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Updated: May 10, 2025

Author Spotlight: Understanding Riverine Nitrogen Impacts and Primary Productivity for Effective Nutrient Management
Published on: July 14, 2023
Topographically driven vigorous vertical mixing supports mesoscale biological production in the Tsugaru Gyre
Hitoshi Kaneko1, Takahiro Tanaka2,3, Masahide Wakita4
1Mutsu Institute for Oceanography, Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 690 Kitasekine, Sekine, Mutsu, Aomori, 035-0022, Japan. h_kaneko@jamstec.go.jp.
Abstract:
The Tsugaru Strait is a critical conduit linking the Sea of Japan and the Pacific Ocean and is characterized by a vigorous eastward current. Here, we use high-resolution surface current data acquired from a high-frequency radar system in conjunction with direct turbulence measurements to show that the large increase in chlorophyll-a within a hundred kilometre-scale anticyclonic gyre is driven by the intensification of turbulence, extraordinarily high diffusive nitrate fluxes and divergent flow fields limited to a very narrow area. Enhanced mixing and nutrient fluxes are caused by the presence of a distinct topographic feature-an underwater seamount-within the path of the Tsugaru Strait water flow. Our long-term datasets reveal a positive correlation between recurring submesoscale divergence related to the topographic features and the downstream distribution of chlorophyll-a. This finding reinforces the significant role of the underwater seamount in enhancing the productivity of the downstream anticyclonic gyre. The results of this study emphasize the importance of re-evaluating nutrient supply processes with respect to submesoscale interactions with underwater seamounts for large-scale enhanced biological productivity.
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