Impact of submesoscale variability in estimating the air-sea CO2 exchange: Results from a model study of the POMME experiment

A high-resolution ocean biogeochemical model is used to estimate oceanic pCO(2) and air-sea CO2 flux in the NE Atlantic. The model is validated against shipboard and Carioca drifting float data acquired during the POMME experiment. Between winter and spring, the seasonal variability is characterized by a rapid drawdown of pCO(2) of similar to 20 mu atm associated with the phytoplankton bloom driving CO2 uptake by the ocean. The model reveals that this uptake propagates northward in response to the northward propagation of the bloom. More remarkably, this study demonstrates intense variability of the carbon system at the submesoscale. Our model predicts filamentary structures of pCO(2) that show gradients of 25 mu atm over 20 km, consistent with observations from Carioca drifting floats. This submesoscale variability is similar in magnitude to the mean seasonal drawdown. Lagrangian diagnostics suggest that pCO(2) small-scale structures are shaped by horizontal stirring of large-scale gradients created by the bloom northward propagation. We compared air-sea flux derived from model pCO(2) and from observed pCO(2) and estimated the error due to data undersampling to similar to 15 to 30%. Results from a simulation at coarser resolution showed that the impact of model resolution on air-sea CO2 flux is only similar to 5%. This suggests that the submesoscale variability of pCO(2), although large in amplitude, accounts for small modulation of the net air-sea CO2 flux in this region. Citation: