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 dataset as the reference to assess the accuracy of in-situ 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) for 1982 to 2020, which is significantly 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 for 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).
