by Rachel Pellegrino
Global temperatures are rapidly increasing, with high-latitude regions like the Arctic warming four times faster than the global average. This phenomenon, called Arctic amplification, leads to various environmental changes including permafrost thaw. Permafrost is defined as ground that remains frozen for two or more years, and is essential for regulating global climate and defining Arctic topography and hydrology. The degradation of permafrost-dominated landscapes leads to an increase in thermokarst (i.e., subsidence) activity resulting in landscape disturbance in the form of mass wasting and alterations to soil and surface water chemistry. Shoreline thermokarst can trigger lake drainage events, with outlets forming within thawing permafrost, diverting water through ice-wedge polygons, and catastrophically affecting lakes in less than 24 hours. Given the prevalence of thermokarst lakes in the Mackenzie Delta region, increased drainage events are expected to impact lake ecosystems.
My research this summer utilized biological indicators within a lake sediment core (the science of paleolimnology) to examine recent changes and the consequences of permafrost thaw and drainage on a small lake in the Mackenzie Delta region of Canada’s western Arctic (Figure 1). My study focused on analyzing the response of diatoms (algae of the class Bacillariophyceae) to reconstruct environmental changes related to regional climate warming, permafrost thaw, and lake drainage occurring in the western Arctic region. Diatoms are a diverse group of single-celled eukaryotes that produce walls of silica (i.e., glass) allowing them to be well-preserved in sediments. They are good indicators of numerous limnological variables, including water chemistry, depth, pH, and habitat making them great paleo-indicators for tracking environmental changes in lakes.
A unique feature of my study is that I am re-examining the environmental changes occurring in a lake that has been previously well-studied using paleolimnological methods. The lake I am interested in was sampled by my supervisor, Prof. Joshua Thienpont, in 2008 during his graduate work. However, as the western Arctic is rapidly changing, the lake in question catastrophically drained in 2012, a date that was determined through remote sensing research by my colleague and fellow MSc student Claire O’Hagan. My research is specifically interested in understanding how the lake changed following the drainage event, and if any recovery has occurred in the following decade.
The results of my research revealed a shift in habitat type associated with the water-level lowering of the lake when it drained in 2012. This manifests as a shift in the dominant diatom taxa from those favouring deeper waters to those found in shallow areas, and living attached to aquatic plants that would be more common with a lower water level. Interestingly, diatom assemblages indicate that the lake has likely been re-filling in the intervening decade, which was confirmed when the lake was visited and sampled this summer (Figure 2).
The findings of my research show that diatom-based paleolimnological techniques are well suited to tracking the interacting effects of multiple environmental stressors, including permafrost thaw, lake drainage, and the overarching driver of anthropogenic climate warming. This unique case study provides crucial insights into the rapid environmental changes associated with lake drainage, including its effects on chemistry, biology, and the physical environment. As thermokarst activity, and the linked impact of lake drainage, is expected to increase with rising global temperatures, this research provides a window into future lake response in the rapidly changing north.
Rachel Pellegrino won the Canadian Association of Geographers (CAG) award as top undergraduate geography student at York University. She graduated summa cum laude with an Honours Bachelor of Arts (HBA) in Geography and is now pursuing Master of Science (MSc) in Geography.