Interannual variation in summer N₂O concentration in the hypoxic region of the northern Gulf of Mexico, 1985-2007

다국어 초록 (Multilingual Abstract)

<P><p><strong>Abstract.</strong> Microbial nitrous oxide (N₂O) production in the ocean is enhanced under low-oxygen (O₂) conditions. This is especially important in the context of increasing hypoxia (i.e., oceanic zones with extremely reduced O₂ concentrations). Here, we present a study on the interannual variation in summertime nitrous oxide (N₂O) concentrations in the bottom waters of the northern Gulf of Mexico (nGOM), which is well-known as the site of the second largest seasonally occurring hypoxic zone worldwide. To this end we developed a simple model that computes bottom-water N₂O concentrations with a tri-linear ΔN₂O/O₂ relationship based on water-column O₂ concentrations, derived from summer (July) Texas-Louisiana shelf-wide hydrographic data between 1985 and 2007. &amp;Delta;N₂O (i.e., excess N₂O) was computed including nitrification and denitrification as the major microbial production and consumption pathways of N₂O. The mean modeled bottom-water N₂O concentration for July in the nGOM was 14.5 ± 2.3 nmol L⁻¹ (min: 11.0 ± 4.5 nmol L⁻¹ in 2000 and max: 20.6 ± 11.3 nmol L⁻¹ in 2002). The mean bottom-water N₂O concentrations were significantly correlated with the areal extent of hypoxia in the nGOM. Our modeling analysis indicates that the nGOM is a persistent summer source of N₂O, and nitrification is dominating N₂O production in this region. Based on the ongoing increase in the areal extent of hypoxia in the nGOM, we conclude that N₂O production (and its subsequent emissions) from this environmentally stressed region will probably continue to increase into the future.</p> </P>