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No topographic highs were encountered on the track of 

 the USS NEREUS, but it is likely that any which exist are 

 rocky or stony areas. This is especially true of topographic 

 highs which are also shoals, but such highs, regardless of 

 depth, are invariably covered with at least coarse sand. For 

 this reason, it is likely that the bottom in the vicinity of 

 Herald Shoal is coarse grained. 



The bottom of the Bering Sea is largely covered by fine 

 sand, whereas the somewhat shoaler Chukchi Sea has typically 

 a mud bottom. This condition is probably related to stronger 

 bottom currents which oceanographic conditions show must 

 exist in the Bering Sea. In the Chukchi Sea, moreover, the 

 tides are smaller than in the Bering Sea; the small tide that 

 does exist (at Point Barrow the mean tide change is only 

 l/Z foot) is caused by the Atlantic tidal wave traversing the 

 Arctic Ocean. Throughout most of the year the Chukchi Sea 

 is ice-covered, promoting quiet bottom conditions. Surface 

 waves of more than a short period are almost entirely absent, 

 and these have little effect on the bottom because waves only 

 generate appreciable bottom currents to a depth equal to 

 one-half their wave length. There is also a large amount 

 of fine sediment carried into the Chukchi Sea by rivers, ice 

 rafting, and currents through the Bering Strait. All these 

 factors probably account for the muddy character of the 

 Chukchi Sea floor. 



Ice Rafting. The most striking method of transportation 

 of sediments in the arctic is ice rafting. Ice is capable of 

 rafting large amounts of detritus of all sizes, from clay up 

 to large boulders, for long distances. The quantitative im- 

 portance of this process is demonstrated by the bottom sedi- 

 ments which, in the Chukchi Sea, are generally poorly sorted. 

 In the mud, pebbles are frequently found which can have 

 reached their present position only by ice rafting (figs. 10 

 and 11). However, some sediments are fairly well sorted, 

 suggesting that there has been some reworking of the bottom 

 sediments. A large percentage of the floebergs observed from 

 the USS NEREUS in the vicinity of the ice pack contained 

 detritus although this ice was 150 miles from the nearest 

 land. Some of the floebergs had the appearance of floating 

 rock piles (fig. 12). 



For geographic reasons, icebergs are only rarely present 

 in this part of the arctic, and the ice rafting is accomplished 

 by river ice washed out to sea and, especially, by fast ice 

 (sea ice which has frozen to the bottom). Sverdrup^ writes 

 that extensive floes become grounded every winter in water 

 depths up to 20 meters. In shallow areas near shore, sediment 



34^ frBSTRIGTED 



