| Summary: | Anthropogenic warming is amplified in the northern high latitudes, and disturbance processes such as wildfire and thermo-erosion (i.e., ground subsidence transport of ice-rich sediments) have increased in frequency and magnitude in tundra ecoregions in recent decades. These novel disturbance regimes could increase the role of the Arctic in exacerbating climate warming through the release of large carbon stocks stored in frozen soils. Fires can directly release soil carbon through combustion, and catastrophic thermo-erosion can rapidly increase the carbon pool available for microbial decomposition. On longer timescales, fires can enhance permafrost thaw by reducing surface albedo, enhancing surface roughness, and facilitating shrub expansion and snow drift, which can alter the soil thermal regime. Thus, these novel disturbance regimes may result in more rapid ecosystem changes in the Arctic compared to warming alone. However, the paucity of observational data from remote tundra ecoregions, spatial heterogeneity of ground-ice deposits, and rare burning in many tundra ecoregions at present limits our understanding of the drivers of and potential interactions between fire and permafrost disturbance. I overcome these challenges with paleoecological techniques to examine these disturbance processes over a broad range of scenarios, which is vital given the novel climate and vegetation settings predicted for the future. The main questions of my dissertation research are: Chapter 2 - How do modern tundra fire regimes compare to long-term natural variability? Chapter 3 - How does catastrophic permafrost thaw vary through time and what are the dominant drivers? Chapter 4 -What is the relationship between wildfire and thermo-erosion? Paleorecords of fire and thermo-erosional activity provide critical information regarding natural variability, which is difficult to assess give the rarity of modern tundra burning and the spatial variability of catastrophic permafrost thaw. To address my first question (Chapter 2), I used ...
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