Three biozones based on the microbiogenic components of sediment are recognized on the continental shelf off the coast of Oregon and Washington. Boundaries of these zones seem to be influenced by the limiting surface-wave and internal-wave turbulence and sediment substrate. The winter plume of the Columbia River transports biogenic particles northward.

The inner zone is influenced by wave turbulence and has a sandy substrate. Living Eggerella advena and Buliminella elegantissima are confined mainly to this zone, but their empty tests also are common in the middle zone. Below the depth influenced by wave turbulence, fine sediments from the Columbia River are deposited; therefore the middle zone has a muddy substrate. It is characterized by dominance of the foraminifers Recurvoides turbinatus, Spiroplectammina biformis, and Nonionella spp., and the planktonic diatom Coscinodiscus spp. In the outer zone which is below the regional halocline, little sediment accumulates--possibly because of turbulence created by internal waves. The substrate therefore generally is sandy, and is characterized by dominance of the foraminifers Angulogerina angulosa, Eilohedra levicula, Epistominella exigena

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Uvigerina juncea, Adercatryma glomeratum, Haplophragmoides bradyi, and abundant radiolarians.

Tintinnids, pennate diatoms, plant fragments, and empty tests of B. elegantissima are more abundant off the mouth of the Columbia River and north of it than they are south of it. These inner shelf and land-derived biogenic particles appear to be distributed by the north-setting winter plume of the Columbia River.

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