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

[摘要] Microbial nitrous oxide (N₂O) production in the ocean is enhanced underlow-oxygen (O₂) conditions. This is especially important in the contextof increasing hypoxia (i.e., oceanic zones with extremely reduced O₂concentrations). Here, we present a study on the interannual variation insummertime nitrous oxide (N₂O) concentrations in the bottom waters ofthe northern Gulf of Mexico (nGOM), which is well-known as the site of thesecond largest seasonally occurring hypoxic zone worldwide. To this end wedeveloped a simple model that computes bottom-water N₂O concentrationswith a tri-linear ΔN₂O/O₂ relationship based onwater-column O₂ concentrations, derived from summer (July)Texas–Louisiana shelf-wide hydrographic data between 1985 and 2007. ΔN₂O (i.e., excess N₂O) was computed including nitrification anddenitrification as the major microbial production and consumption pathways ofN₂O. The mean modeled bottom-water N₂O concentration for July inthe 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 N₂Oconcentrations were significantly correlated with the areal extent of hypoxiain the nGOM. Our modeling analysis indicates that the nGOM is a persistentsummer source of N₂O, and nitrification is dominating N₂Oproduction in this region. Based on the ongoing increase in the areal extentof hypoxia in the nGOM, we conclude that N₂O production (and itssubsequent emissions) from this environmentally stressed region will probablycontinue to increase into the future.

[学科分类] 地球化学与岩石