Geochemical and Sedimentological Evidence of Paleoclimatic Change in a Late Holocene Freeze Core Record from Walsh Lake, Northwest Territories

Climate warming in high-latitude northern environments has the potential to alter cycling of redox-sensitive elements such as arsenic (As) in lacustrine systems (MacDonald et al., 2005). The region around Yellowknife, Northwest Territories (NT), is impacted by widespread As contamination from historical gold mining and mineral processing (Jamieson, 2014). This thesis examines the past response of sediment geochemistry within Walsh Lake, NT, to paleoenvironmental changes in order to inform future mine remediation planning. Grain size, elemental geochemistry, and organic matter (OM) data preserved in an ~1100-year sedimentary freeze core record were analysed. Results suggest that (1) the cycling of trace metals (Cd, Cu, Pb, Sn, Zn) is tied to OM production and sequestration; (2) As sequestration depends on Fe and Mn (oxy)hydroxides; and (3) shifts in sediment geochemistry coincide with the Medieval Climate Anomaly and the Little Ice Age, suggesting that these climate events affected trace metal mobility in Walsh Lake.