Influence of Hydraulic Connectivity on Carbon Burial Efficiency in Mackenzie Delta Lake Sediments

The Arctic is undergoing accelerated changes in response to ongoing modifications to the climate system, and there is a need for local to regional scale records of past climate variability in order to put these changes into context. The Mackenzie Delta region in northern Canada is populated by numerous small shallow lakes. They are classified as no‐, low‐, and high‐closure (NC, LC, and HC, respectively) lakes, reflecting varying degrees of connection to the river main stem, and have different sedimentation characteristics. This study examines sedimentological (mineral surface area, grain size), carbon isotopic (bulk and molecular‐level) and inorganic isotopic (neodymium) characteristics of sediment cores from three lakes representing each class. We find that HC lake sediments exhibit strikingly different properties from the other lake sediments. Specifically, they are characterized by higher organic carbon loadings per unit mineral surface area and with relatively minor influence from allochthonous, petrogenic (rock‐derived) organic carbon. In contrast, LC and NC lakes have the potential to record basin‐scale climatic changes at a high resolution by virtue of enhanced detrital sedimentation. Overall the delta lakes have the capacity to bury about 2 MtC year−1, with little changes in the last 200 years. However, in the (near) future, an increased number of high closure lakes might change the carbon burial efficiency of the Mackenzie Delta as they seem to retain less carbon than NC and LC lakes. The Arctic is rapidly warming compared to other parts of the world, yet the consequences on regional aquatic carbon cycling are unknown. We studied the properties of sediment cores from three different types of lakes within the Mackenzie River Delta to examine relationships between the degree of lake connectivity with the main river channel network and carbon inputs and burial. “High‐closure” lakes that are rarely connected to the river mainstem are markedly different from those that are frequently inundated by the river. Their organic carbon is of local origin, in contrast to the carbon in more connected lakes. Moreover, despite higher carbon contents, high closure lakes bury carbon less efficiently, suggesting that an increase in the abundance of these lakes would lead to a reduction in carbon burial in the delta. No significant changes in carbon burial are, however, apparent in lake sediment records spanning the last ∼200 years. High‐closure lake bury very little petrogenic hydrocarbons in contrast to no‐ and low‐closure lakesHigh closure lakes have higher organic carbon loadings than usually found in freshwater systemsWe found no evidence for a significant change in carbon burial in the lakes over the last 200 years High‐closure lake bury very little petrogenic hydrocarbons in contrast to no‐ and low‐closure lakes High closure lakes have higher organic carbon loadings than usually found in freshwater systems We found no evidence for a significant change in carbon burial in the lakes over the last 200 years