Lacustrine systems contain a small fraction of the world’s water but collectively account for nearly half of the world’s annual total organic carbon (OC) burial. The Laurentian Great Lakes (LGLs) together hold nearly 20% of the Earth’s fresh water and contain ecosystems which are vital to surrounding communities. Despite this, the fate, chemistry, and sources of OC to LGL sediments is poorly understood. In order to address this, we have embarked on a 5-year study to characterize the chemical composition and sources of OC spatially and temporally in all five of the LGLs. Here we will present the results from two LGLs: Lakes Superior (sampled in summer 2021) and Huron (sampled in summer 2022). Surface sediments were collected at 31 sites in each lake and analyzed for bulk elemental composition, stable carbon and nitrogen isotopes, and lignin-phenol biomarkers. Three cores were also taken in Lake Superior to analyze temporal trends in OC source and burial. Interestingly, sediments at some offshore sites in Lake Superior were found to contain higher concentrations of both total OC and total lignin-phenols than nearshore sites, indicating terrestrial carbon delivered by coastal or riverine sources may not be a significant source of OC to the lake. Lignin-phenol ratios of OC in offshore sediments indicate that airborne pollen is likely a major source of terrestrially-sourced OC at these sites, indicating that aeolian inputs of OC into lakes may be influential. Temporal trends show pollen has been a major source of terrestrial OC to Lake Superior sediments for hundreds of years.

Primary Presenter: Kathryn Schreiner, University of Minnesota Duluth (kschrein@d.umn.edu)

Authors:

Jake Zunker, University of Minnesota Duluth  (zunke018@d.umn.edu)

Chan Lan Chun, University of Minnesota Duluth  (chun0157@d.umn.edu)

Christopher Filstrup, University of Minnesota Duluth  (filstrup@d.umn.edu)

Euan Reavie, University of Minnesota Duluth  (ereavie@d.umn.edu)

Bridget Ulrich, University of Minnesota Duluth  (ulrichb@d.umn.edu)