Carbon Data Synthesis and Analysis
In accordance with one of the stated goals of the program, an evaluation of the data set with respect to estimated anthropogenic CO2 distributions in the Indian Ocean has been completed and published by Sabine et al. (1999). The document is appended to this report as Appendix D. Additional crossover comparisons of the survey data with data gathered in the 1980s and in 1993 by French scientists are included. Briefly, the sequestering of anthropogenic CO2 has been estimated by comparing the Indian Ocean survey results with the Indian Ocean GEOSECS expedition data from 1977 to 1978. Although CRM samples were not available for evaluating the earlier data, statistical methods were used to fit these data and correct for calibration offsets so that they could be compared with the current survey data. The data analysis was complicated by regions of pronounced denitrification (Arabian basin) and other regional variations that had to be considered and quantified. In summary, the estimate of the anthropogenic inventory was relatively small in the Indian and Southern Oceans, with anthropogenic carbon uptake lower by a factor of 2 compared to that of the Atlantic Ocean. Importantly, discrepancies between model and data-based estimates were found especially for the Southern Ocean where carbon uptake appears to have been traditionally overestimated by the extant circulation models. (See Appendix D for further details.) The initial data synthesis work indicates that the survey data will provide an important baseline with respect to future studies and that the spatial distribution of anthropogenic carbon can be an important tool for understanding model-based carbon uptake estimates and the response of models to atmospheric increases in CO2.