Collaborative Research: Overturning in the Subpolar North Atlantic Program

自2014年以来，由美国领导的一项国际努力——北大西洋亚极地翻转计划（Overturning in the Subpolar North Atlantic Program，简称opsnap）与英国、荷兰、加拿大和德国合作，提供了北大西洋亚极地的全水柱、跨盆地的热量、质量和淡水通量的连续记录。OSNAP头四年的观测结果挑战了目前对北大西洋次极地翻转环流的理解。这笔赠款为另外四年的观测提供资金，以便向社区提供关于次极盆地经向翻转、热量和淡水通量的十年时间序列。这些量的变化已被用来解释北大西洋、北欧海和北冰洋各种物理、化学和生物参数的变化。因此，通过量化大西洋经向翻转变异性并了解其驱动因素，OSNAP为解决与社会相关的跨学科问题提供了关键的第一步，这些问题涉及格陵兰冰和北极海冰的融化、北冰洋的热含量、北欧海的气候和人为碳储存。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)海洋生物地球化学和碳封存；2)海洋模型倾覆；3)北极冰冻圈；4)北欧海变率。两名新的博士后和一名研究生将在OSNAP的这一阶段得到支持，他们将受益于方法的多样性，并接触到大量的OSNAP国际科学家。此外，到2024年，来自不同美国和国际机构的大约20名研究生将通过参加OSNAP游轮接受实地培训。OSNAP观测系统头四年的数据表明，从格陵兰岛到苏格兰的东部次极区主导着北大西洋次极区平均经向质量和热量输送，而一半以上的经向淡水输送发生在拉布拉多盆地。在以往工作成功的基础上，本项目扩展了时间序列，并解决了以下关键问题：在季节内到年际时间尺度上，是什么支配着北大西洋次极环流的翻转变异性？2. OSNAP部分的淡水来源是什么？是什么决定了它们的变化？3. 次极环流中经向热量和淡水通量的影响是什么？OSNAP下一阶段的另一个动力是，我们对北大西洋亚极地动态和变化的理解取得了根本性的进步，这将由美国四个主要的OSNAP系泊阵列单独或与其他OSNAP观测相结合产生。预计进一步的观测将为该地区的新翻覆范式提供强有力的观测基础，其中将包括对致密水形成与翻覆之间联系的理解——这种联系存在于气候模式中，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西海岸和冰岛盆地内的上深海边界流的结构和运输，并确定其变异性和强迫机制。该奖项反映了美国国家科学基金会的法定使命，并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，被认为值得支持。

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.