THE DISTRIBUTION OF OXYGEN IN THE PACIFIC OCEAN 



INTRODUCTION 



Prior to the last cruise of the Carnegie very little 

 information was available regarding the distribution of 

 oxygen in the deep water of the Pacific. The Challenger 

 expedition (Dittmar, 1884) made about twenty-five de- 

 terminations of oxygen on subsurface water from vari- 

 ous parts of the Pacific but, because the samples were 

 taken in varying depths, and only one at each station, 

 the data are inadequate for any conclusions regarding 

 the distribution of oxygen. On board the Planet. Bren- 

 necke (1909) determined oxygen at several stations be- 

 tween New Guinea and Hong Kong, but the information he 

 obtained is not complete even for this limited area be- 

 cause practically no samples were taken below 1000 me- 

 ters and even above this depth the number was insiiffi- 

 cient. Schmidt (1925) reported the oxygen content of 

 the water down to a depth of 1000 meters at a station oc- 

 cupied by the Dana in the Gulf of Panama. Off the coast 

 of southern California the oxygen content had been de- 

 termined by the Scripps Institution of Oceanography and 

 in Monterey Bay by Bigelow and Leslie (1930). In nei- 

 ther case were observations taken below 1000 meters 

 and at that time it was not known whether the conditions 

 in the coastal areas were representative of the condi- 

 tions in the open Pacific. The Carnegie data give a fair- 

 ly complete picture of the distribution of oxygen in the 

 tropical and eastern North Pacific. Some of these data 

 already have been published (Moberg, 1930; Moberg and 

 Graham, 1930). 



Since the Carnegie cruise (1928-1929) there have 

 been a number of investigations of the oxygen content in 

 the Pacific but additional information is still needed, 

 particularly from the South Pacific. From data obtained 

 by the Dana in 1928 to 1929,Thomsen (1931b) constructed 

 a profile showing the distribution of oxygen in various 

 depths between Panama and New Caledonia. Ito (1930) 

 investigated the oxygen content of the water between New 

 New Guinea and Japan. Thompson, Thomas, and Barnes 



(1934) report the results of oxygen determinations made 

 by the University of Washington at a number of stations 

 in the Gulf of Alaska and near the Aleutian Islands. In 

 1933 R. H. Fleming, of the Scripps Institution of Ocea- 

 nography, made a thorough survey of the oxygen condi- 

 tions in the Gulf of Panama and along the Pacific coasts 

 of Panama and Costa Rica, on board the U. S. & Hannibal. 

 R. R. Revelle, also of the Scripps Institution of Ocea- 

 nography, determined oxygen at five stations off the 

 coast of southern California on board the U. S. Coast 

 and Geodetic steamer Pioneer in 1933, and at eighteen 

 stations between the Aleutian Islands and the Hawaiian 

 Islands on board the U. S. S. Bushnell in 1934. Some of 

 the data obtained by Fleming and Revelle are presented 

 in the present report. 



The Carnegie obtained vertical series of determina- 

 tions of oxygen at all stations occupied during the cruise 

 from San Francisco to Samoa, stations 130 to 162, and at 

 two stations in the North Atlantic and four in the south- 

 eastern Pacific. The data for stations 130 to 162 have 

 been used in the construction of four section diagrams, 

 showing the concentration of oxygen in milliliters per 

 liter, and four diagrams showing the concentration of 

 oxygen in percentage of saturation. R. R. Revelle of the 

 Scripps Institution of Oceanography very generously 

 supplied the authors with the oxygen data which he ob- 

 tained on board the U. S. S. Bushnell in August 1934. 

 ■From these data a section showing the distribution of ox- 

 ygen between the Aleutian Islands and Hawaii (fig. CI 7), 

 in milliliters per liter, has been constructed. In addi- 

 tion to the Carnegie and Bushnell data, the authors have 

 had access to the unpublished oxygen data obtained by 

 Revelle on the U. S. Coast and Geodetic steamer Pioneer 

 off the California coast and by Fleming on the U. S. S. 

 Hannibal in the Gulf of Panama and off the coast of Cen- 

 tral America in 1933. For the use of these data the 

 authors wish to express their gratitude. 



VERTICAL DISTRIBUTION 



The quantity of dissolved oxygen in sea water is con- 

 trolled by a number of physical, chemical, and biologi- 

 cal factors. At the surface of the sea the oxygen content 

 of the water is approximately in equilibrium with that of 

 the atmosphere and, since the solubility of oxygen varies 

 with the temperature, and to a much lesser extent with 

 the salinity, its quantity ranges from about 4.5 ml per 

 liter in the tropics to about 8 ml per liter in the polar 

 regions. In the photosynthetic zone, that is, in the upper 

 50 or 100 meters or at even greater depths in some lo- 

 calities, oxygen is liberated by plants during photosyn- 

 thesis, and when photosynthesis takes place rapidly in 

 water not in contact with the atmosphere the concentra- 

 tion of oxygen may rise considerably above the satura- 

 tion point. Since plants ordinarily are most abundant 

 some distance below the surface, the highest concentra- 

 tions of oxygen are usually encountered at some level in 

 the upper 100 meters. At all depths oxygen is con- 

 sumed by plants and animals during respiration and by 

 the decomposition of organic material. 



To account for the distribution of oxygen in a body 

 of water it is necessary to consider also the circulation 

 of the water. Since the sea derives its oxygen only at 

 or near the surface, from the atmosphere or from photo- 

 synthetic organisms, and since oxygen diffuses through 

 the water exceedingly slowly, the deep water depends 

 entirely on water movements for its supply of oxygen. 



Although different localities exhibit marked differ- 

 ences in the vertical distribution of oxygen, it is possi- 

 ble to recognize a general type of distribution which is 

 common to all areas in the Pacific investigated by the 

 Carnegie and to distinguish the following four layers of 

 water which differ from each other with respect to the 

 oxygen content. 



1. A narrow surface layer in which the oxygen con- 

 tent is approximately In equilibrium with the atmos- 

 phere and nearly uniform. In this layer the quantity of 

 oxygen is determined largely by the oxygen-retaining 

 capacity of the water, hence chiefly by the temperature. 



2. A layer in which the oxygen content is higher 



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