Through the greater part of the inner sublittoral zone of the Alaskan and Siberian shelves, the foraminiferal fauna is dominated by species with an arenaceous test wall. Species are few and generally one species is overwhelmingly dominant, but the dominant species is different from one area to the next as a result of changes in the oceanographic regime.
Oceanographic conditions in the Chukchi Sea are dominated by northward flow of water from the Bering Sea through Bering Strait. In both seas adjacent to the coast of Alaska the water is warmer and less saline and Eggerella advena is dominant in bottom sediments. Farther offshore in both seas Reophax arctica is dominant. Dominance by these two species extends northward to the limits of the permanent ice pack beyond which Textularia torquata is dominant on the Siberian shelf and Spiroplectammina biformis on the Alaskan shelf. High relative frequencies of S. biformis also characterize the Gulf of Anadyr where very cold bottom waters persist all year.
Two calcareous faunas exist. An Elphidium clavatum-dominated fauna is associated with deltaic environments or more polar shelf environments. The other calcareous fauna has a greater diversity, especially in Elphidium spp. and Buccella spp., and generally is associated with coarser grained sediment in straits and nearshore areas. This latter calcareous fauna may represent, in part, reworked or relict faunas.