FIRE RECONSTRUCTIONS IN THE FAR NORTH: LATE HOLOCENE ECOLOGICAL RESPONSES TO FIRE IN NORTHERN ALASKA
Date of Award
5-12-2024
Degree Type
Thesis
Degree Name
Master of Science (MS)
Department
Earth & Environmental Sciences
Advisor(s)
Melissa Chipman
Keywords
charcoal;fire;holocene;paleoclimate;paleolimnology
Subject Categories
Earth Sciences | Geology | Physical Sciences and Mathematics
Abstract
Palaeoecological reconstruction can characterize regional fire-regimes and reveal how drivers such as anthropogenic warming and vegetation change influence the fire system. This thesis adds to our knowledge of millennial-scale tundra fire-regimes by creating four new charcoal-based paleoecological records from lake sediment cores on the Alaskan North Slope. Statistical analyses of charcoal accumulation rate (CHAR # particles cm-2 yr-1) at three different size fractions were used to identify centennial-scale variability in biomass burned through time and identify individual fire events. These analyses were coupled with morphological identification and classification of charcoal particles to link charcoal production to hypothesized fuel source. The resultant fire records were divided into those with CHAR values influenced by terrestrial sediment in-wash, and those with uninterrupted sediment accumulation that can provide baseline estimates of fire activity. For the two sediment cores with uninterrupted charcoal deposition, charcoal peak identification on the 125 and 90 μm charcoal size fractions was used to identify past fire events and calculate mean fire-return intervals (FRI; years between fire) at local and regional scales, respectively. Individual and mean FRIs were compared to existing regional paleofire records, a new local paleoclimate reconstruction, and pollen-based vegetation reconstructions. The longer core, RTS7U2, has a basal date of 7046 cal yr BP, and analyses of the smallest charcoal size fraction (90 μm; signal of regional burning) shows a significant shift in calculated FRIs after ~3000 cal yr BP, which coincides with the onset of Neoglacial cooling and decreasing moisture in the region. A shorter supporting record, RTS5U3, spans the past 743 years and shows a similar magnitude of background charcoal as RTS7U2 as well short FRIs (mFRI = 198 (105-133) years) comparable to the late Holocene portion of RTS7U2 (mFri = 239 (167-321) years). Comparisons of fire peak estimates on larger charcoal size fractions (125 μm; signal of local fires at each site) show mean FRIs that overlap with the calculated regional fire rotation period (FRP) based on modern fires observed in the region, suggesting that modern burning is comparable to the recent past. However, the RTS5 record demonstrates significantly shorter FRIs from locally-sourced charcoal than other fire history records from the region, which may be related to its larger proportion of watershed shrub cover. These new analyses broadly show that tundra fire regimes on the North Slope are strongly related to climate variability at centennial to millennial timescales. Additionally, local-scale controls such as feedbacks between fire and vegetation composition can result in heterogenous burning, with important implications for ongoing Arctic greening and continued warming in this region.
Access
Open Access
Recommended Citation
Frank-DePue, Lee, "FIRE RECONSTRUCTIONS IN THE FAR NORTH: LATE HOLOCENE ECOLOGICAL RESPONSES TO FIRE IN NORTHERN ALASKA" (2024). Theses - ALL. 831.
https://surface.syr.edu/thesis/831
