[A-OS16] Chemical and Biological Oceanography

[AOS16-02] Seasonal variations of oceanic CO₂ disequilibrium and anthropogenic CO₂ in the subarctic North Pacific

*Bofeng Li¹, Shukuta Satori¹, Kasai Hiromi², Hiroshi Kuroda², Taniuchi Yukiko², Daisuke Hasegawa³, Yutaka Watanabe¹ (1.Hokkaido University, 2.Hokkaido National Fisheries Research Institute, Japan Fisheries and Education Research , 3.Tohoku National Fisheries Research Institute, Japan Fisheries and Education Research )

Keywords:Air-sea CO2 disequilibrium, Anthropogenic CO2, Subarctic North Pacific

Assuming that the CO₂ above the surface mixed layer depth (MLD) mixes very well with air, we used a simple and new method to estimate air-sea CO₂ disequilibrium value at the MLD (C_diseq) as follow [Li et al., 2019];

C_diseq = C_MLD – C_{sat, MLD} – C_{soft, MLD} – C_{carb, MLD}

where C_MLD is the observed dissolved inorganic carbon (DIC); C_{sat, MLD} is saturated DIC; C_{soft, MLD} is derived from the remineralization of organic matter; C_{carb, MLD} is derived from the dissolution of CaCO₃ in the MLD. We collected the DIC and total alkalinity (TA) samples in the subarctic North Pacific in four seasons, and measured all the DIC and TA by using semi-closed cell simultaneous method [Li et al., 2016].

C_diseq in this region changed from –38.29 to −56.93 μmol kg^-1 in wintertime and from −9.65 to 1.02 μmol kg^-1 summertime, indicating a strong seasonal change in C_diseq. Appling these values of C_diseq to the approach for estimating C_ant in this region, we also found a strong seasonal variation in C_ant.