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，深海底环浮力通量的很大一部分发生在海底山谷，例如覆盖在缓慢扩张的洋中脊两侧的数千个峡谷，以及轴向裂谷。从水文和动力学的角度来看，这些深谷中的许多都是相似的，沿着山谷密度梯度，低频流动上叠加了强烈的潮汐速度。导致准定常平均状态的横涡混合的影响平衡了相应的浓水沿谷平流。然而，为了参数化机械混合对水的性质和动力学的影响，必须知道的基本过程。两种不同的过程已被提出来解释观测到的高混合附近粗糙的地形：打破潮汐强迫内波，和溢出的窗台。然而，来自深海谷的唯一现有微结构（混合）数据集的水平分辨率不足以确定这两个过程对混合收支的相对贡献;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进行水文测量，利用CTD、LADCP和微结构剖面仪，对Lucky Strike段（北纬37度，大西洋中脊）的裂谷进行了速度和混合测量。由两个平行岩床连接的两个深盆地是好彩段裂谷的特征。在整个勘测过程中，将对底床和深盆地进行采样，并使用底部安装的ADCP监测近底床速度场。目前，现有的数据表明，潮汐速度很强，以及低频流动的门槛。 从这项工作中收集的结果将阐明和量化的主要模式的水文，流通和混合的好彩段，并确定不同的过程，已被提议占强混合和粗糙的地形之间的关联的相对贡献。 这一信息将有助于在现实的混合参数化方面取得进展，以便纳入数值模式，例如用于气候研究的数值模式。 除了一名研究生的参与外，更广泛的影响还包括可能利用这些数据调查Lucky Strike热液喷口区附近的平流和涡流扩散，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).