A model study on the sensitivity of surface ocean CO₂ pressure with respect to the CO₂ gas exchange rate

Abstract. Rising CO₂ concentrations in the atmosphere and a changing climate are expected to alter the air-sea CO₂ flux through changes in the respective control factors for gas exchange. In this study we determine the sensitivity of the CO₂ fluxes on the gas transfer velocity using the MICOM-HAMOCC isopycnic carbon cycle model. The monthly generated MICOM-HAMOCC output data are suitable to investigate seasonal variabilities concerning the exchange of CO₂. In a series of 3 sensitivity runs the wind dependent gas exchange rate is increased by 44%, both in the northern and southern westerly regions, as well as in the equatorial area to investigate the effect of regional variations of the gas transfer rate on the air-sea fluxes and the distribution of the ocean surface pCO₂. For the period between 1948–2009, the results show that locally increasing gas transfer rates do not play an important role concerning the global uptake of carbon from the atmosphere. While effects on a global and annual scale are low, the regional and intra-annual variability shows remarkable variations in the gas fluxes and the surface pCO₂. An accurate quantification of the variable gas transfer velocity therefore provides a potential source to enhance model predictions over small spatial and temporal scales and to successfully reconcile model results on surface pCO₂ and air-sea CO₂ fluxes with observations.