2000年5-6月の日本周辺海域表聞におけるサイズ分画クロロフィルa濃度の地理的分布

抄録

Concentrations of size-fractionated (<2, 2-10 and > 10 μm) chlorophyll a and nutrients (nitrite+nitrate, phosphate and silicate) were measured at the sea surface in the offshore waters around Japan in May-June 2000. According to Nagata and Ogawa (1997), the investigated waters were divided in eight regions: Oyashio waters, Perturbed waters, Tsugaru Current waters, Kuroshio axis waters, Coastal waters of the Kuroshio, Tsushima Current waters, Northern cold waters of the Japan Sea and Coastal waters of the East China Sea. Total chlorophyll a concentrations in the Oyashio waters and the Perturbed waters were more than 1.0 μgl^-1 and higher than the other regions where were less than 0.5 μgl^-1. The<2 μm fraction accounted for more than 50% of the total chlorophyll a concentrations at almost stations. However, the>10 μm fraction dominated at some stations in the Oyashio waters, the Coastal waters of the East China Sea and the Kuroshio axis waters. The chlorophyll a concentrations of the <2 and 2-10 μm fraction positively correlated with the nitrite +nitrate concentrations, where as there was not a significant correlation for the > 10 μm fraction. The small-sized phytoplankton seems to be related to the availability of nitrite+nitrate, whereas the large-sized phytoplankton may be affected by the other factors at the Sea surface in the offshore waters around Japan in late spring.