Continental Shelf Sedimentation in an Arctic Environment

A factor analysis of 579 bottom sediment samples from the Continental Shelf in the Chukchi and northeastern Bering Seas identified three factors that “explain” 92 percent of the variation of ten granulometric variables. Factor I represents deposition of silts and clays by settling from the water column. Although Factor I is extensively distributed in the areas of quieter water, the extreme values occur where there is an abrupt reduction in transporting capacity. Factor II represents both the provenance of the sand and the deposition or modification of sands by nearshore processes. Factor III represents beach processes and also several processes producing a poorly sorted sediment.

The silts and clays from the Yukon River cover the bottom of Norton Sound and are encroaching onto the relict sands of the Chirikov Basin. Together with the muds from other Alaskan rivers, the Yukon sediment is also transported into the Chukchi Sea, in both the coastal water and offshore water. The coastal flow leaves the coast at Point Hope, diverges, and enters the complex circulation in the Chukchi Basin that is controlled by regional winds. Depending upon the atmospheric pressure distribution, the currents may carry much of the sediment off the shelf down Herald Canyon or into the East Siberian Sea, or the bottom water and sediment may remain in residence on the shelf even to a point of minor stagnation of the circulation. Sufficient mud has been deposited to floor the basin. The compensation current from the East Siberian Sea may be a more significant sediment supplier than previously thought, and the northward flow of the Bering Strait current from Point Hope to Point Barrow may be sporadic.

The nearshore sands of the southeastern Chukchi Sea are modern, wave sorted in places, and current deposited in other places. Along the Siberian coast and in the northeastern Chukchi Sea, the sands are relict and residual. Residual sediment also occurs on Herald Shoal.

Although the seas are ice covered for 9 to 10 months annually, ice rafting is not a dominant sedimentary process. Deposition of fine sediment may occur during this time by settling from the homogeneous water.