SOME RECENT TEMPERATURE SECTIONS ACROSS THE 

 ANTARCTIC CONVERGENCE 



By D. W. Pritchard and E. C. LaFond, U.S. Navy Electronics 

 Laboratoiy, San Diego 52, California 



Introduction 



The temperature data discussed in this paper represent a portion of the 

 oceanographic information obtained during the U.S. Navy Antarctic 

 Development Project of 1947 (operation HIGH JUMP). In order to 

 secure these oceanographic data Dr. Robert S. Dietz and Mr. Herbert 

 J. Mann, civilian representatives of the U.S. Navy Electronics Laboratory, 

 accompanied two of the ships of the Western Task Group — The U.S.S. 

 " Henderson " and the U.S.S. " Cacopan " — on operation HIGHJUMP. 

 A treatment of aU of the oceanographic and geological data obtained by 

 the Western Task Group on this operation is presented in USNEL Report 

 No. 55, Some Oceanographic Observations on Operation HIGHJUMP, 

 July, 1948. ' This paper deals with five bathythermograph sections made 

 b}^ individual ships while crossing the Antarctic Convergence. 



General 



Proceeding southward from the region of warm surface water in low 

 latitudes one encounters first gradually decreasing temperatures. How- 

 ever, in a region between 55° S. and 65° S. the temperature decreases 

 markedly within a short distance. Beyond this region of strong horizontal 

 temperature gradients the surface temperatures remain rather constant 

 and near the freezing-point. This boundary is a region where part of the 

 cold Antarctic surface water, brought northward by the transverse 

 circulation created by the westerly wind system, sinks below the warmer 

 water transported southward by the thermohaline circulation which 

 dominates in the subantartic region. This area of sinking is called the 

 " Antartic Convergence." 



As reported b}^ Dr. Dietz, the convergence was quite apparent as 

 an abrupt water-mass boundary in the south central Pacific, north of the 

 Ross Sea. Soon after crossing it, observers on the " Henderson " 

 encountered their first group of icebergs. As the convergence was 

 crossed the water changed in colour from blue to grey, new types of 

 birds appeared, and the sky cleared. These changes closely followed 

 the drop in temperature, which was more than 2-5° c. in about 20 miles. 



Location of the Convergence 



To aid in locating the Antarctic Convergence, as well as to show the 

 complexities of the antarctic thermal structure, horizontal temperature 

 plots and vertical cross-sections of temperature versus depth have been 

 constructed for five locations as shown in Figure 1 . The horizontal plots 

 are numibered A, B, C-1, C-2, and C-3 for reference. 



Both the plots and cross-sections are based on a series of bathythermo- 

 graph observations taken by individual ships on nearly straight runs 

 across the convergence. Three of the sections-^C-1, C-2, and C-3- — ■ 

 were taken in the same locality and serve to indicate the seasonal trends 

 in the location of the convergence. These features are discussed more 

 fully below. 



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