Strengthening stratification due to ongoing global warming on the outer shelf of the East China Sea: oligotrophication and deoxygenation and the impact on ecosystems

2022 Fiscal Year Final Research Report

• Project/Area Number: 20H04319
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 63010:Environmental dynamic analysis-related
• Research Institution: University of Toyama
• Principal Investigator: Zhang Jing 富山大学, 学術研究部理学系, 教授 (20301822)
• Co-Investigator(Kenkyū-buntansha): 郭 新宇 愛媛大学, 沿岸環境科学研究センター, 教授 (10322273) ; 遠藤 貴洋 九州大学, 応用力学研究所, 准教授 (10422362)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: 貧/低酸素水 / 化学トレーサー / 形成メカニズム / 定量評価 / 外部陸棚域 / 東シナ海

Outline of Final Research Achievements

The study aims to understand the changes in water structure and mechanism of bottom hypoxia under ongoing global warming on the outer-edge shelf of the East China Sea (ECS ~200 m). A mixed model with various chemical tracers (rare earth elements, 226Ra,137Cs, and δ34S) and CTD observations inferred that low dissolved oxygen water (LOW) on the outer shelf of ECS is formed by Kuroshio subsurface water (60~80%) and the inner-middle shelf water (~10%). LOW transports downstream along with isopycnals to the Kuroshio region, mixes with the surrounding seawater, about 70% of which flows into the Sea of Japan through the Tsushima Strait. Physical observations show that turbulence and horizontal advection caused by semidiurnal tides are involved in the distribution and transport of LOW. Furthermore, analysis result based on the World Ocean Database 2018 (1951-2006) shows that the maximum reduction of dissolved oxygen in shelf water occurs at 30 m depth in summer and at 50 m depth in autumn.

Free Research Field

海洋科学

Academic Significance and Societal Importance of the Research Achievements

本研究の成果は、温暖化が日々進行する中で、世界有数の好漁場である東シナ海における低酸素水の発生頻度増加とその面積拡大に関する基礎的知見を提供するものである。特に、東シナ海内部陸棚・中央陸棚水との繋がりや低酸素水発生の要因・メカニズムへの理解深化により、沿岸海洋生態系ダイナミクスの詳細解明や海域保全にも貢献する。また、東シナ海における低酸素水塊の日本海ならびに黒潮域への輸送メカニズムが確認されたことで、低酸素海域の動向と下流域へ主要栄養塩・微量栄養塩への供給や、それらによる影響の理解が深まったと考えられる。