Clyde Foreland Lake, Nunavut CO2 Concentration and d14C Data over the past 12.5 kiloannum

Recent 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 to 8 kiloannum (ka) at our study site), may serve as an analogue for how the Arctic carbon cycle responds to ongoing warming. We reconstructed accumulation rates of three OC endmembers (contemporaneous aquatic biomass, postglacial soil, and MIS 5 soil) at Lake CF8, northeastern Baffin Island, during the 12.4 kyr (kiloyear) since local deglaciation. We characterized OC endmembers and downcore sediment mixtures using Ramped Pyrolysis/Oxidation (RPO), radiocarbon (14C) age offsets between bulk sediment and macrofossils, and stable carbon isotopes (δ13C). We modeled endmember contributions to the lake sediment using the Bayesian mixing framework, MixSIAR. RPO revealed similar patterns between OC volatilization and pyrolysis temperature indicating minimal OC degradation between source and sink. Endmember OC accumulation rates, accounting for MixSIAR results, sedimentation, and total OC content, showed that mean postglacial soil inputs to Lake CF8 were greatest between 11.9 and 9.0 ka, 1.5 times greater than the rest of the record. This period coincided with regional peak Holocene summer temperatures (up to 5 °C (celsius) warmer than the pre industrial average), despite having low 14C age-offsets. Since modern Arctic temperatures have already warmed by 2-3 °C, similar to the HTM, regional permafrost may be mobilized at the same rates that we estimate for the early Holocene.