Millennial-scale carbon-source changes revealed by sedimentary radiocarbon in Arctic lakes

Organic carbon (OC) stored in Arctic watersheds for millennia can be remobilized and transported to lakes as climate change alters environmental conditions. The radiocarbon ( 14 C) age of OC in lake sediments provides insight into carbon storage and cycling. Bulk lake sediment 14 C ages integrate many OC pools, whereas macrofossil 14 C ages generally represent the time of sediment deposition. The offset between them (Δ age) provides insight into lateral carbon transfer. We analyzed Δ age from five lakes in Alaska, Russia and Siberia, using 191 bulk sediment 14 C ages paired with new ( n = 87) and existing macrofossil 14 C ages spanning 20,000 years. Lake-averaged Δ age ranges from several hundred to nearly 10,000 years. By comparing Δ age with sediment physical properties, we find that petrographic OC provides a first-order control on Δ age magnitude, followed by impacts of productivity (driven by climate) and erosion rates (driven by landscape stability). Δ age was much larger in the late Pleistocene than the Holocene, reflecting more productive vegetation and thicker organic horizons during the Holocene, which reduced older OC release and increased younger OC production. On millennial time scales, total productivity is a major control on the proportion of old carbon that accumulates in Arctic lakes, but sediment flux exerts a stronger influence on OC accumulation overall. These results underscore complex interactions between climate, geomorphology and carbon storage, with implications for understanding past and future carbon fluxes in a warming Arctic.