Subduction of North Pacific Central Mode Water and its decadal variability

2019 Fiscal Year Final Research Report

• Project/Area Number: 17K05652
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Meteorology/Physical oceanography/Hydrology
• Research Institution: The University of Tokyo
• Principal Investigator: Oka Eitarou 東京大学, 大気海洋研究所, 准教授 (60360749)
• Project Period (FY): 2017-04-01 – 2020-03-31
• Keywords: 中央モード水 / サブダクション / 十年規模変動 / フロント・中規模渦

Outline of Final Research Achievements

Subduction of Central Mode Water (a mode water is a voluminous, vertically homogeneous water mass) north of the Kuroshio Extension and its impact on the physical and biogeochemical structure in the lower permanent pycnocline of the North Pacific subtropical gyre were examined through analyses of observation data by research vessels, Argo profiling floats, and satellite altimeter. High-resolution hydrographic observations that we performed in two cruises of R/V Hakuho-maru clarified the relation between the formation of mode waters and fronts/eddies, and presented a new mechanism of mode water subduction in association with eddy-to-eddy interaction. Analyses of the 137E section by the Japan Meteorological Agency clarified decadal variability and long-term change of physical and biogeochemical properties of Subtropical Mode Water.

Free Research Field

海洋物理学

Academic Significance and Societal Importance of the Research Achievements

巨大な体積を持つモード水は、熱の偏差や二酸化炭素等の物質とともに海面から海洋内部に沈み込むことで、気候変動や海洋内部の物質循環に大きな影響を与えている。そのため、各モード水がどこで沈み込み、その後海洋内部をどのように循環し、最終的に海面にどのように再出現するのか（あるいはしないのか）、またそれらがどのように時間変動するのかを解明することが重要である。本研究は未解明の点が多い、本州東方域からの中央モード水の沈み込みの実態とメカニズムを明らかにした。