SECT. 4] BIOLOGICAL SPECIES, WATER-MASSES AJSTD CUKBENTS 405 



breaker Burton Island in the Chukchi and Beaufort Seas in 1950 and 1951. 

 Thus, a seasonal picture of the plankton was obtained which shows its relative 

 stability with respect to occurrence and distribution of certain species for 

 separate years. The study will suffice to illustrate the kind of integrated in- 

 formation that can be gleaned by piecing together oceanographic observations 

 that are applicable to conditions in new or little known areas. Additional details 

 of the plankton analysis made on these surveys is given by Johnson (1953, 

 1956). 



In the eastern portion of the Bering Sea and the southeastern Chukchi Sea, 

 there is a characteristic assemblage of holoplanktonic species of copepods 

 which, while not always abundant, are found at many scattered sampling 

 stations over much of the area. Most of these species are also common along 

 the coast of North America for varying distances south of the Aleutian Islands 

 in subarctic water. To the north in the Chukchi Sea and along the Alaskan 

 coast into the Beaufort Sea, the frequency of catches of these species falls off, 

 and eventually the species disappear in the northern reaches of the Chukchi 

 Sea and in all but the near-shore stations in the Beaufort Sea (Figs. 10 and 

 11). The abrupt disappearance of Acartia clausi, Calanus tonsus, Epilabi- 

 docera amphitrites , Eucalanus bungii bungii, Eurytemora herdmani, Metridia 

 lucens and Tortanus discatidatus in the region of Point Barrow, Alaska, is 

 interpreted as resulting from an eastward flow along the coast to this area, 

 where it is met by a clockwise flow from the Beaufort Sea as it swings to the 

 northwest in this region. It is obvious that these copepods found off Point 

 Barrow have their main connection with the major population to the south- 

 west in the Chukchi and Bering Seas, where, as a group, they occurred at about 

 80% of the stations. 



Probably the most striking example of this kind in these waters is shown by 

 the distribution of Acartia longiremis, a more abundant species of wide distribu- 

 tion in coastal waters of the arctic and subarctic regions (Fig. 11). This is 

 generally considered a coastal species, but with a wide tolerance for offshore 

 conditions. It is abundant in the Bering Sea and southeastern Chukchi Sea. 

 where in 1934 and 1947 it was found at 75% and 85% respectively of the 

 oceanographic stations. From here it may be carried in considerable numbers 

 far into the Arctic Ocean to 74° 17'N, 168° 56'W, where, in 1951, a single 

 station yielded 1040 adult or submature specimens in a 0-100-m haul with a 

 -£-m net. The species was absent from stations north of 76°N, and also totally 

 absent from the many offshore stations in the Beaufort Sea, where in the 

 summer the ice-free water would appear to be as ecologically suitable as the 

 northern Chukchi Sea. This absence in the main part of the Beaufort Sea may 

 be explained by assuming that, except at the near-shore stations, the water 

 entering the Beaufort Sea flows down from high arctic regions as the eastern 

 portion of a large clockwise gyral, the southern part of which is shown in Fig. 

 10. That such a gyral does exist is also evidenced by physical studies ( Worthing - 

 ton, 1953). The offshore portions of the Beaufort Sea affected by such a current 

 could not be expected to harbor any Acartia longiremis, which, as shown in 



