The taxonomy and the distributional pattern of Radiolaria in surface sediments of the northeast Pacific Ocean have been investigated from more than 50 sediment cores collected in the area from 40° N. lat. northward to the coast of Alaska and from the west coast of the North American continent westward to approximately 160° W. long. Previous knowledge of these microorganisms from the area has been limited.

The results of the present study strongly suggest that it is possible to delineate the biogeographic distributional pattern of Radiolaria of the area into subarctic and transitional faunas. It is found also that the southern limit of transitional fauna possibly would lie slightly south of the so-called subarctic boundary (approximately at 40° N.). Because of the pronounced variation of the oceanographic conditions in the region, both northern and southern boundaries of the transitional zone cannot be defined sharply at present. Nevertheless, on the basis of the relative abundance and the general biogeographic occurrence of the studied taxa, such a distributional pattern in the area could be ascertained reasonably. The observed biogeographic differentiation agrees in general with hose of previous studies made by physical oceanographers and the results of the earlier researches on diatoms, planktonic Foraminifera, and zooplankton in the North Pacific.

Therefore it can be concluded from the present study that Radiolaria in the northeast Pacific could be used as a water-mass indicator and thus may be useful in the interpretation of paleoecology of deep-sea sediments as well as marine deposits on land.

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