[A-OS26] Global ocean observing systems, their recent status, research results and future directions

[AOS26-P03] Progress of the decadal scale anthropogenic CO₂ in the Southern Ocean

*BOFENG LI¹, Xianliang Pan¹, Shun Yunoki¹, Yutaka Watanabe¹ (1.Hokkaido University)

Keywords:Southern Ocean, Air-sea CO2 disequilibrium, Anthropogenic CO2

In this study, large CO₂ disequilibrium (C_diseq) was found in the range of –70 to –10 μmol kg^-1 in the Southern Ocean (SO). When we tried to formulate this C_diseq, C_diseq had a strong correlation with the potential water temperature (θ) (C_diseq = 1.766θ – 45.07; R = 0.71, RMSE = 9.05 μmol kg^-1). This equation was applied to the vertical data obtained in the cruise of KARE22_UM-18-08. From the distributions of C_diseq and anthropogenic CO₂ (C_ant) in the north-south direction, we found that a large amount of C_anth is absorbed from the atmosphere to the ocean surface in high-latitude where high-density seawater exists.

Then, we constructed simple equations to predict dissolved inorganic carbon (DIC) and pH with high precision in the entire SO (south of 30° S) by using a hydrographic general dataset for dissolved oxygen, water temperature, salinity, and pressure. To estimate ΔC_ant variation in the SO, we applied a new method (that combined the parameterization technics with observational data (Watanabe et al., 2018)) to high-resolution grid data constructed based on ship-based observations from 1990 to 2017. As a result, we determined the ocean uptake of C_ant in the SO over the past two decades. DIC increases by anthropogenic effect account for 60% of the variation of DIC in the SO_.