by Claire O'Hagan
Permafrost is permanently frozen ground, and is critical to the ecosystem health and function in northern landscapes. It is important for maintaining the stability of the soil, as well as the welfare of the organisms that inhabit northern areas. Permafrost thaw, ongoing as a result of anthropogenic climate change, has increased the formation of retrogressive thaw slumps, a mass wasting feature that occurs as a result of the thaw of ice-rich permafrost. Retrogressive thaw slumps can impact water bodies such as lakes, rivers and marine systems, affecting the quality of water. Understanding the effects that thaw slumps have on lakes and the surrounding landscape is important to understand the current trends of permafrost thaw, as well as predicting future trends as the climate continues to change.
Paleolimnology is the scientific discipline that uses physical, chemical and biological data preserved in lake sediments to understand past environmental conditions. Understanding past data and patterns allows for a better understanding of how the current conditions came to be, and allows for predictions to be made about future physical environmental changes, particularly in areas that lack direct monitoring data. It allows us to understand the effects (both direct and indirect) that humans have had on the environment. This data is obtained by collecting lake sediment using sediment cores and analysing the sediment, which can reveal the environmental conditions in the lake and its catchment at the time of deposition. This research aims to use lake sediment to gain insight into the environmental conditions of the Mackenzie Delta region, related to permafrost thaw.
My EUCURA project focused on testing to see if loss on ignition (LOI) could prove to be a reliable indicator of changes in a lake due to thaw slump activity. To do this, I measured the LOI in lake sediments from twelve lakes that either have slump activity or do not, in the Mackenzie Delta region. LOI is a common technique that is used to estimate the organic matter content of soil and sediments. By burning the sediment at different temperatures and then taking the weight of that sediment, the composition of the soil is able to be analysed by calculating the loss of weight with a series of sequential ignitions. Sediments are first burned at 550°C, which allows for the percentage of the soul that is made up of organic matter (primarily carbon and nitrogen) to be calculated. The remaining sediment is then burned 950°C. This allows the calculation of the percentage of soil that is composed of carbonate minerals, which is lost during heating at 950°C, and silicate minerals, which is most of the remaining minerals. LOI is a useful tool in paleolimnology because it is cheap, can be run quickly on multiple samples at a time, and uses a relatively small amount of sediment, however, until now, it has not been specifically studied as a potential, faithful indicator of permafrost thaw slumping activity. The results from this project allow for a comparison of the sediment composition between lakes impacted by thaw slump and those with no slump activity.
Sediment samples being used for LOI.
This research will determine if LOI is a reliable indicator to track slump activity, which can then be applied in future to paleolimnological investigations of permafrost thaw. The results of my EUCURA project indicate that there are some notable differences in the sediment composition between lakes with and without thaw slumps. Slump lakes tend to have a higher percentage of its sediment composed of silicate materials, likely derived from the input of minerogenic soils when thaw slumping occurs. In contrast, non-slump lakes had a higher percentage of organic matter in their sediment profile, likely indicative of greater in- lake production and limited movement of soil from the catchment to the lake. The final phase of this research will be to format the results for submission as a research manuscript which will occur during the fall term. Once published, this research will provide insights into a tool for tracking permafrost thaw using lake sediments that can be applied by researchers, including here at the Faculty of Environmental and Urban Change at York University.
Claire O'Hagan is one of the recipients of the inaugural EUC Undergraduate Research Awards (EUCURA) in 2022. As part of the award, she worked with Professor Joshua Thienpont on a project titled Assessing a potential tool for rapid assessment of shoreline permafrost thaw impacts to lake sediments.