NO. 9 MARINE INVERTEBRATES, ALASKA — MacGINITIE 21 



of very low salinity. The lower salinity of the water at Eluitkak Pass 

 is probably the main reason for the absence of echinoderms in that 

 locality. It would be interesting to test the tolerance to lowered salini- 

 ties of a number of Arctic marine invertebrates and of the same 

 species in the North Atlantic and the North Pacific, and compare the 

 results. 



The average of the highest salinities is 33.54 parts per thousand. 

 This no doubt approximates, or is perhaps a little higher than, the 



Table 3. — Highest and lozvest surface salinities, Arctic Ocean, Point Barrow, 

 Alaska, July-September 1948, and July 1949 to August 1950 



Year Month and day Highest Month and day Lowest 



1948 July 28 32.37 July 17 S.26 



Aug. 7,9.11,20 30.43 Aug. 4 23.79 



Sept. 27 34.30 Sept. I 27.67 



1949 July 26 35.00 July 13 4.20 



Aug. 24 34.30 Aug. 3 30.40 



Sept. 26 34-20 Sept. i, 12 32.00 



Oct. I 34.20 Oct. 21 30.11 



Nov. 8 34.52 Nov. 2 31.10 



Dec. 25,29 34-30 Dec. 6 30.90 



1950 Jan. 6 34.00 Jan. 3 32.60 



Feb. 2 33.40 Feb. i 28.60 



Mar. 16 32.60 Mar. 2,5,6 31.80 



Apr. 7 32.50 Apr. 19 31.80 



May 3, 24 32.40 May 14, 21, 26 32.00 



June 6 33-40 June 16 1.40* 



July* 



Aug. 4 33-70 Aug. 7 28.00 



* Because of the melting ice, the surface water during the latter half of June and until the 

 ice went out in July did not give a true picture of the salinity of the ocean, for it was only 

 slightly salty while the water lo ft. or more below the surface was much more saline. It was 

 impossible to get out more than once or twice where samples of deeper water could be taken. 



salinity of the deeper waters of the ocean off Point Barrow. The 

 average for these deeper waters can be determined only by extensive 

 deep-water sampling by a ship with oceanographic equipment. 



LIGHT 



On March 22 and September 21 the length of time the sun is above 

 the horizon is equal to the time it is obscured. There are, however, 

 many more than 12 hours of daylight. The sun rises and sets at such 

 a small angle to the horizon that there are 16 hours of daylight on 

 these dates. On June 22 there are 24 hours of daylight, and on Decem- 

 ber 21 there are about 2.5 hours of twilight. When the sun is on the 

 meridian at noon on June 22 it is 42° 10' above the horizon and at 



