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Seasonal Variations and Drivers of Surface Ocean pCO 2 in the Seasonal Ice Zone of the Eastern Indian Sector, Southern Ocean
Author(s) -
Tozawa Manami,
Nomura Daiki,
Nakaoka Shinichiro,
Kiuchi Masaaki,
Yamazaki Kaihe,
Hirano Daisuke,
Aoki Shigeru,
Sasaki Hiroko,
Murase Hiroto
Publication year - 2022
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1029/2021jc017953
Subject(s) - salinity , alkalinity , carbon dioxide , sink (geography) , environmental science , oceanography , chlorophyll a , dissolved organic carbon , total inorganic carbon , carbon cycle , carbon sink , photosynthesis , atmospheric sciences , climate change , geology , chemistry , geography , ecology , biology , botany , cartography , organic chemistry , ecosystem
To quantitatively assess the inorganic carbon cycle in the eastern Indian sector of the Southern Ocean (80–150°E, south of 60°S), we measured ocean surface temperature, salinity, total alkalinity (TA), the partial pressure of carbon dioxide (pCO 2 ), and concentrations of chlorophyll‐ a (chl a ), dissolved inorganic carbon (DIC), and nutrients during the KY18 survey (December 2018–January 2019). The sea–air CO 2 flux in this region was −8.3 ± 12.7 mmol m −2 day −1 (−92.1 to +10.6 mmol m −2 day −1 ). The ocean was therefore a weak CO 2 sink. Based on the DIC and TA in the temperature minimum layer, we estimated the change of pCO 2 from winter to summer (δpCO 2 ) due to changes in water temperature, salinity, and biological activity (photosynthesis). The spatial distribution of pCO 2 in the western part (80–110°E) of the study area was mainly driven by biological activity, which decreased pCO 2 from December to early January, and in the eastern part (110–150°E) by temperature, which increased pCO 2 from January to February. We also examined the changes in the CO 2 concentrations (xCO 2 ) over time by comparing data from 1996 with our data (2018–2019). The oceanic and atmospheric xCO 2 increased by 23 and 45 ppm in 23 years, respectively. These changes of ocean xCO 2 were mainly driven by an increase in CO 2 uptake from the atmosphere as a result of the rise in atmospheric xCO 2 and increase in biological activity associated with the change in the water‐mass distribution.