A GENERAL ACCOUNT OF THE HYDROLOGY 

 OF THE SOUTH ATLANTIC OCEAN 



By G. E. R. Deacon, b.Sc. 

 (Plates VIII-X; text-figs. 1-24.) 



INTRODUCTION 



OR some years past the Discovery Committee has been conducting a series of 



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observations on the hydrology and plankton of the South Atlantic and Southern 

 Oceans. During this period a large quantity of hydrological data has been accumulated, 

 and as soon as the analyses of the results are completed, detailed papers on difli'erent 

 aspects of the work will be published in this series of reports. In the meantime, and 

 because such knowledge is of importance to those who are studying the plankton, the 

 following general account of the hydrology of the area has been prepared. 



THE SURFACE WATERS OF THE SOUTH 

 ATLANTIC OCEAN 



An examination of the distribution of temperature and salinity in the surface layers of 

 the South Atlantic Ocean shows that there are four kinds of water at the surface. Each 

 of these waters has a typical range of temperature and salinity, and typical conditions for 

 the support of animal and plant life. The different bodies of water are closely dependent 

 on the climatic conditions of the regions in which they lie, and they owe their existence 

 partly to these conditions. The Antarctic climate in the south gives rise to a cold poorly 

 saline surface layer of Antarctic surface water, and the tropical conditions near the 

 Equator to a very warm surface layer of tropical water. Also, in addition to these two 

 extremes, there are two intermediate types, sub-Antarctic and sub-tropical waters, 

 which are affected less directly by Antarctic and tropical conditions. The geographical 

 distribution of the four kinds of water affords a very convenient and significant method 

 by which the surface of the South Atlantic Ocean can be divided into four zones, and a 

 description of the hydrological conditions in each zone is almost all that is necessary to 

 define the conditions over the whole ocean. The four zones have been called : Antarctic, 

 sub-Antarctic, sub-Tropical, and Tropical. 



In this report an account is given of all four types of water, and of the geographical 

 limits in which they are found ; but the paper is concerned principally with the hydro- 

 logical conditions in the Antarctic and sub-Antarctic Zones. 



ANTARCTIC SURFACE WATER 



NATURE OF THE ANTARCTIC SURFACE LAYER 

 In the Antarctic Zone the surface layer is composed of cold poorly saline water, which 

 lies in a shallow well-defined layer above warmer deep water. It has a depth of 100- 



