Seasonal Variations and Drivers of Surface Ocean pCO(2) in the Seasonal Ice Zone of the Eastern Indian Sector, Southern Ocean

• Published in: Journal of Geophysical Research: Oceans
• Main Authors: Tozawa, Manami, Nomura, Daiki, Nakaoka, Shin-ichiro, Kiuchi, Masaaki, Yamazaki, Kaihe, Hirano, Daisuke, Aoki, Shigeru, Sasaki, Hiroko, Murase, Hiroto
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Geophysical Union
• Subjects: carbonate chemistry; sea-air CO2 flux; carbon cycle; Southern Ocean; 452; Indian
• Online Access: http://hdl.handle.net/2115/84341; https://doi.org/10.1029/2021JC017953

To quantitatively assess the inorganic carbon cycle in the eastern Indian sector of the Southern Ocean (80-150 degrees E, south of 60 degrees 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 CO2 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 CO2 sink. Based on the DIC and TA in the temperature minimum layer, we estimated the change of pCO(2) from winter to summer (delta pCO(2)) due to changes in water temperature, salinity, and biological activity (photosynthesis). The spatial distribution of pCO(2) in the western part (80-110 degrees 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 degrees E) by temperature, which increased pCO(2) from January to February. We also examined the changes in the CO2 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 CO2 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.