[M-IS05] Global climate change driven by the Southern Ocean and the Antarctic Ice Sheet

[MIS05-02] Carbon and nutrient cycles in and around the Cape Darnley polynya

★Invited Papers

*Michiyo Yamamoto-Kawai¹, Yoshihiko Ohashi¹ (1.Graduate School of Marine Science and Technology, Tokyo University of Marine Science and Technology)

Keywords:carbon cylce, nutrient cycle, polynya, Southern Ocean

In polynyas around the Antarctic coast, cold dense shelf water (DSW), the precursor to Antarctic Bottom Water (AABW), is formed by enhanced sea-ice production. The outflow of this DSW into the abyss links biogeochemistry of the upper and deeper oceans. As part of the GRAntarctic project, we have investigated carbon and nutrient cycles in and around the Cape Darnley polynya region, where DSW and AABW are formed. Data of transient tracers CFCs and SF₆ are also used to estimate time-scale of AABW transport from the polynya to the deep ocean.

Ship-based and moored observations have shown large seasonal and interannual changes in carbon and nutrient concentrations in the polynya, due to production and decomposition of organic matter. Estimates of carbon and nutrient budgets in the polynya indicate the net removal of silicate and dissolved inorganic carbon (DIC) on the shelf. As a result, low DIC and silica concentrations characterize the newly formed AABW in this region. CFC and SF₆ showed a rapid transport of well-ventilated AABW from the Cape Darnley polynya region to the north and west. During this rapid transport, the effect of decomposition of organic matter was not evident in DIC or nutrient concentrations. These results revealed that Cape Darnley polynya acts as a significant sink of DIC and silicate, lowering DIC and silicate concentrations of AABW.