MID-PACIFIC OCEANOGRAPHY, PART VIII, MIDDLE LATITUDE WATERS, 



JANUARY-MARCH 1954 



By James W. McGary, Oceanographer , 



and 



E. D. Stroup, Physical Science Aid 



This report is concerned with 

 cruise 25 of the M/V Hugh M. Smith , the 

 first of a series of surveys planned to des- 

 cribe the oceanography of the central temper- 

 ate North Pacific by the Pacific Oceanic Fish- 

 ery Investigations, U. S. Fish and Wildlife 

 Service. These studies are designed to des- 

 cribe the physical environment in the region 

 north of Hawaii in connection with investiga- 

 tions on the albacore tuna, Germo alalunga 

 (Bonnaterre). This cruise was concurrent 

 with fishing by the John R. Manning , cruise 

 23, the results of which will appear separately. 



The survey, made during January- 

 March 1954, covered an area bounded roughly 

 by 141 and 165 W. longitude, and by 24 and 

 38 N. latitude (fig. 1). Serial measurements 

 of temperature, salinity, oxygen, and inorgan- 

 ic phosphate were made to a depth of approxi- 

 mately 1,200 meters; quantitative zooplankton 

 collections were taken by oblique tows through 

 the upper 200 meters and meteorological data 

 were recorded. The surface currents were 

 measured with the Geomagnetic Electrokine- 

 tograph during part of the cruise. This report 

 presents the tabulated station data (except for 

 the results of the plankton collections which 

 will appear separately), meridional sections, 

 and horizontal plots of oceanic and meteorolo- 

 gical features, and brief analyses and descrip- 

 tions of the results. 



PROCEDURES 



The vessel equipment and the 

 methods of collecting and correcting the raw 

 data have been described in previous reports 

 (Cromwell 1951, Stroup 1954); the methods of 

 analysis of the observed data leading to their 

 presentation as meridional sections have also 

 been described in detail (Stroup 1954). In es- 

 sence, the analysis attempts to use all the 

 data to achieve a comprehensive, consistent 

 description of the distributions of the several 

 variables. In the analysis of the individual 

 stations, the vertical distribution of each vari- 

 able is referred to temperature, as this is the 

 only quantity measured continuously with depth. 

 Rather than analyze each station independently , 



observed values from nearby stations are 

 considered during the construction of the sta- 

 tion curves. The vertical sections of density 

 (sigma-t) distribution are influenced by the 

 structure of the detailed bathythermograph 

 (BT) temperature sections, and the sections 

 of the other quantities are in turn influenced 

 by the sigma-t distribution, in accordance with 

 the principles of isentropic analysis. Insofar 

 as possible, no quantity is considered inde- 

 pendently of the over-all description. 



The horizontal plots (excepting figs. 



2-4) are based on a simple conic projection 



o o 



with standard parallels at 25 and 4 5 N. ; the 



distance scale is the same as that used in the 

 meridional sections. There is slight distortion, 

 nowhere greater than about 1 percent, along 

 the central and marginal parallels of latitude . 

 The horizontal plots are based on values inter- 

 polated from the station curves and, whenever 

 possible, the meridional sections were used to 

 determine the contour intervals between stations. 



The meteorology of the region is 

 discussed in somewhat greater detail than in 

 previous reports. The storm tracks were taken 

 from the daily (1200Z) surface weather charts 

 published by the U. S. Weather Bureau. The 

 monthly positions of the limits of the trades and 

 westerlies and the positions of the "Eastern 

 North Pacific High" and the "Aleutian Low" 

 (these are average, climatological features) 

 during the period the cruise were obtained from 

 the monthly average charts supplied by the Ex- 

 tended Forecast Section of the U. S. Weather Bu- 

 reau. The long-term average monthly positions 

 of these features are from Technical Paper No. 

 21, U. S. Weather Bureau, "Normal Weather 

 Charts for the Northern Hemisphere, " and from 

 the U. S. Navy Hydrographic Office Pilot Charts 

 for the North Pacific (H.O. 1401). 



CLIMATE AND WEATHER 



The oceans are a flexible medium 

 whose circulation, temperature structure, sali- 

 nity, and dissolved oxygen content are largely 

 dependent upon the exchange of energy between 

 the atmosphere and water. A discussion of 



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