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

知识价值：20世纪90年代在北大西洋亚极西部进行的剖面浮子观测似乎与目前关于西部深边界流（DWBC）是拉布拉多海水（LSW）从亚极到亚热带纬度的主要出口途径的理解相矛盾。所有在DWBC离开拉布拉多海的剖面浮子都离开了大浅滩尾部以北的边界，沿着北大西洋洋流（NAC）的路径在北纬50°左右向东进入海洋内部。这一意想不到的观测结果激发了长期的观测努力，通过新的浮子观测和历史水文数据分析，更好地了解LSW路径及其变异性。该项目的现场部分于2003年开始，目前已接近完成。三年来，每六个声学跟踪的RAFOS浮标名义上每三个月在50ºN附近的DWBC上LSW和classic LSW水平释放一次。当最后一个浮标在2008年11月浮出水面时，来自大约62个RAFOS浮标的两年高分辨率轨迹将可用于分析。迄今为止，对已经浮出水面的RAFOS浮子和由海洋涡旋解析一般环流模型产生的“e-浮子”的研究得出了两个重要的结果。首先，几乎没有证据表明沿DWBC有一条从亚极地到亚热带盆地的“快速通道”。其次，大量的RAFOS和e-浮子追踪了LSW从纽芬兰盆地向南到副热带东部环流的内部路径，这一路径完全没有被剖面浮子观测到。这些结果提出了关于DWBC作为新通气水域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，AMOC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，以及生成e-浮子轨迹的能力的掌握，研究人员现在准备在理解LSW的出口路径及其对AMOC的影响方面取得重大进展。本分析的具体目标是：1。完成完整的RAFOS浮子数据集的统计分析，并与使用海洋环流模型生成的e-浮子的类似研究进行比较。2 .调和纽芬兰盆地DWBC浮子的快速损失与DWBC作为从亚极地到亚热带的直接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内部通道的重要性，相对于DWBC，对AMOC的体积和性质运输。更广泛的影响：通过提供对亚极地到亚热带海洋路径的更好理解，这项拟议的研究将有助于揭示海洋在全球气候中的作用。拉格朗日视角将为AMOC下肢的连续性提供有价值的信息，因此将有助于监测程序的设计。该项目还将产生更广泛的影响，因为它将有助于杜克大学的一名研究生和伍兹霍尔海洋研究所的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.