Biogenic nitrogen gas production at the oxic–anoxic interface in the Cariaco Basin, Venezuela
- 1College of Marine Science, University of South Florida, St. Petersburg, Florida, USA
- 2School of Marine Science and Technology, University of Massachusetts Dartmouth, New Bedford, Massachusetts, USA
- 3School of Marine and Atmospheric Science, Stony Brook University, Stony Brook, New York, USA
- 4Marine Science Program & Department of Earth and Ocean Sciences, University of South Carolina, Columbia, South Carolina 29208, USA
- 5Estación de Investigaciones Marinas de Margarita, Fundación La Salle de Ciencias Naturales, Apartado 144, Porlamar, Estado Nueva Esparta, Venezuela
Abstract. Excess nitrogen gas (N2xs) was measured in samples collected at six locations in the eastern and western sub-basins of the Cariaco Basin, Venezuela, in September 2008 (non-upwelling conditions) and March 2009 (upwelling conditions). During both sampling periods, N2xs concentrations were below detection in surface waters, increasing to ~ 22 μmol N kg−1 at the oxic–anoxic interface ([O2] < ~ 4 μmol kg−1, ~ 250 m). Below the oxic–anoxic interface (300–400 m), the average concentration of N2xs was 24.7 ± 1.9 μmol N kg−1 in September 2008 and 27.5 ± 2.0 μmol N kg−1 in March 2009, i.e., N2xs concentrations within this depth interval were ~ 3 μmol N kg−1 higher (p < 0.001) during the upwelling season compared to the non-upwelling period. These results suggest that N-loss in the Cariaco Basin may vary seasonally in response to changes in the flux of sinking particulate organic matter. We attribute the increase in N2xs concentrations, or N-loss, observed during upwelling to: (1) higher availability of fixed nitrogen derived from suspended and sinking particles at the oxic–anoxic interface and/or (2) enhanced ventilation at the oxic–anoxic interface during upwelling.