Papers in Marine Biology and Oceanography, Suppl. to vol. 3 of Deep-Sea Research, pp. 418-425. 



Characteristics of the water-masses of the Philippine, Kermadec 



and Tonga Trenches 



By Anton Fr. Bruun and A. Kiilerich 

 The Galathea Expedition 1950-52, Copenhagen 



The chief purpose of the Galathea Expedition 1 950-52, The Danish Deep Sea Expedi- 

 tion around the World, was to study the organisms in the deepest parts of the oceans. 

 A considerable number of hydrographic observations, however, were made to learn 

 about the environmental conditions. At least one full series from the surface to the 

 bottom was made in each of the regions where biological work was concentrated. 

 The hydrographic instruments were standard types. During the expedition a total 

 number of 16 reversing thermometers were lost, six of them being simply crushed by 

 pressure at the greater depths in the Philippine Trench. 



The greatest care was taken in making observations. Even when only one ther- 

 mometer was available for each water-bottle, most doubtful temperature readings 

 were repeated. We are therefore fairly confident that our observations, including 

 those presented here, are as exact as any made by specially equipped hydrographic 

 expeditions. 



Many technical difficulties resulted from the extreme depth of the PhiHppine 

 Trench. The effect of high pressure has been mentioned. It was furthermore very 

 difficult to keep the ship exactly above the bottom of the narrow trench, often less 

 than one kilometre wide. We are extremely indebted to Captain S. Greve, R.D.N. 

 and his officers, for their untiring efforts in fulfilling our requirements. Because of 

 these difficulties we had to repeat the deepest series in the Philippine Trench no less 

 than 10 times, but the efforts were rewarded by 17 observations from depths exceeding 

 6000 m. The skill and patience of our two assistant hydrographers, Mr. Ingolf 

 Crossland and Mr. Ulrik Klaning, is also gratefully acknowledged. 



All the observations of the Galathea Expedition are to be pubhshed in the scientific 

 report of the expedition, but we think it of interest to pubhsh our observations from 

 the Philippine and the Tonga-Kermadec Trenches at once. The first section of the 

 lists of observations (Table I) gives the values observed while the second section 

 (Table II) contains average figures and graphically interpolated figures derived from 

 the total number of reliable observations. 



THE PHILIPPINE TRENCH 



The temperature from the observations of the Snellius Expedition (van Riel, 

 Hamaker and van Eyck, 1950) and the Swedish Deep-Sea Expedition (Bruneau, 

 Jerlov and Koczy, 1953) in the deep water of the trench, are plotted in Fig. 1. The 

 agreement between these and those of the Galathea is obvious. The characteristics 

 of the deep water of the trench appears to be very uniform. A minimum of 1-59° C 

 occurs between 3500 and 4000 m. Below this, the temperature increase is very close 



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