Andrew Watson, U. Exeter, will present the first OASIS Science Webinar on May 26, 2021 at 1400 GMT on “Revised estimates of ocean-atmosphere CO2 flux are consistent with ocean carbon inventory”.  If you would like to attend, please register at the following link (you should automatically receive call-in details after registering): https://zoom.us/meeting/register/tJUucO-tpz0sEtcV-tx6KoK92_Y9UnvdRFQb.

Authors:Andy Watson, Ute Schuster, Jamie Shutler, Thomas Holding, Ian Ashton, Peter Landschützer, David Woolf and Lonneke Goddijn-Murphy.

Abstract:  The ocean is a sink for ~25% of the atmospheric CO2 emitted by human activities, an amount in excess of 2 petagrams of carbon per year (PgC yr-1) . Regional and global time-resolved estimates of the ocean-atmosphere CO2 flux provide an important constraint on the carbon budget and a test for Earth system models. In recent years, an international effort to assemble quality-controlled data sets for surface ocean CO2 concentrations has enabled several such estimates. However, previous studies have not corrected the data for temperature gradients between the surface and sampling depth at a few metres or for the effect on fluxes of the cool ocean surface skin. Here we calculate a time history of ocean-atmosphere fluxes of CO2 in recent decades corrected for these effects. These increase the calculated net flux into the oceans by ~0.8- gCyr-1 on average since 1992, at times doubling the uncorrected values. We estimate the uncertainty in our flux calculations by using both simple and sophisticated interpolation methods, but all configurations give convergent results when estimating fluxes globally after about 2000, or over the northern hemisphere throughout the period. Our corrections reconcile surface fluxes with independent estimates of the increase in ocean CO2 inventory, without the need to assume a substantial outgassing “natural” of CO2 from the oceans over recent decades, and suggest that most global models underestimate uptake.