We measured carbon and nitrogen isotope ratios (¹³C : ¹²C and ¹⁵N : ¹⁴N) in peat cores in a northern Minnesota bog to understand how climate, vegetation type, and decomposition affected C and N budgets over the last 9000 years. ¹³C : ¹²C patterns were primarily influenced by shifts in temperature, peatland vegetation and atmospheric CO₂, whereas tree colonization and upland N influxes affected ¹⁵N : ¹⁴N ratios. Isotopic markers provided new insights into long-term patterns of CO₂ and nitrogen losses.