The Upstream Sources of the Denmark Strait Overflow

关于气候系统的一个关键开放问题是北半球大气和淡水强迫的变化将如何影响大尺度的海洋环流，通常被称为大西洋经向翻转环流。特别是，北欧海是北大西洋环流和缓和我们气候的重要区域。温暖的表层亚热带海水在大西洋中向北流动，进入北欧海，在那里它们的特性被强烈的海气通量改变，它们向大气释放热量，然后以稠密的水的形式返回南方，从格陵兰岛和苏格兰之间的山脊缝隙中溢出。这个过程通过为大西洋向北的热量流动提供一种机制来调节我们的气候。从北欧海流出的最大和最密集的水流经过位于冰岛和格陵兰岛之间的丹麦海峡。丹麦海峡溢流水（DSOW）约占美国东海岸向南流动的深海流的总稠密水的一半。丹麦海峡上游的源水和动力影响溢流的下游命运和大西洋经向翻转环流最深分支对气候强迫变化的敏感性。这项研究将通过识别和量化不同的路径，它们如何相互作用，以及它们的潜在动力，显著提高我们对丹麦海峡北部环流的理解。此外，该项目将阐明海床上DSOW明显变化的性质和原因。这在以前的许多研究中已经观察到，但尚未用观测数据充分解释。国际合作者将为该项目提供他们在北欧海域收集的额外观测资料。研究中使用的所有系泊数据（包括欧洲合作者提供的数据）将被存档在一个可公开访问的数据门户网站中。将开展一项外联计划，在全国媒体上分享结果，并创建适合公立学校的科学课程内容。这项研究将由一名博士后研究员领导。拟议项目的目的是量化丹麦海峡溢流水（DSOW）的上游来源，并将不同来源的变化与在海底观察到的变化联系起来。为了完成这项工作，调查人员将使用四个不同机构提供的时间序列数据，这些机构在2011年8月至2012年8月期间，在平台以北200公里的海峡上部署了12个系泊点，加上平台本身的系泊点。虽然部分数据之前已由个别调查人员分析过，但以前从未同时考虑过所有数据。第一个目标是量化海峡中心部分新发现的密集水通道，即分离的东格陵兰洋流。这条通道最近在少量的船上过境中被发现，被认为是位于格陵兰斜坡上的边界流（Shelfbreak东格陵兰流）和冰岛斜坡（北冰岛急流）之间的自由射流。在长达一年的时间里，系泊数据将用于量化这个新发现的特征的结构、运输和动态。在此之后，第二个目标是制作第一张海峡宽度的图片，显示将稠密的水输送到丹麦海峡的随时间变化的通道，以及运输如何在三个溢出通道之间进行划分。一旦确定了这一点，第三个目标是阐明联合上游环流系统的动力学，并评估它如何影响海底的运输和水文变化。目的是确定海床上普遍存在的DSOW天气尺度变化是否由任何路径上的上游波动驱动，以及/或者海床上的水力过程是否影响上游环流。该研究的最终目标是设计一个稀疏系泊阵列，该阵列可以在未来实施，以在年际到十年的时间尺度上最佳地监测DSOW的上游来源。

One of the key open issues regarding the climate system is how changes in atmospheric and freshwater forcing in the Northern Hemisphere will influence the large scale ocean circulation often referred to as the Atlantic Meridional Overturning Circulation. In particular, the Nordic Seas are a vital region for the circulation of the North Atlantic and for the moderation of our climate. Warm, surface sub-tropical waters flow northward in the Atlantic Ocean and pass into the Nordic Seas where their properties are modified by intense air-sea fluxes and they release heat to the atmosphere before returning south at depth as dense water that spills through the gaps in the ridge that runs between Greenland and Scotland. This process regulates our climate by providing a mechanism for the northward flow of heat in the Atlantic Ocean. The largest and densest of the outflows from the Nordic Seas occurs through the Denmark Strait, located between Iceland and Greenland. This Denmark Strait Overflow Water (DSOW) accounts for roughly half of the total dense water feeding the deep ocean current flowing southward along the east coast of the U.S. The source waters and dynamics upstream of the Denmark Strait affect the downstream fate of the overflow and the sensitivity of the deepest limb of the Atlantic Meridional Overturning Circulation to changes in climate forcing. This study will significantly improve our understanding of the circulation north of Denmark Strait by identifying and quantifying the different pathways, how they interact with each other, and their underlying dynamics. Furthermore, the project will shed light on the nature and causes of the pronounced variability of the DSOW at the sill. This has been observed in many previous studies but is yet to be fully explained using observational data. The international collaborators will contribute additional observations they collected in the Nordic Seas to the project. All of the mooring data used in the study (including those provided by the European collaborators) will be archived in a publicly accessible data portal. An outreach program will be carried out to share the results in the national media and to create science lesson content appropriate for public schools. The study will be led by a post-doctoral investigator.The aim of the proposed project is to quantify the upstream sources of the Denmark Strait Overflow Water (DSOW) and relate the variability in the different sources to that observed at the sill. To accomplish this, the investigators will use time series data provided by four different institutions who together deployed 12 moorings spanning the strait 200 kilometer north of the sill from August 2011 to August 2012, plus a mooring at the sill itself. While parts of the data have been analyzed previously by the individual investigators, never before have all of the data been considered in tandem. The first objective is to quantify a newly discovered pathway of dense water in the central portion of the strait, known as the Separated East Greenland Current. This pathway was recently revealed in a small number of shipboard crossings and is thought to be a free-jet located between the boundary current on the Greenland slope (the Shelfbreak East Greenland Current) and the Iceland slope (the North Icelandic Jet). The mooring data will be used to quantify the structure, transport, and dynamics of this newly recognized feature over a year-long period. Following this, the second objective is to produce the first strait-wide picture of the time-varying pathways carrying dense water into the Denmark Strait, and how the transport is partitioned between the three overflow pathways. Once this is established, the third objective is to elucidate the dynamics of the combined upstream circulation system and assess how this impacts the transport and hydrographic variability at the sill. The aim is to determine if the ubiquitous synoptic scale variability of the DSOW at the sill is driven by upstream fluctuations in any of the pathways, and/or if hydraulic processes at the sill influence the upstream circulation. The final objective of the study is to devise a sparse mooring array that could be implemented in the future to optimally monitor the upstream sources of DSOW over interannual to decadal time scales.