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MEPS prepress abstract   -  DOI:

Benthic oxygen fluxes in a coastal upwelling system (Ria de Vigo, NW Iberia) measured by aquatic eddy covariance

M. Amo-Seco*, C. G. Castro, N. Villacieros-Robineau, F. Alonso-Pérez, R. Graña, G. Rosón, P. Berg

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ABSTRACT: Organic carbon mineralization and nutrient cycling in benthic environments are critically important for their biogeochemical functioning, but poorly understood in coastal upwelling systems. The main objective of this study was to determine benthic oxygen fluxes in a muddy sediment in the Ria de Vigo (NW Iberian coastal upwelling), by applying the aquatic eddy covariance (AEC) technique during two campaigns in different seasons (June & October 2017). The main drivers of benthic fluxes were studied and compared among days in each season and between seasons. The two campaigns were characterized by an upwelling-relaxation period followed by a downwelling event, the last one due to the extratropical cyclone, Ophelia, in October. The mean seasonal benthic oxygen fluxes were not significantly different for the two campaigns despite differences in hydrodynamic and biogeochemical conditions (June: –20.9 ± 7.1 mmol m–2 d–1 vs. October: –26.5 ± 3.1 mmol m–2 d–1). Benthic fluxes were controlled by different drivers depending on the season. June was characterized by sinking labile organic material, which enhanced benthic fluxes in the downwelling event, whereas October had a significantly higher bottom velocity that stimulated the benthic fluxes. Finally, a comparison with a large benthic chamber (0.50 m2) was made during October. Despite methodological differences between AEC and chamber measurements, concurrent fluxes agreed within an acceptable margin (AEC: benthic chamber ratio = 0.78 ± 0.13; mean ± SD). Bottle incubations of water sampled from the chamber interior indicated that mineralization could explain this difference. These results show the importance of using non-invasive techniques as AEC to resolve benthic flux dynamics.