SAVI: Collaborative Research: Overturning in the Subpolar North Atlantic - Labrador Basin and Floats

该项目是美国主导的北大西洋次极翻转(OSNAP)国际项目的两个组成部分之一，该项目旨在提供北大西洋次极地区全水柱、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格陵兰的西南端，穿过拉布拉多海的入海口(OSNAP West)，第二条从格陵兰的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)，以追踪盆地中溢流水的路径，并评估横跨OSNAP线的洋流的连通性。OSNAP东西支线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；德国的拉布拉多海西部边界阵列；将在伊明格海西南部建立的全球海洋观测站倡议节点；跨越伊尔明格盆地和冰岛盆地的重复水文测段；以及罗卡尔地区的埃利特线。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，这一拟议的观测系统与26°N的快速/MOCHA阵列和欧洲联盟北欧海洋溢流区的NACLIM计划相结合，将首次提供对大西洋子午线翻转环流(AMOC)的全面三维测量，并提供一种评估北大西洋环流间连通性的手段。该合作项目将实施OSNAP西段和OSNAP浮动计划。主要的观测组成部分是：(I)横跨拉布拉多海东部边缘的系泊阵列，亚极边界流在那里进入盆地。该阵列将补充位于拉布拉多海出口点、横跨西部边缘的类似阵列，由德国和加拿大的机构负责维护；(2)在OSNAP东边界阵列和OSNAP西边界阵列依次释放AMOC下端的声迹浮标。这些浮标将在测量计划的四年期间(2014-2018年)被播撒在北大西洋深水(NADW)密度最高的两个组成部分中。智慧价值：几十年来，海洋学家一直认为AMOC对NADW产量的变化非常敏感。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可变性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，该系统将确定中深层水团形成和盆地规模的风强迫在倾覆和相关的极地热量输送中所起的作用，目前这些评估只被理论和模拟，但没有被观察到。这项拟议的工作通过在北大西洋次极地设计一个AMOC观测系统直接解决了这一优先事项。虽然研究AMOC可变性的一个主要动机是它对气候系统的潜在影响，但衡量北大西洋次极地的热量、质量和淡水通量的另一个动机是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，海洋在北冰洋海冰减少和格陵兰冰盖质量损失方面发挥了作用--这两者都归因于海洋向极地热量输送的变化。此外，海洋在碳循环中发挥着至关重要的作用，它通过将人为碳固定在深海中来减缓大气中不断增加的二氧化碳浓度。预计AMOC的可变性将影响这一自动减支。更广泛的影响还包括对5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面对面访问与国际同行合作，并将得到多名顾问的指导。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机构科学(SAVI)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 OSNAP West section and the OSNAP Float program. The primary observational components are: (i) a mooring array across the eastern margin of the Labrador Sea, where the subpolar boundary current enters the basin. This array will complement an analogous array across the western margin at the exit point of the Labrador Sea, maintained by institutions in Germany and Canada; (ii) a sequential release of acoustically tracked floats in the lower limb of the AMOC at the OSNAP East and OSNAP West boundary arrays. These floats will be seeded in the two densest components of North Atlantic Deep Water (NADW) over the four-year period of the measurement program (2014-2018).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 CO2 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) that is co-funded by NSF's Office of International and Integrative Activities.