Analysis of eddies, mixing, and dense overflows at the Iceland-Faroe Ridge in the Northern Atlantic Ocean observed with Seagliders

用海洋滑翔机观测到的北大西洋冰岛-法罗海脊的涡流、混合和稠密溢流分析

• 批准号: 1029344
• 负责人: Peter Rhines
• 金额: $ 50.64万
• 依托单位: University of Washington
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-09-01 至 2014-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1029344&HistoricalAwards=false
• 关键词: Analysis; eddies; mixing; dense; overflows

The northern Atlantic Ocean, near the seafloor ridge between Greenland and Scotland, is a particularly active part of the global climate system. This project will analyze observations from a recently completed 3-year program of Seaglider deployments in this sub-polar region. It is the first time that robotic gliders have been used to observe the dense overflow waters of the global meridional overturning circulation, and with them the warm northward flowing branch of the AMOC (Atlantic Meridional Overturning Circulation). 17,800 profiles of hydrography, dissolved oxygen, bio-optical variables and depth-averaged velocity were retrieved in 23 successful deployments during this NSF-sponsored work from November 2006 to November 2009.The primary foci of the proposed work are (i) an analysis of the water masses involved in the deep branch of the AMOC, the polar front and warm branch of the AMOC at this site, (ii), a study of mixing, dense-water transformation, and internal waves inferred from glider profiles of vertical velocity, optical backscatter, temperature and salinity at 1m vertical resolution, and (iii) an analysis of horizontal velocity using glider depth-averaged velocity, geostrophic shear and satellite altimetry, emphasizing dense overflow plume structure, polar front structure, and vertical structure of the strong eddy field.This new observational dataset will be combined with historical hydrographic sections, gridded climatology and with models of the Atlantic circulation. The statistical strength of the new data lies in the multiple occupations of the southern slopes of the Iceland Faroe Ridge over 3 years. Top-to-bottom profiles of horizontal velocity normal to the sections are recovered from the hydrography and glider-measured depth-averaged horizontal velocity. The new measurements of fine-scale vertical velocity by the gliders are particularly exciting. "Hot-spots" of turbulent mixing are visible throughout the water column, but particularly intense in the dense overflow water plume near the exit of the Faroe Bank Channel. Complementary observations from moorings and lowered turbulence probes have been made by Norwegian colleagues. Fine structure of temperature and salinity and optical backscatter observed at the 1m scale will be related to the vertical-velocity mixing signature. In parallel laboratory experiments have been investigating mixing induced by flow over seafloor topography. Together, these observations will provide a significant coverage of eddies, water masses, circulation and mixing in an important sector of the global climate system.Intellectual Merit: Human-induced global climate change is accelerating, and yet the natural variability of climate is strong and difficult to predict. Multi-decadal variability of the AMOC is being advanced as a contributor to the rapid late 20th Century global warming, which is largely thought to be driven by greenhouse gases. While climate models are centerpieces of the global warming/climate change debate, it is widely acknowledged that these models (and indeed higher resolution ocean circulation models) are deficient in representing dynamics in these key high-latitude regions. It is necessary to make direct observations of mixing, sinking, water-mass transformation, topographic control and boundary layers. These need to be targeted, and dense in space and time, which is the virtue of gliders. The motivations for this work go back through many years of research with theoretical dynamics of the ocean, which guide the analysis of observations.Broader Impacts: The investigators on this project interact with students through detailed research with graduate students to undergraduate teaching about the global environment. A key argument made to undergraduate students is that scientific technology has reached the point where it can contribute more effectively in assessing environmental problems. This project will foster on-going collaborations with oceanographers in Norway and the Faroe Islands interested in climate issues affecting sustainability of fisheries, dislocation of ecosystems and the precarious nature of human communities at the rim of the Arctic. Seagliders can be applied widely to address such issues as biological productivity and ecosystem change. The links between countries at the rim of the Arctic are strengthened by growing collaborations in climate- and environmental sciences.This project is a contribution to the US AMOC (Atlantic Meridional Overturning Circulation) project of the CLIVAR (CLImate VARiability and predictability) program.

位于格陵兰岛和苏格兰之间海底脊附近的北大西洋，是全球气候系统中特别活跃的一部分。该项目将分析最近完成的一项为期3年的滑翔机部署计划在该次极地地区的观测结果。这是首次利用机器人滑翔机观测到全球经向翻转环流的密集溢水，以及大西洋经向翻转环流的温暖北流分支。2006年11月至2009年11月，在美国国家科学基金会（nsf）资助的23次成功部署中，获得了17800条水文、溶解氧、生物光学变量和深度平均速度剖面。拟开展的工作的主要重点是：(1)分析该站点AMOC深层分支、极锋和暖支所涉及的水团；(2)研究从垂直速度、光学后向散射、垂直分辨率为1m的温度和盐度的滑翔机剖面推断的混合、密水转换和内波；(3)利用滑翔机深度-平均速度、地转切变和卫星测高分析水平速度。强调密集溢流羽流结构、极锋结构和强涡旋场的垂直结构。这个新的观测数据集将与历史水文剖面、网格气候学和大西洋环流模型相结合。新数据的统计强度在于冰岛法罗海岭南部斜坡在3年内的多次占领。通过水文测量和滑翔机测量的平均水平速度，可以获得垂直于剖面的水平速度从上到下的剖面。滑翔机对精细垂直速度的新测量结果尤其令人兴奋。湍流混合的“热点”在整个水柱中都是可见的，但在法罗河岸通道出口附近密集的溢流水羽中尤为强烈。挪威同事从系泊处和降低的湍流探测器进行了补充观测。在1m尺度观测到的温度、盐度精细结构和光学后向散射与垂直速度混合特征有关。在平行的实验室实验中，研究了海底地形上水流引起的混合。总之，这些观测将提供全球气候系统一个重要部门的涡旋、水团、环流和混合的重要覆盖范围。智力价值：人类引起的全球气候变化正在加速，然而气候的自然变异性很强，难以预测。AMOC的多年代际变率被认为是20世纪后期全球快速变暖的一个因素，而全球变暖主要被认为是由温室气体驱动的。虽然气候模型是全球变暖/气候变化辩论的核心，但人们普遍认为，这些模型（以及更高分辨率的海洋环流模型）在代表这些关键高纬度地区的动态方面存在缺陷。有必要对混合、下沉、水团转化、地形控制和边界层进行直接观测。这些需要有针对性，并且在空间和时间上密集，这是滑翔机的优点。这项工作的动机可以追溯到多年来对海洋理论动力学的研究，这些研究指导了观测结果的分析。更广泛的影响：该项目的研究人员通过与研究生和本科生进行详细的全球环境研究，与学生进行互动。向本科生提出的一个关键论点是，科学技术已经达到了可以更有效地评估环境问题的程度。该项目将促进与挪威和法罗群岛的海洋学家的持续合作，这些海洋学家对影响渔业可持续性、生态系统失调和北极边缘人类社区不稳定性质的气候问题感兴趣。滑翔机可以广泛应用于解决诸如生物生产力和生态系统变化等问题。在气候和环境科学方面日益增长的合作加强了北极边缘国家之间的联系。该项目是对CLIVAR（气候变率和可预测性）计划的美国大西洋经向翻转环流（AMOC）项目的贡献。