[M-IS10] Global climate change driven by the Southern Ocean and the Antarctic Ice Sheet

[MIS10-11] Effects of glacier and sea ice meltwater on sea surface pCO₂ in the vicinity of Mertz Glacier, East Antarctica

*Nana Samori¹, Daiki Nomura^1,2,3, Manami Tozawa¹, Shin-ichiro Nakaoka⁴, Kaihe Yamazaki^5,6, Daisuke Hirano⁷, Shigeru Aoki⁸, Hiroto Murase⁹ (1.Faculty of Fisheries sciencies,Hokkaido University, 2.Field Science Center for Northern Biosphere, Hokkaido University, 3.Arctic Research Center, Hokkaido University, 4.National Institute for Environmental Studies, 5.Institute for Marine and Antarctic Studies, University of Tasmania, 6.The Australian Centre for Excellence in Antarctic Science, 7.National Institute of Polar Research, 8.Institute of Low Temperature Science, 9.Tokyo University of Marine Science and Technology)

Keywords:Southern Ocean, pCO2, glacier, sea ice

It is important to determine the factors of the variability in the partial pressure of carbon dioxide at the sea surface (pCO₂) because pCO₂ is a major determinant of the air−sea CO₂ flux. In recent years, the effect of glacier melting on sea surface pCO₂ in East Antarctica has been reported. In the Southern Ocean, glacier and sea ice meltwater are known to be one of the major factors of variation in pCO₂. To clarify the impact of glacier and sea ice melting on pCO₂ in the vicinity of Mertz Glacier, East Antarctica, where changing the environment due to the calving of glacier tongue in 2010, we have examined the oceanographic observation near Mertz Glacier (140–150ºE) during the 10^thexpedition by R/V Kaiyo–Maru (January 26, 2019 to February 4, 2019). During the cruise, sea surface pCO₂ was measured continuously, and CTD observations at all the layers were also conducted at the stations near Mertz Glacier (140–150ºE) for analysis of stable oxygen isotope ratios (δ¹⁸O), dissolved inorganic carbon (DIC) and total alkalinity (TA). Based on the vertical profiles of δ¹⁸O and water temperature, we identified the Circumpolar Deep Water (CDW) flowed at depth of 100–2000 m at 63.5–65ºS. The vertical profiles of the freshwater fraction above 500 m calculated using δ¹⁸O and salinity, indicated that sea ice meltwater was widely distributed in the surface layer from north to south. On the other hand, glacial meltwater was located near the bottom layer of the Mertz Glacier as well as in the surface layer along the 150ºE, suggesting the basal melting of the glacier. The dilution effect by the meltwaters on surface pCO₂ based on the fractional calculation indicated that the glacial and the sea ice meltwater reduced a comparable amount of 2.1 ± 0.5% (9.1 ± 2.3 µatm) and 1.5 ± 0.6% (6.3 ± 2.5 µatm) of pCO₂ for CDW, respectively. Therefore, meltwaters accounted for about 20% of the total reduction in pCO₂ (about 94 µatm). The relationship between nDIC and nTA (normalized to salinity of 34.73 to correct for dilution effects) suggested biological production by photosynthesis in the surface layer. In this study, we separate freshwater origins by δ¹⁸O and quantitatively evaluate the impact of each on pCO₂, suggesting glacier meltwaters contribute to decrease pCO₂ as sea ice meltwaters.