Abstract

GREGOR, Luke  and  MONTEIRO, Pedro M.S.. Is the southern Benguela a significant regional sink of CO₂?. S. Afr. j. sci. [online]. 2013, vol.109, n.5-6, pp.01-05. ISSN 1996-7489.

This study was undertaken to characterise the seasonal cycle of air-sea fluxes of carbon dioxide (CO₂) in the southern Benguela upwelling system off the South African west coast. Samples were collected from six monthly cross-shelf cruises in the St. Helena Bay region during 2010. CO₂ fluxes were calculated from pCO₂ derived from total alkalinity and dissolved inorganic carbon and scatterometer-based winds. Notwithstanding that it is one of the most biologically productive eastern boundary upwelling systems in the global ocean, the southern Benguela was found to be a very small net annual CO₂ sink of -1.4 ± 0.6 mol C/m² per year (1.7 Mt C/year). Regional primary productivity was offset by nearly equal rates of sediment and sub-thermocline remineralisation flux of CO₂, which is recirculated to surface waters by upwelling. The juxtaposition of the strong, narrow near-shore out-gassing region and the larger, weaker offshore sink resulted in the shelf area being a weak CO₂ sink in all seasons but autumn (-5.8, 1.4 and -3.4 mmol C/m² per day for summer, autumn and winter, respectively).

Keywords : southern Benguela; eastern boundary; carbon dioxide; CO₂; remineralisation.

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