Numerical Modeling of the Greenhouse-Icehouse Transition: Eocene-Oligocene Boundary

EAR-0652020KUMP目前可用的数值模型不足以研究生物圈历史上最重要的事件。一个这样的事件是大约3400万年前在始新世-渐新世边界从温室到冰室的重大转变，第一次在南极洲建立了大冰盖和其他世界性的气候重组。这类事件在几十万到几百万年的时间尺度上发生，而且本质上是时间连续的，长期成分(如冰盖、二氧化碳)的剧烈变化取决于短期准平衡成分(大气、上层海洋)的当前状态，并以其为反馈。全球生物地球化学循环的盒子模式对于研究海洋、大气和生物群的长期演化是有用的，而海洋-大气耦合大气环流模式是研究几个平衡态和十年至百年气候变化的理想模式。然而，这些工具都不能以足够的空间和时间分辨率模拟重要的长期事件和感兴趣的转变，以提供可测试的预测。该项目将把长期生物地球化学成分与为长期物理气候模拟开发的新可用的耦合技术结合起来，对始新世-渐新世过渡进行第一次空间和时间分辨的生物地球化学调查。耦合技术包括A/OGCM解决方案的矩阵查找表和由R.DeConto和D.Pollard在NSF资助的其他项目中开发的3D冰盖模型的异步驱动。生物地球化学组分已被L.Kump及其合作者广泛开发和应用，包括二维陆地风化和OGCM生物地球化学。最近，J.Zachos和L.Kump应用了这些组件的盒子模型版本，跨越了几百万年的E-O转换。他们发现，生物地球化学反馈可能与物理气候系统有重要的相互作用，导致过渡后超调和海底18O记录中观察到的百万年振荡。使用新的耦合技术和2-D/3-D模型，我们将检验关于E-O转变之前、期间和之后事件的五个具体假设。我们将把结果与广泛的和时间上可分辨的古海洋学数据进行比较和验证，并用陆地代用品加以补充：-底栖生物氧和碳同位素记录限制了底水温度加上冰量、平均海洋同位素组成和深盆梯度；-温度的镁/钙记录；-被动边缘的层序地层记录进一步限制了海平面；-对大气二氧化碳的地质限制；-陆地风化强度、速率和海洋输入的代用品。一名本科生(正在写她的毕业论文)和一名研究生将参与这项研究，本科生主要关注我们关于碳酸盐沉积陆架盆地划分的假设之一。我们将在世界大学网络(WUN；wun.ac.uk)赞助的这个项目的资助期间，通过在宾夕法尼亚州立大学举办夏季讲习班，促进数值模拟专业知识的传播。第一次WUN-SIES/TA研讨会的主题将是深度研究中的建模和数据解释，主要面向研究生、博士后和职业生涯早期的地球科学专业人员。L.Kump在宾夕法尼亚州立大学WUN赞助的活动中发挥了重要作用，包括每月的视频研讨会、研究生交流和研讨会。通过WUN，参与该项目的学生将有机会前往英国南安普敦，与他们的气候建模小组一起工作。

EAR-0652020KUMPCurrently available numerical models are inadequate for the study of the most important events in the history of the biosphere. One such event is the major transition from Greenhouse to Icehouse conditions at the Eocene-Oligocene boundary ~34 million years ago, with the first establishment of a large ice sheet on Antarctica and other worldwide climate reorganizations. Such events have taken place over time scales of a few hundred thousand to millions of years, and are inherently time continuous, with drastic changes in long-term components (e.g., ice sheets, CO2) depending on and feeding back on the current state of short-term quasi-equilibrium components (atmosphere, upper ocean). Box models of global biogeochemical cycles are useful for studying long-term evolution of the oceans, atmosphere and biota, while coupled ocean-atmosphere general circulation models are ideal for studying a few equilibrium states and decadal to centennial climate change. However, none of these tools is able to simulate important long-term events and transitions of interest with adequate spatial and temporal resolution to provide testable predictions.Intellectual Merit. This project will combine long-term biogeochemical components with newly available coupling techniques developed for long-term physical climate modeling, to perform the first spatially and temporally resolved biogeochemical investigation of the Eocene-Oligocene transition. The coupling techniques involve a matrix look-up table of A/OGCM solutions and asynchronous driving of a 3-D ice sheet model, developed by R. DeConto and D. Pollard in other NSF-funded projects. The biogeochemical components have been developed and used extensively by L. Kump and collaborators, and include 2-D land weathering and OGCM biogeochemistry. Recently J. Zachos and L. Kump have applied box-model versions of these components through several million years spanning the E-O transition. They found that biogeochemical feedbacks can have important interactions with the physical climate system, resulting in post-Transition overshoots and million-year oscillations as observed in benthic -18O records. Using the new coupling techniques and 2-D/3-D models, we will test five specific hypotheses concerning events leading up to, during and after the E-O transition. We will compare and validate results against extensive and temporally resolved paleoceanographic data, augmented by terrestrial proxies: - Benthic oxygen and carbon isotopic records constraining bottom-water temperatures plus ice volume, mean ocean isotopic composition and deep basin gradients; - Mg/Ca records for temperature; - Sequence stratigraphic records on passive margins further constraining sea level; - Geologic constraints on atmospheric CO2; - Proxies for terrestrial weathering intensities, rates, and inputs to the ocean.Broader Impacts. One undergraduate (doing her senior thesis) and one graduate student will be involved in this research, with .the undergraduate focusing primarily on one of our hypotheses concerning shelf-basin partitioning of carbonate deposition. We will facilitate the dissemination of numerical modeling expertise by holding a summer workshop at Penn State during the funding interval of this project, sponsored by the Worldwide Universities Network (WUN;wun.ac.uk). The theme of this first WUN-SIES/TA workshop will be on modeling and data interpretation in deep-time studies, primarily for graduate students, postdocs, and early-career Earth science professionals. L. Kump has been instrumental in WUN-sponsored activities at Penn State, including monthly video seminars, graduate student exchanges and workshops. Through WUN, students involved in this project will have the opportunity to travel to Southampton (UK) to work with their climate modeling group.