在深渊中缓慢持续的混合
Slow persistent mixing in the abyss
摘要：
关于深海湍流混合和深海丘陵平原上的水流循环的知识，对于在湍流源预计相对较弱的地区建立沉积物再悬浮和扩散模型的量化过程十分重要。湍流可能会将深海人工采矿活动产生的沉积物分散到很远的地方。为了量化4000米深度左右的深底土上方的湍流混合，从近赤道东南太平洋（7°S，88°W）获得了高分辨率的系泊温度传感器观测结果。模型显示，该地区赤道气流动力学、内潮和表面近惯性运动活动性较低。目前的观测结果表明，在海底以上7米和406米之间的保守温差约为0.012°C（以下简称mab），这是绝热递减率的四分之一。浮力周期在6小时到1天之间的非常弱的分层水域允许缓慢变化的混合。计算的湍流耗散率值比远离海底地形和表面边界的公海湍流交换值大半到一个数量级。在深处，湍流翻转延伸到100米高，在海洋内部，也达到最低的传感器。翻转是由内部波剪切和对流。湍流惯性子区被观察到延伸到内波频带。相关的混合是不相关的底摩擦过程，但内波破碎和近惯性剪切。混合有利于悬浮沉积物的长时间（数小时到一天）和高浓度（超过100 mab）分散。
英文摘要：
Knowledge about deep-ocean turbulent mixing and flow circulation above abyssal hilly plains is important to quantify processes for the modelling of resuspension and dispersal of sediments in areas where turbulence sources are expected to be relatively weak. Turbulence may disperse sediments from artificial deep-sea mining activities over large distances. To quantify turbulent mixing above the deep-ocean floor around 4000 m depth, high-resolution moored temperature sensor observations have been obtained from the near-equatorial southeast Pacific (7°S, 88°W). Models demonstrate low activity of equatorial flow dynamics, internal tides and surface near-inertial motions in the area. The present observations demonstrate a Conservative Temperature difference of about 0.012°C between 7 and 406 meter above the bottom (hereafter, mab, for short), which is a quarter of the adiabatic lapse rate. The very weakly stratified waters with buoyancy periods between about six hours and one day allow for slowly varying mixing. The calculated turbulence dissipation rate values are half to one order of magnitude larger than those from open-ocean turbulent exchange well away from bottom topography and surface boundaries. In the deep, turbulent overturns extend up to 100 m tall, in the ocean-interior, and also reach the lowest sensor. The overturns are governed by internal-wave-shear and -convection. The turbulence inertial subrange is observed to extend into the internal wave frequency band. The associated mixing is not related to bottom friction processes but to internal wave breaking and near-inertial shear. The mixing facilitates long (hours to day) and high (exceeding 100 mab) dispersal of suspended sediments.
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