[A-CG45] 海洋表層－大気間の生物地球化学

[ACG45-02] Distribution and determinants of nutrients and primary production in the eastern Indian sector of the Southern Ocean

*戸澤 愛美¹、野村 大樹^1,2,3、山崎 開平⁴、木内 政彰¹、平野 大輔^4,5、青木 茂⁶、佐々木 裕子⁷、村瀬 弘人⁸ (1.北海道大学大学院水産科学院、2.北海道大学北方生物圏フィールド科学センター、3.北海道大学北極域研究センター、4.国立極地研究所、5.総合研究大学院大学、6.北海道大学低温科学研究所、7.水産研究・教育機構、8.東京海洋大学)

キーワード：栄養塩、群集純生産、南極海インド洋セクター、季節海氷域

To investigate the spatial distributions and determinants of nutrient concentrations, we measured NO₃⁻+NO₂⁻, PO₄³⁻, and Si(OH)₄concentrations in the eastern Indian Ocean sector of the Antarctic Ocean (80−150°E, south of 60°S) between December 2018 and February 2019. In the Antarctic Circumpolar Current (ACC) domain, nutrient concentrations were increased by nutrients supplied from the deep layer and by organic matter decomposition and remineralization within the seasonal pycnocline after the development of strong stratification. Strong stratification also enhanced phytoplankton growth and nutrient consumption by photosynthesis. In contrast, in the subpolar region, nutrient concentrations were increased by nutrients supplied by brine discharged during sea ice formation and decreased by dilution with sea ice meltwater. Although high salinity in the surface and subsurface layers corresponded well to upwelling areas around subpolar subgyres, high salinity was not necessarily correlated with nutrient concentrations. We estimated primary production both from in situ nutrient data and from satellite-acquired chlorophyll-a data. According to both estimation methods, primary production was high in the subpolar region, especially around 120−130°E. However, nutrient-based estimation also showed high production in coastal areas where, because of sea ice and cloud cover, estimation based on satellite data was not possible. To understand primary production in seasonal ice areas, the best estimation method should be selected for the research goals or multiple methods should be used in combination.