Abstract. We used δ15N and δ13C patterns from 16 peat depth profiles to interpret changes in C and N cycling in the Marcell S1 forested bog in northern Minnesota over the past ~ 10 000 years. In multiple regression analyses, δ15N and δ13C correlated strongly with depth, plot location, C / N, %N, and each other. Continuous variables in the regression model mainly reflected 13C and 15N fractionation accompanying N and C losses, with an estimated 40 % of fractionations involving C-N bonds. In contrast, nominal variables such as plot, depth, and vegetation cover reflected peatland successional history and climate. Higher δ15N and lower δ13C in plots closer to uplands may reflect distinct hydrology and accompanying shifts in C and N dynamics in the lagg drainage area surrounding the bog. The Suess effect (declining δ13CO2 since the Industrial Revolution) and aerobic decomposition lowered δ13C in recent surficial samples. A decrease of 1 ‰ in the depth coefficient for δ15N from −35 cm to −25 cm probably indicated the depth of ectomycorrhizal activity after tree colonization of the peatland. Low δ13C at −213 cm and −225 cm (~ 8500 years BP) corresponded to a warm period during a sedge-dominated rich fen stage, whereas higher δ13C thereafter reflected subsequent cooling. Because of multiple potential mechanisms influencing δ13C, there was no clear evidence for the influence of methanogenesis or methane oxidation on bulk δ13C.
