The impact of changing wind speeds on gas transfer and its effect on global air-sea CO2 fluxes

An increase in global wind speeds over time is affecting the global uptake of CO2 by the ocean. We determine the impact of changing winds on gas transfer and CO2 uptake by using the recently updated, global high-resolution, cross-calibrated multiplatform wind product (CCMP-V2) and a fixed monthly pCO(2) climatology. In particular, we assess global changes in the context of regional wind speed changes that are attributed to large-scale climate reorganizations. The impact of wind on global CO2 gas fluxes as determined by the bulk formula is dependent on several factors, including the functionality of the gas exchange-wind speed relationship and the regional and seasonal differences in the air-water partial pressure of CO2 gradient (pCO(2)). The latter also controls the direction of the flux. Fluxes out of the ocean are influenced more by changes in the low-to-intermediate wind speed range, while ingassing is impacted more by changes in higher winds because of the regional correlations between wind and pCO(2). Gas exchange-wind speed parameterizations with a quadratic and third-order polynomial dependency on wind, each of which meets global constraints, are compared. The changes in air-sea CO2 fluxes resulting from wind speed trends are greatest in the equatorial Pacific and cause a 0.03-0.04PgCdecade(-1) increase in outgassing over the 27year time span. This leads to a small overall decrease of 0.00 to 0.02PgCdecade(-1) in global net CO2 uptake, contrary to expectations that increasing winds increase net CO2 uptake. Plain Language Summary The effects of changing winds are isolated from the total change in trends in global air-sea CO2 fluxes over the last 27years. The overall effect of increasing winds over time has a smaller impact than expected as the impact in regions of outgassing is greater than for the regions acting as a CO2 sink.

http://dx.doi.org/10.1002/2016gb005592

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