Department of Earth, Ocean and Atmospheric Sciences, Florida State University, Tallahassee, FL, USA.
Center for Ocean-Atmospheric Prediction Studies, Florida State University, Tallahassee, FL, USA.
Nat Commun. 2021 Jun 3;12(1):3325. doi: 10.1038/s41467-021-23678-9.
In contrast to its productive coastal margins, the open-ocean Gulf of Mexico (GoM) is notable for highly stratified surface waters with extremely low nutrient and chlorophyll concentrations. Field campaigns in 2017 and 2018 identified low rates of turbulent mixing, which combined with oligotrophic nutrient conditions, give very low estimates for diffusive flux of nitrate into the euphotic zone (< 1 µmol N m d). Estimates of local N-fixation are similarly low. In comparison, measured export rates of sinking particulate organic nitrogen (PON) from the euphotic zone are 2 - 3 orders of magnitude higher (i.e. 462 - 1144 µmol N m d). We reconcile these disparate findings with regional scale dynamics inferred independently from remote-sensing products and a regional biogeochemical model and find that laterally-sourced organic matter is sufficient to support >90% of open-ocean nitrogen export in the GoM. Results show that lateral transport needs to be closely considered in studies of biogeochemical balances, particularly for basins enclosed by productive coasts.
与生产力较高的沿海边缘不同，开阔的墨西哥湾（GoM）以高度分层的地表水为特征，其营养物质和叶绿素浓度极低。2017 年和 2018 年的实地考察确定了低湍动混合率，再加上贫营养条件，导致硝酸盐向透光带的扩散通量极低（<1µmol N m d）。对局部固氮的估计也同样较低。相比之下，从透光带下沉颗粒有机氮（PON）的测量输出率要高 2-3 个数量级（即 462-1144µmol N m d）。我们根据遥感产品和区域生物地球化学模型独立推断的区域尺度动态，对这些差异显著的发现进行了协调，发现侧向来源的有机物质足以支撑 GoM 中超过 90%的开阔海域氮输出。结果表明，在生物地球化学平衡的研究中，特别是在被生产力较高的海岸包围的盆地中，侧向运输需要密切考虑。
