HOLOCENE TERRESTRIAL AND LACUSTRINE CARBON CYCLING HISTORY OF NORTHEASTERN BAFFIN ISLAND, ARCTIC CANADA

Rapid warming in the Arctic over the past several decades has been altering regional carbon cycling dynamics. For example, permafrost has been thawing at an increasing rate, leaching more ancient organic carbon (OC) into rivers and lakes while destabilizing the terrestrial landscape. To contextualize how these modern changes compare to past episodes of Arctic warming, we use sediments from Lake CF8, Baffin Island, Nunavut, Canada, to reconstruct how Holocene climate variability impacted the flux of aged carbon to a lacustrine environment. We used ramped pyrolysis-oxidation (RPO) and radiocarbon dating of the released OC in downcore sediment to estimate the relative contributions of OC endmembers, mainly aquatic primary productivity and the in-wash of terrestrial carbon, including pre-aged permafrost and contemporaneous soil. RPO OC from eight bulk sediment samples produced five CO₂ splits each, allowing us to differentiate OC sources via a spectrum of thermal stability and radiocarbon ages. We calculate age offsets of the pyrolyzed bulk OC splits from aquatic plant macrofossil radiocarbon ages, assumed to provide true depositional ages where present in the sediment cores. By combining our RPO results with additional proxy data from Lake CF8 sediments, we infer a Holocene carbon cycling history of this site in four phases: 1. (>12 ka; thousands of years before present) Large age offsets (up to 2,300 yrs) suggest that, following deglaciation of the catchment by cold-based ice, terrestrial OC relict from the Last Interglacial mixes with aquatic OC; 2. (12-10 ka) Minimal age offsets (250-450 yrs) represent relatively minimal contributions of aged terrestrial soil compared to aquatic primary productivity during the warm early Holocene; 3. (10-6 ka) Larger age offsets (900-1,100 yrs) suggest an increased flux of terrestrial OC from a potentially deeper, older active layer to the lake; 4. (6 ka-present) Decreasing age offsets (400-900 yrs) indicate reduced terrestrial OC flux to the lake, suggesting more terrestrial carbon storage and proportionately more lacustrine OC production as temperatures cooled. Our results show that carbon cycling in Lake CF8 evolved with the local climate, where the warmer early Holocene was likely a period of increased permafrost mobility, similar to present day.