Towards two decades of ocean mass and heat transports at 26.5N: Extension of the RAPID-MOCHA Array

气候模式表明，大西洋经向翻转环流（AMOC）的变率与海面温度在年际到几十年时间尺度上的变化有关，这可能产生深远的社会影响。此外，气候模式继续预测下个世纪AMOC的显著减弱，这可能通过减少向北的热量输送以及北大西洋二氧化碳吸收的减少而反馈给气候系统。由于缺乏对其变率的长期测量，AMOC在气候系统中的具体作用一直难以确定。在当前阶段结束时，沿26.5°N的RAPID-MOCHA观测系统将提供近19年的AMOC连续估计，这是目前可用的最长的全深度、全流域海洋运输测量。这些观测结果为评估强迫的、数据同化的和耦合的气候模式提供了一个关键的基准，并形成了一个基本的基石，围绕着这个基石，国际项目正在开发，以监测整个大西洋盆地的AMOC。从2023年1月到2026年6月，该项目将使美国对RAPID-MOCHA的贡献再延长42个月，将海洋质量、热量和淡水运输的时间序列延长至22.3年。该项目的结果将继续为评估和改进强迫、数据同化和耦合气候模式提供至关重要的海洋观测。拟议的项目继续了私家侦探和私人侦探之间的成功合作来自英国国家海洋学中心（National Oceanography Centre）的研究人员正在提交一份配套提案，要求通过英国的资金来源在同一时期维持他们的观测系统。该项目还与美国国家海洋和大气管理局（NOAA）的西部边界时间序列项目合作，并为研究生和博士后研究人员提供培训。(1)使用海底电缆监测佛罗里达海流，通过定期巡航进行水文和速度测量校准；(2)在巴哈马以东的深西部边界海流和安的列斯海流区域内进行连续的系泊时间序列测量，包括大约11个月的水文和速度剖面。重复水文剖面的维护将与NOAA合作进行，NOAA也独立支持佛罗里达洋流的监测。英国合作者将为东部盆地系泊提供支持，以完成26.5°N跨盆地时间序列观测系统。还将包括系泊处有限的新仪器，以获得巴哈马以东边界的海底压力梯度。RAPID-MOCHA观测将使研究小组能够记录和理解AMOC年际和年代际变化的原因和影响，研究西部边界压力对输送的控制，并将在26.5°N观测到的AMOC变化与其他AMOC指数和大西洋盆地周围正在进行的AMOC测量项目的结果联系起来。通过量化北大西洋26.5°N地区质量、热量和淡水经向环流的年际至年代际变化，该项目将进一步有助于了解导致海面温度、海气通量、海洋热量和淡水储量变化的过程，这些变化是北大西洋区域气候和全球气候的组成部分。到目前为止，时间序列显示，相对于该计划的早期，气温出现了较长期的下降，其起源——自然变率或对人为气候变化的反应——尚需通过更长的观测来确定。AMOC在大气和深海之间形成了一个相对快速的通道，对于在与气候相关的时间尺度上持续观测以了解人为强迫气候变化的后果至关重要。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。

Climate models suggest that variability of the Atlantic meridional overturning circulation (AMOC) is linked to sea surface temperature changes on interannual to multi-decadal time scales that can have far reaching societal impacts. Additionally, climate models continue to project a substantial weakening of the AMOC over the next century that could feed back on the climate system through reduced northward heat transport as well as reduced CO2 uptake in the North Atlantic. The specific role of the AMOC in the climate system has been difficult to determine due to a lack of long term measurements of its variability. At the end of its current phase, the RAPID-MOCHA observing system along 26.5°N will have provided continuous estimates of the AMOC for just under 19 years, the longest full-depth, basinwide measurements of oceanic transport currently available. These observations have provided a critical benchmark for the evaluation of forced, data-assimilative, and coupled climate models, and have formed a fundamental building block around which international programs are being developed to monitor the AMOC throughout the Atlantic basin. This project will continue the U. S. contribution to RAPID-MOCHA for an additional 42 months, from January 2023 to June 2026, extending the time series of oceanic mass, heat, and freshwater transports to 22.3 years. The results from this program will continue to provide oceanic observations crucial for the assessment and improvement of forced, data-assimilative, and coupled climate models. The proposed program continues a successful collaborative effort between the P.I.'s and investigators from the U.K. National Oceanography Centre, who are submitting a companion proposal to maintain their part of the observing system for the same time period through U.K. funding sources. The program also collaborates with NOAA AOML in their Western Boundary Time Series program, and provides training for graduate students and postdoctoral researchersThe U.S. contribution to the in-situ observation system includes: (1) Florida Current monitoring using a submarine cable, calibrated by regular cruises with hydrographic and velocity measurements, and (2) continuous moored time series measurements within the Deep Western Boundary Current and Antilles Current region east of the Bahamas, including hydrographic and velocity sections at approximately 11-month intervals. The maintenance of the repeat hydrographic sections will be conducted in collaboration with NOAA which also supports independently the Florida Current monitoring. U.K. collaborators will provide support for the eastern basin moorings that complete the 26.5°N trans-basin time series observing system. Limited new instrumentations on moorings will also be included to derive ocean bottom pressure gradient on the boundary east of the Bahamas. The RAPID-MOCHA observations will allow the team to document and understand the causes and impacts of the AMOC interannual to decadal variability, to investigate the control of western boundary pressure on transports, and to link changes observed at 26.5°N to other AMOC indices and results from on-going AMOC measurement programs around the Atlantic basin. By quantifying the interannual to decadal variability of the meridional circulations of mass, heat, and freshwater in the North Atlantic Ocean at 26.5°N, this project will further contribute to the understanding of the processes leading to changes of sea surface temperature, air-sea fluxes, and ocean heat and freshwater storage that are integral components of the North Atlantic regional climate and global climate. The time series so far have shown a longer-term decline with respect to the early years of the program, the origin of which---natural variability or response to anthropogenic climate change---is yet to be determined from longer observations. The AMOC constitutes a relative rapid conduit between the atmosphere and the deep ocean that is crucial to continuously observe on climate-relevant temporal scales to understand the ramifications of anthropogenically-forced climate change.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.