Denali Ice Core stable water isotopes in basal ice, 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.

北太平洋中晚全新世时期曾发生多起剧烈气候波动事件，包括学界熟知的小冰期、中世纪气候异常期以及4.2 ka（千年前）事件，这些事件为探究区域气候与环境对半球尺度气候变化的响应提供了绝佳契机。研究团队从阿拉斯加贝吉亚高原获取了两根地表直达基岩的冰芯（总长210米），其年层计数年代标尺可追溯至公元800年左右（对应冰芯深度190米处），该冰芯已被用于记录北太平洋晚全新世的气候变异性。本文介绍了针对两根冰芯底部20米段开展的稳定水同位素分析方法及所获新数据，用于探究贝吉亚高原全新世与晚更新世的气候环境状况。研究团队已完成两根冰芯完整的δ¹⁸O-H₂O同位素剖面，结果显示在被认为包含4.2 ka事件的冰芯段内，同位素数值相对均一。与之形成鲜明对比的是，在距基岩约2米处，δ¹⁸O-H₂O值出现了显著且持续的5‰（千分比）升高。基于这些变化的位置与结构特征，研究团队初步推断，冰芯底部附近的同位素与化学组分偏移代表了晚更新世-全新世过渡阶段，该区域的同位素剖面或可反映出类似新仙女木事件的气候反转迹象。