RII Track-4:NSF: Evaluating the Role of Deep Ocean Equilibration in Warmer Climates

RII Track-4：NSF：评估深海平衡在温暖气候中的作用

• 批准号: 2327230
• 负责人: Weimin Si
• 金额: $ 27.08万
• 依托单位: Brown University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2024
• 资助国家: 美国
• 起止时间: 2024-01-01 至 2025-12-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2327230&HistoricalAwards=false
• 关键词: RII; Track; NSF; Evaluating; Role

This Research Infrastructure Improvement Track-4 EPSCoR Research Fellows project will provide a fellowship to a Senior Research Associate and training for a graduate student at Brown University. This work would be conducted in collaboration with researchers at the National Center for Atmospheric Research (NCAR). The Intergovernmental Panel on Climate Change (IPCC 2021) predicts that atmospheric pCO2 will likely reach 940-1490 ppm by the end of the century. Consequently, global temperature is expected to increase by 1.5-4.5°C. This relationship between pCO2 levels and the magnitude of warming estimated from climate models is known as climate sensitivity. Models, however, are built upon an incomplete understanding of Earth’s climate system and, to some extent, upon simplifications of biogeochemical- and physical processes that drive climatic feedback due to our limited computational capability to fully grasp the vast complexity of the system. On the other hand, reconstructions of past climate change using deep-time archives, although sparse in time and space, offer ground truths of equilibrium climatic responses to elevated pCO2, allowing climatologists to benchmark the performance of climate models. In this proposed study, the PI and researchers at NCAR will collaborate to integrate paleoclimate reconstructions of 15 million years ago (aka. the Middle Miocene) with climate model simulations. Current studies suggest that the Middle Miocene was ~6-10°C warmer than today while estimated pCO2 was only 200-300 ppm higher. This suggests a climate sensitivity of 6-10°C warming per doubling of pCO2, much higher than the 1.5-4.5°C suggested by IPCC 2021. The new study aims to explore possible explanations for this model-data discrepancy, with the hope that insights we gain from studying climatic processes under past warm conditions can improve our knowledge about future climate changes.Projections of future global warming depend critically on our knowledge of climate sensitivity, which is continually refined by emerging reconstructions of past warm climates. The mid-Miocene Climate Optimum (MMCO, ~17.5-13.9 Ma) is one such period that has recently inspired the development of paleoclimate simulations, aimed at improving our understanding of climatic dynamics when estimated pCO2 was higher than today. Paleoclimate records, however, pose several challenges to climate models, including high climate sensitivities and flat meridional temperature gradients, both of which are difficult to reproduce in models. This proposal puts forth a hypothesis that a possibly overlooked contributing factor to MMCO warming and model-data disagreement is the equilibrium responses of the deep ocean under elevated CO2 forcing. Unlike SST, Miocene deep-ocean temperature and circulation have not received much attention. Yet increasing evidence suggests that the equilibrium responses of the deep ocean differ from transient responses, and significantly affect the spatial and temporal patterns of surface warming. Evolving feedback with changing SST patterns and the degree of equilibration in turn influences equilibrium climate sensitivity. This proposed study seeks to address this gap by (1) performing long-running MMCO simulations (6000 years) in collaboration with Jiang Zhu at NCAR (host institution) to produce equilibrium responses of the deep ocean; (2) comparing simulated MMCO oceans with paleo-proxies including benthic δ13C and Neodymium isotopes (ɛNd) to explore patterns of Miocene ocean circulation; and (3) examining whether modeled equilibrium responses of the deep ocean reduce model-data mismatches in deep-water temperatures as well as the spatial patterns of SST, with focuses on the warming anomalies in the North Atlantic and the flat meridional temperature gradients during the MMCO.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.

该研究基础设施改进 Track-4 EPSCoR 研究员项目将为布朗大学的高级研究员提供奖学金，并为研究生提供培训。这项工作将与国家大气研究中心（NCAR）的研究人员合作进行。 政府间气候变化专门委员会 (IPCC 2021) 预测，到本世纪末，大气中的 pCO2 浓度可能会达到 940-1490 ppm。因此，全球气温预计将上升 1.5-4.5°C。 pCO2 水平与根据气候模型估计的变暖程度之间的关系称为气候敏感性。然而，模型是建立在对地球气候系统的不完全理解的基础上的，并且在某种程度上是建立在生物地球化学和物理过程的简化基础上的，这些过程推动了气候反馈，因为我们的计算能力有限，无法完全掌握系统的巨大复杂性。另一方面，利用深度档案重建过去的气候变化，尽管在时间和空间上都很稀疏，但提供了平衡气候对二氧化碳浓度升高的反应的基本事实，使气候学家能够对气候模型的性能进行基准测试。在这项拟议的研究中，PI 和 NCAR 的研究人员将合作将 1500 万年前（又名中中新世）的古气候重建与气候模型模拟结合起来。目前的研究表明，中中新世的温度比现在高约 6-10°C，而估计的 pCO2 仅高出 200-300 ppm。这表明pCO2每增加一倍，气候敏感性就会升高6-10°C，远高于IPCC 2021建议的1.5-4.5°C。这项新研究旨在探索这种模型数据差异的可能解释，希望我们从研究过去温暖条件下的气候过程中获得的见解可以提高我们对未来气候变化的了解。对未来全球变暖的预测主要取决于我们对 气候敏感性，通过对过去温暖气候的不断重建而不断完善。中新世中期气候最适期（MMCO，~17.5-13.9 Ma）就是这样一个时期，它最近激发了古气候模拟的发展，旨在提高我们对估计 pCO2 高于今天时的气候动态的理解。然而，古气候记录对气候模型提出了一些挑战，包括高气候敏感性和平坦的经向温度梯度，这两者都很难在模型中重现。该提案提出了一个假设，即 MMCO 变暖和模型数据不一致的一个可能被忽视的影响因素是深海在二氧化碳强迫作用下的平衡响应。与海表温度不同，中新世深海温度和环流并未受到太多关注。然而，越来越多的证据表明，深海的平衡响应与瞬态响应不同，并且显着影响表面变暖的空间和时间模式。随着海温模式和平衡程度变化的反馈不断变化，进而影响平衡气候敏感性。本研究旨在通过以下方式解决这一差距：(1) 与 NCAR（主办机构）的 Zhuiang Zhu 合作进行长期运行的 MMCO 模拟（6000 年），以产生深海的平衡响应； （2）将模拟的MMCO海洋与包括底栖δ13C和钕同位素（ɛNd）在内的古代理进行比较，以探索中新世海洋环流的模式； (3) 研究深海的模拟平衡响应是否减少深水温度以及海表温度空间模式的模型数据不匹配，重点关注北大西洋的变暖异常和 MMCO 期间平坦的经向温度梯度。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的评估进行评估，认为值得支持。 影响审查标准。