[A-OS17] 沿岸域の海洋循環と物質循環

[AOS17-12] Inter-annual changes in summer phytoplankton community composition in relation with water mass variability in the East China Sea

*徐 倩¹、鋤柄 千穂^9,2、ゴーズ ジョアキム^3,2、ゴメス ヘルガ^3,2、朱 元励²、王 盛強⁴、沈 盎緑⁵、マウレ エリジオ.デ.ラウシ²、松野 健⁶、渡辺 雄二⁷、ユ シンジェ⁸、石坂 丞二² (1.名古屋大学、2.名古屋大学宇宙地球環境研究所、3.コロンビア大学、4.南京情報科学技術大学、5.中国東海漁業研究所、6.九州大学 応用力学研究所、7.株式会社環境総合テクノス、8.韓国海洋科学技術研究所、9.東京海洋大学)

キーワード：植物プランクトン群集、東シナ海、長江希釈水、リン制限、経年変化

Surface distribution of phytoplankton communities were investigated in July 2009, 2010, 2011 and 2013 in the mid-shelf East China Sea (ECS) which comes under the influence of Changjiang River Diluted Water (CDW) and the Kuroshio current. Phytoplankton distribution based on CHEMTAX analysis of HPLC-pigments revealed the dominance of cyanobacteria and prochlorophytes in the eastern ECS which was perennially under influence of the oligotrophic Kuroshio surface water in all four years. Towards the west, in the mid-shelf ECS, the composition of phytoplankton communities varied from year to year. Diatoms dominated in 2009 and 2013 when dissolved inorganic phosphate (DIP) concentrations were higher than during the other two years. On the other hand, cyanobacteria, chlorophytes and other groups composed a mixed population of phytoplankton during the high-nitrate-years of 2010 and 2011. Cluster analysis based on the information of phytoplankton community composition, together with PCA analysis of shipboard hydrographic, nutrient and biological data for all four years helped confirm that summer phytoplankton community structure of the ECS is regulated by mixing of water masses and variability of nutrient status within them. Our results show that elevated DIP concentrations favor the growth of diatoms and dinoflagellates. The primary pathway for DIP inputs in all probability being via upwelling induced by the on-shelf intrusion of Kuroshio Intermediate Waters along the coast of China, and eastward advection of DIP-rich CDW with phytoplankton blooms lead to variations on phytoplankton compositions in the mid-shelf ECS.