Collaborative Research: Characterizing spatiotemporal heterogeneity of carbon cycling across ice-wedge permafrost landscapes and projecting vulnerability to change

Thaw-induced carbon release from the large, frozen organic matter pool in Arctic permafrost is one of the most significant positive feedbacks to the climate, with ice-rich areas particularly susceptible to degradation. The strength and timing of permafrost carbon release is highly uncertain due to (1) the complex processes driving carbon dynamics in permafrost ecosystems, (2) the multiple spatial and temporal scales at which these processes interact, (3) the sheer size and data scarcity of the permafrost zone. Process-based terrestrial biosphere models (TBMs) represent the main processes driving vegetation and soil carbon dynamics, and have been used to predict the permafrost carbon-climate feedback (PCF) under warming scenarios. Recent model intercomparisons have revealed large uncertainties in the estimation of this feedback, currently limiting their use to inform mitigation strategies at global scales. Additionally to this and a dearth in long-term, year-round observations, a major source of uncertainty relates to the resolution at which biogeochemical processes are represented, with typical models using coarse scales inadequate to capture landscape heterogeneity. Over half of the Alaskan tundra land surface is characterized by ice wedge polygons, which are almost entirely found in the moist non-acidic tundra of the coastal plain. Polygonal tundra is characterized by fine scale spatial heterogeneity in drainage conditions, vegetation composition, and nutrient cycling. Climate driven thawing of ice wedges can drive abrupt changes in local topography and drainage conditions, impacting the carbon cycle, though this kind of landscape heterogeneity is not yet captured in TBMs. The proposed research will improve predictions of the PCF in polygonal tundra by integrating (1) surface water calculations to represent degrading ice-wedges, (2) subgrid parameterization to capture spatial heterogeneity, in a TBM designed for the high latitudes, DVM-DOS-TEM. In parallel, field characterization of carbon flux dynamics will be conducted at The Natural Ice-Rich Permafrost Observatory (NIRPO) established through the Navigating the New Arctic (NNA) Project (#1928237) in Prudhoe Bay, to capture seasonal and interannual variation, to determine drivers and vulnerability across representative landscapes, and provide data for model benchmarking and comparison. Combining field and modeled data, carbon budgets for the North American Coastal Plain will be projected at decadal to centennial scales and evaluated.