Spatiotemporal variation of the halocline and its impact on biological production in the North Pacific

2020 Fiscal Year Final Research Report

• Project/Area Number: 18K03736
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 17020:Atmospheric and hydrospheric sciences-related
• Research Institution: Hokkaido University
• Principal Investigator: Ueno Hiromichi 北海道大学, 水産科学研究院, 准教授 (90421875)
• Co-Investigator(Kenkyū-buntansha): 三寺 史夫 北海道大学, 低温科学研究所, 教授 (20360943)
• Project Period (FY): 2018-04-01 – 2021-03-31
• Keywords: 塩分躍層 / 成層構造

Outline of Final Research Achievements

A halocline is a layer containing a strong vertical salinity gradient. In the subarctic North Pacific, the permanent halocline depth and intensity distributions corresponded to those of winter mixed layer depth and sea surface salinity, respectively, implying that the permanent halocline forms in association with winter mixing throughout the subarctic North Pacific. We also found that stratification in early summer in the northern Bering Sea was significantly weaker in 2018 than in 2017. This result is consistent with the extremely low sea-ice extent present in the winter of 2017/2018. We further investigated the distribution and interannual variation in the winter halocline in the upper layers of the world ocean. A halocline was observed in the tropics, equatorward portions of subtropical regions, the subarctic North Pacific and Southern Ocean, but was absent in the central subtropics.

Free Research Field

海洋物理学

Academic Significance and Societal Importance of the Research Achievements

海洋は、大まかに「暖かくて密度の低い表層」と「冷たくて密度の高い中深層」の２層に分かれています。その２層を分ける層として水温が急激に下がる層（水温躍層）が存在しており、水温躍層の深さや強さは大気海洋相互作用や生物生産に重要な役割を果たしていることが知られています。しかし、海洋の密度は塩分の影響も受けており、特に高緯度域では塩分が深さとともに大きく増加する塩分躍層が存在しています。本研究では、広範囲にわたる塩分躍層の分布と形成メカニズムを初めて調べ、海域による違いを明らかにしました。