Numerous paleoclimate studies have focused on climatic variation of the past two millennia. These studies reveal distinct climatic events characterized by temperature fluctuations of ~0.5-1.5 ºC and provide baseline knowledge of natural variation against which anthropogenic effects can be evaluated. In this study, we took advantage of the wealth of paleoclimatic records over the past two millennia to assess fire-climate linkages. We conducted macroscopic-charcoal (>180µm) analysis on sediment cores from 17 lakes in south-central Alaska. Biomass burning in the region was inferred from a standardized composite of charcoal-accumulation-rate (CHAR) records, and local fire return intervals were quantified from CHAR peak analysis. We compared these two components of the fire regime to climate anomalies over the last two millennia. Results/Conclusions
The composite CHAR record reveals marked shifts of biomass burning coincident with climatic fluctuations over the past 2000 years. Minima in biomass burning occurred during the Little Ice Age (~100-450 cal BP) and First Millennial Cooling (centered around 1400 cal BP). Maxima in biomass burning occurred during the Medieval Climate Anomaly (centered around 975 cal BP), and during the first half of the 20th century. In contrast to the prominent changes in biomass burning, fire frequency remained low (0.0034 fires/yr/site) throughout much of the past 2000 years, except during 50-0 cal BP (CE 1900-1950) when fires were more frequent (0.0118 fires/yr/site). Taken together, these biomass-burning and fire-frequency patterns suggest that area burned and/or fuel loads were larger under warmer conditions and smaller under colder condition. These results demonstrate that the regional fire regime is highly sensitive to relatively small changes in temperature.
