Revised estimates of ocean-atmosphere CO2 flux are consistent with ocean carbon inventory

• Published in: Nature communications Vol. 11; no. 1; p. 4422
• Main Authors: Watson, Andrew J., Schuster, Ute, Shutler, Jamie D., Holding, Thomas, Ashton, Ian G. C., Landschützer, Peter, Woolf, David K., Goddijn-Murphy, Lonneke
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 04.09.2020; Nature Publishing Group; Nature Portfolio
• Subjects: 704/106/694; 704/47/4113; 704/829/827; Atmosphere; Atmospheric models; Carbon dioxide; Climate models; Estimates; Fluctuations; Fluxes; Humanities and Social Sciences; Interpolation; Measuring instruments; multidisciplinary; Northern Hemisphere; Ocean models; Ocean surface; Oceans; Science; Science (multidisciplinary); Temperature gradients; Water analysis; Water depth; Water sampling
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-020-18203-3

The ocean is a sink for ~25% of the atmospheric CO 2 emitted by human activities, an amount in excess of 2 petagrams of carbon per year (PgC yr −1 ). Time-resolved estimates of global ocean-atmosphere CO 2 flux provide an important constraint on the global carbon budget. However, previous estimates of this flux, derived from surface ocean CO 2 concentrations, have not corrected the data for temperature gradients between the surface and sampling at a few meters depth, or for the effect of the cool ocean surface skin. Here we calculate a time history of ocean-atmosphere CO 2 fluxes from 1992 to 2018, corrected for these effects. These increase the calculated net flux into the oceans by 0.8–0.9  PgC yr −1 , at times doubling uncorrected values. We estimate uncertainties using multiple interpolation methods, finding convergent results for fluxes globally after 2000, or over the Northern Hemisphere throughout the period. Our corrections reconcile surface uptake with independent estimates of the increase in ocean CO 2 inventory, and suggest most ocean models underestimate uptake. Ocean uptake of carbon dioxide impacts the climate, but flux estimates from surface measurements have not been corrected for temperature differences between surface and water sampling depth. Making that correction, the authors find previous estimates for ocean uptake have been substantially underestimated.