been reviewed by Richards (1957). For the purposes of this paper, it is necessary merely to show that a surface of minirnirn oxygen concentration exists throughout the Pacific Ocean and to display its significant characteristics. To dothis we have compiled charts of the depth of the oxygen minimum layer ( Fig. 1)) the oxygen con1 This work was carried out under National Science Foundation Grant No. GP-2044 and Office of Naval Research Contract Nonr-1286( 10 ) Project NR 083-102. centration at the minimum (Fig. 2) and the ut value at the oxygen minimum surface (Fig. 3). These charts are based on the atlas of Muromtsey ( 1958), supplemented by data from oceanographic cruises in the Pacific Ocean. In many areas, the exact location of the oxygen minimum surface is not well defined, and only the general trend of the surface is shown in the figures. The surface is at a depth of 500 m near the Antarctic Ocean, then drops approximately along a ut surface to about 2 km at 50” S lat (Fig. 1). At about 20” S lat, the surface rises to about 500 m across the ut surfaces, and drops again to about 1 km at 30” N lat. Superposed on the general change with latitude there is a longitudinal asymmetry, with greater depths and higher oxygen levels in the west. The oxygen concentration at the minimum level (Fig. 2) is 4 ml/liter in the south and decreases rapidly north of 20” S lat. The lowest values are found along the west coast of Central America, where the oxygen concentration is below 0.1 ml/liter. In the North Pacific Ocean, the average minimum oxygen level is about 0.5 ml/liter, with a general decrease from west to east. The average oxygen concentration below the oxygen minimum decreases from slightly above 4 ml,/liter near the Antarctic Ocean to about 3 ml/liter at the equator and about 2 ml/liter in northern latitudes. Oxygen cross sections at northern latitudes indicate that there is no significant addition of oxygen to the deep Pacific Ocean from the Arctic Ocean or the North Pacific Ocean. The data indicate that all the oxygen for the deep Pacific Ocean is supplied by inflow from the circum-Antarctic waters. The aver-