Increase of anthropogenic CO2 in the Pacific Ocean over the last two decades

Abstract

Abstract The multiple-parameter linear regression method (Monitoring global ocean carbon inventories. Ocean Observing System Development Panel, Texas AM Global Biogeochem. Cycles 13 (1999) 179) is used to compare inorganic carbon data from the GEOSECS CO 2 survey in the Pacific Ocean in 1973 to the WOCE/JGOFS global CO 2 survey in the 1990s. A model of total dissolved inorganic carbon (DIC) as a function of five variables (AOU, θ , S, Si, and PO 4 ) has been developed from the recent CO 2 survey data (namely CGC91 and CGC96) in the Pacific Ocean. After correcting for a systematic DIC offset of −30.3±7 μmol kg −1 from the GEOSECS data, the residual DIC based on this model as computed from GEOSECS data has been used to estimate the anthropogenic CO 2 penetration in the Pacific Ocean. In the Northeast Pacific, we obtained an increase of CO 2 of 21.3±7.9 mol m −2 over the period from GEOSECS in 1973 to CGC91 in 1991. This gives a mean anthropogenic CO 2 uptake rate of 1.3±0.5 mol m −2 yr −1 over this 17 year time period. In the South Pacific, north of 50°S between 180° and 120°W region, the integrated anthropogenic CO 2 inventory is estimated to be 19.7±5.7 mol m −2 over the period from GEOSECS in 1974 to CGC96 in 1996. The equivalent mean CO 2 uptake rate is estimated to be 0.9±0.3 mol m −2 yr −1 over the 22 years. These results are compared with the isopycnal method (Nature 396 (1998) 560) to estimate the anthropogenic CO 2 signal in the Northeast Pacific (30°N, 152°W) at the crossover region between CGC91 and GEOSECS. The results of the isopycnal method are consistent with those derived from the MLR method. Both methods show an increase in anthropogenic CO 2 inventory in the ocean over two decades that is consistent with the increase expected if the ocean uptake has kept pace with the atmospheric CO 2 increase.