CO2 fluxes in the South African Coastal Region

Abstract

Surface water and atmospheric fugacity of carbon dioxide (fCO2) parameters were measured in the South African Coastal Region (18º25’E ̶ 31º25’E) using volunteer observing ships (VOS) equipped with an automated underway xCO2 system. The ships operated along the QUIMA-VOS line in two different periods (2005-2008 and 20112012) and provided 16 records. From west to east the vessel track crossed three regions with different oceanographic conditions characterized by boundary currents and upwelling cells. Seasonal cycles of sea surface temperature (SST) and fCO2 integrated over each 0.5º presented a stable behavior with maximum values during Austral summer and minimum values during Austral winter related with climatological annual variability. fCO2 distribution showed saturated areas close to Cape Town, Port Alfred and, occasionally, Durban that acted as a CO2 source related with upwelling process. The area visited by the VOS line highlighted that this coastal region acted a sink of CO2 (mean ΔfCO2=fCO2,sw ̶ fCO2,atm =-33.05±34.07 μatm). The interannual changes from 2005 to 2012 indicate that surface temperature decreased while fugacity increased over that period.