Collaborative Research: Evolution and Fate of Eighteen Degree Water in the North Atlantic Subtropical Gyre

该项目将研究与北大西洋亚热带环流内18度水（EDW）的演变（形成，循环和破坏）相关的物理过程。EDW是所有亚热带西部边界流系统的典型的异常厚和垂直均匀模式沃茨的原型。EDW与向北输送热量的浅层翻转环流有关，是异常热量、营养物和CO2的年际储存库。了解EDW演变的年周期，特别是其相关的环流途径和破坏机制，是很重要的，因为尽管EDW在每个冬季结束时被隔离在分层的上层海洋之下，但它可能在随后的几年中重新出现，影响混合层特性，从而影响海气相互作用和初级生产力。研究EDW在调节海洋-大气热交换和真光层营养物质供应中的作用。该计划是综合广泛的观测，包括在最近完成的CLIVAR模式水动力学实验（CLIMODE）收集的大量现场数据集。这一协调一致的实地工作包括一个大型剖面浮标阵列、一个系泊阵列和几次水文测量。为了补充这一独特的数据集，研究人员还将研究当代和历史水文学、Argo剖面浮标、表面漂移、卫星测高和海洋颜色场，以及几个涡分辨OGCM模拟的输出。该项目将测试长期假设的EDW气候重要性，作为北大西洋浅层翻转环流的一个要素，以及作为热量，营养物质，和碳。重要的是，这项研究将促进对破坏EDW的各种过程的理解。此外，本研究还将首次比较和对比大尺度低频环流和中尺度涡动场在EDW扩散和破坏中的作用。最后，由于模式沃茨在每个海洋basin.Broader影响：澄清EDW在大气和海洋之间的热交换中的作用，将支持正在进行的社区努力，以提高年际到十年的可预测性，拟议的工作将提供一个基础的比较研究。例如，EDW及其相关的海气热通量可能会对墨西哥湾流附近北大西洋风暴路径的地面风暴幅度的年与年的变化产生直接影响。此外，了解EDW在营养物质储存和交换中的作用将促进我们对初级生产力年际变化的理解。使用独特的CLIMODE数据集进行严格的模型数据比较也将通过提供对涡分辨数值模型保真度的客观评估来帮助更广泛的社区。最后，该项目将支持两名博士后研究人员和一名研究生的培训。该项目是对美国CLIVAR（CLImate Variability and Predictability）计划的贡献。

This project will examine the physical processes associated with the evolution (formation, circulation, and destruction) of Eighteen Degree Water (EDW) within the subtropical gyre of the North Atlantic Ocean. EDW is the archetype for the anomalously thick and vertically homogenous mode waters that are typical of all subtropical western boundary current systems. EDW is associated with a shallow overturning circulation that carries heat northward and is an interannual reservoir of anomalous heat, nutrients and CO2. Understanding the annual cycle of EDW evolution, and in particular its associated circulation pathways and destruction mechanisms, is important because though EDW is isolated beneath the stratified upper-ocean at the end of each winter, it may reemerge in subsequent years to influence mixed layer properties and consequently air-sea interaction and primary productivity.The pathways of EDW circulation, the processes of EDW destruction, and the role of EDW in modulating ocean-atmosphere heat exchange and nutrient supply to the euphotic zone will be investigated. The plan is to synthesize a broad spectrum of observations including a substantial in-situ dataset collected during the recently completed CLIVAR Mode Water Dynamics Experiment (CLIMODE). This coordinated field effort included a large array of profiling floats, a moored array, and several hydrographic surveys. To supplement this unique dataset the investigators will also examine contemporary and historical hydrography, Argo profiling floats, surface drifters, satellite altimetry and ocean color fields, and output from several eddy-resolving OGCM simulations.Intellectual Merit: This project will test the long-hypothesized climatic importance of EDW as an element of the North Atlantic's shallow overturning circulation and as a short-term reservoir of heat, nutrients, and carbon. Significantly, this study will advance understanding of the various processes that destroy EDW. In addition, this study will, for the first time, compare and contrast the roles of the large-scale, low-frequency circulation and the mesoscale eddy field in EDW dispersal and destruction. Finally, the proposed work will provide a foundation for comparative studies since mode waters are found in every ocean basin.Broader Impacts: Clarifying the role of EDW in the exchange of heat between the atmosphere and ocean will support ongoing community efforts to improve interannual-to-decadal predictability. For example, EDW and its associated air-sea heat flux may have a direct impact on the year-to-year variability of surface storm amplitude in the North Atlantic storm track near the Gulf Stream. In addition, understanding the role of EDW in the storage and exchange of nutrients will advance our understanding of interannual variability in primary productivity. Rigorous model-data comparisons using the unique CLIMODE dataset will also aid the broader community by providing an objective assessment of the fidelity of eddy-resolving numerical models. Finally, the project will support the training of two postdoctoral investigators and a graduate student.This project is a contribution to the U.S. CLIVAR (CLImate VARiability and predictability) program.