Northeastern (46th Annual) and North-Central (45th Annual) Joint Meeting (20–22 March 2011)

Paper No. 8
Presentation Time: 8:00 AM-12:00 PM


POMPEANI, David P., ABBOTT, Mark B., BAIN, Daniel J., STEINMAN, Byron A. and PURCELL, Christopher C., Geology and Planetary Science, University of Pittsburgh, 4107 O'Hara Street, 200 SRCC Building, Pittsburgh, PA 15260,

An 11,000 year record of forest fires is reconstructed at Copper Falls Lake using macroscopic fossil charcoal (>125 μm) preserved in lake sediment. Copper Falls Lake (47.418° N, 88.192° W; 392 m above sea level) is situated along the elevated copper-bearing ridge in the interior of Keweenaw Peninsula, on the south shore of Lake Superior. Charcoal in lake sediment records have been shown both empirically and through models to reflect the local (0–1.0 km) occurrence of individual or multiple high-severity forest fires (“fire events”). Charcoal was counted from continuous 1 cm3 samples, and dated using 210Pb, 137Cs, and nine AMS 14C ages to document the temporal patterns of fire occurrence over the interglacial (~1,000-12,000 BP). A charcoal accumulation rate (CHAR, counts cm-2 year-1) was calculated and linearly interpolated to 10-year time steps. CHARBack levels were estimated using a 500-year moving average to quantify background “red-noise” in the series to estimate residual CHAR “peaks.” Current research seeks to develop a statistical threshold to identify significant fire-related CHARPeaks from CHARBack to distinguish local fire events. CHARBack could be influenced by a wide range of factors including: vegetation shifts, summer temperature, and effective moisture.

Following deglaciation ~12,100 (cal 14C year) BP and transition to interglacial conditions, Copper Falls Lake records an abrupt rise in CHARBack. Distinct CHARPeaks occur at ~11,600, ~9,900, and ~9,600 BP as a result of local fire events during the early interglacial. A pollen reconstruction from nearby Mud Lake (47.128° N, 88.320° W; 189 m asl) find a ~300 year rise in CHARBack at ~8,600 BP coincides with the rapid migration of white pine (Pinus Strobus) into the region (Booth et al. 2002). By ~7,000 BP, CHARBack levels decline to levels typical of the late Holocene, possibly influenced by lake-effect snow development in the region. At ~5,600 BP, a ~200 year rise in CHARBack and distinct CHARPeaks correspond to a rise in birch (Betula) and hemlock (Tsuga) across the region. The Copper Falls charcoal record highlights the role of vegetation change on the development of fires.

Booth RK, Jackson ST, Thompson TA (2002). Paleoecology of a Northern Michigan lake and relationship among climate, vegetation, and Great Lakes water levels. Quaternary Research. 57:120-130.