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

Carmen Rodriguez, University of Miami, RSMAS, Miami, FL, United States and Frank J Millero Jr, University of Miami, RSMAS, Ocean Sciences, Miami, FL, United States
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 (ΔCAnth) and pH (ΔpHAnth) 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 40oS (+ 20 μmol/kg ΔCAnth; - 0.04 ΔpHAnth) and the inflow of Persian Gulf and Red Sea Waters near 10oN (+ 40 μmol/kg ΔCAnth; - 0.06 ΔpHAnth). 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 ΔCAnth inventory in the Indian Ocean will be discussed here.