[A-CG44] 海洋表層－大気間の生物地球化学

[ACG44-03] Summer carbonate chemistry near the Totten Ice Shelf, Sabrina Coast, East Antarctica

*田村 哲也¹、野村 大樹^1,2,3、平野 大輔^3,4、田村 岳史⁵、木内 政彰¹、橋田 元⁵、青木 茂⁴、佐々木 裕子⁶、村瀬 弘人⁷ (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.北海道大学低温科学研究所、5.国立極地研究所、6.水産研究・教育機構国際水産資源研究所、7.東京海洋大学)

キーワード：南極海、棚氷、底面融解、炭素循環

To clarify the effect of basal melting of Antarctic ice sheet on the marine biogeochemical components in the coast of the Southern Ocean, dissolved inorganic carbon (DIC), total alkalinity (TA), nutrients (NO₃^-, PO₄^3-, Si(OH)₄), oxygen stable isotope ratio (δ¹⁸O), chlorophyll a were measured off from offshore slope (ice margin area) to Totten Ice Shelf ice front (sea ice area) during summer 2018 and 2019 conducted by Kaiyo-maru and Shirase. The distribution of DIC concentration, TA and nutrients concentration was corresponded to a following ocean current: (1) mCDW existing on the offshore slope flows beneath the Totten Ice Shelf along the trough, (2) the flow mixes with Totten Ice Shelf basal melt water and (3) the becomes low density and rises to the surface. DIC concentration and TA on the surface of the ice front were strongly influenced by the dilution effect of the ice shelf basal melt water and the inflow of mCDW. The ratio of ice shelf basal melt water with respect to the other water masses (sea ice water and mCDW) calculated using δ¹⁸O was about 1.4% and the ratio of sea ice melt water was 2.9 % and the rest ratio was inflow of mCDW. Because of the dilution effect, DIC concentration decreased about 80 µmol kg⁻¹, and this decrease was corresponded to a decrease of about 64 µatm for the partial pressure of carbon dioxide (pCO₂). However, the surface of the ice front was strongly influenced by biological processes. The nDIC and nTA that normalized to salinity (34.3 pus) to remove the dilution effect of melt water were changed along nDIC:nTA = 106:16 by the photosynthesis of phytoplankton. Furthermore, the net community production (NCP) from 20 to 100 dbar was higher than that for the previous study (December 31^st, 2014-January 1^st, 2015, [Arroyo et al., 2019]) because the open water area was higher and availability of light for phytoplankton during this study observation was greater in our study period than those in previous study. Therefore, the decrease of more than 150 µatm for pCO₂ would be resulted by the biological productivity in this study. On the west side of the ice shelf, both the ratio of ice shelf basal melt water and NCP were higher and pCO₂ was lower than those of east side of the ice shelf. Therefore, the mCDW mixed with the ice shelf basal melt water floats on the west side of the ice shelf. This study highlighted that ice shelf basal melt water has a significant impact on marine biogeochemical components.