Collaborative Research: Overturning in the Subpolar North Atlantic Program

美国领导的国际努力，颠覆在亚极地北大西洋计划（OSNAP），自2014年以来，与英国，荷兰，加拿大和德国合作，提供了完整的水柱，跨流域的热量，质量和淡水通量的连续记录。OSNAP观测头四年的结果挑战了目前对副极地北大西洋翻转环流的理解。 这笔赠款为另外四年的观测提供资金，以便向社区提供亚极地盆地的纬向翻转、热量和淡水通量的十年时间序列。这些数量的变化被用来解释北大西洋、北欧海和北冰洋的各种物理、化学和生物参数的变化。因此，通过量化大西洋纬向翻转变异性并了解其驱动因素，OSNAP为解决有关格陵兰冰和北极海冰融化、北冰洋热含量、北欧海洋气候和人为碳储存的社会相关跨学科问题迈出了关键的第一步。研究人员将通过四个研讨会积极参与更广泛的国际社会，每个研讨会都针对一个与社会相关的主题：1）海洋地球化学和碳封存; 2）海洋模型的翻转; 3）北极冰冻圈; 4）北欧海洋的变化。两个新的博士后和一名研究生将在OSNAP的这一阶段得到支持，并将受益于方法的多样性和接触到大量的OSNAP国际科学家。此外，来自不同美国和国际机构的约20名研究生将通过参加OSNAP巡航到2024年接受实地培训。来自OSNAP观测系统的前四年数据表明，从格陵兰到苏格兰的东副极地地区主导着副极地北大西洋的平均纬向质量和热量输送，而超过一半的跨大西洋淡水运输发生在拉布拉多盆地。 在前人工作成功的基础上，本项目扩展了时间序列，并解决了以下关键问题：1。在季节内到年际时间尺度上，是什么支配着北大西洋副极地环流的翻转变率？2. OSNAP部分的淡水来源是什么，是什么控制了它们的变化？3.副极地环流中的纬向热量和淡水通量的影响是什么？OSNAP下一阶段的额外动力来自于我们对北大西洋副极地动力学和变化的理解的根本性进步，这将来自于美国四个主要的OSNAP系泊阵列，单独和与其他OSNAP观测相结合。预计进一步的观测将为该地区的新翻转模式提供强有力的观测基础，其中包括对密集水形成和翻转之间联系的理解-这是气候模型中存在的一种联系，但迄今尚未观测到。此外，这项工作将进一步量化格陵兰岛东海岸和西海岸以及冰岛盆地内的上层和深海边界流的结构和运输，并确定其变化和强迫机制。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估来支持。

A US-led international effort, Overturning in the Subpolar North Atlantic Program (OSNAP), has provided a continuous record of the full-water column, trans-basin fluxes of heat, mass, and freshwater in the subpolar North Atlantic since 2014, in partnership with the UK, Netherlands, Canada and Germany. Results from the first four years of OSNAP observations have challenged the current understanding of overturning circulation in the subpolar North Atlantic. This grant provides funding for an additional four years of observations in order to deliver to the community a ten-year time series of the meridional overturning, heat and freshwater fluxes in the subpolar basin. Variations in these quantities have been invoked to explain changes in a wide range of physical, chemical and biological parameters in the North Atlantic, Nordic Seas, and Arctic Ocean. Thus, by quantifying Atlantic meridional overturning variability and understanding its drivers, OSNAP is providing a critical first step towards addressing societally-relevant, interdisciplinary questions concerning the melting of Greenland ice and Arctic sea-ice, heat content in the Arctic Ocean, climate of the Nordic Seas, and anthropogenic carbon storage. The researchers will actively engage the broader international communities through four workshops, each targeting a societally relevant theme: 1) ocean biogeochemistry and carbon sequestration; 2) overturning in ocean models; 3) Arctic cryosphere; and 4) Nordic Seas variability. Two new postdocs and one graduate student will be supported in this phase of OSNAP and will benefit from the diversity of methodologies and exposure to the large number of OSNAP international scientists. In addition, approximately 20 graduate students from different US and international institutions will receive field training through participation in OSNAP cruises through 2024.The first four years of data from the OSNAP observing system have shown that the eastern subpolar region, from Greenland to Scotland, dominates the mean meridional mass and heat transport in the subpolar North Atlantic, while more than half of the total meridional freshwater transport occurs across the Labrador basin. Based on the success of the previous work, this project extends the time series and address the following critical questions: 1. What governs overturning variability in the North Atlantic subpolar gyre on intra-seasonal to interannual time scales? 2. What are the sources of freshwater across the OSNAP section and what governs their variability? 3. What are the impacts of the meridional heat and freshwater fluxes in the subpolar gyre? Additional motivation for this next phase of OSNAP is provided by the fundamental advancements in our understanding of subpolar North Atlantic dynamics and variability, that will result from the four main U.S. OSNAP mooring arrays, individually and in combination with other OSNAP observations. Further observations are expected to provide a strong observational basis for a new paradigm of overturning in this region, which will include an understanding of the linkage between dense water formation and overturning - a connection present in climate models, yet unobserved to date. Additionally, this this work will further quantify the structure and transport of the upper and deep ocean boundary currents off the east and west coasts of Greenland and within the Iceland Basin, as well as determine their variability and forcing mechanisms.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.