SAVI: Collaborative Research: Overturning in the Subpolar North Atlantic--the Irminger and Iceland Basins

该项目是美国主导的国际项目“北大西洋亚极区翻转”（Overturning in the subpolar North Atlantic，简称opsnap）的两个组成部分之一，该项目旨在提供北大西洋亚极区全水柱、跨盆地热量、质量和淡水通量的连续记录。OSNAP观测系统由两条腿组成：一条从拉布拉多南部延伸到横跨拉布拉多海口的格陵兰岛西南端（OSNAP西），另一条从格陵兰岛东南端延伸到苏格兰（OSNAP东）。观测系统还包括水下浮子（opsnap浮子），以追踪盆地溢流的路径，并评估穿越opsnap线的水流的连通性。OSNAP东线和西线的位置有意地与北大西洋的一些长期观测工作相融合：加拿大拉布拉多海重复水文计划；位于北纬53°的德国拉布拉多海西部边界阵；全球海洋观测站倡议节点将放置在伊尔明格海西南部；横跨伊尔明格和冰岛盆地的重复水文剖面；以及罗考尔地区的埃利特线。OSNAP已经获得了大量的国际合作，包括来自英国、德国、荷兰和加拿大的测量贡献。重要的是，该观测系统与26°N的RAPID/MOCHA阵列和北欧海溢出的欧盟NACLIM计划相结合，将提供大西洋经向翻转环流（AMOC）的第一个全面的三维测量，并提供评估北大西洋环流间连通性的手段。该合作项目将与英国和荷兰合作实施OSNAP的东部部分。沿着复合跨盆地段的测量将包括系泊和滑梯，这将允许测量由丹麦海峡和冰岛-苏格兰溢流引起的北大西洋东部亚极地环流的净倾覆率，随后的溢流夹带，穿过OSNAP东线的亚热带水域的净流入，当地（i…e）。亚热带水域的转变，以及淡水通过东格陵兰流从北极进入伊尔明格盆地。知识价值：几十年来，海洋学家已经认识到AMOC对NADW产生的变化非常敏感。然而，最近的一些观测和模拟研究对这一假设提出了质疑，因为人们对风强迫在AMOC变率中的作用有了更多的了解。因此，该项目的总体目标是建立一个观测系统，以确定中深水团的形成和盆地尺度的风强迫在倾覆和相关的极地热输送中所起的作用，目前的评估只是理论化和建模，而不是观测。更广泛的影响：2007年1月，美国海洋科学和技术联合小组委员会将AMOC的研究确定为美国海洋研究优先计划中的四个近期优先事项之一。这项提议的工作通过设计北大西洋亚极地的AMOC观测系统直接解决了这一优先问题。虽然研究AMOC变率的主要动机来自其对气候系统的潜在影响，但测量北大西洋亚极地的热量、质量和淡水通量的另一个动机来自它们对海洋生物地球化学和冰冻圈的潜在影响。越来越多的证据表明，海洋已经（并且正在）在北极海冰的减少和格陵兰冰盖的质量损失中发挥了作用——这两者都被归因于海洋向极地热输送的变化。此外，海洋在碳循环中发挥着至关重要的作用，通过在深海中封存人为碳，减缓大气中二氧化碳浓度的增加。预计AMOC的变化将影响这种封存。更广泛的影响还包括培训五名研究生学习航海作业和处理和分析观测数据。研究生将有机会通过虚拟会议和亲自访问与他们的国际同行合作，并将由多位顾问指导。该研究奖包括对跨虚拟研究所科学（SAVI）组件的支持，该组件由NSF的国际和综合活动办公室共同资助。

This project is one of two components of a US-led international program, Overturning in the Sub-polar North Atlantic (OSNAP), designed to provide a continuous record of the full-water column, trans-basin fluxes of heat, mass and freshwater in the subpolar North Atlantic. The OSNAP observing system consists of two legs: one extending from southern Labrador to the southwestern tip of Greenland across the mouth of the Labrador Sea (OSNAP West), and the second from the southeastern tip of Greenland to Scotland (OSNAP East). The observing system also includes subsurface floats (OSNAP Floats) in order to trace the pathways of overflow waters in the basin and to assess the connectivity of currents crossing the OSNAP line. The location of the OSNAP East and West legs purposefully melds with a number of long-term observational efforts in the North Atlantic: the Canadian repeat hydrography program in the Labrador Sea; the German Labrador Sea western boundary array at 53°N; the global Ocean Observatories Initiative node to be placed in the southwestern Irminger Sea; the repeat hydrographic sections across the Irminger and Iceland basins; and the Ellett line in the Rockall region. Substantial international collaboration has been garnered for OSNAP, including measurement contributions from the UK, Germany, the Netherlands and Canada. Importantly, this proposed observing system, in conjunction with the RAPID/MOCHA array at 26°N and the European Union NACLIM program at Nordic Seas overflows, will provide the first comprehensive three-dimensional measure of the Atlantic Meridional Overturning Circulation (AMOC) and provide a means to evaluate inter-gyre connectivity in the North Atlantic. This collaborative project will implement the eastern section of OSNAP in partnership with the U.K. and the Netherlands. Measurements along the composite trans-basin section will consist of a mix of moorings and gliders that will allow for the measure of the net overturning rate in the eastern North Atlantic sub-polar gyre resulting from the Denmark Strait and Iceland-Scotland overflows, the subsequent entrainment into these overflows, the net inflow of subtropical waters across the OSNAP East line, the local (i..e., within the Irminger and Iceland basins) transformation of subtropical waters, and the freshwater transport from the Arctic into the Irminger basin via the East Greenland Current.Intellectual Merit: For decades oceanographers have understood the AMOC to be highly susceptible to changes in the production of NADW. However, a number of recent observational and modeling studies have called into question this supposition, as more has been learned about the role of wind forcing in AMOC variability. Thus, the overall goal of this project is to establish an observing system that will determine the role that intermediate and deep water mass formation and basin-scale wind forcing play in the overturning and associated poleward heat transport, assessments that currently have only been theorized and modeled, but not observed.Broader Impact: In January of 2007, the US Joint Subcommittee on Ocean Science and Technology identified the study of the AMOC as one of four near-term priorities in the US Ocean Research Priorities Plan. This proposed work directly addresses that priority via a design of an AMOC observing system in the sub-polar North Atlantic. While a primary motivation for studying AMOC variability comes from its potential impact on the climate system, additional motivation for the measure of the heat, mass and freshwater fluxes in the sub-polar North Atlantic arises from their potential impact on marine biogeochemistry and the cryosphere. There is growing evidence that the ocean has played (and is playing) a role in the reduction of Arctic sea ice and in mass loss from the Greenland Ice Sheet - both of which have been attributed to changes in the poleward heat transport by the ocean. Also, the ocean plays an essential role in the carbon cycle by moderating increasing atmospheric concentrations of carbon dioxide through the sequestration of anthropogenic carbon in the deep ocean. Variability in the AMOC is expected to impact this sequestration. Broader impacts also include the training of five graduate students in seagoing operations and in the processing and analysis of observational data. The graduate students will have an opportunity to collaborate with their international counterparts through virtual meetings and in-person visits and will be mentored by multiple advisors. This research award includes support for a Science Across Virtual Institutes (SAVI) component that is co-funded by NSF's Office of International and Integrative Activities.