Inferring thermokarst landscape dynamics in the recent past using lacustrine sediments:
Towards a “pan-Hudsonian” perspective
Frédéric Bouchard, Ph.D.
Département de Géographie & Centre d’études nordiques (CEN), Université Laval, Québec (QC)
Visiting postdoc, Department of Geography and Environmental Studies, Wilfrid Laurier University
Thermokarst (thaw) lakes are widespread in northern Canada and particularly vulnerable to climate change. Moreover, these freshwater landscapes can play a vital role in biogeochemical cycles by transferring to the atmosphere vast amounts of organic carbon (formerly trapped in permafrost), thus contributing a positive feedback to climate warming. Yet, little is known about the hydrological and limnological evolution of these freshwater basins, how they have responded to environmental change in the recent past and how they will evolve in the future.
The Hudson Bay region has experienced severe warming episodes over the last decades, and projected increases in temperature and precipitation for the late 21st century are significant. Thermokarst lakes along the coast of Hudson Bay are typically less than a few meters deep and are thus susceptible to becoming ephemeral, which would have severe ecological consequences. Lack of baseline hydrological and limnological information impedes assessment of future water resource availability and biogeochemical fluxes in this region. To address this knowledge gap, paleolimnological investigations are being conducted. Findings will generate new knowledge of the hydrological and limnological behavior of thermokarst lakes in central Canada, over a range of temporal and spatial scales, and provide the basis to anticipate how these aquatic ecosystems will respond to ongoing climate change and variability.
At WLU (supervisor: B. Wolfe), we focus on a suite of paleolimnological tools that are being developed for down-core reconstructions in Wapusk National Park (WNP) in the western Hudson Bay Lowlands (HBL). In September 2012, surface-sediments were obtained from 37 lakes in WNP, which span a vegetation gradient from the boreal forest to the arctic tundra. Surface sediments will be analyzed for a suite of biological (diatoms, pigments) and geochemical (organic carbon and nitrogen elemental and stable isotope composition, cellulose oxygen isotope composition) indicators. Biological and geochemical data in the surface-sediments will be compared to hydrological (water isotope composition) and limnological (water chemistry) data collected during the last three years to inform and constrain paleohydrological and paleolimnological reconstructions.
Paleolimnological reconstructions in WNP will be compared to lithostratigraphic and biostratigraphic data obtained in thermokarst lakes spanning a comparable latitudinal gradient along the southeastern coast of Hudson Bay, near the hamlets of Kuujjuarapik-Whapmagoostui and Umiujaq (Nunavik, northern Québec). This broad-scale approach aims to generate a pan-Hudsonian perspective of hydrological and limnological variations of thermokarst lake systems in the recent past. This multi-faceted integration of paleolimnological records is facilitated by collaborations through ADAPT (Arctic Development and Adaptation to Permafrost in Transition), a new Canada-wide research program focused on diverse aspects of thawing permafrost conditions in the Canadian Arctic.