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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. 

Lead (Pb) has been used in human civilization for centuries, but the quantity and source of Pb pollution released into the environment varies spatially and temporally. Ice cores and snowpits are an excellent record of past Pb use. 

Abstract. Warming in high alpine regions is leading to an increase in glacier surface melt production, firn temperature, and firn liquid water content, altering regional hydrology and climate records contained in the ice. Here we use field observations and firn modeling to show that although the snowpack at Eclipse Icefield at 3000 m a.s.l. in the St. Elias Range, Yukon, Canada, remains largely dry, meltwater percolation is likely to increase with an increase in intense melt events associated with continued atmospheric warming. In particular, the development of year-round deep temperate firn at Eclipse Icefield is promoted by an increase in the number of individual melt events and in average melt event magnitude combined with warmer wintertime temperatures, rather than an earlier or prolonged melt season. Borehole temperatures indicate that from 2016 to 2023 there was a 1.67 °C warming of the firn at 14 m depth (to -3.37±0.01 °C in 2023). Results from the Community Firn Model show that warming of the firn below 10 m depth may continue over the next decade, with a 2 % chance of becoming temperate year-round at 15 m depth by 2033, even without continued atmospheric warming. Model results also show that the chance of Eclipse Icefield developing year-round temperate firn at 15 m depth by 2033 increases from 2 % with 0.1 °C atmospheric warming over the period 2023–2033 to 12 % with 0.2 °C warming, 51 % with 0.5 °C warming, and 98 % with 1 °C warming. As the majority of the St. Elias Range's glacierized terrain lies below Eclipse Icefield, the development of temperate firn at this elevation would likely indicate widespread meltwater percolation in this region and a wholesale change in its hydrological system, reducing its capacity to buffer runoff and severely limiting potential ice core sites. It is therefore urgent that a deep ice core be retrieved while the record is still intact. 

This project intends to use the Mount Denali ice core archive to develop the most comprehensive suite of North Pacific fire and summer climate proxy records since about 2500 years before present. Wildfire is a key component of summer climate in the North Pacific where wildfires are projected to increase with continued summer warming. Studies that combine paleorecords of summer climate and wildfire are therefore critically needed, especially in the North Pacific region where fire recurrence rate and decadal-to-centennial scale climate fluctuations occur over longer time periods than are covered by direct observations. The goal of the proposed research is to improve our understanding of relationships between summertime climate and wildfire activity, focusing especially on the Medieval Climate Anomaly (MCA), when regional temperatures were perhaps as warm as the 20th century. Recent advances now permit the measurement of new fire-related (pyrogenic) compounds in ice cores, enabling the development of a robust fire record capable of rigorous comparison with regional paleoclimate reconstructions. 

Monosaccharide anhydrides (MAs), or anhydrosugars which include levoglucosan, mannosan, and galactosan are combustion products of cellulose and hemicellulose that are used as biomass burning tracers. These fire biomarkers are incorporated into smoke plumes, transported through the atmosphere, and return to the surface through wet and dry deposition that can be archived in ice cores. Here, we quantify levoglucosan, mannosan, and galactosan through the Denali ice core to investigate past North Pacific fire activity.