Vertical distribution of living planktonic foraminifera in the seas around Japan

Planktonic foraminifera keep records of the upper ocean environments in their assemblage and individual tests. In order to determine the factors controlling the vertical distribution of planktonic foraminifera as a proxy for reconstruction of paleoenvironments, we collected samples by plankton tows and pumping in the seas off the Japan Sea and Pacific coasts of Japan. We found that the distribution of each foraminiferal species is controlled by various factors such as temperature, chlorophyll-a concentration, and light intensity. The geographic distribution of Neogloboquadrina pachyderma is mainly controlled by seawater temperature, yet, its vertical distribution was related to the location of the pycnocline. The vertical distribution of its coiling direction was not controlled by temperature alone. Neogloboquadrina incompta preferred waters that are more shallow and warmer than those preferred by N. pachyderma, and its abundance was correlated with the chlorophyll-a concentration. Two morphotypes of Globigerinoides ruber (G. ruber s.s. and G. ruber s.l.) showed different vertical distributions, with G. ruber s.s. predominant in surface waters and G. ruber s.l. in a deeper ones. This difference in habitat can be attributed to a difference in light intensity and food availability, with the shallower morphotype more dependent upon symbionts. In comparison, Globigerinoides sacculifer preferred warmer water than G. ruber, was more abundant at a shallower depth and might be more influenced by light intensity. The maximum abundance of Globigerina quinqueloba was associated with higher chlorophyll-a concentrations. Neogloboquadrina dutertrei showed two different distribution patterns: one population preferred higher temperatures, whereas another population dwelled in colder waters. Differences in symbiont photosynthesis and diet might also be responsible for the different distribution profiles of N. dutertrei and Globigerina bulloides. Overall, the vertical distribution of many species of planktonic foraminifera appears to be linked not just to water temperatures, but to light penetration and prey availability.