452 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1963 



perature difference of 2° C, lies the body of the subantarctic water, 

 dominated and moved by the West Wind Drift. This water is warmer 

 than the Antarctic Surface water and is less variable in its salinity. 

 Because of the rouglmess of the region, the surface-water zone is very 

 thick and well mixed. The Subtropical Convergence is a region of 

 very sharp temperature changes, the average change from one side to 

 the other being about 4° to 5° C. 



At the Antarctic Convergence, the northward moving Antarctic 

 Surface water meets the Subantarctic Surface water and, because 

 it is denser by reason of being colder, slides beneath the Subantarctic 

 Surface water and forms the Antarctic Intermediate Current. Lying 

 beneath that mass is a warm, deep current of water which formed well 

 to the north of the Southern Ocean. The most important water body 

 of the Southern Ocean is probably the Antarctic Bottom water, for 

 this is the water which flows along the bottom of the entire Southern 

 Ocean region and is the water which is in contact with the benthic 

 animals, although the effect of the surface conditions upon bottom 

 animals is not to be underestimated. During the winter, as the freez- 

 ing of ice withdraws fresh water from the sea, the cold, saline, dense 

 water formed sinks below the surface waters and slowly flows outward 

 along the bottom to the edge of the Antarctic Continental Shelf and 

 thence outward to the deep waters below the West Wind Drift. 

 Knowledge of this body of water is not complete for there is still 

 much to be learned about where it forms, and to what extent it main- 

 tains its identity. G. E. R. Deacon stated that deep water formation 

 was largely in the region of the Wedell Sea and that Antarctic Bottom 

 water then flowed eastward about the continent. Bottom water form- 

 ing in other areas is kept isolated by the ridges of the bottom topog- 

 raphy. 



The cold salme waters of the Antarctic sink below the warmer, less 

 saline waters of the West Wind Drift along the Antarctic Convergence, 

 the boundary between the eastward- and westward-flowing currents 

 (fig. 4) and then flow northward along the bottom as the Antarctic 

 Bottom current. In general then, the bottom animals of the Antarctic 

 are living in an environment which is broadly uniform and one which 

 has very little seasonal change when considered from the aspects of 

 temperature, salinity, oxygen content, and nutrients and in compari- 

 son with the variation of these factors in the shallow tropical en- 

 vironment. The glacial history of the region has made one feature of 

 the environment quite variable : The bottom sediments, which change 

 constantly, both laterally and in time, imparting a variety of habitats 

 upon the scene. This aspect of the environment seems to have a par- 

 ticularly striking effect upon corals. 



Still to be answered is the question "Wliy study the corals of the 

 Southern Ocean in preference to the deep water corals of other oceans ?" 



