Update on the Temperature Corrections of Global Air‐Sea CO2 Flux Estimates.

The oceans are a major carbon sink. Sea surface temperature (SST) is a crucial variable in the calculation of the air‐sea carbon dioxide (CO2) flux from surface observations. Any bias in the SST or any upper ocean vertical temperature gradient (e.g., the cool skin effect) potentially generates a bias in the CO2 flux estimates. A recent study suggested a substantial increase (∼50% or ∼0.9 Pg C yr−1) in the global ocean CO2 uptake due to this temperature effect. Here, we use a gold standard buoy SST data set as the reference to assess the accuracy of insitu SST used for flux calculation. A physical model is then used to estimate the cool skin effect, which varies with latitude. The bias‐corrected SST (assessed by buoy SST) coupled with the physics‐based cool skin correction increases the average ocean CO2 uptake by ∼35% (0.6 Pg C yr−1) from 1982 to 2020, which is substantially smaller than the previous correction. After these temperature considerations, we estimate an average net ocean CO2 uptake of 2.2 ± 0.4 Pg C yr−1 from 1994 to 2007 based on an ensemble of surface observation‐based flux estimates, in line with the independent interior ocean carbon storage estimate corrected for the river induced natural outgassing flux (2.1 ± 0.4 Pg C yr−1). Plain Language Summary: The global oceans play a major role in taking up carbon dioxide (CO2) released by human activity from the atmosphere. Accurate sea surface temperature (SST) measurements and quantification of any upper ocean temperature gradients (e.g., cool skin effect) are critical for ocean CO2 uptake estimates. We determine a slight warm bias in the SST data set used for CO2 flux calculation by utilizing a gold standard reference buoy SST data set. We then derive a physics‐based temperature correction for the ubiquitous cool skin effect on the ocean surface. The temperature revised CO2 flux bridges the gap between estimates from the surface observation‐based air‐sea CO2 fluxes and from the independent ocean carbon inventory. Key Points: The impact of the warm bias in an in situ sea surface temperature data set and the cool skin effect on air‐sea carbon dioxide (CO2) flux estimates are revisitedThe updated temperature corrections imply a smaller increase in net ocean CO2 uptake (∼35%) compared to a previous study (∼50%)The revised observation‐based CO2 flux agrees well with the independent ocean carbon inventory [ABSTRACT FROM AUTHOR]