RECONSTRUCTION OF PALEOENVIRONMENTAL CONDITIONS AND TEMPORAL PATTERNS OF ANCIENT MINING ON ISLE ROYALE USING BIOGEOCHEMICAL ANALYSES OF LAKE SEDIMENT

Isle Royale and the Keweenaw Peninsula of Michigan are home to some of the oldest examples of native North American metalworking and land use. The overarching objective of this research is to produce a reconstruction of the timing, spatial patterns, and environmental impacts of mining activities on Isle Royale through sedimentological and biogeochemical analysis of lacustrine sediments. We also seek to produce a parallel record of paleoenvironmental conditions to assess the potential impacts of environmental change on ancient mining cultures.

In 2016, we collected a 7.5 m long sediment core sequence from Lily Lake on Isle Royale, MI. Lily Lake lies approximately 100 m above the current water level of Lake Superior, and formed ~11,000 years before present following the retreat of the Laurentide ice sheet. Lily Lake has been exposed to very little human land use change relative to other lakes on Isle Royale (e.g. there are no ancient mine pits in the immediate catchment), and thus is well suited for reconstructing past environmental changes. We analyzed weakly sorbed metal concentrations using ICP-MS to test hypotheses on the timing and transport mechanisms of potential metal pollution derived from ancient mining activities. In addition, we conducted EA-IRMS analysis (including carbon/nitrogen ratios, and the isotopic composition of organic C and N) on bulk organic sediment to provide a record of natural paleoenvironmental changes.

Preliminary results from the metals analysis provide evidence of Middle Archaic mining activity that is temporally consistent with radiocarbon dated artifacts and similar evidence from other lakes located adjacent ancient mine pits on Isle Royale and the Keweenaw Peninsula of Michigan. Additional work is required to assess the relative influence of natural versus anthropogenic processes that may have influenced metal concentrations in Lily Lake sediment and to determine a transport mechanism for the putative mining related pollution.

This study will provide a record of spatial/temporal patterns of mining activity and paleoenvironmental change in the Great Lakes region that will aid in our understanding of large scale continental climate patterns, environmental responses, and the potential influence of climate/environmental variability on ancient land use and mining practices.