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

在最后一次消冰期（21000 - 11000年前），全球气候发生了巨大变化，全球变暖约3.5°C，海平面上升约80米，大型大陆冰盖消失。信号的大幅度和广泛的古气候数据的可用性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）的绝佳目标。然而，到目前为止，模型模拟还不能直接与古气候记录进行比较，因为模型没有模拟重建所依据的地球化学示踪剂（“代用物”）。为了解决这一问题，并提供关于消冰期间海洋翻转环流演变的几个长期存在的科学问题的见解，本项目将使用群落地球系统模型（CESM1）海洋模型中新开发的同位素模块进行第一次消冰瞬态海洋模拟，允许对多个海洋古代用物的直接模式数据进行比较。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，并为一名早期职业女性科学家提供项目领导经验，从而促进STEM劳动力的发展，该女性科学家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和研究生课程，并将通过项目网站和普通听众讲座纳入公共宣传。模拟的输出（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将其用于他们的研究。模拟结果也将提供给古气候模式比对项目瞬态冰川消融工作组，以便将CESM C-iTRACE与其他esm的冰川消融模拟结果进行比较。通过直接模拟海洋碳同位素（d13C和D14C）、钕（eNd）和镤/钍（231Pa/230Th）的消冰过程，并通过灵敏度实验研究瞬态模拟中引起同位素和地质示踪剂分布变化的物理机制，将有可能通过与观测结果的直接比较和评估模式本身的示踪-环流关系来解决一些长期存在的科学问题。例如：-神秘间隔期间释放的低放射性二氧化碳的来源和路径是什么？-最后一次消冰期大西洋d13C的演变对深海环流的影响是什么？ d13C的变化在多大程度上是由营养物和海气交换效应与环流变化引起的？为什么南极中间水的去冰演化在代用物中存在争议，特别是在eNd和碳同位素中？231Pa/ 230Th如何代表北大西洋深层环流和南大洋上升流的去冰演化？

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?