Biogenic nitrogen gas production at the oxic–anoxic interface in the Cariaco Basin, Venezuela

Montes, E.; Altabet, M. A.; Muller-Karger, F. E.; Scranton, M. I.; Thunell, R. C.; Benitez-Nelson, C.; Lorenzoni, L.; Astor, Y. M.

Excess nitrogen gas (N 2xs) 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, N 2xs concentrations were below detection in surface waters, increasing to ~ 22 μmol N kg −1 at the oxic–anoxic interface ([O 2] < ~ 4 μmol kg −1, ~ 250 m). Below the oxic–anoxic interface (300–400 m), the average concentration of N 2xs 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., N 2xs 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 N 2xs 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.

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Montes, E. / Altabet, M. A. / Muller-Karger, F. E. / et al: Biogenic nitrogen gas production at the oxic–anoxic interface in the Cariaco Basin, Venezuela. 2013. Copernicus Publications.

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