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.

这个研究基础设施改善轨道-4 EPSCoR研究员项目将提供奖学金，以高级研究助理和培训研究生在布朗大学。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，到世纪末，大气pCO 2可能达到940-1490 ppm。因此，全球气温预计将上升1.5-4.5°C。pCO 2水平与气候模型估计的变暖幅度之间的这种关系被称为气候敏感性。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，在某种程度上，由于我们有限的计算能力，无法完全掌握系统的巨大复杂性，模型是建立在对驱动气候反馈的地球化学和物理过程的简化基础上的。另一方面，使用深时档案重建过去的气候变化，虽然在时间和空间上稀疏，但提供了对pCO 2升高的平衡气候反应的地面事实，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的研究人员将合作整合1500万年前的古气候重建。中中新世）与气候模型模拟。目前的研究表明，中新世中期比今天高出约6-10°C，而估计的pCO 2仅高出200-300 ppm。这表明pCO 2每增加一倍，气候敏感性为6-10°C，远高于IPCC 2021建议的1.5-4.5°C。这项新的研究旨在探索这种模式-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认识。未来全球变暖的预测主要取决于我们对气候敏感性的认识，这是通过对过去温暖气候的重建不断完善的。中新世中期气候适宜期（MMCO，~17.5-13.9 Ma）就是这样一个时期，最近激发了古气候模拟的发展，旨在提高我们对pCO 2估计值高于今天时气候动力学的理解。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纬向温度梯度，这两者都难以在模型中重现。该提案提出了一个假设，即MMCO变暖和模式数据不一致的一个可能被忽视的因素是深海在CO2强迫升高下的平衡响应。与SST不同，中新世深海温度和环流没有受到太多的关注。然而，越来越多的证据表明，深海的平衡响应不同于瞬态响应，并显着影响表面变暖的空间和时间模式。随着SST型和平衡程度的变化而不断发展的反馈反过来又影响着平衡气候的敏感性。这项拟议的研究旨在解决这一差距，通过（1）执行长期运行的MMCO模拟（6000年）与NCAR的Jiang Zhu合作（2）将模拟的MMCO海洋与海底δ ~（13）C和Neo_3 ~（Nd）同位素等古代用指标进行对比，探讨中新世海洋环流模式;以及（3）检验模拟的深海平衡响应是否减少了深海温度以及SST空间模式中的模型数据不匹配，重点关注北大西洋的变暖异常和MMCO期间的平纬向温度梯度。该奖项反映了NSF的法定使命，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，