Multiscale Temporal Variability of the Global Air‐Sea CO 2 Flux Anomaly

The global air-sea CO2 flux (F) impacts and is impacted by a plethora of climate-related processes operating at multiple time scales. In bulk mass transfer formulations, F is driven by physico- and bio-chemical factors such as the air-sea partial pressure difference ( increment pCO(2)), gas transfer velocity, sea surface temperature, and salinity-all varying at multiple time scales. To de-convolve the impact of these factors on variability in F at different time scales, time-resolved estimates of F were computed using a global data set assembled between 1988 and 2015. The F anomalies were defined as temporal deviations from the 28-year time-averaged value. Spectral analysis revealed four dominant timescales of variability in F-subseasonal, seasonal, interannual, and decadal with relative amplitude differences varying across regions. A second-order Taylor series expansion was then conducted along these four timescales to separate drivers across differing regions. The analysis showed that on subseasonal timescales, wind speed variability explains some 66% of the global F anomaly and is the dominant driver. On seasonal, interannual, and decadal timescales, the increment pCO(2) effect controlled by the increment pCO(2) anomaly, explained much of the F anomaly. On decadal timescales, the F anomaly was almost entirely governed by the increment pCO(2) effect with large contributions from high latitudes. The main drivers across timescales also dominate the regional F anomaly, particularly in the mid-high latitude regions. Finally, the driver of the increment pCO(2) effect was closely connected with the relative strength of atmospheric pCO(2) and the nonthermal component of oceanic pCO(2) anomaly associated with dissolved inorganic carbon and alkalinity