SECT. 4] 



BIOLOGICAL SPECIES, WATER-MASSES AND CURRENTS 



407 



Fig. 11, was eliminated by either high arctic or oceanic conditions in the 

 northern portion of the Chukchi Sea. 



It should be further pointed out that the occurrence of Metridia luce?is at 

 73° 42'N, 169° 01'W and 76° 22'N, 163° 16'W in the Chukchi Sea can also be 

 taken to indicate an influx of Bering Sea water into the Arctic Ocean, at least 

 to that latitude. A comparison with Fig. 12 shows this to be farther than 

 reported for penetration of Bering Sea water based on earlier physical-chemical 

 studies (Barnes and Thompson, 1938; LaFond and Pritchard, 1952; Saur, 



Northernmost extent ot Acortn 

 for years indicated 



Southernmost extent of choroctenstic 

 arctic species 



Fig. 11. The extent of observed arctic penetration of Acartia longiremis for 1947, 1949, 

 1950 and 1951. The species occurred at 73%, 100%, 100% and 97% respectively for 

 each year within the distributional areas outlined by light lines. The southernmost 

 observed extent of the two characteristically arctic species, Calamus hyperboreus and 

 Metridia longa, is shown by the heavy line. The former occurred at 96% of the stations 

 above the line in 1950 and 82% in 1951 ; and the latter at 83% in 1950 and 82% in 

 1951. All stations south of the line were negative. 



Solid triangles, 1947 stations; open triangles, 1949 stations; open circles, 1950 

 stations; solid circles, 1951 stations. 



Water structure along line E-E' is shown in Fig. 12. 



Tully and LaFond, 1954) made concurrently with plankton collecting. More 

 recent studies (Coachman and Barnes, 1961) do, indeed, indicate the presence 

 in the Arctic Basin of a stratum of water between 50 and 130 m with tempera- 

 tures as much as 0.5 to 0.8°C warmer than the water immediately above or 

 below it. It diminishes from the Chukchi Sea toward the Pole and toward 

 Ellsmere Island. It is probable that certain hardy expatriates of Metridia 

 lucens, found near 74°N in the Chukchi Sea, Calanus cristatus, near 72°N in 



