Topographic enhancement of vertical turbulent mixing in the Southern Ocean.
Topographic enhancement of vertical turbulent mixing in the Southern Ocean.
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DOI：
10.1038/ncomms14197
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发表时间：
2017-03-06
影响因子：
16.6
通讯作者：
Garabato AN
中科院分区：
文献类型：
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作者：
Mashayek A;Ferrari R;Merrifield S;Ledwell JR;St Laurent L;Garabato AN
跨越密度面的湍流混合是否足够大以在关闭海洋纬向翻转环流的深分支中起主导作用，这是一个悬而未决的问题。在南大洋进行的纵贯和等密度混合实验发现，从示踪剂的垂直扩散推断的湍流扩散率比从德雷克海峡平均示踪剂深度1 500米处的微结构剖面推断的湍流扩散率大一个数量级。使用高分辨率的海洋模式，它表明，快速垂直传播的示踪剂发生时，它与混合热点接触粗糙的地形。这种热点的稀疏性是由增强示踪剂在其附近的停留时间，由于向弱底流扩散。示踪剂停留时间的增加可以解释关闭深海环流所需的大量热盐垂直通量。粗糙地形特征附近的湍流混合被认为是深海环流闭合的关键。在这里，使用南大洋数据，作者表明，混合热点捕获流体并长时间混合，解释了相对较少的混合热点的全球影响。
It is an open question whether turbulent mixing across density surfaces is sufficiently large to play a dominant role in closing the deep branch of the ocean meridional overturning circulation. The diapycnal and isopycnal mixing experiment in the Southern Ocean found the turbulent diffusivity inferred from the vertical spreading of a tracer to be an order of magnitude larger than that inferred from the microstructure profiles at the mean tracer depth of 1,500 m in the Drake Passage. Using a high-resolution ocean model, it is shown that the fast vertical spreading of tracer occurs when it comes in contact with mixing hotspots over rough topography. The sparsity of such hotspots is made up for by enhanced tracer residence time in their vicinity due to diffusion toward weak bottom flows. The increased tracer residence time may explain the large vertical fluxes of heat and salt required to close the abyssal circulation. Turbulent mixing next to rough topographic features is believed to be key in the closure of the abyssal ocean circulation. Here, using Southern Ocean data, the authors show that mixing hotspots trap fluid and mix it for long periods, explaining the global impact of relatively few mixing hotspots.