A PALEOLIMNOLOGICAL STUDY RECONSTRUCTING ORGANIC CARBON ACCUMULATION AND CLIMATE HISTORY; MEALY MOUNTAINS, LABRADOR, CANADA

Over the past century, the global climate system has experienced unprecedented warming due to the rapid increase of greenhouse gas concentrations. Thus, understanding the fate of CO₂ once it is released is critical to evaluating the impacts of future climate change. Lake sediments have the potential to store large quantities of CO₂ in the form of organic carbon, yet the factors which control organic carbon burial efficiency in lakes are not fully understood. Consequently, this project examines the sedimentary record from three lakes spanning the boreal forest-tundra ecotone in the eastern Mealy Mountains of southeastern Labrador, Canada in order to identify lake and watershed controls on organic carbon accumulation and evaluate the sensitivity of organic matter accumulation to changing climatic conditions. The pronounced environmental gradient and significant post-glacial environmental changes in this region provide an ideal setting for testing controls on organic matter accumulation.

This study presents preliminary results for three sediment cores recovered from three different lakes located in the Mealy Mountains (53°N, 58°W). Gravity percussion cores (0.5 and 0.8 m) and a modified piston percussion core (1.43 m) were collected from the three lakes in summer 2014. All cores include a visible transition from organic rich sediments which overly inorganic-rich units, characteristic of glacial outwash. Basal radiocarbon ages determined from organic matter directly overlying the transition from inorganic sediments place this transition at 3698 and 5022 radiocarbon years BP. Loss on Ignition (LOI) analysis indicates an overall increase in the organic content of the sediment throughout the post glacial portion of the record. Ongoing work includes chlorophyll pigment analysis in order to gain further insight into past lake productivity. Overall, these results are quantifying past organic carbon accumulation rates in the target lakes and evaluating environmental and climatic controls on the process of organic matter accumulation. In addition, this work is helping to constrain our understanding of past climate and environmental change in a region where very little prior information is available.