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

北大西洋位于格陵兰岛和苏格兰之间的海底脊附近，是全球气候系统中特别活跃的一部分。这个项目将分析最近完成的在这个亚极地地区部署Seaglider的3年计划的观测结果。这是首次使用机器人滑翔机观测到全球经向翻转环流的稠密溢流水域，以及伴随着它们的大西洋子午线翻转环流(AMOC)温暖的北上流动分支。在2006年11月至2009年11月期间，在这项由NSF赞助的23次成功部署中，共反演了17,800条水文、溶解氧、生物光学变量和深度平均速度剖面。拟议工作的主要重点是(I)分析该站点AMOC深支、极锋和暖支所涉及的水团，(Ii)研究混合、密水转化和从1米垂直分辨率的滑翔机垂直速度、光学后向散射、温度和盐度剖面推断的内波，以及(Iii)利用滑翔机深度平均速度分析水平速度，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式相结合。新数据的统计力量在于冰岛法罗山脉南坡三年来的多重职业。根据水文和滑翔机测量的深度平均水平速度，恢复了垂直于剖面的自上而下的水平速度剖面。滑翔机对细微尺度垂直速度的新测量尤其令人兴奋。湍动混合的“热点”在整个水柱中都可见，但在法罗浅滩海峡出口附近密集的溢流水羽流中尤为强烈。挪威的同事们从系泊和降低湍流探测器上进行了补充观察。在1m尺度上观测到的温度、盐度和光学背向散射的精细结构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流动引起的混合。总而言之，这些观测将提供对全球气候系统重要部分中的涡旋、水团、环流和混合的重要覆盖。智力上的优点：人类导致的全球气候变化正在加速，但气候的自然变异性很强，很难预测。AMOC的数十年变化被认为是20世纪末快速变暖的原因之一，而全球变暖在很大程度上被认为是由温室气体推动的。虽然气候模型是全球变暖/气候变化辩论的核心，但人们普遍承认，这些模型(甚至是更高分辨率的海洋环流模型)在描述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的海洋理论动力学研究，这些研究指导了观测分析。广泛的影响：这个项目的研究人员通过与研究生的详细研究到本科生关于全球环境的教学与学生互动。向本科生提出的一个关键论点是，科学技术已经到了可以在评估环境问题方面做出更有效贡献的地步。该项目将促进与挪威和法罗群岛海洋学家正在进行的合作，这些海洋学家对影响渔业可持续性、生态系统混乱和北极边缘人类社区不稳定性质的气候问题感兴趣。海滑器可以广泛应用于解决生物生产力和生态系统变化等问题。由于在气候和环境科学方面的合作不断增加，北极边缘国家之间的联系得到了加强。该项目是对CLIVAR(气候可变性和可预测性)计划的美国AMOC(大西洋子午线颠覆环流)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.