. The Eastern Bering Sea Shelf : oceanography and resources / edited by Donald W. Hood and John A. Calder . CLflf C/.l Figure 19-7. Southeastern Bering Sea shelf: Abundance of clay-sized sediment (%). concentrations, however, occur in a number of isolated patches (K. Tommos, unpubhshed data). The mean concentration of clay-sized sediment is around 7 percent, with greater (but never dominant) contents north of Unimak Pass and St. Matthew Island, adjacent to St. George Island, and generally in the northwest part of this shelf region. Large gradients in grain size, sorting, and sand and silt cont
. The Eastern Bering Sea Shelf : oceanography and resources / edited by Donald W. Hood and John A. Calder . CLflf C/.l Figure 19-7. Southeastern Bering Sea shelf: Abundance of clay-sized sediment (%). concentrations, however, occur in a number of isolated patches (K. Tommos, unpubhshed data). The mean concentration of clay-sized sediment is around 7 percent, with greater (but never dominant) contents north of Unimak Pass and St. Matthew Island, adjacent to St. George Island, and generally in the northwest part of this shelf region. Large gradients in grain size, sorting, and sand and silt content which are evident adjacent to the 40-50 m zone are believed to be the result of, or at least influenced by, the presence of the seasonally stable oceanographic front which here separates the coastal and central shelf domains. The pronounced gradients in turbulence and hence transport efficiency result in deposition of coarser-grained sediment landward and finer-grained sediment seaward of this zone. Across the remainder of the shelf, the relative amount of the sand component decreases discontinuously. Sedi- ments having a larger mean 0 (very fine sand) and improved sorting were collected near the shelf edge at around 150 m. This supports the presence of the permanent current proposed by Barnes and Thomp- son (1938). More recent investigations (Coachman and Charnell 1979) have emphasized the presence of a very low velocity northwesterly drift along the outer shelf. But Coachman (1979) has noted that sporadic eddies along the shelf edge may produce local transient flow of basin water onto the shelf. The effect of this on the energy regime could account for the increasing mean grain size and improved sort- ing in this zone. At this time it is possible to give only a general description of the textural variations in the surface sediments of the southeastern Bering Sea shelf. The preliminary assumption can be made that this sedi- ment is in dynamic equilibrium with the present e
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