A Late Pleistocene/Early Holocene Fire Record from Appleman Lake, Indiana: The Use of Charcoal Analysis in Investigating Landscape Change
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Charcoal analysis was conducted on a sediment core from Appleman Lake, Indiana. Appleman Lake is a kettle lake that was formed as the Laurentide Ice Sheet retreated during the last deglaciation. Macroscopic charcoal (particles >125?m) indicates local fires. Charcoal analysis was connected to other proxies, such as pollen analysis (a proxy for vegetation), the presence of Sporormiella spores (a proxy for megafaunal abundance), and magnetic susceptibility (a proxy for erosion), to understand long-term landscape change. The late Pleistocene/early Holocene time period was the focus of the study. During this period, rapid climate change occurred, many megafaunal species became extinct, no-analogue vegetation assemblages were present, and humans arrived. Charcoal concentrations (particles/cm3) were transferred into charcoal accumulation rate (CHAR, expressed as particles/cm2/yr) by dividing the charcoal concentrations by the sedimentation rate for the core. Using Charster, a program developed by Dan Gavin, the charcoal record was decomposed into a background component (slowly varying) and a peaks component (used to infer fire events). A threshold value was applied to the peaks component to separate noise from inferred fire events. In the Appleman Lake charcoal record, there are three inferred time periods displaying different fire characteristics. During the late glacial period, from 17,600 to 15,900 cal yr BP, there are few charcoal particles and zero inferred fire events. Picea is the dominant vegetation, indicating a cold climate, and megafaunal abundance is high. In the transitional period, from 15,900 to 10,800 cal yr BP, the fire return interval is 1.55/1000yr with 8 inferred fire events. During the transitional period, a fire peak occurs almost simultaneously with the inferred extinction of many megafaunal species, possibly indicating that as megafauna became extinct, fuel load increased and a major fire event occurred. A fire peak occurs contemporaneously with the onset of the Younger Dryas climatic event at 12,900 cal yr BP, supporting the hypothesis of an extraterrestrial impact at that time. In the early Holocene time period, from 10,800 to 7,100 cal yr BP, the background level of CHAR increases significantly, alongside increases in Quercus and other deciduous taxa. The fire return interval in the early Holocene is 3.24/1000yr, with 12 inferred fire events. Increased fire activity and more deciduous taxa indicate a warmer climate in the early Holocene. Charcoal analysis and other proxies provide a long-term history of landscape change in northern Indiana during the late Pleistocene/early Holocene time period.