Collaborative Research: P2C2--isotope-enabled TRAnsient Climate Evolution of the last 21,000 years (iTRACE21)----Understanding Deglacial Climate/Isotope Changes Using iCESM

本研究利用最先进的同位素地球系统模型（ESM）研究了最后一次消冰期（21,000至11,000年前）的气候变化机制。本项目要解决的主要科学问题是：(1)全球水的同位素组成与气候变化之间的关系是什么？(2)气候系统如何响应末次冰消期不断变化的气候强迫，以及每种强迫（日照、大气温室气体、大陆冰盖和融水）的贡献是什么？这些模拟将使人们能够从年际到轨道时间尺度上研究气候的连续演变和突变。瞬态模拟类型标志着模式-数据比较的革命性突破，允许直接数据和模式时间序列比较，并将对未来使用模式和观测的古气候研究产生重大影响。提出的模拟将对古气候社区的研究产生开创性的影响，为许多其他社区项目提供模型数据。这将为未来几代冰冻圈和生物地球化学耦合模型的系统测试奠定基础。具体来说，新版本的NCAR社区ESM (CESM)，启用了水同位素示踪剂，将在21,000至11,000年前的完全耦合模式下运行。主要模拟将受到日照、大气温室气体浓度、大陆冰盖、海平面和融水等规定变化的强迫，而敏感性模拟将分别研究不同强迫的影响。与CCSM3运行的上一代瞬态模式（3度）相比，该模拟将以更高的分辨率运行（大气2度，海洋1度）。此外，稳定的水同位素示踪剂已被包括在大气、陆地、海洋和海冰模型中，并将首先在末次极大冰期（LGM， 21000年前）和当前气候时间片中进行测试，然后在末次冰消期的瞬态模式中运行。提出的瞬态模拟的一个中心任务是与数据社区密切合作，探索一种新的模式-数据比较范式，重点是同位素的直接时间序列比较。同位素时间序列的模拟将显著改善古气候模式数据的比较，因为它将减少同位素推断和代用记录的绝对年代学所产生的不确定性。该项目将为威斯康星大学和俄勒冈州立大学的学生提供研究生研究的基础。

This research investigates the mechanisms of climate changes during the last deglaciation (21,000 to 11,000 years ago) using a state-of-the-art isotope-enabled Earth System Model (ESM). The major scientific questions to be addressed in this project are: (1) What are the relationships between the isotopic composition of water and climate changes over the globe? (2) How does the climate system respond to changing climate forcings of the last deglaciation, and what is the contribution from each forcing: insolation, atmospheric greenhouse gases, continental ice sheets, and meltwater? The simulations will allow the study of the continuous evolution and abrupt changes of climate from interannual to orbital time scales. The type of transient simulation marks a transformative breakthrough in model-data comparison, allowing for direct data and model time series comparisons, and will have a significant impact on future paleoclimate studies using both models and observations. The proposed simulations will have a ground breaking impact on research in the paleoclimate community, providing model data for a number of other community projects. It will lay a foundation for a systematic test of future generations of ESMs with coupled cryosphere and biogeochemical models. Specifically, the new version of NCAR's community ESM (CESM), enabled with water isotope tracers, will be run in fully-coupled mode for the period 21,000 to 11,000 years ago. The main simulation will be forced by prescribed changes in insolation, atmospheric greenhouse gas concentrations, continental ice sheets, sea level, and meltwater, while sensitivity simulations will investigate the effect of the different forcings separately. This simulation will be run at a higher resolution (2 degrees in the atmosphere and 1 degree in the ocean) than the previous generation transient model run with CCSM3 (3 degrees). Furthermore, stable water isotope tracers have been included in the atmosphere, land-surface, ocean, and sea-ice models and will be tested first for the Last Glacial Maximum (LGM, 21,000 years ago) and present climate time slices before being run in transient mode for the last deglaciation. One central task of the proposed transient simulations is to explore a new paradigm of model-data comparison in close collaboration with the data community, focusing on direct time series comparisons of isotopes. The simulation of isotope time series will improve paleoclimate model-data comparison significantly, because it will reduce the uncertainties arising from both the inference of isotopes and the absolute chronology of the proxy records. The project will provide the basis for graduate research for students from the University of Wisconsin and Oregon State University.