OXYGEN ISOTOPIC ANALYSIS OF PEATLAND PLANT CELLULOSE AS A PROXY FOR HOLOCENE HYDROCLIMATE ON THE KENAI PENINSULA, ALASKA

Understanding environmental responses to past climate variability on decadal to millennial timescales using proxy records is important to help interpret and predict present and future changes. Recent studies suggest that the oxygen isotopic signature preserved in alpha cellulose extracted from plant macrofossils is likely related to the isotopic composition of source water, and can therefore provide information on long-term changes in past atmospheric circulation and hydroclimate variability. In this study, we assessed differences in isotopic signatures between plant species along a hydrological gradient on the Kenai Peninsula and reconstructed regional moisture source and distribution patterns during the last ~5000 years. We collected modern plants (mosses and sedges), water, and a peat core from hydrologically distinct peatland sites with order-of-magnitude differences in precipitation across a relatively small (<40 miles) area that extends across the Kenai Mountains (~1025 m) from the leeward to the windward side. The core was taken from a kettle bog (Gold Fin bog, informal name) on the leeward side of the Kenai Mountains with the goal of comparing down-core isotopic shifts to an existing peat cellulose record (Horsetrail fen) from the windward side. We extracted cellulose from modern plants to perform oxygen isotopic analysis to help establish the range of isotopic fractionation between species and plant components. Preliminary results from the modern samples show a range in oxygen isotope values (δ¹⁸O) of 13.9‰ to 20.8‰, with a mean of 17.4 ± 1.6‰. The results suggest that biological fractionation factors offset the oxygen isotope values by approximately 3‰. Despite oxygen isotopic variability among species, distinct patterns emerged that reflect local hydrologic conditions (drier v. wetter). Generally, results suggest that submerged species were more depleted in δ¹⁸O relative to those species on hummocks. These results will be used to help interpret down-core results of the Gold Fin bog core and to reconstruct regional hydroclimate variability on the Kenai Peninsula during the Holocene.