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。它的上肢由温暖的南极起源的水组成，向极地流动穿过格陵兰-苏格兰海脊，在北欧海和北冰洋高地转化。稠密的水质量产品然后返回南部，并通过格陵兰-苏格兰海脊的间隙进入亚极地北大西洋。最大的密集溢出是丹麦海峡溢出水，它为深层西部边界流的最底部成分提供水源。以前的观点认为，丹麦海峡溢出水的主要来源是东格陵兰海流向赤道输送的南极水。在这个方案中，水的暖到冷的转变发生在北欧海的边缘流系统中。然而，最近的观测表明，多达一半的丹麦海峡溢出水（特别是丹麦部分）来自北冰岛急流，它沿沿着冰岛北坡平流输送北极中层水。那么问题就来了，北冰岛急流的来源是什么，在哪里发生了由暖到冷的转变，产生了这些水？为了了解AMOC的工作原理以及它如何应对气候变化，必须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。在此，将在冰岛和格陵兰海进行冬季实地项目，并进行协调的建模研究，以从根本上提高我们对这种新发现的稠密水源及其与AMOC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与大气强迫有关的对流，确定转换的横向范围以及新通风水的体积和水团特征，并描述对流发生的环流。通过这样做，水团的转换过程，北冰岛急流的出口途径，和AMOC的深翼之间的联系将被量化。 一个推广方案将吸引中学生和公众参与，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提高我们对冰岛北部新发现的密集水源及其与AMOC的联系的认识。实地活动包括在冬季对该区域进行为期六周的水文考察，与联合王国的大气实地活动同时进行。建模部分将有助于解释和联系将获得的广泛的国际观测。冬季巡航有四个组成部分：（1）对西北冰岛海和东南格陵兰海进行大规模调查，据信密集的北冰岛急流来自该地区（该地区基本上没有冬季观测）。这包括到每个环流中心的短途旅行;（2）与飞机活动相结合的适应性取样，以测量海洋对冰缘下游目标地区冷空气爆发的反应，那里的混合层应该是最深和密集的;（三）在扬马延断裂带附近进行集中取样，以评估新通风的密集水从格陵兰海向南流动的程度冰岛海;（4）对北冰岛急流形成区域的详细调查。该项目是美国对一个更广泛的国际项目的贡献，该项目被称为冰岛-格陵兰海项目（IGP），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。IGP的贡献者来自英国，冰岛，加拿大，挪威和荷兰，包括一个与海洋实地工作密切相关的飞机运动，以及大气和海洋建模。

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.