Postglacial Carbon Cycling History of a Northeastern Baffin Island Lake Catchment Inferred From Ramped Pyrolysis Oxidation and Radiocarbon Dating

Abstract Anthropogenic warming in the Arctic has caused accelerated permafrost thaw, leading to the export of relict organic carbon (OC) to the atmosphere and surrounding depositional environments. Past episodes of warmth exceeding pre‐industrial temperatures, such as the Holocene Thermal Maximum (HTM; 11–8 ka at our study site), may serve as an analog for how the Arctic carbon cycle responds to ongoing warming. Here, we reconstructed accumulation rates of three OC endmembers (aquatic biomass, postglacial soil, and MIS 5 soil) in downcore sediments from Lake CF8, northeastern Baffin Island, during the 12.4 kyr since local deglaciation. We characterized endmembers and sediment mixtures using Ramped Pyrolysis/Oxidation (RPO), radiocarbon ( 14 C) age offsets between bulk sediment and macrofossils, and stable carbon isotope ratios (δ 13 C). We then modeled endmember contributions to the lake sediments using MixSIAR. RPO revealed similar patterns between OC volatilization and pyrolysis temperature indicating minimal OC degradation between endmembers and mixtures. MixSIAR‐derived endmember accumulation rates showed that mean soil‐derived OC inputs to Lake CF8 were proportionally greatest between 11.9 and 9.0 ka (5.2 ± 1.9 g OC/m 2 /yr), 1.5 times greater than the rest of the record (3.4 ± 1.5 g OC/m 2 /yr). This period coincided with regional rapid warming and peak Holocene summer temperatures. Since modern Arctic temperatures have already warmed by 2–3°C, similar to the HTM, modern regional permafrost OC may be mobilized at the same rates that we estimate for that period.