7th National Oceanographic Conference and International Symposium of Zoological Society of Southern Africa

Thermal infra-red satellite imagery and ship-borne studies of ¹⁵N stable isotopes are used to provide a first estimate of the quantity of carbon exported from the Benguela upwelling system during summer 1983/84. From satellite imagery, a region where cold water of upwelling origin was present on a quasi-permanent basis and a more offshore region where the presence of such water was intermittent were designated. New production inside the 200 m isobath was excluded from the calculations because an unknown proportion of it may be recycled within the continental shelf system and would not therefore constitute export production and hence potential sequestration. Total production can be apportioned between new and regenerated production depending on the relative utilization of NO₃–N or NH₄–N and urea respectively. New production generally results from the input of NO₃–N to the euphotic zone via upwelling and/or turbulent diffusion and is the only portion of the total production which, in the long term, constitutes a carbon sink. This principle is modified to address the problem of possible new-production recycling on the continental shelf on short time-scales. Nitrate-uptake experiments conducted in the euphotic zone of aged upwelled and filament water throughout the Benguela yielded values of new production, and the mean of these data was applied to the appropriate areas identified by satellite imagery. New production off the continental shelf during summer 1983/84 attributable to upwelling-derived water was 2,14 × 10¹³ ± l,77 × 10¹³ g. An attempt is made to place this value in the context of new-production pathways in the Benguela.