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

北方大西洋靠近格陵兰岛和苏格兰之间的海底山脊，是全球气候系统中特别活跃的部分。该项目将分析最近完成的在该次极地地区部署海滑翔机的3年计划的观测结果。这是第一次使用机器人滑翔机观测全球纬向翻转环流的密集溢出沃茨，以及与之一起的AMOC（大西洋经向翻转环流）的温暖向北流动分支。在2006年11月至2009年11月的23次成功部署中，获得了17，800个水文、溶解氧、生物光学变量和深度平均速度的剖面。拟议工作的主要重点是（i）分析该站点AMOC的深分支、AMOC的极锋和暖分支中的水团，（ii）对混合、密水转化和内波的研究，这些研究是从垂直速度、光学后向散射、温度和盐度的滑翔机剖面图中以1米的垂直分辨率推断出来的，以及（iii）利用滑翔机深度平均速度、地转切变和卫星测高对水平速度进行分析，强调密集的溢流羽流结构、极锋结构、这一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。新数据的统计优势在于冰岛法罗海脊南坡3年多来的多次占领。垂直于剖面的水平速度的顶部到底部剖面从水文学和滑翔机测量的深度平均水平速度恢复。滑翔机对精细尺度垂直速度的新测量特别令人兴奋。湍流混合的“热点”在整个水柱中可见，但在法罗银行通道出口附近的密集溢流水羽中特别强烈。挪威的同事从系泊和降低的湍流探测器进行了补充观测。在1米尺度上观测到的温度和盐度的精细结构以及光学后向散射将与垂直速度混合特征有关。在平行的实验室实验中，一直在研究海底地形上的水流引起的混合。这些观测将为全球气候系统的一个重要部分提供大量的涡旋、水团、环流和混合的资料。知识成果：人类引起的全球气候变化正在加速，但气候的自然变率很强，难以预测。AMOC的多年代际变化被认为是世纪后期全球变暖的一个贡献者，这在很大程度上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（实际上是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不足。有必要对混合、下沉、水团变化、地形控制和边界层进行直接观测。这些需要有针对性，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的研究与海洋的理论动力学，这指导了观测的分析。更广泛的影响：这个项目的调查人员与学生互动，通过详细的研究与研究生本科教学有关的全球环境。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的气候问题感兴趣。海洋滑翔机可广泛应用于解决生物生产力和生态系统变化等问题。气候和环境科学领域的合作日益增多，加强了北极边缘国家之间的联系。该项目是对CLIVAR（气候变化和可预测性）计划中美国AMOC（大西洋经向翻转环流）项目的贡献。

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.