Collaborative research: Quantifying Global and Regional Impacts of the Atlantic Meridional Overturning Circulation (AMOC) Slowdown in the 21st (twenty-first) Century

合作研究：量化 21 世纪大西洋经向翻转环流 (AMOC) 放缓对全球和区域的影响

• 批准号: 2053121
• 负责人: Wei Liu
• 金额: $ 32.5万
• 依托单位: University of California-Riverside
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-07-15 至 2024-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2053121&HistoricalAwards=false
• 关键词: Collaborative; research; Quantifying; Global; Regional

A denser liquid will sink below a lighter one just as vinegar sinks below oil in a salad dressing. This sinking effect happens in the North Atlantic around Greenland and Iceland, where warm surface water brought by the Gulf Stream cools in the subarctic climate and becomes denser than the water below it. The cold surface water sinks to great depth where it flows slowly southward, circulating throughout the world's oceans before resurfacing and returning to the North Atlantic. The resulting Atlantic Meridional Overturning Circulation (AMOC) moves surface water northward and deep water southward throughout the entire Atlantic basin. The AMOC transports heat northward over its whole length, not just from the warmer tropics to the colder high latitudes of the Northern Hemisphere but across the equator as well, transferring heat from the Southern Hemisphere into the Northern Hemisphere.Simulations of the response of climate to increases in greenhouse gas concentrations consistently show a slowdown of the AMOC as climate warms, a consequence of warming-induced reductions in the density of surface water in the northern North Atlantic. Density reduction is a direct consequence of warmer water temperature but reductions in saltiness also contribute, as fresh water (which is less dense) is added by melting ice sheets and increased precipitation. Also, the increased moisture content of warmer surface air reduces evaporation, and reduced evaporation means less salty surface water since evaporation removes fresh water leaving salt behind. There is observational evidence for AMOC slowdown but the period of record is somewhat short for a definitive assessment.Several climatic effects of AMOC slowdown have been claimed, including changes in precipitation over Europe, an increase in North Atlantic storms tracking into Europe, changes in the frequency and strength of El Nino events, and a southward shift in the intertropical convergence zone (ITCZ), the narrow rain band that typically sits north of the equator over the tropical oceans. Many authors have argued that the AMOC slowdown is responsible for the North Atlantic Warming Hole (NAWH), a region of minimal warming or even slight cooling found in the North Atlantic south of Greenland in most climate change simulations. A reduction in AMOC heat transport into the northern North Atlantic is a reasonable explanation for the warming hole, but it is possible to produce a NAWH in global warming simulations using a model that does not allow AMOC slowdown.Work supported through this award uses a novel methodology to examine the effects of AMOC slowdown and their connection to the NAWH using simulations from an ensemble of four climate models. The simulations use a novel methodology in which just enough salt is removed from the surface ocean in the northern North Atlantic to prevent the AMOC slowdown that would otherwise occur due to greenhouse gas-induced warming. A preliminary simulation performed with a version of the Community Earth System Model (CESM) produces the NAWH as a consequence of AMOC slowdown, along with a reduction in rainfall over the warming hole and several other climatic impacts. But results from a single model are not definitive given that differences in model formulation can lead to substantial differences in model behavior. The project also includes a detailed examination of the mechanisms through which AMOC slowdown causes local and remote responses.The work has societal relevance due to the human impacts of climate change and the need to help decision makers confronting climate change. The Principal Investigators conduct outreach activities at two museums, the Museum of Riverside and the Peabody Museum of Natural History, including public lectures and symposia as well as teacher development workshops. The project supports a graduate student and a postdoctoral fellow, thereby supporting workforce development in this research area.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.

密度大的液体会沉到密度小的液体下面，就像沙拉酱中的醋沉到油下面一样。 这种下沉效应发生在格陵兰岛和冰岛周围的北大西洋，墨西哥湾流带来的温暖的地表水在亚北极气候下冷却，变得比下面的水更稠密。寒冷的地表水下沉到很深的地方，缓慢地向南流动，在重新浮出水面并返回北大西洋之前，在世界各地的海洋中循环。由此产生的大西洋经向翻转环流（AMOC）使整个大西洋盆地的表层水向北移动，深层水向南移动。 AMOC在其整个长度上向北输送热量，不仅从较温暖的热带地区向北方半球较冷的高纬度地区输送热量，而且还穿过赤道，将热量从南半球输送到北方半球。气候对温室气体浓度增加的响应的模拟一致显示，随着气候变暖，AMOC的减缓，这是北大西洋北方表层水密度因变暖而减少的结果。 密度降低是水温升高的直接后果，但盐度的降低也有贡献，因为冰盖融化和降水增加增加了淡水（密度较低）。此外，较温暖的地表空气中水分含量的增加减少了蒸发，而蒸发的减少意味着含盐的地表水减少，因为蒸发会将淡水带走，留下盐。 有观测证据表明AMOC减速，但记录的时间有点短，无法进行明确的评估。AMOC减速的几种气候影响已经被声称，包括欧洲降水量的变化，进入欧洲的北大西洋风暴的增加，厄尔尼诺事件的频率和强度的变化，以及热带辐合带（ITCZ）的南移，典型地位于赤道以北热带海洋上方的狭窄雨带。 许多作者认为，AMOC减速是北大西洋变暖洞（NAWH）的原因，在大多数气候变化模拟中，在格陵兰岛以南的北大西洋发现了最小变暖甚至轻微冷却的区域。 进入北大西洋北方的AMOC热量传输减少是变暖洞的合理解释，但使用不允许AMOC减速的模型在全球变暖模拟中产生NAWH是可能的。通过该奖项支持的工作使用一种新颖的方法来检查AMOC减速的影响及其与NAWH的联系，使用四个气候模型的集合模拟。 这些模拟使用了一种新的方法，即从北大西洋北方的表层海洋中去除足够的盐，以防止由于温室气体引起的变暖而发生的AMOC减缓。 用社区地球系统模型（CESM）的一个版本进行的初步模拟产生了NAWH，这是AMOC减速的结果，沿着变暖洞降雨量的减少和其他几个气候影响。但是，单一模型的结果并不是决定性的，因为模型表述的差异可能导致模型行为的实质性差异。 该项目还包括详细研究AMOC减缓导致当地和偏远地区响应的机制。由于气候变化对人类的影响以及帮助决策者应对气候变化的必要性，这项工作具有社会意义。 主要研究人员在两个博物馆开展外展活动，即滨江博物馆和皮博迪自然历史博物馆，包括公开讲座和研讨会以及教师发展研讨会。 该项目支持一名研究生和一名博士后研究员，从而支持该研究领域的劳动力发展。该奖项反映了NSF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。

项目成果

The Impacts of a Weakened Atlantic Meridional Overturning Circulation on ENSO in a Warmer Climate

• DOI: 10.1029/2023gl103025
• 发表时间: 2023-04
• 期刊: Geophysical Research Letters
• 影响因子: 5.2
• 作者: Wei Liu;David Duarte Cavalcante Pinto;A. Fedorov;Jiang Zhu

The Role of a Weakened Atlantic Meridional Overturning Circulation in Modulating Marine Heatwaves in a Warming Climate

• DOI: 10.1029/2021gl095941
• 发表时间: 2021-11
• 期刊: Geophysical Research Letters
• 影响因子: 5.2
• 作者: Xianglin Ren;Wei Liu

Interaction between Arctic sea ice and the Atlantic meridional overturning circulation in a warming climate

• DOI: 10.1007/s00382-021-05993-5
• 发表时间: 2021-10-20
• 期刊: CLIMATE DYNAMICS
• 影响因子: 4.6
• 作者: Liu, Wei;Fedorov, Alexey
• 通讯作者: Fedorov, Alexey