Dynamics and Consequences of Increasing Ice-wedge Degradation

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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.