The Bay of Bengal hosts persistent, measurable, but sub-micromolar, concentrations of oxygen in its oxygen-minimum zone (OMZ). Such low-oxygen conditions are not necessarily rare in the global ocean and seem also to characterize the OMZ of the Pescadero Basin in the Gulf of California, as well as the outer edges of otherwise anoxic OMZs, such as can be found, for example, in the Eastern Tropical North Pacific. We show here that biological controls on oxygen consumption are required to allow the semistable persistence of low-oxygen conditions in OMZ settings; otherwise, only small changes in physical mixing or rates of primary production would drive the OMZ between anoxic and oxic states with potentially large swings in oxygen concentration. We propose that two controls are active: an oxygen-dependent control on oxygen respiration and an oxygen inhibition of denitrification. These controls, working alone and together, can generate low-oxygen concentrations over a wide variability in ocean mixing parameters. More broadly, we discuss the oxygen regulation of organic matter cycling and N2 production in OMZ settings. Modern biogeochemical models of nitrogen and oxygen cycling in OMZ settings do contain some of the parameterizations that we explore here. However, these models have not been applied to understanding the persistence of low, but measurable, concentrations of oxygen in settings like the Bay of Bengal, nor have they been applied to understanding what biological/physical processes control the transition from a weakly oxygenated state to a “functionally” anoxic state with implications for nitrogen cycling. Therefore, we believe that the approach here illuminates the relationship between oxygen and the biogeochemical cycling of carbon and nitrogen in settings like the Bay of Bengal. Furthermore, we believe that our results could further inform large-scale ocean models seeking to explore how global warming might influence the spread of low-oxygen waters, influencing the cycles of oxygen, carbon, and nitrogen in OMZ settings.

中文翻译：

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海洋缺氧区氧气浓度调节

孟加拉湾在其最低氧区 (OMZ) 中拥有持久的、可测量的但亚微摩尔浓度的氧气。这种低氧条件在全球海洋中不一定罕见，似乎也是加利福尼亚湾佩斯卡德罗盆地 OMZ 的特征，以及其他缺氧 OMZ 的外边缘，例如可以发现，在东热带北太平洋。我们在这里表明，需要对耗氧量进行生物控制，以允许 OMZ 环境中低氧条件的半稳定持续存在；否则，只有物理混合或初级生产速率的微小变化才会驱动 OMZ 在缺氧和有氧状态之间，氧浓度可能会有很大的波动。我们建议激活两个控件：氧呼吸的氧依赖控制和反硝化的氧抑制。这些控制单独或一起工作，可以在海洋混合参数的广泛变化中产生低氧浓度。更广泛地说，我们讨论了 OMZ 环境中有机物质循环和 N2 产生的氧调节。OMZ 设置中氮和氧循环的现代生物地球化学模型确实包含我们在此处探索的一些参数化。然而，这些模型并未用于了解在孟加拉湾等环境中低但可测量的氧气浓度的持续性，也未用于了解哪些生物/物理过程控制着从弱含氧状态到对氮循环有影响的“功能性”缺氧状态。所以，我们相信这里的方法阐明了在孟加拉湾等环境中氧气与碳和氮的生物地球化学循环之间的关系。此外，我们相信我们的结果可以进一步为大型海洋模型提供信息，以探索全球变暖如何影响低氧水域的扩散，影响 OMZ 环境中的氧、碳和氮循环。