A Process Study of the Atlantic Water Transport over the Greenland-Scotland Ridge

格陵兰-苏格兰海脊（GSR）系统在气候系统中起着巨大的作用。在近地层中，温暖和含盐的大西洋水向北穿过海槽，而轻度极地沃茨主要通过丹麦海峡向南移动。在低层，溢流将冷水和浓水输送到大西洋。大西洋水的流入是北冰洋和北欧海的主要海洋热传输。海槽地区这种输送的变化影响到北欧海和北冰洋的海洋、气候、海冰和生态系统的状况。然而，在了解大西洋水的运输如何响应大气强迫的变化方面仍然存在重大差距。大西洋水流入的平均输送主要是由浮力通量强迫的。季节到年际时间尺度的变化是由于风应力和浮力通量，但仍然有许多不确定性，如何以及从大气强迫影响大西洋水运输。大西洋水的流入不仅受到海平面升降区当地大气强迫的影响，而且还受到与之相连的两个盆地的影响。它还与北欧海洋溢出相互作用。拟议的研究旨在确定将大气变化与大西洋水输送联系起来的基本机制和过程。它将有助于评估气候预测模型，并减少北极气候系统未来变化的潜在关键驱动因素的不确定性。这项研究将有助于海洋展望倡议，这是世界卫生组织和挪威卑尔根海洋研究集群于2015年成立的一个合资企业，也将进一步促进高威协议中概述的加强跨大西洋合作的目标。格陵兰-苏格兰海脊（GSR）是大西洋和北欧海/北冰洋之间的主要地形屏障。它限制了温暖和含盐的大西洋与寒冷和新鲜的北冰洋之间的流动。大西洋水在海平面上的交换流受多个复杂过程和强迫的影响。该项目将研究大西洋和北欧海之间的交换流动的主要动力过程，这两个海洋之间被一个浅的海脊分隔开。将利用具有现有观测数据和数据同化海洋估计值的数值模型进行过程研究，以审查本地和远程强迫如何引起海平面以上大西洋水输运的变化。其目标是更好地了解管理大西洋水流入及其在海平面区域变化的关键机制和过程。首先，一个2层模型将被用来开发直觉，并检查领先的顺序动态平衡。该模型的效率允许在几十年内进行多次模拟。动态的简单性和透明度非常适合于发展想法和阐明竞争机制以及隔离关键过程。在2层模型中确定的机制和过程将通过使用更现实的1/12度混合坐标模型（HYCOM）进行检查。HYCOM模式也将被用来研究浮力强迫在大西洋水运输的变化中的作用。利用同化的海洋环流气候估算第四版（ECCO 4）资料和现场及卫星观测资料对模式进行检验。与观测数据和数据同化估计的一致性。其前提是，ECCO 4，其同化的温度/盐度廓线，卫星海面高度和海底压力，比没有数据同化的海洋模式更现实地代表的变化。总的来说，这项研究将提高目前对一个关键海洋过程的认识，这个过程对北极和大西洋的海洋环流和气候都非常重要。两个盆地之间的地形交换流是世界上的共同特征。海洋循环系统。其他的例子包括从太平洋到北冰洋的流量通过白令海峡，在日本海的通流等，这项研究将导致更好地了解内在的动态，是重要的一般情况下，跨脊流在世界海洋两个盆地之间。

The Greenland-Scotland Ridge (GSR) system plays an outsized role in the climate system. In the surface layer, the warm and saline Atlantic Water flows northward across the GSR and the light Polar Waters moves southward mainly through the Denmark Strait. In the lower layer, the overflow transports the cold and dense water over the GSR into the Atlantic Ocean. This inflow of Atlantic Water is the primary oceanic heat transport to the Arctic Ocean and the Nordic Seas. Changes in this transport over the GSR affect the state of the ocean, climate, sea ice and ecosystem in the Nordic Seas and the Arctic Ocean. Yet there is still a significant gap in understanding how the transport of the Atlantic Water is responding to changes in atmospheric forcing. The mean transport of the Atlantic Water inflow is primarily forced by buoyancy flux. Variability on seasonal to inter-annual time scales are attributable to both wind stress and buoyancy fluxes, but there remain many uncertainties regarding how and from where the atmospheric forcing influences the Atlantic Water transport. The Atlantic Water inflow is influenced not only by atmospheric forcing locally at the GSR, but in the two basins that it is connected with. It also interacts with the Nordic Seas Overflow. The proposed study seeks to identify essential mechanisms and processes that link changes in the atmosphere to Atlantic Water transport. It will help assessments of climate prediction models and reduce uncertainties of a potential key driver for future changes in the Arctic climate system. This study will contribute to the Ocean Outlook initiative, a joint venture established in 2015 between WHOI and the Bergen Marine Research Cluster in Norway and will also further the goal of enhancing trans-Atlantic collaborations as outlined in the Galway agreement.The Greenland-Scotland Ridge (GSR) is the main topographic barrier between the Atlantic and the Nordic Seas/Arctic Ocean. It restricts flows between the warm and saline Atlantic Ocean and the cold and fresh Arctic Ocean. The exchange flow of Atlantic Water over the GSR is influenced by multiple and complex processes and forcing. This project will examine key dynamical processes that govern exchange flows between the Atlantic Ocean and the Nordic Seas that are separated by a shallow GSR. Process studies using numerical models with available observations and a data-assimilated ocean estimate will be conducted to examine how local and remote forcing gives rise to variations in Atlantic Water transport over the GSR. The goal is to develop a better understanding of key mechanisms and processes that govern the Atlantic Water inflow and its variability across the GSR. First a 2-layer model will be used to develop intuitions, and to examine leading order dynamical balances. The efficiency of the model allows multiple simulations over several decades. The simplicity and transparency in dynamics are ideally suited for developing ideas and elucidating competing mechanisms and in isolating key processes. The mechanisms and processes that are identified in the 2-layer model will be examined by using the more realistic 1/12 degree Hybrid Coordinate Model (HYCOM). The HYCOM model will also be used to examine the role of buoyancy forcing in the variability of Atlantic Water transport. The data-assimilated Estimating the Circulation & Climate of the Ocean version 4 (ECCO 4) and in situ and satellite observations will be used to check the model?s consistency with observational data and data-assimilated estimates. The premise is that the ECCO 4, with its assimilation of temperature/salinity profiles, satellite sea surface height and bottom pressure, represents the variability more realistically than ocean models without data assimilation. Overall, the study will improve current understanding of a key oceanic process that is very important for ocean circulation and climate in both Arctic and Atlantic. Exchange flows over topography between two basins are common features in the world?s ocean circulation system. Other examples include the flow from the Pacific to the Arctic Ocean through Bering Strait, throughflows in the Japan Sea, etc. This study will result in a better understanding of intrinsic dynamics that are important to general cases of cross-ridge flows between two basins in the world ocean.