POSTER Session 4

SEASONAL AND INTERANNUAL VARIATIONS OF SEA SURFACE NITRATE IN THE NORTH PACIFIC AS ESTIMATED FROM GCOM-C/SGLI AND IN-SITU DATA

Changes in marine environments associated with climate change, including global warming, will affect not only nitrogen and carbon dynamics in the ocean but also higher trophic organisms, such as zooplankton and fishes, through changes in the abundance, community structure, and productivity of phytoplankton as principal primary producers. In the North Pacific, multi-CMIP6 models projected sea surface warming to exceed 2°C and a decline in nitrate concentrations within the euphotic zone exceeds 1 mmol m-3 by the end of this century. Thus, to evaluate the impacts of climate change on marine ecosystems, it is essential to understand spatiotemporal variability in sea surface nutrient concentration in this basin. We present the spatiotemporal changes in sea surface nitrate concentrations in the North Pacific using GCOM-C/SGLI data from 2018 to 2023. SGLI-derived sea surface nitrate was calculated using SGLI version 3 chlorophyll a concentration and sea surface temperature. Additionally, surface nitrate levels were continuously measured with an in situ ultraviolet spectrophotometer to validate the accuracy of SGLI-derived sea surface nutrient concentrations. As a result, SGLI accurately estimated sea surface nitrate concentration in the North Pacific (RMSE = 1.0 µM). In the Bering Sea, interannual changes in SGLI-derived sea surface nitrate were significant in October. During 2018–2019, strong marine heat waves (MHWs) occurred in this region, and distinct differences in nitrate concentration could be caused by MHWs and their related environmental changes.

Shintaro Takao, National Institute for Environmental Studies, Japan, [email protected]

Koji Suzuki, Hokkaido University, Japan, [email protected]

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