Preliminary Results of Marine 



Geologic Studies off the 



Northern Coast of Alaska 



By Peter W. Barnes 



Abstract 



During the past three years of Arctic shelf studies the U.S. Geological 

 Survey endeavored to outline the geologic processes unique to this environ- 

 ment and to obtain a suite of background data. The Arctic shelf of Alaska 

 slopes gradually from the coast out 50-75 km to a shelf break at 60 to 80 meters 

 of water depth. A small number of 2-10 m high ridges occur near the coast and 

 along the shelf break. Contemporary ice gouging is the most significant 

 microrelief feature on the shelf, occurring at all water depths. 



A complex pattern of turbidity and particulate transport is developed over 

 the shelf. Surface values of suspended particulate matter range from 0.5 to 2 

 mg/1 over the central shelf. Values systematically increase near river ef- 

 fluents. A more vigorous shelf circulation during the 1972 season is reflected 

 in a doubling of particulate matter values and an increase in turbidity over the 

 1971 season. Vertical turbidity profiles delineate three water types: a) surfi- 

 cial melt water, b) coastal water, and c) oceanic water. Near-bottom water 

 generally is more turbid owing to waves, bioturbation, or ice gouging. 



Sediments of the central shelf are mostly fine-grained silts with ice-rafted 

 pebbles. Towards the shelf break they coarsen to gravelly muds. Inshore, 

 cleaner sand and gravels are associated with the barrier island and ridge 

 complex, while the lagoons are flooded with sandy muds. Cores of the upper 50 

 cm of sediment indicate a midshelf region of homogeneous mud interspersed 

 with pebbles probably resulting from ice gouge mixing. Inshore, sediment 

 layering is commonly present, suggesting more rapid sedimentation and/or 

 less ice mixing. Along the shelf break and upper slope, bioturbation is 

 common along with a relict or residual surface gravel. 



Background values of lead, copper, zinc, arsenic, mercury and cadmium 

 are low compared to lower latitude shelves. The organic fraction is derived 

 primarily from plant detritus. 



184 



