Characteristics of hydrogen/oxygen isotopes in water masses and implications for spatial distribution of freshwater in the Amundsen Sea, Southern Ocean

• Main Authors: Hebin, Shao, Jianfeng, He, Guangfu, Luo, Musheng, Lan, Lejiang, Yu, Guijun, Guo, Ergang, Lian
• Format: Article in Journal/Newspaper
• Language: English
• Published: Polar Research Institute of China - PRIC 2021
• Subjects: Atmosphere; Oceans; Antarctic; Southern Ocean; The Antarctic; Amundsen Sea; Advances in Polar Science; Antarc*; Antarctica; Ice Shelves; Polar Science; Sea ice
• Online Access: http://library.arcticportal.org/2757/; http://library.arcticportal.org/2757/1/A2103005.pdf

Antarctica’s marginal seas are of great importance to atmosphere–ocean–ice interactions and are sensitive to global climate change. Multiple factors account for the freshwater budget in these regions, including glacier melting, seasonal formation/decay of sea ice, and precipitation. Hydrogen (H) and oxygen (O) isotopes represent useful proxies for determining the distribution and migration of water masses. We analyzed the H and O isotopic compositions of 190 seawater samples collected from the Amundsen Sea during the 34th Chinese Antarctic Research Expedition in 2017/2018. The upper-oceanic structure (<400 m) and freshwater (meteoric water and sea ice melt) distribution in the Amundsen Sea were identified based on conductivity–temperature–depth data and the H and O isotopic composition. Antarctic Surface Water, characterized as cold and fresh with low H and O isotopic ratios, was found distributed mainly in the upper ~150 m between the Antarctic Slope Front and Polar Front, where it had been affected considerably by upwelled Upper Circumpolar Deep Water (UCDW) between 68°S and 71°S. A three-endmember (meteoric water, sea ice melt, and Circumpolar Deep Water) mixing model indicated that waters with relatively high proportions (>3%) of freshwater generally lie in the upper ~50 m and extend from Antarctica to ~65°S in the meridional direction (anomalously low freshwater proportion occurred between 68°S and 71°S). Winter Water mainly occupied the layer between 50 and 150 m south of 71°S in the western Amundsen Sea. The water structure and spatial distribution of freshwater in the upper Amundsen Sea were found influenced mainly by the rates of basal and surficial melting of ice shelves, seasonal alternation of sea ice melt/formation, wind forcing, and regional bathymetry. Owing to the distance between heavy sea ice boundary (HSIB) and ice shelves is much shorter in the western HSIB than the east HSIB, the western part of the heavy sea ice boundary includes a higher proportion of freshwater than the eastern ...