Collaborative Research: Enhancing our Understanding of North Atlantic Deep Water Pathways using Nonlinear Dynamics Techniques

在上个世纪的大部分时间里，拉布拉多海和北欧海从高纬度向赤道扩散的冷水团预计将沿着亚极地和亚热带北大西洋的深层西部边界流得到很大程度的遏制。自本世纪初以来，在这些水团中发射的观测浮标打破了这种预期。取而代之的是，横跨北大西洋的无数内部路径被揭示。与此同时，一份人为二氧化碳的清单显示，北大西洋次极地是所有海洋盆地中最强烈的(单位面积)汇，这一特征可归因于该盆地新形成的水团的深度渗透。虽然大西洋子午线翻转环流的深层长期以来一直被认为是一个热量和淡水储存库，但它作为碳储存库的作用现在是显而易见的。因此，在对这些深水团路径的传统理解被颠覆的时候，比以往任何时候都更有理由理解这些水团的扩散和命运。在过去的十年里，模拟的漂浮轨迹扩大了北大西洋相对较少的观测漂浮物的数量，以便对水团路径有更广泛的了解。然而，对观测和模拟的轨迹的分析在很大程度上使用了传统方法来确定有限数量的流动特性。这项研究将利用非线性动力学的最新进展，以便对这些水团和流动的有限观测提供更全面的描述和理解。因此，通过使用这些工具来揭示深水通道，该项目将有助于我们理解北大西洋是一个深层碳库，从而产生重大的社会影响。这项拟议工作的更广泛影响还包括培训一名博士后研究员以促进独立的研究生涯，以及培训一名物理海洋学学生使用非线性动力学工具。这个项目将通过使用在非线性动力学和流体动力学交界处出现的两个互补工具来解决现代物理海洋学中的一个基本问题。将使用概率工具通过构建拉格朗日地理来揭示深水的变化和命运，拉格朗日地理限制了连通性、在水团省份内的停留时间、首选的循环路径、沿这些路径的传输时间以及跨省边界的运输。最近被证明在提取持久运输路径方面有效的确定性工具也将被用来划定首选的运输路径，从而将被用来框定深水路线。这为传统的物理海洋学研究领域提供了一种很有前途的非线性动力学工具。具体地说，这项工作将应用动力系统工具来：1)确定长期命运并阐明深水团的首选路径；2)确定位涡守恒或其他动力学对这些路径的限制程度；以及3)确定界定水团居留的空间省(域)并评估它们之间的交换。这项分析将使用少量但不断增加的观测浮标，包括最近从北大西洋次极地计划(OSNAP)倾覆中发现的浮标，以及ARGO数据和海洋环流模型模拟的浮标轨迹。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

For most of the last century, the equatorward spread of cold water masses from high latitudes in the Labrador and Nordic Seas was expected to be largely contained along the Deep Western Boundary Current in the subpolar and subtropical North Atlantic. Since the turn of this century, observational floats launched within these water masses have defied this expectation. Instead, myriad interior pathways have been revealed across the North Atlantic. Contemporaneously, an inventory of anthropogenic carbon dioxide has shown the subpolar North Atlantic to be the most intense (per unit area) sink of all ocean basins, a characteristic attributable to the deep penetration of newly-formed water masses in that basin. While the deep limb of the Atlantic Meridional Overturning Circulation has long been appreciated as a heat and freshwater reservoir, its role as a carbon reservoir is now apparent. Thus, at a time when the conventional understanding of these deep water mass pathways has been upended, there is a stronger reason than ever to understand the spread and fate of these water masses. Over the past decade, simulated float trajectories have augmented the relatively small number of observational floats in the North Atlantic in order to gain a broader understanding of water mass pathways. However, analyses of the observed and modeled trajectories have largely used conventional methods to ascertain a limited number of flow characteristics. This study will capitalize on recent advances in nonlinear dynamics in order to provide a more comprehensive description and understanding of these water masses and flows limited observations. Thus, by using these tools to unravel deep water pathways, this project will aid our understanding of the North Atlantic as a deep carbon reservoir, and thereby have a significant societal impact. Broader impacts with this proposed work also include the training of a postdoctoral researcher to facilitate an independent research career and the training of a physical oceanography student in the use of nonlinear dynamical tools. This project will address a fundamental question in modern physical oceanography through the use of two complementary tools emerging at the interface of nonlinear dynamics and fluid dynamics. Probabilistic tools will be used to cast new light on the transformation and fate of the deep waters through the construction of Lagrangian geographies that constrain connectivity, residence times within water mass provinces, preferred circulation pathways, transit times along these pathways, and transport across province boundaries. Deterministic tools that have recently proven efficient at extracting persistent transport pathways will also be used to delineate preferred transport pathways, and thus will be used to frame deep water routes. This offers a promising fertilization of nonlinear dynamical tools into a traditional physical oceanographic area of study. Specifically, this work will apply dynamical systems tools to: 1) determine the long-term fate and elucidate the preferred pathways of the deep water masses; 2) ascertain the extent to which potential vorticity conservation or other dynamics constrains these pathways; and 3) identify spatial provinces (domains) that define water mass residence and evaluate exchanges among them. The small, but growing number of observational floats, including those recently recovered from the Overturning in the Subpolar North Atlantic Program (OSNAP), as well as Argo data and simulated float trajectories from ocean general circulation models, will be used in this analysis.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.