Dynamics and Consequences of Increasing Ice-wedge Degradation

这项研究将量化冰楔退化的性质和程度，评估控制退化和稳定动态的反馈，并评估退化对北极生态系统的后果。巨大的冰在冰楔的形式占10？70%的近地表永久冻土，并从根本上影响北极生态系统对气候变化的动态和脆弱性。北极永久冻土被认为是稳定的，因为地面温度仍然很低，但最近在阿拉斯加北方观察到冰楔退化的突然增加，表明即使是北极的永久冻土也容易因气候变化而退化，因为在活动层下面形成了大量的冰。阿拉斯加和俄罗斯的高分辨率卫星图像显示，由于这种近地表冰，北极的冰楔退化比亚北极更广泛。冰楔退化的动力学已被证明受到蓄水的地表水的正反馈和负反馈的快速植被和泥炭积累，能够稳定退化的冰楔，但一直没有量化的物理机制控制的过程。这种冰楔的退化通过改变表面地形、改变排水网络、增加泥炭积累和厌氧条件下的甲烷产量以及从根本上改变植被组成，极大地影响了北极生态系统，但人们对这些后果知之甚少。鉴于冰楔退化直接或间接地影响到大多数北极地形，因此量化冰楔退化的动态和后果至关重要，本项目通过全面评估冰楔退化的性质和程度、控制冰楔动态的反馈以及退化对生态系统模式和过程的后果来解决这些不确定性。该研究汇集了一个跨学科的团队，他们在永久冻土和土壤，土壤地球化学和痕量气体排放，植被和遥感方面具有专业知识，通过实地调查，遥感和建模来解决假设。将通过按地形单位比较冰楔体积、描述退化和稳定阶段、量化整个环北极地区的退化情况、开发用于绘制热岩溶图的图像处理算法以及通过航空照片分析量化退化率，评估各种地貌和气候的冰楔退化程度和速度。冰楔退化和稳定的动态如何受到正反馈和负反馈的控制，将通过以下方式进行评估：确定保护冰楔的表层土壤的结构特性;量化退化阶段之间净辐射和土壤热通量的差异;通过数值模拟确定热岩溶的阈值。冰楔退化的后果将通过量化冰楔退化造成的微地形变化、地表水储存和排水模式的变化、退化序列中的土壤有机碳储存、退化阶段之间甲烷排放的差异以及退化序列中植被组成的变化来记录。这项研究对于了解气候变化对永久冻土和北极生态系统的影响至关重要，因为冰楔是北极陆地生态系统特别敏感的组成部分。冰楔的性质和范围的知识将改善土地管理，影响评估，并在冰丰富的永久冻土地带的设施设计。需要关于冰楔退化所涉及的动态和反馈的信息，以尽量减少扰动的影响，并改进目前缺乏关键反馈的全球气候变化模型。需要记录退化的后果，以更好地评估分散的排水网络在环北极水文评估中的作用，帮助解决北极土壤未来是否会增加或减少碳，为评估动态变化的生态系统中的甲烷排放提供信息，并提供植被变化率的数据，这些数据可能会影响植被评估期间对植被生产力的卫星测量北极的绿化。

This research will quantify the nature and extent of ice-wedge degradation, evaluate the feedbacks controlling the dynamics of degradation and stabilization, and assess the consequences of the degradation to arctic ecosystems. Massive ice in the form of ice wedges occupies 10?70% of near- surface permafrost and fundamentally influences the dynamics and vulnerability of arctic ecosystems to climate change. Arctic permafrost has been considered stable because ground temperatures remain low, but recent observations in northern Alaska of an abrupt increase in degradation of ice-wedges, indicate that even permafrost in the Arctic is susceptible to degradation from climate change because of the massive ice that has formed just below the active layer. High-resolution satellite images of Alaska and Russia reveal that ice-wedge degradation is more extensive in the Arctic than in the subarctic because of this near-surface ice. The dynamics of ice-wedge degradation has been shown to be affected by the positive feedback of impounded surface water and negative feedbacks from rapid vegetation and peat accumulation that are able to stabilize degrading ice wedges, yet there has been no quantification of the physical mechanisms controlling the processes. This degradation of ice wedges greatly affects arctic ecosystems by altering surface topography, modifying drainage networks, enhancing peat accumulation and methane production under anaerobic conditions, and radically shifting vegetation composition, but these consequences are poorly understood. Given that ice-wedge degradation directly or indirectly affects most arctic terrain it is critical to quantify the dynamics and consequences of ice-wedge degradation.This project addresses these uncertainties through a comprehensive assessment of the nature and extent of ice-wedge degradation, the feedbacks controlling ice-wedge dynamics, and the consequences of degradation on ecosystem patterns and processes. The research brings together an interdisciplinary team with expertise in permafrost and soil, biogeochemisty and trace gas emissions, vegetation, and remote sensing to address hypotheses through field surveys, remote sensing, and modeling. The extent and rate of ice-wedge degradation across landscapes and climates will be assessed by comparing the ice-wedge volume by terrain units, describing stages of degradation and stabilization; quantifying degradation across the circumarctic; developing image processing algorithms for mapping thermokarst; and quantifying degradation rates through aerial photo analysis. How the dynamics of ice- wedge degradation and stabilization are controlled by positive and negative feedbacks will be assessed by identifying structural properties of surface soils that protect ice wedges; quantifying differences in net radiation and soil heat flux among degradation stages; and identifying thresholds for thermokarst through numerical modeling. The consequences of ice-wedge degradation will be documented by quantifying micro-topographic changes caused by ice-wedge degradation; changes in surface water storage and drainage patterns; soil-organic carbon stocks through degradation sequence; differences in methane emissions among degradation stages; and quantifying shifts in vegetation composition through degradation sequence. The research is essential for understanding of the effects of climate changes on permafrost and arctic ecosystems because ice wedges are especially sensitive component of terrestrial arctic ecosystems. Knowledge of the nature and extent of ice wedges will improve land management, impact assessment, and facility design in ice-rich permafrost terrain. Information on the dynamics and feedbacks involved in ice-wedge degradation is needed to minimize effects of disturbance and to improve global climate change models that currently lack critical feedbacks. Documentation of the consequences of degradation is needed to better assess the role of fragmenting drainage networks in assessments of circumarctic hydrology, help resolve whether arctic soils will gain or lose carbon in the future, contribute information for assessing methane emissions across dynamically changing ecosystems, and provide data on the rates of vegetation change which can affect satellite measurement of vegetation productivity during assessments of vegetation greening in the Arctic.