Comment on “Anthropogenic CO2 inventory of the Indian Ocean” by C. L. Sabine et al.

Abstract

Recently, Sabine et al. [1999] presented estimates of anthropogenic CO2 inventory tbr Indian Ocean (20.3 + 3 Pg C). These were based mainly on data collected tkom 19941996 World Ocean Circulation Experiment/Joint Global Ocean Flux Study (WOCE/JGOFS). Sabine et al. also calculated increase in inventory since Geochemical Ocean Sections Program (GEOSECS) in 1978 and claimed that improvements in estimation of pretbrmed end-member concentrations together with significant improvements in accuracy and spatial coverage of global carbon data give us much more confidence in these results. The present author takes issue with above statement and certainly feels that their work should have been compared with earlier findings by Chen [1993a]. Had that been done, Sabine et al. paper could have been improved tkom two fi•ndamental perspectives. First, tkom historical perspective, it should be noted that anthropogenic CO2 inventory tbr Indian Ocean had previously been published by Chen [1993a] but, unlbrtunately, that work was not mentioned by Sabine et al. Sabine et al. concluded that the anthropogenic inventory of Indian Ocean was shown to be relatively small; approximately half of that lbund in Atlantic. Chen [1993a], based mainly on GEOSECS data, had earlier reported 16.6 + 3 Pg C lbr Indian Ocean (1978 data) and 34.4 + 7 Pg C Ibr Atlantic Ocean ( 1972-1973 data) Thus first bit of new-inlbrmation that can be obtained here by comparing results of these two studies is that 20 years ago Indian Ocean inventory was half of that lbr Atlantic, just as it was more recently (1994-1996). In other words, relative inventory has not changed. The implications are that Weddell Sea is still not a significant sink Ibr anthropogenic CO2. Chen [1982] and Poisson and Chen [1987] Ibund little or no anthropogenic CO2 in Antarctic Bottom Water (AABW) based on International Geophysical Year (IGY) data collected in 1950s, 19721973 GEOSECS data, and 1981 Weddell Polynya Expedition (WEPOLEX) data. If AABW had started to absorb much anthropogenic CO2 since 1981, recent Atlantic inventory would have increased relative to that of Indian Ocean. Of