Beyond the instrumental record: Reconstructing Atlantic overturning over the past 7000 yrs (ReconAMOC)

超越乐器记录：重建过去 7000 年的大西洋倾覆 (ReconAMOC)

• 批准号: NE/S009736/1
• 负责人: David Thornalley
• 金额: $ 71.66万
• 依托单位: University College London
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2019
• 资助国家: 英国
• 起止时间: 2019 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FS009736%2F1
• 关键词: Beyond; instrumental; record; Reconstructing; Atlantic

The Atlantic meridional overturning circulation (AMOC) - part of the so-called 'ocean conveyor belt' - is a key component of Earth's climate system. It involves the northward transport of warm surface waters to the high latitude North Atlantic, where they cool (releasing heat to the atmosphere), sink and flow back southwards at depth. Changes in the AMOC are thought to alter global temperature and precipitation patterns, regional sea-level, and socio-economically important marine ecosystems. There are concerns regarding the strength and stability of AMOC in the future. This is because predicted surface ocean warming and freshening could weaken the formation of dense water that helps drive the AMOC. Earlier research suggests that the AMOC may have different stable states, raising the possibility that the AMOC could rapidly switch to a weaker, or even an 'off', state, having a severe impact on global climate. IPCC models do not predict an abrupt weakening of the AMOC under typical 21st century scenarios; yet there are suggestions that current climate models may be excessively stable.NERC and the international community have invested heavily in monitoring the AMOC, including the implementation of the RAPID array since 2004 and more recently the OSNAP array. Since observations began in 2004, AMOC has weakened at a rate ten times faster than predicted by most models. Yet the extent to which this decline can be attributed to natural multi-decadal variability is uncertain. The limited time span of the RAPID array means we are unable to gain an understanding of the nature of AMOC variability on timescales longer than interannual-to-decadal. Therefore we must turn to geological archives to reconstruct AMOC changes beyond the instrumental record. Yet there are no existing records to provide perspective on recent AMOC variability at multi-decadal and longer timescales. Using recent, novel techniques to constrain past variability, coupled with exceptional sediment archives, ReconAMOC will constrain past AMOC variability on decadal to centennial timescales, generating records for the last 7000 years that will become benchmark constraints on AMOC behaviour. We will focus on the past 7000 years because the climate was not dramatically different to the present day, and remnant glacial ice sheets had melted away so that the major features of deep Atlantic circulation were broadly similar to modern. ReconAMOC deploys a twin approach that utilizes (i) the characteristic subsurface temperature AMOC fingerprint, and (ii) the deep western boundary current response to AMOC change. We have verified these new paleoclimate approaches against variability in the instrumental record and demonstrated their applicability through an extensive pilot study. ReconAMOC is therefore a low risk yet ambitious project, bringing together an international team of collaborators, that will meet a long-sought and much-needed requirement of a wide range of climate scientists and modellers. ReconAMOC will enable testing and improvement of model simulations of AMOC that help facilitate assessment of the vulnerability of the AMOC to climate change, and permit the investigation of the role of AMOC on other components of the climate system. The topics addressed by ReconAMOC are key research targets at national UK (e.g. identified strategic science themes and goals within the NERC strategy) and international (e.g. CMIP6, IMAGESII, SCOR, PAGES, IODP and NSF) levels. Specifically, the ReconAMOC proposal builds on the NERC programmes RAPID, RAPID-WATCH, and RAPID-AMOC, in which interannual to multi-decadal variability in the AMOC is a central focus, as well as NERC programme ACSIS examining interannual to decadal climate variability in the Atlantic.

大西洋纬向翻转环流（AMOC）-所谓的“海洋传送带”的一部分-是地球气候系统的关键组成部分。它涉及到温暖的表层沃茨向北输送到高纬度的北大西洋，在那里它们冷却（向大气释放热量），下沉并在深处向南回流。AMOC的变化被认为会改变全球温度和降水模式、区域海平面以及具有社会经济重要性的海洋生态系统。有人担心AMOC未来的实力和稳定性。这是因为预测的表层海洋变暖和淡化可能会削弱有助于驱动AMOC的稠密水的形成。早期的研究表明，AMOC可能有不同的稳定状态，这增加了AMOC可能迅速切换到较弱甚至“关闭”状态的可能性，从而对全球气候产生严重影响。IPCC的模型并没有预测在典型的21世纪世纪情景下AMOC会突然减弱;但也有人认为目前的气候模型可能过于稳定。NERC和国际社会在监测AMOC方面投入了大量资金，包括自2004年以来实施的RAPID阵列和最近的OSNAP阵列。自2004年开始观测以来，AMOC的减弱速度比大多数模型预测的要快10倍。然而，这一下降在多大程度上可归因于自然的多年代际变率是不确定的。RAPID阵列的时间跨度有限，这意味着我们无法了解AMOC变化的性质，时间尺度长于年际到年代际。因此，我们必须求助于地质档案来重建仪器记录之外的AMOC变化。然而，没有现有的记录，以提供对最近的AMOC变化在几十年和更长的时间尺度的观点。使用最近的新技术来限制过去的变化，再加上特殊的沉积物档案，ReconAMOC将限制过去AMOC的变化在十年到百年的时间尺度上，产生过去7000年的记录，这将成为AMOC行为的基准约束。我们将重点放在过去的7000年，因为气候与今天没有显着不同，残留的冰川冰盖已经融化，因此大西洋深层环流的主要特征与现代大致相似。ReconAMOC部署了一种双方法，该方法利用（i）特征地下温度AMOC指纹，以及（ii）深部西部边界电流对AMOC变化的响应。我们已经验证了这些新的古气候方法对仪器记录的变化，并通过广泛的试点研究证明其适用性。因此，ReconAMOC是一个低风险但雄心勃勃的项目，汇集了一个国际合作者团队，将满足广泛的气候科学家和建模者长期寻求和迫切需要的要求。ReconAMOC将能够测试和改进AMOC的模型模拟，帮助评估AMOC对气候变化的脆弱性，并允许调查AMOC对气候系统其他组成部分的作用。ReconAMOC所涉及的主题是英国国家（例如NERC战略中确定的战略科学主题和目标）和国际（例如CMIP 6，IMAGESII，SCOR，PAGES，IODP和NSF）级别的关键研究目标。具体地说，ReconAMOC建议是建立在NERC的RAPID、RAPID-WATCH和RAPID-AMOC方案的基础上的，其中AMOC的年际至多年代变率是核心重点，NERC的ACSIS方案则研究大西洋的年际至十年期气候变率。

项目成果

No consistent simulated trends in the Atlantic Meridional Overturning Circulation for the past 6,000 years

过去 6000 年来大西洋经向翻转环流没有一致的模拟趋势

• DOI: 10.22541/essoar.167591075.56722533/v1
• 发表时间: 2023
• 作者: Jiang Z

Indian Ocean variability changes in the Palaeoclimate Model Intercomparison Project

古气候模型比对项目中的印度洋变率变化

• DOI: 10.5194/egusphere-2022-1102
• 发表时间: 2022
• 作者: Brierley C

No changes in overall AMOC strength in interglacial PMIP4 timeslices

间冰期 PMIP4 时间片中 AMOC 整体强度没有变化

• DOI: 10.5194/cp-2022-63
• 发表时间: 2022
• 作者: Jiang Z

Current Atlantic Meridional Overturning Circulation weakest in last millennium

• DOI: 10.1038/s41561-021-00699-z
• 发表时间: 2021-02-25
• 期刊: NATURE GEOSCIENCE
• 影响因子: 18.3
• 作者: Caesar, L.;McCarthy, G. D.;Rahmstorf, S.
• 通讯作者: Rahmstorf, S.

No changes in overall AMOC strength in interglacial PMIP4 time slices

• DOI: 10.5194/cp-19-107-2023
• 发表时间: 2023-01
• 期刊: Climate of the Past
• 影响因子: 4.3
• 作者: Zhiyi Jiang;C. Brierley;D. Thornalley;Sophie E. Sax