AN ICE-CORE-BASED RECORD OF BIOMASS BURNING IN THE ARCTIC AND SUB-ARCTIC, 1750-1980

Ammonium records from 3 ice cores, 20D and GISP2 (Greenland) and Mt. L ogan (Yukon), covering the period from 1750 to the 1980s are analyzed. For each data set, samples with NH4+ concentrations greater than one standard deviation above the mean value also tend to be enriched in NO 3- and K+, similar to the chemical composition of aerosols from aged b iomass burning plumes. We believe the NH4+ spikes originate from bioma ss burning events. There is not a one to one correspondence between do cumented large fires and NH4+ spikes, nor are specific annual layers w ith elevated NH4+ concentrations often found in more than one core. Ho wever, frequency of NH4+ spikes increase during periods of more extens ive and intensive biomass burning in the NH4+ source areas for the ice core sites. The 20D and GISP2 records are characterized by increased spike frequency from 1790 to 1810 and from 1830 to 1910. This latter t ime coincides with a period of increased biomass burning documented in the historical fire records for northern North America. In contrast t o both Greenland ice core records, the Mt. Logan NH4+ record shows per iods of increased spike frequency from 1770-1790, 1810-1830, 1850-1870 and 1930-1980. The poor agreement between the Mt. Logan record and th e records from Greenland suggests that another source area, perhaps Si beria, may be the dominant summertime source area for NH4+ spikes in M t. Logan snow.