Collaborative Research: Mixing, Flow and Hydrography in the Rift Valley of the Lucky Strike Segment (37:20N, Mid-Atlantic Ridge)

观测证据表明，深渊中相当大一部分的潜流浮力通量发生在海底山谷中，例如在缓慢扩张的洋中脊两侧形成波纹状的数千个峡谷，以及轴向裂谷。在水文学和动力学上，这些深谷中的许多都是相似的，强烈的潮汐速度叠加在沿山谷密度梯度向下的低频流上。深水流混合的作用，导致相应的密集水沿山谷平流的准稳定平均状态平衡。然而，为了参数化机械混合对水性质和动力学的影响，必须知道潜在的过程。人们提出了两种不同的过程来解释在粗糙地形附近观察到的高混合现象：破碎的潮汐强迫内波，以及跨越山岩的溢出。然而，仅有的来自深海山谷的现有微观结构（混合）数据集的水平分辨率不足以确定这两个过程对混合预算的相对贡献；特别是，在技能附近没有可用的微观结构剖面。在这项研究中，哥伦比亚大学和佛罗里达州立大学的研究人员将使用CTD、LADCP和微观结构剖面仪，在Lucky Strike段（37 N，中大西洋脊）的裂谷进行水文、速度和混合测量。由两个平行基台连接的两个深盆地是Lucky Strike段裂谷的特征。在整个勘探过程中，将对基岩和深盆地进行采样，并使用底部安装的ADCP监测基岩附近的速度场。目前，可用的数据表明有很强的潮汐速度，以及低频水流穿过浅滩。从这项工作中收集的结果将阐明和量化Lucky Strike段的水文、环流和混合的主要模式，并确定已提出的不同过程的相对贡献，以解释强混合和粗糙地形之间的关联。这些信息对于在数值模式（例如用于气候研究的数值模式）中实际混合参数化方面取得进展是有价值的。除了一名研究生的参与外，更广泛的影响还包括可能使用这些数据来调查Lucky Strike热液喷口附近的平流和涡流扩散扩散，这是正在进行的大西洋中脊国际监测工作（MoMAR项目）的主要焦点。

Observational evidence suggests that a significant portion of the diapycnal buoyancy fluxes in the abyss take place in sub- marine valleys, such as the thousands of canyons that corrugate the flanks of slow-spreading mid-ocean ridges, as well as the axial rift valleys. Hydrographically and dynamically, many of these deep valleys are similar, with strong tidal velocities superimposed on low-frequency flows down along-valley density gradients. The effects of diapycnal mixing, leading to a quasi-steady mean state balance the corresponding along-valley advection of dense water. However, in order to parameterize the effects of mechanical mixing on the water properties and dynamics, the underlying processes must be known. Two different processes have been proposed to account for the observations of elevated mixing near rough topography: breaking tidally forced internal waves, and overflows across sills. However, the only existing microstructure (mixing) data set from an abyssal valley is of insufficient horizontal resolution to determine the relative contributions of the two processes to the mixing budget; in particular, there are no microstructure profiles available in the vicinity of sills.In this study, researchers at Columbia University and Florida State University will perform a hydrographic, velocity and mixing survey in the rift valley of the Lucky Strike segment (37 N, Mid-Atlantic Ridge), using CTD, LADCP and microstructure profilers. Two deep basins connected by two parallel sills characterize the rift valley of the Lucky Strike segment. Both sills and deep basins will be sampled and the near-sill velocity field will be monitored throughout the survey using a bottom-mounted ADCP. Currently, available data indicate strong tidal velocities, as well as low-frequency flows across the sills. The results gathered from this work will elucidate and quantify the dominant patterns of the hydrography, circulation and mixing in the Lucky Strike segment and determine the relative contributions of different processes that have been proposed to account for the association between strong mixing and rough topography. This information will be of value for making progress toward realistic mixing parameterizations for inclusion in numerical models, e.g. those used for climate research. In addition to the involvement of a graduate student, the broader impacts also include the potential use of the data to investigate advective and eddy diffusive dispersal near the Lucky Strike hydrothermal vent field, which is the main focus of an on-going inter- national monitoring effort on the Mid-Atlantic Ridge (the MoMAR project).