Turbulent mixing in the ocean exerts an important control on the rate and structure of the overturning circulation. However, the balance of processes underpinning this mixing is subject to significant uncertainties, limiting our understanding of the overturning’s deep upwelling limb. Here, we investigate the hitherto primarily neglected role of tens of thousands of seamounts in sustaining deep-ocean upwelling. Dynamical theory indicates that seamounts may stir and mix deep waters by generating lee waves and topographic wake vortices. At low latitudes, stirring and mixing are predicted to be enhanced by a layered vortex regime in the wakes. Using three realistic regional simulations spanning equatorial to middle latitudes, we show that layered wake vortices and elevated mixing are widespread around seamounts. We identify scalings that relate mixing rate within seamount wakes to topographic and hydrographic parameters. We then apply such scalings to a global seamount dataset and an ocean climatology to show that seamount-generated mixing makes an important contribution to the upwelling of deep waters. Our work thus brings seamounts to the fore of the deep-ocean mixing problem and urges observational, theoretical, and modeling efforts toward incorporating the seamounts’ mixing effects in conceptual and numerical ocean circulation models.

中文翻译：

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海山通过湍流混合在深海海水上涌中的作用


海洋中的湍流混合对翻转环流的速率和结构具有重要的控制作用。然而，支撑这种混合的过程的平衡受到很大的不确定性的影响，限制了我们对倾覆深层上升流边缘的理解。在这里，我们调查了数以万计的海山在维持深海上升流方面迄今为止主要被忽视的作用。动力学理论表明，海山可能通过产生背风波和地形尾涡来搅动和混合深水。在低纬度地区，尾流中的分层涡流状态预计会增强搅拌和混合。通过跨越赤道到中纬度的三个真实区域模拟，我们表明分层尾流涡和增强混合在海山周围广泛存在。我们确定了将海山尾迹内的混合率与地形和水文参数相关的比例。然后，我们将这种缩放应用于全球海山数据集和海洋气候学，以表明海山产生的混合对深水上升流做出了重要贡献。因此，我们的工作将海山带到了深海混合问题的前沿，并敦促观测、理论和建模工作将海山的混合效应纳入概念和数值海洋环流模型中。