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

[摘要] Excess nitrogen gas (N₂^xs) was measured in samples collected atsix 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, N₂^xsconcentrations 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). Belowthe oxic–anoxic interface (300–400 m), the average concentration ofN₂^xs was 24.7 ± 1.9 μmol N kg⁻¹ inSeptember 2008 and 27.5 ± 2.0 μmol N kg⁻¹ in March2009, i.e., N₂^xs concentrations within this depth interval were~ 3 μmol N kg⁻¹ higher (p < 0.001) during theupwelling season compared to the non-upwelling period. These results suggestthat N-loss in the Cariaco Basin may vary seasonally in response to changesin the flux of sinking particulate organic matter. We attribute the increasein N₂^xs concentrations, or N-loss, observed during upwelling to:(1) higher availability of fixed nitrogen derived from suspended and sinkingparticles at the oxic–anoxic interface and/or (2) enhanced ventilation at theoxic–anoxic interface during upwelling.

[学科分类] 地球化学与岩石