Arctic condensed aromatic carbon budget reveals efficient fluvial transfer and shelf storage

Arctic–Boreal ecosystems hold vast carbon stocks, yet intensifying wildfires threaten to shift them from net sinks to net sources. Fires produce condensed aromatic carbon (ConAC), a chemically stable form of pyrogenic carbon that accumulates in terrestrial and marine reservoirs. However, ConAC mobilization, retention, and export along the riverine continuum remain poorly constrained. Here, we present a comprehensive source-to-sink ConAC budget for the Mackenzie River–Beaufort Sea system, quantifying wildfire production, riverine transport, and shelf accumulation. Between 2001 and 2017, fires burned 9.7% of the basin and generated 36.5 Tg ConAC, while soils stored ~4 Pg ConAC with millennial-scale turnover. Fluvial export averaged 0.42 Tg ConAC yr ^–1 . The dissolved fraction reflected modern pyrogenic sources, in contrast to particulate ConAC dominated by radiocarbon-depleted carbon derived from sedimentary rocks. On the Beaufort Shelf, waters retained ~1.2 Tg ConAC with a ~6-year residence time, whereas sediments accumulated ~0.14 Tg ConAC yr ^–1 . This budget reveals that basin properties including lithology, geomorphic routing, and sediment trapping control the composition and efficiency of land-to-ocean ConAC transfer. It establishes a quantitative baseline for assessing how ongoing environmental change will reshape ConAC cycling across high-latitude systems.