Collaborative Research: Export Pathways from the Subpolar North Atlantic: Phase Two

智力优势：20世纪90年代在北大西洋西部副极地进行的剖面浮标观测似乎与目前对深层西部边界流（DWBC）作为拉布拉多海水（LSW）从副极地到亚热带纬度的主要出口途径的理解相矛盾。DWBC中离开拉布拉多海的所有剖面浮标都离开了大浅滩尾部以北的边界，并在北纬50°左右沿北大西洋海流（NAC）的路径沿着向东进入海洋内部。这个意想不到的观察动机长期的观测工作，以获得更好地了解LSW的路径和他们的变化与新的浮子观测和历史水文数据analysis.The领域的这一项目，于2003年开始的组成部分，已接近完成。三年来，名义上每隔三个月在DWBC上LSW和经典LSW水平的50ºN附近释放一组六个声学跟踪RAFOS浮子。2008年11月，当最后一个浮标浮出水面时，将可获得大约62个RAFOS浮标的两年高分辨率轨迹，以供分析。迄今为止，对已经浮出水面的RAFOS浮标和海洋涡流分辨环流模型产生的“e-浮标”的研究得出了两个重要结果。首先，几乎没有证据表明沿着DWBC存在从副极地到亚热带盆地的“快速通道”。第二，大量的RAFOS和电子浮标追踪LSW从纽芬兰盆地向南到东副热带环流的内部路径，这是一条剖面浮标根本没有观察到的路径。这些结果提出了关于DWBC作为新通风沃茨出口通道的重要性的关键问题，因此它在大西洋经向翻转环流（AMOC）中的作用是海洋研究优先计划（ORPP）的近期优先事项。随着RAFOS现场工作的结束，以及产生电子浮标轨迹的能力，研究人员现在准备在了解LSW的输出途径及其对AMOC的影响方面取得重大进展。本文分析的具体目标是：1.完成RAFOS浮标数据集的统计分析，并与使用海洋环流模式生成的电子浮标进行的类似研究进行比较。解释纽芬兰盆地DWBC漂浮物的快速损失与DWBC作为从副极地到副热带地区的直接LSW输出通道的概念之间的明显矛盾。阐明中尺度、年际和年代际变化对LSW路径的影响.评估LSW的内部路径的重要性，相对于DWBC，AMOC.Broader影响的体积和财产运输：通过提供一个更好的了解亚极地到亚热带海洋路径，这项拟议中的研究将有助于解开海洋在全球气候中的作用。拉格朗日的观点将提供有价值的信息的连续性的下肢的AMOC，因此将有助于监测方案的设计。该项目还将产生更广泛的影响，因为它将有助于杜克大学一名研究生和伍兹霍尔海洋研究所一名博士后研究员的培训和教育。

Intellectual Merit: Profiling float observations in the western subpolar North Atlantic made in the 1990s appeared to contradict the current understanding of the Deep Western Boundary Current (DWBC) as the dominant export pathway for Labrador Sea Water (LSW) from subpolar to subtropical latitudes. All of the profiling floats that exited the Labrador Sea in the DWBC left the boundary well north of the Tail of the Grand Banks, turning eastward into the ocean interior along the path of the North Atlantic Current (NAC) at about 50°N. This unexpected observation motivated a long-term observational effort to obtain a better understanding of LSW pathways and their variability with new float observations and historical hydrographic data analyses.The field component of this project, which began in 2003, is nearly complete. For three years, groups of six acoustically tracked RAFOS floats were released nominally every three months in the DWBC near 50ºN at Upper LSW and Classical LSW levels. When the last floats surface in November 2008, two-year high-resolution trajectories from about 62 RAFOS floats will be available for analysis. Two important results have emerged to date from a study of RAFOS floats that have already surfaced and "e-floats" generated from an ocean eddy-resolving general circulation model. First, there is little evidence for a "fast-track" from the subpolar to the subtropical basin along the DWBC. Second, a significant number of RAFOS and e-floats trace an interior pathway for LSW southward from the Newfoundland Basin to the eastern subtropical gyre, a pathway that was not observed at all by the profiling floats. These results raise critical questions about the importance of the DWBC as an export pathway for newly-ventilated waters, and hence its role in the Atlantic Meridional Overturning Circulation (AMOC) which is a near-term priority of the Ocean Research Priorities Plan (ORPP).With the conclusion of the RAFOS field work in sight, and the capability to generate e-float trajectories in hand, the investigators are now poised to make significant advances in the understanding of the export pathways of LSW and their impact on the AMOC. The specific objectives of this analysis are to:1. Complete the statistical analysis of the full RAFOS float data set and compare to a similar study using e-floats generated from an ocean general circulation model.2. Reconcile the apparent contradiction between the rapid loss of floats from the DWBC in the Newfoundland Basin and the concept of the DWBC as a direct LSW export pathway from the subpolar to subtropical region.3. Elucidate the impact of mesoscale, interannual and decadal variability on LSW pathways.4. Assess the importance of the interior pathway of LSW, relative to the DWBC, to the volume and property transport of the AMOC.Broader Impacts: By providing an improved understanding of subpolar-to-subtropical ocean pathways, this proposed research will contribute to an unraveling of the ocean's role in global climate. The Lagrangian perspective will provide valuable information on the continuity of the lower limb of the AMOC and as such will aid in the design of monitoring programs. This project will also have a broader impact in that it will contribute to the training and education of a graduate student at Duke University and a postdoctoral investigator at Woods Hole Oceanographic Institution.