Preliminary Results of Geologic Studies in the Eastern Central Chukchi Sea^ 



Peter W. Barnes ^ 



INTRODUCTION 



During late September and October 1970, the 

 U.S. Geological Survey participated in the 

 Western Beaufort Sea Ecological Cruise 

 aboard the U.S. Coast Guard icebreaker 

 GLACIER, in the eastern central Chukchi Sea. 

 Seventy stations were occupied for geological 

 sampling purposes (fig. 1). These studies were 

 undertaken primarily to provide background 

 data for interpreting ecological relationships, 

 to locate and define these relationships, and to 

 outline the processes of sediment transport and 

 deposition. This report vdll deal with the first 

 and third aspects of the overall program. 



Considerable knowledge of the geology of 

 the Chukchi Sea existed prior to the 1970 cruise 

 of the GLACIER. Moore (1964) and Grantz 

 and his co-workers (1970) studied the bottom 

 geology and found only a thin sedimentary 

 cover overlying rocks that extend west from 

 the Prudhoe Bay and Naval Petroleum Reserve 

 geologic provinces. The surficial sediments, 

 morphology, and currents have been the subject 

 of studies by the Navy and the University of 

 Washington during their extensive investiga- 

 tions of the Bering and Chukchi Seas (Dietz 

 and others, 1964 ; Fleming and Heggarty, 1966 ; 

 Creager and McManus, 1967; McManus and 

 others, 1969). Studies have indicated a shelf of 

 low relief with a broad north-south trending 

 trough 50 meters deep between the mainland 

 and Herald Shoal. Relict and residual sediments 

 dominate the area owing to minimal local sedi- 

 ment contribution and to sporadic northward 

 currents that introduce material from outside 

 the region (McManus and others, 1969). 



Sampling on this cruise focused on sediment- 

 transport processes with near-bottom current 



' Publication authorized by the Director, U.S. Geolog- 

 ical Survey. 



' U.S. Geologrical Survey, Menlo Park, California 

 94025. 



measurements and water-column turbidity de- 

 terminations, supplemented by suspended sedi- 

 ment measurements made at the same time by 

 the University of Alaska (see Naidu and 

 Sharma, this Oceanographic Report) . 



METHODS 



Current measurements were made with a 

 film recording Savonius-type meter, accurate to 

 0.05 knots but readable to 0.01 knots. The sen- 

 sor was deployed 1.5-2 meters above the bottom 

 while at anchor. A 3-meter chain pendant be- 

 low the meter served to dampen oscillations. 

 The meter recorded for periods of up to 35 

 hours at 12 locations (fig. 1 and table I, ap- 

 pendix A). Due to the movement of the ship at 

 anchor and the resultant introduction of arti- 

 ficial currents, data were analyzed by vector 

 summation. Sequential current speeds and di- 

 rections were vectorially added, and the vectors 

 generated by this summation were used in re- 

 porting the currents for the interval summed. 



Bottom samples were obtained with a 10- 

 gallon Van Veen grab except when ship motion 

 or bottom conditions necessitated the use of a 

 Shipek grab. Additional samples were obtained 

 with a modified Reineck box corer with box 

 dimensions of 20 X 20 X 60 cm, and a Hydro 

 plastic corer rigged either as a gravity or a 

 piston corer. All sediment samples were stored 

 at 3-5° C prior to analysis (see Bouma, 1969, 

 p. 313, 317, 332, for discussion of these 

 sampling devices). 



Textural analysis involved standard tech- 

 niques. Sieves were used for gravels and sands 

 and hydrometer for silt- and clay-sized ma- 

 terials. Box cores were extruded laterally from 

 one side of the box and sliced vertically into 

 1-2 cm slabs, then placed on a Plexiglas sheet 

 and radiographed using techniques outlined by 

 Bouma (1969). 



87 



