Ventilation of Denmark Strait Overflow Water in the Iceland and Greenland Seas

大西洋经向翻转环流(AMOC)是全球气候系统的重要组成部分。它的上肢由温暖的大西洋起源的水组成，这些水向极地流经格陵兰-苏格兰山脊，在那里它在北欧海和高北冰洋转换。然后，稠密的水团产品返回南方，通过格陵兰-苏格兰山脊的缝隙进入亚极地北大西洋。在这些密集的溢流中，最大的是丹麦海峡溢流水，它是深西部边界流最底层的部分。以前的观点认为，丹麦海峡溢流水的主要来源是东格陵兰海流中向赤道输送的大西洋来源的水。在这个方案中，水的冷暖转变发生在北欧海缘洋流系统中。然而，最近的观测表明，丹麦海峡溢流水的多达一半(特别是密度最大的部分)来自北冰岛急流，该急流沿着冰岛北坡平流北极中层水。然后问题出现了，北冰岛急流的来源是什么，产生这种水的从暖到冷的转变发生在哪里？为了了解AMOC的运作以及它可能如何应对气候变化，至关重要的是确定其下肢的所有密集水源，并了解形成水的大气和海洋过程。在这里，我们将在冰岛和格陵兰海进行冬季实地考察，同时进行协调的模拟研究，以从根本上提高我们对这一新发现的稠密水源及其与AMOC之间的联系的认识。该项目将首次记录冰岛海西北部和格陵兰海东南部的对流与大气强迫的关系，确定转化的横向范围以及新通风水的体积和水团特征，并描述发生对流的环流特征。通过这样做，将量化水团转化过程、北冰岛急流的出口路径和AMOC深部分支之间的联系。一个外展计划将吸引中学生和普通公众参与，一名研究生将接受该项目的培训。该项目的目的是从根本上促进我们对冰岛北部新发现的稠密水源及其与AMOC的联系的了解。实地活动包括前往该地区的为期六周的冬季水文学巡航，这将与联合王国的大气实地活动同时进行。建模部分将帮助解释将获得的一套广泛的国际观察结果并将其联系起来。冬季巡航由四个部分组成：(1)对冰岛海西北部和格陵兰海东南部的大范围调查，据信密集的北冰岛急流从那里发出(该地区基本上没有冬季观测到的水)。这包括：(1)到每个涡旋中心进行一次漂移；(2)配合飞机活动，测量海洋对冰缘下游目标区域冷空气爆发的反应，那里的混合层应该是最深和最密集的；(3)在Jan Mayen断裂带附近进行重点采样，以评估新通风的致密水从格陵兰海向南流向冰岛海的程度；(4)详细调查冰岛北部急流形成的区域。该项目是美国对一个名为冰岛-格陵兰海项目(IGP)的更广泛国际项目的贡献，该项目旨在研究冰岛海西北部和格陵兰海东南部的海气相互作用以及相关的海洋环流和水团转化。政府间地球科学计划的贡献者来自联合王国、冰岛、加拿大、挪威和荷兰，其中包括一项与海洋实地工作以及大气和海洋模型密切相关的飞机活动。

The Atlantic Meridional Overturning Circulation (AMOC) is a key component of the global climate system. Its upper limb consists of warm Atlantic-origin water that flows poleward across the Greenland-Scotland Ridge where it is transformed in the Nordic Seas and high Arctic Ocean. The dense water mass product then returns southward and enters the sub-polar North Atlantic through gaps in the Greenland-Scotland Ridge. The largest of these dense overflows is the Denmark Strait Overflow Water which feeds the bottom-most component of the Deep Western Boundary Current. Previous thinking has maintained that the dominant source of the Denmark Strait Overflow Water is the Atlantic-origin water transported equatorward in the East Greenland Current. In this scheme the warm-to-cold transformation of water takes place in the rim current system of the Nordic Seas. Recent observations, however, indicate that up to half of the Denmark Strait Overflow Water (in particular, the densest component) emanates from the North Icelandic Jet, which advects Arctic Intermediate Water along the north slope of Iceland. The question then arises, what is the source of the North Icelandic Jet and where does the warm-to-cold transformation occur that produces this water? To understand the workings of the AMOC and how it might respond to changes in climate, it is essential to determine all of the dense water sources to its lower limb and understand the atmospheric and oceanic processes that form the water. Herein a wintertime field program will be conducted in the Iceland and Greenland Seas together with a coordinated modeling study to fundamentally advance our knowledge of this newly identified source of dense water and its link to the AMOC. This project will, for the first time, document convection in the northwest Iceland Sea and southeast Greenland Sea in relation to the atmospheric forcing, determine the lateral extent of the transformation and the volume and water mass characteristics of the newly-ventilated water, and characterize the circulation in which the convection occurs. By doing so, the link between the water mass transformation process, the exit pathway of the North Icelandic Jet, and the deep limb of the AMOC will be quantified. An outreach program will engage secondary school children and the general public, and a graduate student will be trained by the project.The aim of this project is to fundamentally advance our knowledge of this newly identified source of dense water north of Iceland and its link to the AMOC. The field campaign consists of a six-week wintertime hydrographic cruise to the region that will coincide with the atmospheric field campaign from the United Kingdom. The modeling component will help interpret and tie together the extensive set of international observations that will be obtained. The winter cruise has four components: (1) a broad-scale survey of the northwest Iceland Sea and southeast Greenland Sea where the dense North Icelandic Jet water is believed to emanate from (a region essentially devoid of wintertime observations. This includes an excursion into the center of each gyre; (2) adaptive sampling in conjunction with the aircraft campaign to measure the ocean's response to cold-air outbreaks in targeted areas downstream of the ice-edge, where the mixed-layers should be deepest and densest; (3) focused sampling near the Jan Mayen Fracture Zone to assess the degree to which newly ventilated dense water is fluxed southward from the Greenland Sea to the Iceland Sea; and (4) a detailed survey of the region where the North Icelandic Jet is formed. This project is the U.S. contribution to a broader international program, known as the Iceland-Greenland Seas Project (IGP), to study the air-sea interaction in the northwest Iceland Sea and southeast Greenland Sea and the associated ocean circulation and water mass transformation. The IGP has contributors from the United Kingdom, Iceland, Canada, Norway, and the Netherlands and includes an aircraft campaign that is closely coupled to the oceanographic fieldwork, as well as atmospheric and oceanic modeling.