Expendable Bathythermograph Data on Subsurface 



Thermal Structure in the 



Eastern North Pacific Ocean 



By 



J. F. T. SAUR, Oceanographer 



and 



DOROTHY D. STEWART, Fishery Biologist 



Bureau of Commercial Fisheries Biological Laboratory 

 Stanford, California 94305 



ABSTRACT 



This report contains reproductions of original temperature-depth traces, two 

 temperature sections, and synoptic weather observations taken between San Fran- 

 cisco and Honolulu in November-December 1965, using an expendable bathythermo- 

 graph system aboard a merchant ship, A third temperature section derived from 

 closely spaced observations shows the complicated temperature structure with 

 temperature maximums and minimums over a distance of about 45 nautical miles 

 (85 km.) across the outer boundary of the California Current. 



INTRODUCTION 



Knowledge of the mechanisms by which the 

 environment may affect the abundance and 

 availability of commercial fishes and the ap- 

 plication of oceanographic and fishery fore- 

 casting will depend upon the collection of 

 oceanographic data well distributed in space 

 and time, both at the surface of the ocean and 

 below the surface. Near- surface water tem- 

 peratures collected as a part of the marine 

 weather observations are numerous from the 

 middle latitudes of the northern hemisphere 

 where shipping is dense. Instrument programs 

 are underway in the Bureau of Commercial 

 Fisheries, the Navy Oceanographic Office, 

 and the Weather Bureau to improve the quality 

 of the water temperature observations that 

 are now generally obtained by reading com- 

 mercial grade mercury-in-glass thermom- 

 eters mounted in the ship's sea-water intake 

 system in the engineroom and that contain 

 numerous errors (Saur, 1963; Sette, 1965). 



The cost of obtaining the weather observa- 

 tions (including the sea temperatures) aboard 

 merchant ships is low compared with the cost 

 of oceanographic observations by research 

 vessels. The greatest overhead cost, the 

 operation of the ship, is already absorbed 

 because the ship has another primary mission. 

 From the point of view of oceanographic or 

 meteorological observations, a merchant ship 

 is a "ship of opportunity". 



Subsurface oceanographic observations are 

 sparse in comparison with surface data. It 

 seems feasible to improve greatly the time- 

 space distribution of subsurface data by two 

 methods: the use of anchored and drifting 

 oceanographic buoys and the use of ships of 

 opportunity. The latter depends upon instru- 

 ment systems that can obtain the data without 

 interfering with the normal operation of the 

 ship, particularly without having to decrease 

 the speed or change course. One of the first 

 systems of this type to be developed is based 

 on the expendable bathythermograph. 



The Bureau of Commercial Fisheries Bio- 

 logical Laboratory, Stanford, Calif., with the 

 cooperation of the Matson Navigation Com- 

 pany, has begun a pilot project to test the 

 feasibility of using an XBT (expendable bathy- 

 thermograph) system manufactured by the 

 Sippican Corporation 1 aboard a ship of oppor- 

 tunity. George Hansen of the U.S. Fleet Nu- 

 merical Weather Facility, Monterey, Calif,, 

 added a digitizer- encoder unit to the recorder 

 and assisted with the preliminary tests of the 

 system. The system has been placed aboard 

 the SS CALIFORNIAN to obtain subsurface 

 temperature data between Honolulu and San 

 Francisco on approximately a biweekly basis. 

 This project will provide experience to form 

 plans for use of ships of opportunity to obtain 



1 The trade name referred to in this publication does 

 not imply endorsement of the commercial product. 



