LATE HOLOCENE HYDROCLIMATE RECONSTRUCTION FROM A SOUTH-CENTRAL ALASKA PEATLAND

Here we present a late-Holocene record of plant macrofossils and peat cellulose oxygen isotopes (δ¹⁸O_cellulose) from a peat core located on the windward side of the Kenai Mountains on the Kenai Peninsula, Alaska to determine spatial and temporal patterns of late-Holocene hydroclimate variability. The Aleutian Low (AL) is a semi-permanent low-pressure system that has varied in strength and position throughout the Holocene, and dominates hydroclimate in this region. The objective of this study is to explore expressions of AL variability from peatland vegetation and water isotopes. A 7-m peat core was collected in 2014 from Goldfin bog (informal name), a small fen located ~20 km north of Seward, AK. This region experiences average annual precipitation of ~1700 mm per year, with most falling September through November. We used ²¹⁰Pb and ¹⁴C to date the core, measured magnetic susceptibility, and determined organic matter content through loss-on-ignition (LOI). Plant macrofossil assemblages were tallied by categorizing all peat remains >250 µm. We developed a stable oxygen isotopic record following the extraction of α-cellulose from plant macrofossils (mosses and sedges) as well as bulk peat preserved in the peatland portion of the core. Age results indicate the basal age of the core is ~10,000 years old. LOI analysis reveals that the lower ~350 cm of the core has organic matter content of <40%, while the upper ~300 cm has organic matter content of >85%. This increase in organic matter content beginning around 291 cm (~3,000 years ago), combined with macroscopic observations and magnetic susceptibility results, indicates a shift from a lake to a peatland. Preliminary results from plant macrofossil assemblages during the peatland phase of the core show a general shift from a sedge-dominated (Carex spp.) to a Sphagnum-dominated (section Acutifolia) environment at ~20 cm, although Sphagnum spp. becomes more abundant beginning around 40 cm. The shift from sedge-dominance to Sphagnum-dominance suggests a local hydrologic shift in the environment within the last several decades. The δ¹⁸O_cellulose record will be compared to our macrofossil record and other regional records to determine local hydrologic conditions (drier v. wetter), and regional synoptic-scale hydroclimate changes throughout the late-Holocene.