The Mississippi Bight, east of the Mississippi River, is a complex coastal ecosystem that, like the better-known Louisiana Shelf to the west, experiences seasonal bottom water hypoxia. However, input of allochthonous nutrients from the Mississippi River to the Mississippi Bight appears to be limited, begging the question of what drives seasonal hypoxia in this system. Prior research has suggested submarine groundwater discharge (SGD) could be an overlooked component of the Mississippi Bight biogeochemical system. We thus examined the hypothesis that SGD provides a “bottom up” driver for seasonal hypoxia in this area. We used a multi-tracer approach based on known SGD indicators (dissolved Ra, Ba, Si, methane) to: i) demonstrate the presence of SGD as a constituent contributor to Bight bottom waters, ii) constrain the SGD flux of macronutrients, and, iii) investigate the hypoxia-SGD linkage. We found excess SGD tracers in saline bottom waters relative to surface waters, suggesting a bottom source. Examination of other sources for the constituent enrichments besides SGD (e.g., rivers, produced waters from oil wells) appear inadequate to close the bottom water chemical mass balances. Additionally, inverse correlations between DO and SGD indicators in bottom waters support a common mechanism supplying dissolved Ra, Ba, and Si, and decreasing DO concentrations in these waters. Two different approaches to modeling the bottom water Ra distribution both suggest a seepage rate of ~0.055 m³ m⁻² d⁻¹, in line with previous estimates in similar systems. Our more complex model, involving four mass balances, suggests that as much as 10–20% of the bottom water in the Bight circulates through the underlying permeable sediments on a time scale of ~10 days. This circulated water emerges as SGD with completely altered chemistry. More specifically, SGD appears in some cases to be the dominant contributor of nutrients to Bight bottom waters. Additionally, the potential oxygen demand of reduced species within SGD likely contributes significantly to the development of seasonal hypoxia in Bight bottom waters. Further work is needed to better resolve sources of nutrients and additional reduced species within the Mississippi Bight SGD as well as the variability and pathways of this supply. Nonetheless, the bottom-up influence of SGD on the Mississippi Bight appears to be a significant and overlooked aspect of this system. We suggest that such a bottom-up influence may be a generally important feature of coastal ecosystems.

密西西比河以东的密西西比湾是一个复杂的沿海生态系统，与西边著名的路易斯安那大陆架一样，经历了季节性的底水缺氧。然而，从密西西比河到密西西比湾的外来养分输入似乎是有限的，这就引发了这个系统中季节性缺氧的驱动因素的问题。先前的研究表明，海底地下水排放 (SGD) 可能是密西西比湾生物地球化学系统中被忽视的一个组成部分。因此，我们检验了 SGD 为该地区季节性缺氧提供“自下而上”驱动因素的假设。我们使用了一种基于已知 SGD 指标（溶解Ra, Ba, Si, 甲烷) 以：i) 证明 SGD 作为 Bight 底水的成分贡献者的存在，ii) 限制大量营养素的 SGD 通量，以及，iii) 研究缺氧-SGD 联系。我们在含盐底水中发现了相对于地表水过量的 SGD 示踪剂，这表明底源。检查除 SGD 之外的其他成分富集来源（例如，河流、油井产出的水）似乎不足以关闭底部水的化学质量平衡。此外，底层水中 DO 和 SGD 指标之间的负相关支持提供溶解的 Ra、Ba 和 Si 以及降低这些水中 DO 浓度的共同机制。模拟底水 Ra 分布的两种不同方法都表明渗流率为 ~0.055 m ³  m⁻²  d ⁻¹，与之前在类似系统中的估计一致。我们更复杂的模型涉及四个质量平衡，表明在大约 10 天的时间尺度内，海湾中多达 10-20% 的底部水循环通过下面的可渗透沉积物。这种循环水以 SGD 的形式出现，其化学性质完全改变。更具体地说，在某些情况下，SGD 似乎是浅滩底水养分的主要贡献者。此外，SGD 内减少物种的潜在需氧量可能对湾底水域季节性缺氧的发展产生重大影响。需要进一步的工作来更好地解决密西西比湾 SGD 内的营养来源和其他减少的物种，以及这种供应的可变性和途径。尽管如此，新元对密西西比湾自下而上的影响似乎是该系统的一个重要且被忽视的方面。我们认为这种自下而上的影响可能是沿海生态系统的一个普遍重要的特征。