Collaborative Research: The Transition Zone of Upper Permafrost: The Frontline for Permafrost Changes across Climate and Landscape Gradients

永久冻土通常含有大量的地面冰，这使得它很容易受到气候变化和人类活动的影响。这些土壤被表层（夏季解冻，冬季再冻结）和近表层（称为过渡区）保护着不被融化。这个过渡区是通过环境和永久冻土之间复杂的相互作用而发展起来的，控制着永久冻土对地表沉降（热岩溶）的恢复能力。人们预计，随着气候变暖，更深的季节性融化将影响这一过渡区，以及生态系统和基础设施（即道路、机场和建筑物）的稳定性。该项目的目标是评估从高北极到永久冻土区南部边界的过渡带的性质，并了解不同气候区域过渡带的形成、退化和恢复过程。从这项工作中获得的知识将为北极科学和工程提供信息。该项目将支持学生培训。调查人员将与政府机构和工程公司合作，这些公司的工作受到冻土地面沉降问题的影响。在之前的研究中，研究人员确定了永久冻土上部剖面的一个区域，该区域对永久冻土稳定、土壤发育和地貌过程至关重要。然而，过渡带（TZ）的厚度和冰冻结构如何随气候和景观梯度而变化，其在生态演取过程中的形成速率，以及它如何促进永久冻土的脆弱性和恢复力，目前还没有得到很好的理解。我们所拥有的知识是在北极低冻土带，如果应用到其他生物气候地区，可能会产生误导。为了解决这一知识上的差距，我们与蒙特利尔大学的合作研究将重点关注沿南北样带分布的气候区域和景观的TZ，从加拿大具有连续永久冻土的贫瘠极地沙漠到阿拉斯加南部具有零星永久冻土的北方森林。我们的小组还将监测和实验活动层（AL）和TZ之间的质量和热量传递过程，以确定控制分离冰形成的机制。该项目由国际科学与工程办公室共同资助。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Permanently frozen soils, or permafrost, often contain large amounts of ground ice, which make it vulnerable to climate change and human activities. These soils are protected from melting by a surface layer which thaws in summer and refreezes in winter, and a near-surface layer, termed the transition zone. This transition zone, which develops through complex interactions between the environment and permafrost, controls permafrost resilience to ground surface subsidence (thermokarst). Expectations are that as the climate warms, deeper seasonal melting will impact this transition zone, and ecosystems and infrastructure (i.e., roads, airfields, and buildings) stability. The goals of this project are to evaluate the properties of the transition zone from the High Arctic to the southern border of the permafrost region and to understand processes of formation, degradation, and recovery of the transition zone in various climatic regions. The knowledge gained from this work will inform Arctic science and engineering. The project will support student training. The investigators will collaborate with government agencies and engineering companies whose work is impacted by permafrost ground subsidence issues.In previous research, the investigators identified a zone in the upper profile of permafrost soils that is critical to permafrost stability, soil development, and geomorphic processes. However, how the thickness and cryostructures of this transition zone (TZ) vary across climate and landscape gradients, the rates of its formation during ecological succession, and how it contributes to permafrost vulnerability and resilience, is not well understood. What knowledge we have is in low Arctic tundra and can be misleading if applied to other bioclimatic regions. To address this gap in knowledge, our collaborative research with the University of Montreal will focus on the TZ across climatic regions and landscapes distributed along a north-south transect from barren polar deserts with continuous permafrost in Canada, to boreal forests in southern Alaska with sporadic permafrost. Our group will also monitor and experiment with mass and heat transfer processes between the active layer (AL) and the TZ to identify mechanisms controlling segregated ice formation.This project was co-funded by the Office of International Science and Engineering.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.