Aquatic export of young dissolved and gaseous carbon from a pristine boreal fen: Implications for peat carbon stock stability.

The stability of northern peatland's carbon (C) store under changing climate is of major concern for the global C cycle. The aquatic export of C from boreal peatlands is recognized as both a critical pathway for the remobilization of peat C stocks as well as a major component of the net ecosystem C balance (NECB). Here, we present a full year characterization of radiocarbon content (14 C) of dissolved organic carbon (DOC), carbon dioxide (CO2 ), and methane (CH4 ) exported from a boreal peatland catchment coupled with 14 C characterization of the catchment's peat profile of the same C species. The age of aquatic C in runoff varied little throughout the year and appeared to be sustained by recently fixed C from the atmosphere (<60 years), despite stream DOC, CO2 , and CH4 primarily being sourced from deep peat horizons (2-4 m) near the mire's outlet. In fact, the 14 C content of DOC, CO2 , and CH4 across the entire peat profile was considerably enriched with postbomb C compared with the solid peat material. Overall, our results demonstrate little to no mobilization of ancient C stocks from this boreal peatland and a relatively large resilience of the source of aquatic C export to forecasted hydroclimatic changes.