Impact of the Madden-Julian Oscillation on Air-Sea CO2 Fluxes

Two global air-sea CO2 flux datasets are analyzed to understand the impacts of the Madden-Julian oscillation (MJO) on oceanic CO2 fluxes. Global CO2 fluxes are composited using standard realtime multivariate MJO indices (RMM; Wheeler and Hendon, 2004) for each of eight MJO phases. Integrating phase-averaged CO2 flux across all eight phases yields the MJO contribution to the annual mean air-sea CO2 exchange. The MJO positively contributes to East Pacific ocean-to-atmosphere CO2 flux throughout the year. At higher latitudes, circulation anomalies driven by the teleconnection response to tropical MJO heating oppose (promote) atmosphere-to-ocean CO2 fluxes during the May-October (November-April) season. Locally, MJO-driven CO2 fluxes can account for up to ~10% of the annual mean and 25% of total variance of CO2 flux.

CO2 flux variability is further explored by comparing relative contributions from synoptic scale disturbances, intraseasonal (i.e., MJO-like) variability, the annual cycle, and low-frequency disturbances. Tropical air-sea CO2 fluxes are driven by variability across all timescales. Northern and Southern Hemisphere high-latitude fluxes are particularly sensitive to high-frequency and low-frequency disturbances. The MJO is known to interact with low-frequency disturbances and to regulate the global intensity of synoptic scale disturbances. Most modern general circulation models poorly simulate the MJO, thereby missing its contributions to global air-sea CO2 flux. This missing mode of air-sea CO2 exchange may lead to accumulated errors in simulations of gradually increasing atmospheric CO2 concentrations.