Seasonal and mesoscale variability of oceanic transport of anthropogenic CO2

Z. Lachkar (1) , J. Orr (1) , J.-C. Dutay (1, 2)

1 LSCE - Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette]
2 CLIM - Modélisation du climat

Estimates of the ocean's large-scale transport of anthropogenic CO 2 are based on one-time hydrographic sections, but the temporal variability of this transport has not been investigated. The aim of this study is to evaluate how the seasonal and mesoscale variability affect data-based estimates of anthropogenic CO 2 transport. To diagnose this variability, we made a global anthropogenic CO 2 simulation using an eddy-permitting version of the coupled ocean seaice model ORCA-LIM. As for heat transport, the seasonally varying transport of anthropogenic CO 2 is largest within 20 • of the equator and shows secondary maxima in the subtropics. Ekman transport generally drives most of the seasonal variability, but the contribution of the vertical shear becomes important near the equator and in the Southern Ocean. Mesoscale variabilty contributes to the annual-mean transport of both heat and anthropogenic CO 2 with strong poleward transport in the Southern Ocean and equatorward transport in the tropics. This "rectified" eddy transport is largely baroclinic in the tropics and barotropic in the Southern Ocean due to a larger contribution from standing eddies. Our analysis revealed that most previous hydrographic estimates of meridional transport of anthropogenic CO 2 are severely biased because they neglect temporal fluctuations due to non-Ekman velocity variations. In each of the three major ocean basins, this bias is largest near the equator and in the high southern latitudes. In the subtropical North Atlantic, where most of the hydrographic-based estimates have been focused, this uncertainty represents up to 20% and 30% of total merid

Domaines: Océan, Atmosphère; Interfaces continentales, environnement

Z. Lachkar, J. Orr, J.-C. Dutay. Seasonal and mesoscale variability of oceanic transport of anthropogenic CO2. Biogeosciences, 2009, 6 (11), pp.2509-2523. ⟨10.5194/bg-6-2509-2009⟩. ⟨hal-03096727⟩