Changes in Sedimentary Organic Carbon Compositions in the Mackenzie Trough Over Recent Centuries: Insights Into Permafrost Thawing in the Canadian Arctic

Abstract

This study analyzed three sediment cores (ARA08C/02-2BC, ARA08C/03-2BC, and ARA04C-40MUC) from the Mackenzie Trough in the Beaufort Sea, collected in 2013 and 2017. Using bulk sediment properties (carbon and nitrogen contents, stable carbon isotopes, and radiocarbon isotopes) and terrestrial biomarkers (lignin phenols), we examined the impacts of permafrost thaw on sedimentary organic carbon (OC) in the Canadian Beaufort Sea. Our objective was to investigate whether changes in OC sources reflect the environmental changes documented in the region over the past few decades. At the core site of ARA08C/03-2BC, we observed an increase in soil-derived OC accumulation rates (ARs) since the early 20th century, with a noticeable rise over the past few decades, while petrogenic OC ARs showed a slight decline. Grain size end-member (EM) modeling identified three primary EM groups, revealing a general increase in the proportion of coarse grains (sum of EM2 + EM3 end-members) since the early 1900s, with a marked acceleration in recent decades. These trends align with regional surface temperature increases over the past few decades, suggesting that permafrost thaw has increasingly affected sedimentary OC dynamics in the Canadian Beaufort Sea. Given climate models that predict accelerated warming in the Mackenzie Basin, our findings highlight the critical need for precise quantification of OC fluxes to improve projections of regional carbon budgets and climate dynamics in the Arctic.