Short-term patterns of vertical particle flux in northern Benguela: a comparison between sinking POC and respiratory carbon consumption

- We have described vertical carbon fluxes by two approaches on the shelf off the Namibian coast.
- One was a plankton respiration based-carbon flux model, while the other consisted on daily samplings by sediment traps.
- Either upwelling filaments or more oligotrophic waters influenced the study area.
- Differences between the two methods were attributed to differences in the sinking rates and community structure.
- The change in the contribution of zooplankton to the POC attenuation with distance to shore was also determined.

Short-term variability of vertical carbon flux (C-flux) was assessed by two approaches at two stations on the Namibian shelf upwelling system (20°S). The first approach was based on modeling water-column respiratory CO2 production (Fc) by integrating vertical profiles of the respiratory electron transport system. The second approach was based on automated sediment trap sampling daily. In both cases, temporal variability at the same station proved to be greater than the spatial variability between stations. Comparison of the two methods yielded higher C-flux values from the sediment traps in the presence of upwelling filaments (7.85 vs 3.67 mmol C m− 2 d− 1). Contrarily, in the post-filament stage of the upwelling system, the values from the Fc models were higher (1.43 vs 2.57 mmol C m− 2 d− 1). This difference was attributed to compositional changes in sinking particles and their settling velocities. In combination, both approaches served to increase current understanding of the short-term particle fluxes in this northern Benguela upwelling system. The Fc approach was further applied to zooplankton from the same area in order to quantify their importance in attenuating the particulate organic C-flux. This attenuation, as measured by fractional consumption of the primary productivity, ranged from 2% to 20%.