Denali Ice Core stable water isotopes, Begguya Plateau, Denali National Park, Alaska, 2025

In the North Pacific, large swings in climate, such as the so-called Little Ice Age, Medieval Climate Anomaly, and the 4.2 ka (thousand years ago) event, have all occurred during the Middle-Late Holocene, providing an opportunity to investigate the regional climate and environmental response to hemisphere-scale changes. Two surface-to-bedrock ice cores (210 meters) recovered from the Begguya plateau (Alaska) have been used to document late Holocene climate variability in the North Pacific, underpinned by an annual layer counted timescale that extends to ~800 AD (190 meters depth). Here we describe new data and approaches being used to investigate Holocene and late Pleistocene conditions on Begguya through stable water isotope analysis performed in the bottom 20 meters of the cores. We have completed a full δ18O-H2O isotope profile for both cores, showing relatively uniform values through the core section thought to contain the 4.2ka event. In contrast, a pronounced but continuous 5‰ (permil) increase in δ18O-H2O occurs approximately 2 meters above the bed. Based on the location and structure of these changes, we tentatively infer that the isotope and chemistry excursions near the bed represent the late Pleistocene-Holocene transition, and the isotope profile in that area possibly shows evidence of a climate reversal akin to the Younger Dryas.