Late-Holocene Mass Movements in High Arctic East Lake, Melville Island (Western Canadian Arctic Archipelago)

East Lake, located at Cape Bounty (Melville Island, Canadian High Arctic), was mapped using a high-resolution swath bathymetric sonar and a 12 kHz sub-bottom profiler, allowing for the first time the imaging of widespread occurrence of mass movement deposits (MMDs) in a Canadian High Arctic Lake. Mass movements occurred mostly on steep slopes located away from deltaic sedimentation. The marine to lacustrine transition in the sediment favours the generation of mass movements where the underlying massive mud appears to act as a gliding surface for the overlying varved deposits. Based on acoustic stratigraphy, we have identified at least two distinct events that triggered failures in the lake during the last 2000 years. The synchronicity of multiple failures and their widespread distribution suggest a seismic origin that could be related to the nearby Gustaf-Lougheed Arch seismic zone. Further sedimentological investigations on the MMDs are however required to confirm their age and origin.

Gross and net nitrogen transformation rates and availability in late summer in tall shrub and birch hummock ecosystems of the Canadian low Arctic

Climate change is occurring most rapidly in the Arctic where warming has been twice as fast as the rest of the globe over the last few decades. Arctic soils contain a vast store of carbon and warmer arctic soils may mediate current atmospheric CO2 concentrations and global warming trends. Warmer soils could increase nutrient availability to plants, leading to increased primary production and sequestration of CO2. Presumably because of these effects of warming on shrub ecosystems, shrubs have been expanding across the arctic over the last 50 years, Arctic shrub expansion may track or cause changes in nutrient cycling and availability that favour growth of larger, denser shrubs. This study aimed at measuring gross and net nitrogen cycling rates, major soil nitrogen and carbon pool sizes, and elucidating controls on nutrient cycling and availability between a mesic birch (Betula nana) hummock tundra ecosystem and an ecosystem of dense, tall, birch (B. nana) shrubs. Nitrogen cycling and availability was enhanced at the tall shrub ecosystem compared to the birch hummock ecosystem. Net nitrogen immobilization by microbes was approximately threefold greater at the tall shrub ecosystem. This was in part because of larger microbial biomass nitrogen and carbon (interpreted as a larger microbial community) at the tall shrub ecosystem. Nitrogen inputs via litter were significantly larger at the tall shrub ecosystem and were hypothesized to be the major contributor to the higher dissolved organic and inorganic nitrogen pools in the soil at the tall shrub ecosystem. The results from this study suggest a positive feedback mechanism between litter nitrogen inputs and the enhancement of nitrogen cycling and availability as a driver of shrub expansion across the Arctic.

Long-term hydroclimatic change and interannual variability in water sources, Apex River (Iqaluit), Baffin Island, Nunavut

The eastern Canadian Arctic is home to Canada’s largest Indigenous population, which depends on local freshwater sources for drinking water. However, small watersheds have rarely been analyzed for long-term hydrologic response to changing climate. This study aims to address this issue by examining the Apex River, a small watershed with a long hydroclimatic record, near Iqaluit, Nunavut. Particular emphasis was placed on the long-term changes in climate and river discharge, and the seasonal variability of water sources between two snapshots in time, 1983 and 2013. Long-term hydrological data were obtained from gauge station 10UH002, operated by Environment and Climate Change Canada, and long-term meteorological data were acquired from Environment Canada–operated stations near Iqaluit Airport. Breakpoint analysis suggested that long-term mean annual surface air temperatures have increased since 1994. In contrast, no long-term total precipitation or annual discharge changes were observed. However, river flow initiation and cessation analyses of the Apex River flow season indicates that flow extended into the autumn since the 2000s. The 2013 flow season lasted 44 days longer than the 1983 flow season. Systematic river sampling was undertaken throughout the 2013 thaw season to determine contributing proportions of event (snowmelt or rainfall) and pre-event (baseflow) water to river runoff. Results from the stable isotope hydrograph separation for 2013 were compared to findings for 1983. Snow was the main source of water to the river during the snowmelt period in 1983 and 2013, however baseflow was still an important contributor. Although there was high similarity of water sources early in the season in 1983 and 2013, the two years differed during the autumn. In 2013 there was a high rainfall runoff response that was not present in 1983, suggesting high release of late-season sub-surface water storage and an increased sensitivity to late-season rainfall events in 2013. This research provides insights into the hydrologic response of the Apex River to long-term climatic change, and highlights the need for high-quality precipitation and discharge data for effective long-term hydrological assessment.