Paleolimnological assessment of Holocene climatic and environmental change in two lakes located in different regions of the Canadian Arctic Tundra

Paleoclimatic research in the Canadian Arctic has increased in recent decades; however, there is still much to learn about the nature and extent of past climate change in this vast and environmentally sensitive region. This thesis uses primarily diatom assemblages in dated lake sediment cores as proxy indicators to infer how climate has changed over the Holocene in two very different lakes in the central Canadian Arctic: one located in a poorly-studied geographical region, and another possessing limnological characteristics that are unusual in an Arctic context.;Lake TK-2 is located in the low Arctic tundra. Paleolimnological studies from this region are lacking, as most have centered on sites in the High Arctic Archipelago or around Subarctic treeline. Marked changes in the diatom assemblages in TK-2 throughout the Holocene included potential evidence for the 8.2k cooling event, which has not been previously reported from other Canadian Arctic paleolimnological studies. In addition, diatom shifts occurring ∼7000 and ∼3500 cal yr BP are indicative of mid-Holocene warming and subsequent Neoglacial cooling, respectively, the timings of which agree with those from other studies farther south. Finally, shifts in the diatom assemblages in the upper sediment layers, beginning in the early-to-mid 19th century, are consistent with reduced ice cover, related to recent warming.;Stygge Nunatak Pond, a small, closed-basin pond located on a nunatak in the High Arctic on Ellesmere Island, is characterized by water with unusually high ionic concentrations for an inland Arctic pond. As in TK-2, Stygge's diatom assemblages changed substantially throughout the Holocene, but especially in the most recent sediments. Diatom shifts near ∼10,500 cal yr BP suggest an early onset for the Holocene Thermal Maximum (as well as for the successive Neoglacial cooling trend) in this region, consistent with previous studies from the High Arctic. Marked changes in diatom assemblages occurred in the most recent sediments, and, like those in TK-2, are indicative of climate warming and reduced ice cover, as well as increased ionic concentration due to enhanced evaporative concentration. The dynamic nature of the diatom assemblage changes at the Stygge site suggests that sediments from these rare athalassic ponds represent an especially sensitive archive of Arctic climatic and environmental change.