Turbulent mixing and hydraulic control of abyssal water in the Samoan Passage
Turbulent mixing and hydraulic control of abyssal water in the Samoan Passage
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DOI：
10.1002/grl.50684
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发表时间：
2013-09-16
影响因子：
5.2
通讯作者：
Klymak, Jody M.
中科院分区：
文献类型：
--
作者：
Alford, Matthew H.;Girton, James B.;Klymak, Jody M.
我们报告的第一个直接的湍流观测萨摩亚通道（SP），40公里宽的缺口在南太平洋测深通过流的大部分水供应北太平洋深海环流。观察到的湍流是典型深海水平的1000至10，000倍，足以完全混合进入通道的稠密水，证实了先前较粗糙的温度和盐度部分的推断。伴随的拖曳测量速度和温度的水平分辨率约为250米，表明占主导地位的过程负责的湍流。具体地说，水流在通道内的主槛处加速，达到0.55m s（-1）的速度。可以看到强烈的水力反应，地层首先上升以清除岩床，然后向下俯冲数百米。湍流是由于粘性流体下降时在其上方界面处的高剪切力以及形成于底坎下游的水跃引起的。除了主岩床之外，沿着沿着穿过萨摩亚海峡的多个互连通道的其他位置也对稠密水的混合有影响。事实上，在横向相隔几公里的海底特征处观察到了截然不同的水力反应和湍流水平，这表明深海混合敏感地取决于小尺度上的测深细节。
We report the first direct turbulence observations in the Samoan Passage (SP), a 40km wide notch in the South Pacific bathymetry through which flows most of the water supplying the North Pacific abyssal circulation. The observed turbulence is 1000 to 10,000 times typical abyssal levels strong enough to completely mix away the densest water entering the passageconfirming inferences from previous coarser temperature and salinity sections. Accompanying towed measurements of velocity and temperature with horizontal resolution of about 250m indicate the dominant processes responsible for the turbulence. Specifically, the flow accelerates substantially at the primary sill within the passage, reaching speeds as great as 0.55m s(-1). A strong hydraulic response is seen, with layers first rising to clear the sill and then plunging hundreds of meters downward. Turbulence results from high shear at the interface above the densest fluid as it descends and from hydraulic jumps that form downstream of the sill. In addition to the primary sill, other locations along the multiple interconnected channels through the Samoan Passage also have an effect on the mixing of the dense water. In fact, quite different hydraulic responses and turbulence levels are observed at seafloor features separated laterally by a few kilometers, suggesting that abyssal mixing depends sensitively on bathymetric details on small scales.