While the occurrence of seasonal bottom hypoxia in the Northern Gulf of Mexico is an extensively studied subject, most research effort has been put on understanding and quantifying hypoxic extent, and little is known about internal variability and short‐term shifts. We use a realistic hydrodynamic model with a simple oxygen parametrization to demonstrate that hypoxia development in the far‐field of the Mississippi plume is subject to physical processes with spatial scales ranging from (10) to (100 km) and temporal scales from the near‐inertial period to seasonality. We use a budget decomposition of the oxygen equation to explore patterns. The mean spatial structure of the local rate of change reveals features shaped as oxygen loss rings enclosing oxygenation cores. This structure is mainly a balance between net advection (horizontal and vertical) and sediment oxygen demand. In terms of temporal variability, we found a large near‐inertial signal in advection, following a convergence‐divergence pattern, at all spatial scales, and a strong subinertial signal at smaller scales only. Variability in advection increases with decreasing temporal and spatial scales, consistently with a field rich in instabilities introducing small‐scale, strong anomalies. Through a Reynolds decomposition of the budget, we separate anomalies from the main flow and identify the total vertical perturbation flux as the primary counterbalance to sediment oxygen demand during periods when the hypoxic extent is maintained or destroyed. Vertical flux anomalies manifest as bottom water intrusions into the mid water column, which have been captured by high‐resolution observations.

中文翻译：

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墨西哥北部湾底部氧气的小范围变异性

尽管墨西哥湾北部季节性底部缺氧的发生是一个广泛研究的课题，但大多数研究工作都集中在对缺氧程度的理解和量化上，而对内部变异性和短期变化知之甚少。我们使用具有简单氧参量的现实流体力学模型来证明密西西比羽流远场中的低氧发展受物理过程的影响，其空间尺度范围为（10）至（100 km）和从近惯性时期到季节性的时间尺度。我们使用氧方程的预算分解来探索模式。局部变化率的平均空间结构揭示了一些特征，这些特征的形状是围绕着氧合核心的氧损失环。这种结构主要是净对流（水平和垂直）与沉积物需氧量之间的平衡。就时间变化而言，我们发现在所有空间尺度上，遵循对流-发散模式，在平流中发现了一个大的近惯性信号，而在较小尺度上发现了一个强的亚惯性信号。对流变化随时间和空间尺度的减小而增加，这与不稳定的领域一致，引入了小范围的强异常。通过雷诺预算分解，我们将异常与主流分开，并确定总的垂直扰动通量是维持或破坏低氧程度期间沉积物需氧量的主要平衡。垂直通量异常表现为底部水侵入中水柱，这已被高分辨率观测所捕获。