Line W: A Sustained Measurement Program Sampling the North Atlantic Deep Western Boundary Current and Gulf Stream at 39oN

北大西洋中纬度的经向翻转环流主要涉及暖流向极地的输送，以及在西部增强的边界流中较冷的中深水向赤道的流动。对全球洋流系统的这些分支及其相关的区域环流如何在年代际时间尺度上变化的理解是不完整的。特别是，对于高纬度地区海气交换和水团改变的年际变化是如何向赤道传播的，以及这些信号对大西洋环流可能产生的影响或反馈，人们所知甚少。限制理解进展的是缺乏长期的、清晰的记录来记录大西洋的水性质、分层和运输的年际信号。美国西部深边界流（DWBC）系统重要的是，在亚极纬度产生的异常可能会被北大西洋洋流或墨西哥湾流深刻地改变甚至阻断。相反，次极异常可能影响气流的位置、强度和/或稳定性，进而影响整个北大西洋的海气交换模式。这些基本问题激发了W线项目，该项目目前正在返回大浅滩和哈特拉斯角之间北纬39度的DWBC和墨西哥湾流的观测数据。配套的野外项目正在对研究区域的北部和南部的DWBC进行采样，还有几个互补的建模项目正在进行中。综上所述，这些研究将有助于全面调查北大西洋深水向低纬度出口的机制和速率及其与上层海洋环流的关系。学术价值：提出的研究将建立对北大西洋深水向低纬度出口的机制和速率的理解，以及不同的深水流和分层变化与包括墨西哥湾流在内的上层海洋环流的关系。这些知识将有助于阐明海洋对海气交换变化的反应，并最终阐明海洋在全球气候变化中的作用。该项目将延长对DWBC和墨西哥湾流的温度、盐度、示踪剂和速度变化的持续观测到2013年，与计划中的英美观测项目在北纬26度同步产生整整10年的记录。W线项目包括在伍兹霍尔以南的大陆斜坡上系泊阵列，沿着阵列重复测量水文剖面，并向南延伸到马尾藻海。船上可能的高空间分辨率采样验证了阵列在空间上分辨年际信号以及返回水样进行示踪分析。同样重要的是，调查人员将探索当前W线计划的一个子集是否足以索引该地区的水性质和运输变化，为长期海洋观测系统奠定基础。更广泛的影响：提出的观测将探索和测试关于深西部边界流和墨西哥湾流相互作用的理论观点；这是目前W线资助下的一篇博士论文的重点。麻省理工学院/WHOI联合项目的物理海洋学入门课程的学生将参加拟议的巡航，向他们介绍观测海洋学。此外，该项目将继续支持一名来自一个代表性不足的群体的博士生，他的论文研究将集中在获得的数据上。所有的观察结果和结果数据产品将通过互联网尽早提供给社区，目的是促进这些数据的广泛使用，以便社区的任何成员都可以在自己的研究计划中使用它们。随着数据的恢复和处理，任何感兴趣的调查人员都可以使用W线观测结果进行模型验证和区域过程研究。除了原始观测外，正在生产和分发增值产品，如核心性质的时间序列和水团运输。其他研究人员也被鼓励在W线基础设施的基础上进行建设，以增强正在采样的物理场。该项目是对美国CLIVAR（气候变率和可预测性）计划的贡献。

The meridional overturning circulation of the North Atlantic Ocean at mid-latitude principally involves poleward transport of warm water by the Gulf Stream and equatorward flow of colder intermediate and deep waters within a western-intensified boundary current. Comprehension of how these limbs of the global current system and their associated regional recirculations vary on decadal time scale is incomplete. In particular, very little is known on how inter-annual variations in air-sea exchange and water mass modification at high latitudes are transmitted equatorward, and what impacts or feedbacks such signals may have for the Atlantic-wide circulation. Limiting advance in understanding is the lack of long, well-resolved records to document inter-annual signals in water properties, stratification and transport of the Atlantic?s Deep Western Boundary Current (DWBC) system. Importantly, anomalies created at sub-polar latitudes may be profoundly altered or even blocked by the North Atlantic Current or Gulf Stream. Conversely, sub-polar anomalies may influence the position, strength, and/or stability of the Stream, and in turn affect patterns of air-sea exchange throughout the North Atlantic. These basic questions motivate the Line W program that is presently returning observations of the DWBC and Gulf Stream about 39 N between the Grand Banks and Cape Hatteras. Companion field programs are sampling the DWBC both north and south of our study region, and several complementary modeling programs are underway. Taken together, these studies will facilitate a comprehensive investigation of the mechanisms and rates of North Atlantic Deep Water export to lower latitudes and its relationships to the upper ocean circulation.Intellectual Merit: The proposed study will build understanding of the mechanisms and rates of North Atlantic Deep Water export to lower latitudes and the relationships of varying deep-water flow and stratification changes to the upper ocean circulation including the Gulf Stream. This knowledge will help clarify the response of the ocean to variations in air-sea exchange and ultimately, the ocean's role in global climate change. This project will extend the on-going observations of temperature, salinity, tracer and velocity variations of the DWBC and Gulf Stream through 2013, yielding a full 10-year record synchronous with the planned U.K.-U.S. observational program at 26 N. The Line W program consists of a moored array over the continental slope south of Woods Hole, and repeated occupations of a hydrographic section along the array and extending south into the Sargasso Sea. The high spatial resolution sampling possible from ship is verifying that the array is spatially resolving the inter-annual signals as well as returning water samples for tracer analysis. Equally important, the investigators will explore whether a subset of current Line W program is sufficient to index water property and transport variations in this area, setting the stage for a long-term ocean observing system. Broader Impacts: The observations proposed will explore and test theoretical ideas about the interaction of the Deep Western Boundary Current and Gulf Stream; this is the focus of a Ph.D. thesis under current Line W funding. MIT/WHOI Joint Program students enrolled in the introductory physical oceanography course will participate on the proposed cruises, introducing them to observational oceanography Moreover, the program will continue to support one Ph. D. student from an under-represented group whose dissertation research will focus on the acquired data. All observations and resulting data products will be made available to the community at the earliest possible time via the internet with the intention of fostering widespread use of these data so that any member of the community can utilize them in their own research program. As data are recovered and processed, the Line W observations are being made available for model validation and study of regional processes by any interested investigators. In addition to raw observations, value-added products such as time series of core properties and transport by water mass are being produced and distributed. Other researchers are also encouraged to build on the Line W infrastructure to augment the physical fields being sampled.This project is a contribution to the U.S. CLIVAR (CLImate VARiability and predictability) Program.