Interleaving of oxygenized intrusions into the Baltic Sea redoxcline
Interleaving of oxygenized intrusions into the Baltic Sea redoxcline
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DOI：
10.1002/lno.11317
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发表时间：
2019-09-16
影响因子：
4.5
通讯作者：
Umlauf, Lars
中科院分区：
文献类型：
--
作者：
Holtermann, Peter;Prien, Ralf;Umlauf, Lars
像波罗的海这样的半封闭边缘海通常具有永久缺氧的深层特征，因此可以作为重要的模式系统来研究预测的全球氧气最小带扩张的原因和后果。在这里，我们重点研究了侧向侵入体在维持波罗的海“缺氧过渡带”（HTZ）中的作用，该过渡带的特征是位于氧化表面层和硫化物深水区之间的准永久性缺氧区。基于在波罗的海中部的自主剖面系统的长期部署，我们发现含氧水中间侵入是普遍存在的特征，为高氧带提供了最重要的氧气来源，并在很大程度上控制了低氧区的垂直和横向范围。青藏高原的氧收支表明，青藏高原的氧周转首先是由沉积需氧量和侵入性氧气输入之间的长期平衡决定的。向下混合的氧进入高温赫兹区通常是不可忽略的，但不太可能对高温赫兹区氧收支提供一级贡献。在长期平均值上，中水侵入显示每年向永久盐跃层以下的深水区注入30-60 Gmol的氧气。这大约比大规模深水流入事件（主要波罗的海流入）期间输入的平均氧气量大一个数量级，这些事件发生在大约十年的时间尺度上，突出了HTZ作为生物地球化学转换的热点。
Semi-enclosed marginal seas like the Baltic Sea are often characterized by permanently anoxic deep layers, and may therefore serve as important model systems to study the causes and consequences of the predicted global expansion of oxygen minimum zones. Here, we focus on the role of lateral intrusions in maintaining the "hypoxic transition zone" (HTZ) of the Baltic Sea, which characterizes the quasi-permanent hypoxic region located between the oxygenized surface layer and the sulfidic deep-water region. Based on long-term deployments of an autonomous profiling system in the central Baltic Sea, we show that oxic mid-water intrusions are ubiquitous features, providing the most important oxygen source for the HTZ, and largely control the vertical and lateral extent of the hypoxic areas. An oxygen budget for the HTZ suggests that oxygen turnover in the HTZ is, to first order, determined by a long-term balance between sedimentary oxygen demand and oxygen import by intrusions. The downward mixing of oxygen into the HTZ is generally non-negligible but unlikely to provide a first-order contribution to the HTZ oxygen budget. On the long-term average, mid-water intrusions were shown to inject 30-60 Gmol of oxygen per year into the deep-water region below the permanent halocline. This is approximately one order of magnitude larger than the average amount of oxygen imported during the massive deep-water inflow events (Major Baltic Inflows) that occur on an approximately decadal time scale, highlighting the HTZ as a hotspot for biogeochemical turnover.