Late Pleistocene and Holocene climate change on the Kenai Peninsula, Alaska: Interpretation of a marl record from Kelly Lake
Kelly Lake, located in the lowland of the Kenai Peninsula, Alaska, is a non-glacial, organic-rich, subaqueous spring-fed lake. A sediment core (KLY18-4) recovered from 4 m water depth offers multiple proxies including d18Omarl and d13Cmarl values from ~14.1 to ~6.9 cal kyr BP, calcium carbonate content, magnetic susceptibility, and stratigraphic analysis to reconstruct lake level fluctuations, shifts in effective moisture, and precipitation source to the Kenai lowland from ~14.7 cal kyr BP to present. The shallow-water macroalgae, Chara was likely the primary precipitating agent of calcium carbonate, or marl, at the core site from ~14.1 to ~6.9 cal kyr BP when lake level rose and the zone of marl production shifted to shallower water. Calcium carbonate content is used as a proxy for Chara growth and ambient water conditions as Chara prefers clear, shallow water. Kelly Lake experienced overall lower lake levels and was likely a closed basin between the time of lake formation (~14.7 cal kyr BP) and ~6.9 cal kyr BP. Multiple shifts in lake level with periods of basin desiccation at the core site are also apparent during this time. The Younger Dryas exhibits cool and dry conditions at its onset but increasingly warm and evaporative conditions for its duration. The latter part of the Early Holocene shows an oscillatory pattern of lake level rise and fall and stepwise lake level rise beginning at ~7.5 cal kyr BP. Around 6.9 cal kyr BP the lake assumed relatively modern conditions with minimal subsequent fluctuation. Additionally, tephra deposits become more frequent here. Six deposits are found in the stratigraphy between ~6.9 cal kyr BP and present, and only one deposit is found between ~14.7 cal kyr BP and ~6.9 cal kyr BP. This suggests a potential shift to moisture sourced dominantly from the southwest bringing greater rates of precipitation and more ash fall from the Aleutian arc to the Kenai lowland.