Past, Present and Fuuture States and Variations of the late Quarternary Permafrost Subsystem

永久冻土和季节性冻土是动态北极陆地系统的重要组成部分，是一个与积雪、植被和上覆大气相互作用的紧密联系的子系统。这个永久冻土层子系统调节着当地的能量、水和物质（包括碳和氮）交换，它的影响超出了北极陆地，延伸到水圈和热带外气候。此外，冻土动力学的长时间尺度要求评估子系统的演变及其对冰期-间冰期时间框架的影响。虽然最近的一些数值预估显示，本世纪以来，多年冻土因气候变化而迅速而广泛地退化，但基于物理的积雪和多年冻土动力学的全球气候系统模式尚未得到充分检验，使用新的基于观测的证据，以确定该子系统在不同气候条件下（如全新世最佳期或末次冰盛期）的时空变异。对永久冻土的气候敏感性的评估将为未来的情景提供重要的见解，特别是在北半球。重点将放在古气候模式比较项目（PMIP）的合作下广泛进行数值模拟的三个晚第四纪：即前工业时代（0 ka，其中ka =距今1000年），中全新世（6 ka）和LGM （21ka）。本项目将重点评估不同气候条件下冻土子系统的结构和功能。要解决的主要问题是：1。全球气候模型模拟的永久冻土分布与代理数据重建的一致程度如何？2. 在不同的气候条件下，永久冻土层的分布变化有多大？永久冻土的变化会对北极的自然、生活和社会造成严重后果吗？相应地，永久冻土子系统通过哪些过程和相互作用影响过去和现在的气候？植被和土壤类型有多重要？3. 我们可以从不同气候条件下的永久冻土子系统模拟中学到什么，以减轻或适应未来的变化？智力优势：目前可用于气候模式输入的重建植被图将通过结合古植物学研究的最新结果进行更新，为我们的地表边界条件提供基础。来自多个模式的模拟结果（永久冻土分布）以及来自PMIP2输出的强迫数据（地表温度、降水[或湿度]和地面风）将与其他更新的代理衍生图进行比较和评估。一系列有组织的不同复杂程度的雪-多年冻土动力学数值敏感性实验将描述多年冻土子系统内的基本过程。与大气耦合和非耦合模拟的分层实验将量化大气与地下的相互作用，以及子系统在北极和全球气候中的整体作用。更广泛的影响：更广泛的影响活动将侧重于提供有关未来气候变化预测和适应规划的直接影响的信息。对永久冻土子系统的科学认识的提高将加强对气候变化对基础设施和社会的风险的评估，特别是对北极地区生活和文化的风险。该项目还将有助于地球系统建模的新兴努力，这需要真实的地下模拟，以便研究生物地球化学过程，这对水蒸气和其他辐射活性气体的表面交换很重要。白令陆桥过去的永久冻土分布、植被和其他模拟结果的地图为社会科学和人类科学提供了材料，特别是在人类迁移到北美的历史和阿拉斯加原住民的早期历史等主题方面。它还将促进与中学、大学、博物馆和公众的联系。未被充分代表的学生群体，如阿拉斯加原住民、地理上孤立和经济上处于不利地位的学生，都是目标受众。

Permafrost and seasonally frozen ground comprise a critically important component of the dynamic arctic terrestrial system, constituting a closely tied subsystem interacting with snow cover, vegetation, and the overlying atmosphere. This permafrost subsystem regulates the local exchange of energy, water, and materials (including carbon and nitrogen), and its influence extends beyond the arctic land to the hydrosphere and the extra-tropical climate. Furthermore, the long timescale of permafrost dynamics requires evaluation of the evolution and impacts of the subsystem on the glacial-interglacial time frame. While some recent numerical projections show rapid and widespread degradation of permafrost in response to climate change during this century, global climate system models with physically based snow and permafrost dynamics have not been fully tested, using new observationally-based evidence, for spatial and temporal variability of the subsystem under different climate conditions such as the Holocene optimum or the Last Glacial Maximum (LGM). Evaluation of the climate sensitivity to the permafrost will provide vital insight to future scenarios, especially in the Northern Hemisphere. The focus will be on three late Quaternary eras for which numerical simulations are widely performed by the collaborative efforts of the Paleoclimate Model Intercomparison Project (PMIP: i.e., the preindustrial present (0 ka, where ka = thousand years before present), mid-Holocene (6 ka), and the LGM (21ka). This project will focus on evaluating the structure and function of the permafrost subsystem under different climate conditions. The primary questions to be addressed are: 1. How well do the permafrost distributions simulated by global climate models agree with reconstructions from the proxy data? 2. How widely did the permafrost distribution change under different climate conditions? Will permafrost change have serious consequences in nature, life, and societies in the Arctic? Correspondingly, by which processes and interactions does the permafrost subsystem impact the climate of the past and present? How important are the vegetation and soil types? 3. What can we learn from the permafrost subsystem simulations under different climatic conditions to mitigate or adapt to future changes? Intellectual merits: The reconstructed vegetation map currently available for the climate model inputs will be updated by combining recent results from paleobotanic research, providing a basis for our surface boundary conditions. The simulated results (permafrost distribution) from multiple models as well as the forcing data from the PMIP2 outputs (surface temperature, precipitation [or wetness], and surface wind) will be compared and evaluated with other updated proxy-derived maps. A series of organized numerical sensitivity experiments with different levels of complexity in snow-permafrost dynamics will delineate the essential processes within the permafrost subsystem. Hierarchical experiments of coupled and uncoupled simulations with the atmosphere will quantify the interactions between the atmosphere and the subsurface, and the function of the subsystem as a whole in arctic and global climate. Broader impacts: broader impact activities will focus on delivering information about direct implications for future climate change projection, and for adaptation planning. Improved scientific understanding of the permafrost subsystem will enhance assessments of the risks of climate change to infrastructure and society, especially on life and culture in the Arctic. This project will also contribute to emerging efforts in earth system modeling, which requires realistic subsurface simulations in order to study the biogeochemical processes that are important for surface exchanges of water vapor and other radiatively active gases. Maps of past permafrost distribution, vegetation and other simulated results in Beringia provide materials to the social and anthropogenic sciences, particularly in such topics as the history of human migration into North America, and the early history of Alaska Natives. It will also facilitate outreach to secondary schools, universities, museums and the general public. Underrepresented student populations such as Alaska Natives, those geographically isolated and economically disadvantaged are among the target audiences.