An Investigation of Abyssal Mixing and Interior Transports in the North Atlantic

目前为绘制大西洋经向翻转环流的定量图景所作的努力主要侧重于西部边界流系统和北海浮力丧失形成的水团的输送。相比之下，内部深海环流的结构和强度及其浮力增益的采样很差，也不知道太多细节。然而，这些对全球海洋环流和海洋质量、热量和示踪剂的预算至关重要。将进行一项进程研究，以提供深海混合和环流的定量估计，以评估北大西洋内部深海环流水平和垂直部分之间的强度和联系。对气候特征场的分析表明，实现这一目标的合理区域位于百慕大隆起东侧及其东南部的地形盆地。有几条证据表明，这些内部流动是高度结构化和非常活跃的，这意味着，为它们提供食物的昼夜混合特别强烈。该源区位于大西洋中脊(MAR)的西侧，那里崎岖的地形为混合提供了有利的条件。该项目由两部分组成：1)一组系泊剖面仪，旨在测量百慕大隆起东南侧的地转输送，这是内部环流的主要通道；2)船上调查，以获得微结构和速度分布，以及详细的水深测量。这些将被用来建立对一系列地形特征的湍流浮力通量的估计，并描述整个盆地的昼夜强迫场。智力价值拟议的实验的每个组成部分将提供对内陆深海的一个不能量化的部分的直接测量，即沿百慕大海隆的水平流动的结构和强度，以及为这些流动提供补给的昼夜强迫。总之，它们将为评估观测到的环流和基本动力学理论之间的一致性提供一个基础。对内陆盆地的这种关注将补充和补充AMOC新出现的定量图景。具体地说，该过程研究将完成以下工作：1量化百慕大隆起中深部内部流场的结构、强度和变异性。诊断北方(高示踪剂浓度和低营养物质)和南方(低示踪剂浓度和高营养物质)来源对这些流动的相对贡献。2评估供给内部流场的湍流混合的区域结构和强度。3评估观测到的垂直通量和水平通量的大小之间的一致性。4从温度和密度类的不同测量方案合成输送，以构建北大西洋西部盆地冷暖翼转换和深海环流的体积通量收支。广泛影响这一过程的研究和合成结果将为海洋同化和再分析产品的评估提供基准。目前的海洋模式和分析产品都没有显示出4000m以下的结构。大气环流模式中的深海地转流场在加入日周期混合的真实表示时被证明是显著改善的。这项工作将为为海洋模式测试和使用而设计的昼夜强迫动力参数化提供地区性约束。最后，该项目将为学生提供实地参与和分析观测数据的机会。

Ongoing efforts to develop a quantitative picture of the Atlantic meridional overturning circulation (AMOC) have largely focused on the western boundary current system and transports of water masses formed by buoyancy loss in the northern seas. By contrast, the structure and strength of the interior abyssal circulation and its buoyancy gain have been poorly sampled and are not known in much detail. These are, however, fundamentally important to the global ocean circulation and to ocean budgets of mass, heat and tracers. A process study will be conducted to provide quantitative estimates of abyssal mixing and circulation in order to assess the strength of, and linkages between, the horizontal and vertical components of the North Atlantic interior abyssal circulation. Analysis of climatological property fields suggests that a logical region to accomplish this lies along the eastern flank of Bermuda Rise and in the topographic basin to its southeast. Several lines of evidence suggest that these interior flows are highly structured and remarkably vigorous, and by implication, that the diapycnal mixing feeding them is particularly strong. That source region is situated on the western flank of the mid Atlantic Ridge (MAR) where rugged topography provides conditions favorable for mixing. The project is comprised of two elements: 1) An array of moored profilers designed to measure the geostrophic transports along the southeastern flank of Bermuda Rise, a primary pathway for the interior circulation, and 2) A shipboard survey to obtain microstructure and velocity profiles, plus detailed bathymetry. These will be used to construct estimates of turbulent buoyancy fluxes across a range of topographic features and a characterization of the basin-wide diapycnal forcing field.Intellectual meritEach component of the proposed experiment will provide direct measurements of a poorly quantified portion of the interior abyssal ocean, i.e., the structure and strength of horizontal flows along Bermuda Rise, and the diapycnal forcing that feeds those flows. Together, they will provide a basis for evaluating consistency between the observed circulations and the underlying dynamical theory. This attention to the interior basin will both complement and supplement the emerging quantitative picture of the AMOC.Specifically the process study will accomplish the following:1 Quantify the structure, strength, and variability of the intermediate-to-abyssal interior flow field along Bermuda Rise. Diagnose the relative contributions of northern (high tracer concentration and low nutrients) and southern (low tracer concentrations and high nutrients) sources to these flows. 2 Assess the regional structure and strength of turbulent mixing that feeds the interior flow field. Apply these to improve dynamically-based parameterizations of diapycnal forcing.3 Evaluate consistency between the magnitudes of the observed vertical and horizontal fluxes.4 Synthesize transports from various measurement programs in temperature and density classes, to construct volume flux budgets for cold to warm limb transformation and abyssal circulation in the western North Atlantic basins.Broader impactsThe results of this process study and synthesis will provide benchmarks for evaluation of ocean assimilation and reanalysis products. None of the current ocean models and analysis products exhibits much structure below 4000 m. Abyssal geostrophic flow fields in general circulation models have been shown to improve significantly when realistic representations of diapycnal mixing are incorporated. This effort will provide regional constraints for a dynamical parameterization of diapycnal forcing designed for testing and use in ocean models. Finally, the project will provide opportunities for student participation in the field and in the analysis of observational data.