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，深渊中浮力通量的很大一部分发生在海底山谷中，例如在缓慢扩展的大洋中脊两侧形成波纹的数千个峡谷，以及轴向裂谷。在水文和动力方面，许多这些深谷都是相似的，强大的潮汐速度叠加在沿着山谷密度梯度向下的低频水流上。昼夜混合的影响，导致准稳定的平均状态，平衡了相应的沿山谷的稠密水平流。然而，为了对机械混合对水的性质和动力学的影响进行参数化，必须知道潜在的过程。对于观测到的粗糙地形附近的高空混合，人们提出了两个不同的过程：潮汐强迫内波的破裂和跨越门槛的溢流。然而，现有的唯一一组来自深海山谷的微结构(混合)数据不足以确定这两个过程对混合预算的相对贡献；特别是在井眼附近没有可用的微结构剖面。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和微结构剖面仪在Lucky Strike段(37 N，中大西洋海脊)的裂谷进行水文、速度和混合调查。两个由两个平行的基岩连接的深盆地构成了幸运打击段的裂谷。将对基准线和深盆地进行采样，并使用底部安装的ADCP在整个调查过程中监测近基准线的速度场。目前，现有数据表明潮汐速度很强，而且有低频率的水流流过门槛。这项工作收集的结果将阐明和量化幸运打击段的水文、环流和混合的主要模式，并确定已提出的解释强混合和粗糙地形之间联系的不同过程的相对贡献。这些信息将有助于在实际的混合参数化方面取得进展，以便包括在数值模式中，例如用于气候研究的模式。除了一名研究生的参与，更广泛的影响还包括可能利用这些数据调查Lucky Strike热液喷口附近的平流和涡流扩散扩散，这是正在进行的中大西洋海脊国际监测工作(Momar项目)的主要重点。

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).