COLLABORATIVE RESEARCH: EVALUATING DEEP-SEA VENTILATION AND THE GLOBAL CARBON CYCLE DURING EARLY PALEOGENE HYPERTHERMALS

早古近纪（约6500 - 4500万年前）快速、短期的全球变暖事件是由大量温室气体释放到海洋-大气系统造成的。这些变暖事件被称为“超热”，对地球上生命的进化、生态系统和碳循环产生了深远的影响。这些事件中最极端的是古新世-始新世热极大期（~ 5550万年前）。超温现象类似于人为气候变化期间可能发生的情况，并为温室气体排放的影响及其对地球上生命的长期影响提供了类似物。通过测试古近系热活动期间地球系统的相互作用，该跨学科项目将为全球气候-碳循环反馈和极端气候提供新的见解。该研究将通过在高性能计算机上改进广泛使用的社区地球系统模型，并通过综合数据和模型输出与海洋地质和古海洋学中新型同位素和微量元素技术的观测结果，为国家利益服务。将多学科研究和教育活动结合起来，并将导致关于气候突变的教材的开发和广泛传播，从而加强对来自不同背景的本科生和高中生的定量科学培训。具体来说，这项合作包括将新的生物、同位素和微量元素代理与现有数据整合到一个最先进的、高分辨率的、全面的地球系统模型中，以验证深海通风在高温事件期间从难降解的溶解有机质（DOM）池中释放大量碳的假设，增加大气二氧化碳水平，从而通过碳循环反馈放大气候变化。课题组将研究三个古近系不同强度和持续时间的超热活动的环境响应（如海洋酸化和脱氧）及其对远洋生态系统结构的影响。该项目将重点研究海洋中有机质再矿化和DOM池氧化的关键机制，这对未来气候演变具有潜在的重大意义，并解决以下问题：(1)海洋生产力、有机碳再矿化、海洋氧化和超热过程中输出效率的变化如何影响海洋溶解有机质储层的变化？(2)海洋通风增强导致的DOM释放是否至少是古近纪热液形成的部分原因？(3)古近系气候的意义是什么？与DOM储存和释放相关的碳循环变化对未来极端气候和环境的影响？将获得关于浮游和底栖有孔虫以及相同样品上海洋重晶石积累的新数据，并将其与大量现有数据相结合，以深入了解依赖生态系统的出口生产力和再矿化以及区域变化的垂直碳通量。最近从赤道地区收集的数据将被纳入一个数据库，为地球系统模型提供初始条件。该模型的结果将深入了解海洋分层、垂直碳梯度、DOM储层、氧合和生态系统组成在进入和退出超热区过程中的变化。特别是，该小组将评估与生态系统相关的DOM积累波动以及随后的海洋氧化和排放的极端变化的可能性，因为DOM库是易于互换的碳的最大储存库。这一机制尚未被彻底探讨，是否会导致气候转变为具有更极端天气模式的温室气候。

Rapid, short-term global warming events in the Early Paleogene (~65-45 Million years ago) were caused by massive greenhouse gas release into the ocean-atmosphere system. These warming events, called "hyper thermals", had far-reaching effects on the evolution of life on Earth, ecosystems, and the carbon cycle. The most extreme of these events was the Paleocene-Eocene Thermal Maximum (~55.5 Million years ago). Hyperthermals resemble what could happen during anthropogenic climate change, and provide analogs for the effects of greenhouse gas emissions and their long-term effects on life on Earth. By testing earth system interactions during the Paleogene hyperthermals, this interdisciplinary project will provide new insight into global climate-carbon cycle feedbacks and extremes in climate. The research will serve the national interest by improving a widely used Community Earth System Model on high-performance computers, and by synthesizing data and model output with observations from novel isotopic and trace element techniques in marine geology and paleoceanography. Multidisciplinary research and educational activities are integrated and will lead to development and widespread circulation of educational materials on abrupt climate change, thus enhancing training in quantitative science for undergraduate and high school students from diverse backgrounds.Specifically, this collaborative effort involves integration of new biotic, isotopic and trace element proxies with existing data into a state-of-the-art, high-resolution, comprehensive earth system model to test the hypothesis that deep-sea ventilation released a massive amount of carbon from the refractory dissolved organic matter (DOM) pool during hyperthermal events, increasing atmospheric CO2 levels, and thus amplifying climate change through carbon-cycle feedback. The research team will investigate the environmental response (e.g., ocean acidification and deoxygenation) and its impact on pelagic ecosystem structure for three Paleogene hyperthermals with different magnitudes and durations. The project will focus on a key mechanism involving remineralization of organic matter and oxidation of the DOM pool in the ocean, with potentially major implications for future climate evolution, addressing these questions:(1) How might changes in oceanic productivity, organic carbon remineralization, ocean oxygenation, and export efficiency during hyperthermals have contributed to changes in the oceanic dissolved organic matter reservoir? (2) Could DOM release due to enhanced ocean ventilation have been at least a partial cause of Paleogene hyperthermals?(3) What are the implications of Paleogene climate?carbon cycle changes associated with DOM storage and release for future extremes in climate and the environment?New data on planktic and benthic foraminifera, and accumulation of marine barite on the same samples will be obtained and integrated with a large amount of existing data to provide insight into ecosystem-dependent export productivity and remineralization, as well as regionally varying vertical carbon fluxes. Recently gathered data from the equatorial regions will be incorporated in a database to provide initial conditions for the earth system model. The model results will give insight into changes in ocean stratification, vertical carbon gradients, DOM reservoirs, oxygenation, and ecosystem composition during transitions into and out of hyperthermals. In particular, the team will evaluate the possibility of extreme changes in response to ecosystem-related fluctuations in DOM accumulation and subsequent oxidation and emission from the oceans, because the DOM pool is the largest reservoir of easily interchangeable carbon. This mechanism has not been thoroughly explored as a contributor to a transition into a hothouse climate with more extreme weather patterns.