Physical Oceanography of the Eastern Chukchi Sea Off Cape Lisburne-Icy Cape 



Merton C. Ingham' and Bruce A. Rutlandi 



GENERAL DESCRIPTION OF STUDY AREA 



Geography 



The Chukchi Sea is a small (580,000 km-), 

 shallow (<100 fm) sea lying between the 

 Arctic Ocean and Bering Strait, extending 

 from near Wrangel Island (180°) to Point 

 Barrow (156° W), generally bounded on the 

 north by the 100 fm isobath which lies from 

 300 miles (near Cape Lisburne) to about 30 

 miles offshore (near Point Barrow) . The south- 

 eastern portion of this sea lies over the con- 

 tinental shelf off Alaska's north coast adjacent 

 to hilly lowlands of varying width (nonexistent 

 near Cape Lisburne) which separates the sea 

 from the Brooks Range roughly paralleling the 

 coastline (Hunkins and Kaplan, 1966). The 

 portion of the eastern Chukchi Sea studied dur- 

 ing the WEBSEC-70 cruise lay off Cape Lis- 

 burne-Icy Cape in shallow water (<50 m), 

 forming a triangular area about 100 miles off- 

 shore at its farthest point (figs. 1 and 2). 



Ice Cover 



The area of open water in the eastern 

 Chukchi Sea varies seasonally with the position 

 of the polar icepack, which depends on the wind 

 field, and the extent of winter ice, which de- 

 pends on insolation, air temperature, and wind 

 speed. Ice conditions in the Chukchi Sea have 

 been summarized as follows in the Oceano- 

 graphic Atlas of the Polar Seas— Part II The 

 Arctic. (U.S. Navy Hydrographic Office, 



1958) : 



"Chukchi and Beaufort Seas— The waters of 

 the Chukchi and Beaufort Seas are dominated 

 most of the year by winter ice and polar pack 

 ice which includes heavy drift ice from the 

 Arctic Ocean. Of lesser importance is the fast 



> U.S. Coast Guard Oceanographic Unit, Bldg. 159-E, 

 Navy Yard Annex, Washington, D.C. 20390. 



ice which covers the bays and fringes the shores 

 of northern Alaska and Siberia for at least 8 

 months. 



"Generally August and September are the 

 months with the least ice. During this period 

 the northwest coast of Alaska should be free 

 of fast ice northward to Point Barrow and 

 practically ice free from Point Barrow east- 

 ward to Herschel Island. However, the heavy 

 polar pack is never far off the coast between 

 Point Barrow and Herschel Island and can ad- 

 vance onto the shore at any time. Westward of 

 Point Barrow the pack ice usually lies about 

 10 miles offshore at Icy Cape; beyond this pomt 

 the edge of the pack swings northwestward 

 toward Ostrov Geral'd and Wrangel Island. 

 The ice edge then trends southwestward, ap- 

 proaching the Siberian coast at about the 

 vicinity of Mys Shmidta. 



"The existence of an open coastal waterway 

 in the Chukchi-Beaufort Sea sector is strongly 

 dependent upon favorable winds. Easterly and 

 southerly winds hold the pack off the coast, 

 whereas northerly and westerly wmds force 

 the floes against the shore. Even when the mam 

 body of the ice recedes from the coast, driftmg 

 marginal floes and bands of fast ice occur m 

 the inshore waters. 



"The heavy pack ice begins to close in on the 

 coast after about 10 September, and young ice 

 forms along the margins of the drift ice and in 

 any open water that may exist between the 

 pack and the coast by mid-September. 



"The north-setting current in Bering Strait 

 usually keeps the Alaskan coast ice-free 

 throughout September as far north as Cape 

 Lisburne, but before the end of the month the 

 Arctic ice may be expected to begin its ex- 

 pansion and southward movement. Before the 



