Collaborative Research: Carbon Isotope and geotracer-enabled simulation of the Transient Climate Evolution of the Deglacial Ocean (C-iTRACE-O)

在最后一次冰川消融期间(21,000至11,000年前)，全球气候发生了巨大变化，全球变暖约3.5℃，海平面上升约80米，大片大陆冰盖消失。大量的信号和广泛的古气候数据使这一时期成为研究气候变化机制和验证最先进的地球系统模型(ESM)的极佳目标。然而，到目前为止，模型模拟还不能与古气候记录直接比较，因为模型没有模拟重建所基于的地球化学示踪剂(“替代物”)。为了解决这一问题并深入了解有关冰川消融期间海洋翻转环流演化的几个长期存在的科学问题，该项目将利用共同体地球系统模型(CESM1)海洋模型中新开发的同位素模块对冰川消融进行第一次瞬变海洋模拟，从而能够对多个海洋古地理指标进行直接的模型数据比较。该项目将通过支持两名研究生在气候建模和模型数据比较方面的培训，并为一名职业生涯早期的女科学家提供项目领导经验，帮助STEM劳动力发展，她将与美国和国际同事密切合作。该项目的成果将用于科罗拉多大学博尔德分校和威斯康星大学麦迪逊分校的本科生和研究生课程，并将通过项目网站和普通听众讲座纳入公众宣传。模拟的结果(称为C-ITRACE-O)将通过地球系统网格网关免费提供，允许整个古气候社区使用它进行研究。通过直接模拟海洋碳同位素(d13C和d14C)、钕(END)和钚/钍(231Pa230Th)的消冰作用，并通过开展敏感性实验来研究在瞬变模拟中引起同位素和地质示踪剂分布变化的物理机制，通过直接比较观测和评估模型本身中的示踪剂循环关系，将有可能解决一些长期存在的科学问题，例如：-神秘时期释放的低放射性碳二氧化碳的来源和路线是什么？-大西洋d13C的演变对最后一次冰川消融期间的深海环流意味着什么？d13C的变化中有多少是由营养物质和海-气气体交换效应引起的，而不是环流的变化？-为什么南极中间水的去冰川演化在代理人中存在争议，特别是在末端和碳同位素上？-231Pa230如何代表北大西洋深层环流和南大洋上升流的去冰川演化？

Global climate has undergone large changes during the last deglaciation (21,000 to 11,000 years ago), with a warming of ~3.5°C globally, a sea level rise of ~80 m, and the disappearance of the large continental ice sheets. The large magnitude of the signals and the availability of extensive paleoclimate data make this period an excellent target for investigating the mechanisms underlying climate change and for the validation of state-of-the-art Earth System Models (ESMs). However, up until now model simulations could not be directly compared with the paleoclimate records, as the models did not simulate the geochemical tracers ("proxies") on which the reconstructions are based. To address this issue and provide insights into several long-standing scientific questions about the evolution of the ocean's overturning circulation during the deglaciation, this project will perform the first transient ocean simulation of the deglaciation with the newly developed isotope modules in the ocean model of the Community Earth System Model (CESM1), allowing for direct model-data comparison of multiple marine paleo proxies. This project will contribute to STEM workforce development by supporting the training of two graduate students in climate modeling and model-data comparisons and by providing project leadership experience for an early career female scientist, who will work in close collaboration with U.S. and international colleagues. Results from this project will be used in undergraduate and graduate classes at the University of Colorado at Boulder and the University of Wisconsin-Madison and will be incorporated into public outreach through a project website and through general-audience talks. The output of the simulation (called C-iTRACE-O) will be made freely available though the Earth System Grid gateway, allowing the entire paleoclimate community to use it for their research. The simulation will also be contributed to the Paleoclimate Model Intercomparison Project transient deglacial working group, allowing for an evaluation of the CESM C-iTRACE compared to the deglacial simulations from other ESMs.By directly simulating oceanic carbon-isotopes (d13C and D14C), Neodymium (eNd), and Protactinium/Thorium (231Pa/230Th) for the deglaciation and by carrying out sensitivity experiments to investigate the physical mechanisms causing the changing isotopic and geotracer distributions in the transient simulation, it will be possible to address some long-standing scientific questions through direct comparisons to observations and by evaluating tracer-circulation relationships in the model itself, such as:- What was the source and routing of the low-radiocarbon CO2 released during the Mystery Interval? - What is the implication of the d13C evolution in the Atlantic for the deep ocean circulation during the last deglaciation and how much of the d13C change was caused by nutrient- and air-sea gas exchange effects versus circulation changes? - Why is the deglacial evolution of Antarctic Intermediate Water controversial among proxies, notably in eNd and carbon isotopes? - How does 231Pa/ 230Th represent the deglacial evolution of North Atlantic deep circulation and Southern Ocean upwelling?