Despite extensive paleoenvironmental research on the postglacial history of the Kenai Peninsula, Alaska, uncertainties remain regarding the region's deglaciation, vegetation development, and past hydroclimate. To elucidate this complex environmental history, we present new proxy datasets from Hidden and Kelly lakes, located in the eastern Kenai lowlands at the foot of the Kenai Mountains, including sedimentological properties (magnetic susceptibility, organic matter, grain size, and biogenic silica), pollen and macrofossils, diatom assemblages, and diatom oxygen isotopes. We use a simple hydrologic and isotope mass balance model to constrain interpretations of the diatom oxygen isotope data. Results reveal that glacier ice retreated from Hidden Lake's headwaters by ca. 13.1 cal ka BP, and that groundwater was an important component of Kelly Lake's hydrologic budget in the Early Holocene. As the forest developed and the climate became wetter in the Middle to Late Holocene, Kelly Lake reached or exceeded its modern level. In the last ca. 75 years, rising temperature caused rapid changes in biogenic silica content and diatom oxygen isotope values. Our findings demonstrate the utility of mass balance modeling to constrain interpretations of paleolimnologic oxygen isotope data, and that groundwater can exert a strong influence on lake water isotopes, potentially confounding interpretations of regional climate.

Sediments that accumulate in high-latitude lakes serve as valuable environmental archives of changing conditions in a region currently undergoing rapid change. A previously unexplored sedimentary sequence reaching back 16,000 years from Lakes Peters and Schrader (Neruokpuk Lakes) in the northeastern Brooks Range (69°N), Alaska, shows distinct changes in accumulation rates and biophysical properties including bulk density (BD), organic matter (OM) content, and grain-size distribution at five widely distributed core sites. The oldest sediments contain little OM and accumulated rapidly as glaciers retreated around 15 ka. OM peaked between 12 and 10 ka along with Northern Hemisphere summer insolation. BD increased and OM decreased until around 5 ka, possibly reflecting a decrease in river-transported terrestrial OM. From 5–2 ka, OM consistently increased, suggesting a rise in river discharge, or a rise in summer temperatures, which led to higher productivity, or both. After 2 ka, sediments increased in BD and decreased in OM, suggesting glacier growth. Evidence for glacier expansion late during the Little Ice Age is weak, but increased sedimentation rates may reflect glacier retreat during the last century. This study provides a framework for future paleoenvironmental research of a rare archive in a relatively pristine Arctic setting.