HOLOCENE CLIMATIC CHANGES IN THE ALASKAN ARCTIC AS INFERRED FROM SEDIMENTOLOGICAL AND OXYGEN-ISOTOPIC ANALYSES AT WAHOO LAKE

Reconstructions of Holocene climate in the Alaskan Arctic allow for better understanding of how the region may respond to future climate changes, though long-term records are scarce. We conducted sedimentological and isotopic analyses at Wahoo Lake (69º4.612, -146º55.676) to infer Holocene climate variability in northern Alaska. Isotopic composition of modern water from this large, open-basin lake in the northern foothills of the Brooks Range suggests that winter precipitation dominates inputs to the lake. Isotopic composition of Pisidium throughout the past 11,800 years exhibits large variations, with δ¹⁸O values ranging between 11.63 and 14.18‰ (VSMOW) and δ¹³C ranging between -2.30 and -7.10‰ (VPDB). Loss-on-ignition (LOI) shows high carbonate content (8.1-50.9%) in the subbasin sediments between 11.8-6.3 kcal BP, transitioning to lower carbonate (1.3-25.3%) and increased organic content (11.7-65.2%) between 6.3-1.4 kcal BP. High carbonate content and elevated δ¹⁸O values (12.99-13.96‰) from 11.5-8.5 kcal BP likely reflect lower lake level and possibly evaporative enrichment of lake water, suggesting warm, dry summers during the Holocene Thermal Maximum. The disappearance of Pisidium, paired with a decrease in calcite deposition at ~6.5 kcal BP, suggests increasing lake-level in the mid-Holocene, which is supported by a basal date of 5.3 kcal BP from an adjacent, shallow shelf-core. This increase likely resulted from elevated regional effective moisture, as it coincided with lake-level increases in interior Alaska. The shelf sediments exhibit a marked increase in carbonate content at ~3.5 kcal BP and δ¹⁸O values generally rose from 3.5-2.0 kcal BP (range = 11.63-14.18‰). This increased deposition of calcite during high lake level and increasing δ¹⁸O values suggest increasing temperature during this period. After 2.0 kcal BP, δ¹⁸O values fluctuate between 11.88-13.31‰, but generally decline until 1.0 kcal BP, suggesting dramatic temperature fluctuations in the late Holocene. Overall, these Holocene variations in δ¹⁸O values from Wahoo Lake generally correspond to fluctuations in total solar irradiance, suggesting that solar variability may play an important role in the long-term climate of the Alaskan Arctic.