Observations of the horizontal and vertical distributions of modern planktic foraminifera facilitate formation of ecological and geochemical inferences derived from the study of foraminiferal shells. In this study, we used plankton tows to collect planktic foraminifera at nine sites distributed longitudinally throughout the subarctic Pacific. A total of nine planktic foraminiferal species were identified. The horizontal distributions of the foraminiferal assemblages could be assigned to four regions. Characteristics of the foraminiferal assemblages and the horizontal distributions of their shell sizes appeared to be influenced by the sea-surface structure within each water mass. The vertical distributions of Globigerina bulloides and Globigerina quinqueloba were associated with the depth of the pycnocline; those of Neogloboquadrina pachyderma and Neogloboquadrina incompta were different and appeared to reflect a significant difference of optimum habitat temperatures. Based on the vertical distribution of shell sizes, we found evidence of vertical migrations during shell growth of G. bulloides and N. incompta. This information about the distribution of modern planktic foraminifera will facilitate reconstruction of past oceanographic conditions based on geochemical proxies in the subarctic Pacific.
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