Anthropogenic CO2 inventory of the Indian Ocean

This study presents basin-wide anthropogenic CO2 inventory estimates for the Indian Ocean based on measurements from the World Ocean Circulation Experiment/Joint Global Ocean Flux Study global survey. These estimates employed slightly modified Delta C* and time series techniques originally proposed by Gruber et al. [1996] and Wallace [1995], respectively. Together, the two methods yield the total oceanic anthropogenic CO2 and the carbon increase over the past 2 decades. The highest concentrations and the deepest penetrations of anthropogenic carbon are associated with the Subtropical Convergence at around 30 degrees to 40 degrees S. With both techniques, the lowest anthropogenic CO2 column inventories are observed south of 50 degrees S. The total anthropogenic CO2 inventory north of 35 degrees S was 13.6+/-2 Pg C in 1995. The inventory increase since GEOSECS (Geochem ical Ocean Sections Program) was 4.1+/-1 Pg C for the same area. Approximately 6.7+/-1 Pg C are stored in the Indian sector of the Southern Ocean, giving a total Indian Ocean inventory of 20.3 +/-3 Pg C for 1995. These estimates are compared to anthropogenic CO2 inventories estimated by the Princeton ocean biogeochemistry model. The model predicts an Indian Ocean sink north of 35 degrees S that is only 0.61-0.68 times the results presented here; while the Southern Ocean sink is nearly 2.6 times higher than the measurement-based estimate. These results clearly identify areas in the models that need further examination and provide a good baseline for future studies of the anthropogenic inventory.