Anthropogenic CO2 accumulation in the Indian Ocean (1995 to 2018). Results from the GO-SHIP I07N repeat-hydrography transect.

The CO₂ system in the Indian Ocean was evaluated using observational data collected from the I07N repeat-hydrography cruise transect. This meridional transect in the western Indian Ocean has been sampled over multiple decades, under the GEOSECS (1977-1978), WOCE (1995), and GO-SHIP (2018) programs. In this project, the accumulation of anthropogenic carbon (ΔC_Anth) and pH (ΔpH_Anth) has been estimated via an extended multi-linear regression (e-MLR) analysis. Focusing on the WOCE and GO-SHIP occupations (the last 23 years), significant increases in anthropogenic carbon were observed in the upper 1500m. The greatest signals were consistent with regions of transport, such as the subduction of mode waters near 40^oS (+ 20 μmol/kg ΔC_Anth; - 0.04 ΔpH_Anth) and the inflow of Persian Gulf and Red Sea Waters near 10^oN (+ 40 μmol/kg ΔC_Anth; - 0.06 ΔpH_Anth). Given the non-linear rise of anthropogenic CO₂ in the atmosphere, and the highly variable circulation and productivity of the Indian Ocean, these preliminary results prompt further evaluation of CO₂ in the Indian Ocean. Additional Indian Ocean GO-SHIP transects have been completed in recent years and will be integrated with the I07N results. The distribution of the ΔC_Anth inventory in the Indian Ocean will be discussed here.