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

该项目是美国领导的国际项目“北大西洋次极地翻转”（OSNAP）的两个组成部分之一，该项目旨在提供北大西洋次极地的完整水柱，跨流域热量，质量和淡水通量的连续记录。OSNAP观测系统由两条腿组成：一条腿从拉布拉多南部延伸到格陵兰岛西南端，穿过拉布拉多海（OSNAP West），另一条腿从格陵兰岛东南端延伸到苏格兰（OSNAP East）。观测系统还包括地下浮标（OSNAP浮标），以追踪盆地中溢出沃茨的路径，并评估穿过OSNAP线的水流的连通性。OSNAP东西两段的位置有意与北大西洋的一些长期观测工作相结合：加拿大在拉布拉多海的重复水文测量方案;德国在北纬53度的拉布拉多海西部边界阵列;全球海洋观测站倡议节点将设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测量剖面;以及罗卡尔地区的埃利特线OSNAP获得了大量的国际合作，包括来自英国、德国、荷兰和加拿大的计量贡献。重要的是，这一拟议的观测系统，连同26°N的RAPID/MOCHA阵列和欧洲联盟北欧海溢流NACLIM方案，将首次提供对大西洋经向翻转环流的全面三维测量，并提供一种评价北大西洋环流间连通性的手段。该合作项目将与英国合作实施OSNAP的东部部分。和荷兰。沿复合跨流域部分沿着的测量将包括系泊和滑翔机的混合，这将允许测量由丹麦海峡和冰岛-苏格兰溢出、随后夹带到这些溢出中、穿过OSNAP东线的亚热带沃茨的净流入、当地（即，例如，Irminger和冰岛盆地内）亚热带沃茨的转化，以及通过东格陵兰海流从北极向Irminger盆地的淡水输送。知识价值：几十年来，海洋学家已经了解到AMOC对NADW产生的变化非常敏感。然而，最近的一些观测和建模研究对这一假设提出了质疑，因为人们对风强迫在AMOC变化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，以确定中层和深层水团的形成以及流域尺度的风强迫在翻转和相关的向极热量输送中所起的作用，目前仅进行了理论和建模，但尚未观察到这些评估。2007年1月，美国海洋科学与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的四个近期优先事项之一。这项拟议的工作通过设计北大西洋次极地的AMOC观测系统直接处理这一优先事项。虽然研究AMOC变异性的主要动机来自其对气候系统的潜在影响，但测量次极地北大西洋热量、质量和淡水通量的其他动机来自其对海洋地球化学和冰冻圈的潜在影响。越来越多的证据表明，海洋在北极海冰减少和格陵兰冰盖的质量损失方面发挥了（并且正在发挥）作用-这两种情况都归因于海洋向极地热传输的变化。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类活动产生的碳，减缓大气中二氧化碳浓度的增加。AMOC的变化预计会影响这种封存。更广泛的影响还包括对五名研究生进行海上作业以及观测数据处理和分析方面的培训。研究生将有机会通过虚拟会议和亲自访问与国际同行合作，并将由多名顾问指导。该研究奖包括对由NSF国际和综合活动办公室共同资助的跨虚拟研究所科学（SAVI）组成部分的支持。

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.