15:45 〜 16:00
[ACG44-02] Seasonal and interannual variations of surface water carbonate chemistry in the Indian sector of the Southern Ocean
キーワード：南極海、炭素循環、二酸化炭素分圧、大気−海洋間二酸化炭素フラックス
To assess carbon cycling in the Indian sector of the Southern Ocean (80°E–150°E, south of 60°S) quantitatively, we measured seawater temperature, salinity, chlorophyll-a concentration, partial pressure of carbon dioxide (pCO2), dissolved inorganic carbon (DIC) concentration, alkalinity (TA), and nutrient concentrations.
The air-sea CO2 flux in this region was evaluated to be –7.6±10.9 mmol C m–2 day–1 (–75.6 − +14.1 mmol C m–2 day–1) suggesting that the region was a weak sink. Then, we estimated the change in pCO2 from winter to summer ( pCO2) due to changes in seawater temperature, salinity, and biological activity on the basis of the assumption that the observed values of DIC concentration and TA in the temperature minimum layer remain the same as in the winter under sea-ice with a temperature of –1.8℃ and salinity of 34.25. The spatial distribution of pCO2 in the western area (80°E–120°E) observed from December to early January was influenced by biological activity, and that in the eastern area (120°E–150°E) observed from January to February was influenced by temperature and salinity.
We also examined the annual change in oceanic and atmospheric CO2 concentrations (xCO2) between 1996 and 2019. The mean values of oceanic and atmospheric xCO2 increased by 24 ppm and 45 ppm, respectively. This suggests that the main reason of the rise in oceanic xCO2 is that the ocean have absorbed CO2 from atmosphere as a result of the rise in atmospheric xCO2. However, it also indicates that the oceanic xCO2 rise is due to the rise in sea water temperature and changes in the ocean circulation.
The air-sea CO2 flux in this region was evaluated to be –7.6±10.9 mmol C m–2 day–1 (–75.6 − +14.1 mmol C m–2 day–1) suggesting that the region was a weak sink. Then, we estimated the change in pCO2 from winter to summer ( pCO2) due to changes in seawater temperature, salinity, and biological activity on the basis of the assumption that the observed values of DIC concentration and TA in the temperature minimum layer remain the same as in the winter under sea-ice with a temperature of –1.8℃ and salinity of 34.25. The spatial distribution of pCO2 in the western area (80°E–120°E) observed from December to early January was influenced by biological activity, and that in the eastern area (120°E–150°E) observed from January to February was influenced by temperature and salinity.
We also examined the annual change in oceanic and atmospheric CO2 concentrations (xCO2) between 1996 and 2019. The mean values of oceanic and atmospheric xCO2 increased by 24 ppm and 45 ppm, respectively. This suggests that the main reason of the rise in oceanic xCO2 is that the ocean have absorbed CO2 from atmosphere as a result of the rise in atmospheric xCO2. However, it also indicates that the oceanic xCO2 rise is due to the rise in sea water temperature and changes in the ocean circulation.