PATTERNS OF HOLOCENE SEDIMENTATION IN WESTERN LAKE SUPERIOR

This interdisciplinary investigation describes a high-density survey of western Lake Superior (WLS) that integrates high-resolution acoustic remote sensing, trace element analysis, and radiometric dating. This investigation is the first large-scale multidisciplinary effort to examine sedimentation patterns on temporal and spatial scales in WLS. Lead-210 and trace element analysis are used to reconstruct decadal sedimentation patterns for the past century; a period during which sedimentation was dramatically affected by changes in land use. Seismic data are used to reconstruct post-glacial sedimentation patterns on a millennial scale. Sedimentation patterns derived for post-glacial and modern times suggest that sedimentation in Western Lake Superior is not focused into traditional bathymetric depositional basins. Instead, sedimentation occurs in regions surrounding a marginally depositional zone that cross-cuts lake basin bathymetry.

Results of this research suggest that 1) Holocene sediment accumulation in WLS is very patchy, 2) recent sedimentation rates are two times higher than average post-glacial rates (implies changing land use has resulted in enhanced surface erosion throughout the basin), 3) the accumulation pattern of post-glacial and modern sediments are generally similar (implies circulation patterns and current activity have been relatively constant throughout these times), 4) there appears to be significant suspension and redeposition of sediments deep within the basin (> 200 meters), which makes the fate of anthropogenic pollutants in Lake Superior particularly difficult to predict, and 5) slight differences in long and short term accumulation patterns may be a function of the number of focusing events to which sediments are exposed (millennial events vs. hundred year events).