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The Denali Ice Cores were collected from the summit of Begguya (Mt. Hunter), Denali National Park, Alaska in the summer of 2013. Sampling permits were granted by Denali National Park for the drilling and removal of the ice cores. Here, we use the Cameca SX100 at the University of Maine to examine tephra particles recovered from the ice cores. 

In 2013, two parallel ice cores (commonly referred to as the Denali Ice Cores) were drilled to bedrock on the summit plateau of Begguya, Alaska (62.93 N 151.083 W, 3912 m asl; also known as Mount Hunter). A robust chronology has been developed using a combination of techniques including annual layer counting, sulfate peaks (volcanics), radiocarbon dating and the 1963 atmospheric nuclear weapons testing horizon. Here, we employed tephrochronology practices to isolate and document the presence of the Lena Ash Layer and White River Ash east (WRAe) volcanic eruptions within the ice. We separated tephra from the meltwater and analyzed them using SEM-EDS and EPMA methodologies. The data are not immediately conclusive, and work is still ongoing to understand the findings. 

The Denali Ice Cores were collected from the summit of Begguya (Mt. Hunter), Denali National Park, Alaska in the summer of 2013. Sampling permits were granted by Denali National Park for the drilling and removal of the ice cores. Here, we use the Tescan II at the University of Maine to examine tephra particles recovered from the ice cores. 

A robust chronology has been developed for the Denali Ice Cores, Begguya, Alaska (62.93 N 151.083 W, 3912 m asl (meters above sea level); also known as Mount Hunter) using a combination of techniques including annual‑layer counting, volcanics, radiocarbon dating, and the 1963 atmospheric nuclear‑weapons‑testing horizon. Radiocarbon dating confirms that there is early Holocene ice preserved at the bottom of the Denali Ice Cores. To confirm this, researchers at the University of Maine have produced oxygen‑isotope records. Examining the data from the twin cores, we see replicate isotope profiles in the bottom 8 meters of ice, showing a sharp decrease of δ^18O (oxygen‑18 isotope ratio) of nearly 6 ‰ (permil) near the bottom. To investigate whether this decrease is a climate signal or an artifact of basal‑ice dynamics, we collected trace‑element data across the oxygen‑isotope decrease. Because the basal ice of the Denali Ice Cores contains too high a sediment load to be melted and analyzed with aqueous inductively coupled plasma mass spectrometry (ICP‑MS), we analyzed Na (sodium), Mg (magnesium), Cu (copper), Pb (lead), Al (aluminum), Ca (calcium), Fe (iron), and S (sulfur) in the basal ice (207.35 m to 208.76 m depth) using laser‑ablation inductively coupled plasma mass spectrometry (LA‑ICP‑MS). The data are still being analyzed and compared with data from other methods to determine the cause of the oxygen‑isotope‑signal decrease. Researchers seeking to use this dataset should proceed with caution, as there is some evidence of contamination in the Pb and Cu analyses. 

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. 

Abstract. Investigating North Pacific climate variability during warmintervals prior to the Common Era can improve our understanding of thebehavior of ocean–atmosphere teleconnections between low latitudes and theArctic under future warming scenarios. However, most of the existing icecore records from the Alaskan and Yukon region only allow access to climateinformation covering the last few centuries. Here we present asurface-to-bedrock age scale for a 210 m long ice core recovered in 2013from the summit plateau of Begguya (Mt. Hunter; Denali National Park,Central Alaska). Combining dating by annual layer counting with absolutedates from micro-radiocarbon dating, a continuous chronology for the entireice core archive was established using an ice flow model. Calibrated14C ages from the deepest section (209.1 m, 7.7 to 9.0 ka cal BP)indicate that basal ice on Begguya is at least of early Holocene origin. Aseries of samples from a shallower depth interval (199.8 to 206.6 m) weredated with near-uniform 14C ages (3 to 5 ka cal BP). Our resultssuggest this may be related to an increase in annual net snow accumulationrates over this period following the Northern Hemisphere Holocene ClimateOptimum (around 8 to 5 kyr BP). With absolute dates constraining thetimescale for the last >8 kyr BP, this paleo-archive will allowfuture investigations of Holocene climate and the regional evolution ofspatial and temporal changes in atmospheric circulation and hydroclimate inthe North Pacific. 

Abstract. Remote sensing data are a crucial tool for monitoring climatological changes and glacier response in areas inaccessible for in situ measurements. The Moderate Resolution Imaging Spectroradiometer (MODIS) land surface temperature (LST) product provides temperature data for remote glaciated areas where air temperature measurements from weather stations are sparse or absent, such as the St. Elias Mountains (Yukon, Canada). However, MODIS LSTs in the St. Elias Mountains have been found in prior studies to show an offset from available weather station measurements, the source of which is unknown. Here, we show that the MODIS offset likely results from the occurrence of near-surface temperature inversions rather than from the MODIS sensor’s large footprint size or from poorly constrained snow emissivity values used in LST calculations. We find that an offset in remote sensing temperatures is present not only in MODIS LST products but also in Advanced Spaceborne Thermal Emissions Radiometer (ASTER) and Landsat temperature products, both of which have a much smaller footprint (90–120 m) than MODIS (1 km). In all three datasets, the offset was most pronounced in the winter (mean offset >8 ∘C) and least pronounced in the spring and summer (mean offset <2 ∘C). We also find this enhanced seasonal offset in MODIS brightness temperatures, before the incorporation of snow surface emissivity into the LST calculation. Finally, we find the MODIS LST offset to be consistent in magnitude and seasonal distribution with modeled temperature inversions and to be most pronounced under conditions that facilitate near-surface inversions, namely low incoming solar radiation and wind speeds, at study sites Icefield Divide (60.68∘N, 139.78∘ W; 2,603 m a.s.l) and Eclipse Icefield (60.84∘ N, 139.84∘ W; 3017 m a.s.l.). Although these results do not preclude errors in the MODIS sensor or LST algorithm, they demonstrate that efforts to convert MODIS LSTs to an air temperature measurement should focus on understanding near-surface physical processes. In the absence of a conversion from surface to air temperature based on physical principles, we apply a statistical conversion, enabling the use of mean annual MODIS LSTs to qualitatively and quantitatively examine temperatures in the St. Elias Mountains and their relationship to melt and mass balance. 

Investigation of North Pacific climate variability during warm intervals outside of the Common Era is essential for addressing questions regarding ocean-atmosphere teleconnections between low latitudes and the Arctic under future warming scenarios. However, most of existing ice cores extracted from Alaska/Yukon region archive climate information from the last few centuries. This dataset contains radiocarbon (14C) data from a 208 meter surface-to-bedrock ice core recovered from the summit plateau of Mt. Hunter in central Alaska in 2013. By applying radiocarbon dating on carbonaceous aerosols, a continuous depth-age relationship has been established in the Mt. Hunter ice core. Calibrated 14C ages from the two lowest samples (7,946-10,226 cal BP and 7,018-7,975 cal BP) indicate that basal ice on Mt. Hunter has an early Holocene (&gt; 8 kyr) origin. We also show that samples from depth of 161.0-166.1 m weq have nearly uniform 14C ages (3,200 to 3,500 cal BP). One possible explanation is an increase in snow accumulation at Mt. Hunter during regional neoglaciation. When paired with the Mt. Logan PRCol record, the only other Holocene-length ice core from North Pacific region, the Mt. Hunter ice core provides the possibility to investigate spatial changes in high-elevation Holocene hydroclimate.