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Basal materials in ice cores hold information about paleoclimate conditions, glacial processes, and the timing of past ice-free intervals, all of which aid understanding of ice sheet stability and its contribution to sea level rise in a warming climate. Only a few cores have been drilled through ice sheets into the underlying sediment and bedrock, producing limited material for analysis. The last of three Camp Century ice cores, which the U.S. Army collected in northwestern Greenland from 1963–1966 CE, recovered about 3.5 m of subglacial material, including ice and sediment. Here, we document the scientific history of the Camp Century subglacial material. We present our recent core-cutting, sub-sampling, and processing methodology and results for this unique archive. In 1972 CE, curators at the Buffalo, New York, Ice Core Laboratory cut the original core sections into 32 segments that were each about 10 cm long. Since then, two segments were lost and are unaccounted for, two were thawed, and two were cut as pilot samples in 2019 CE. Except for the two thawed segments, the rest of the extant core has remained frozen since collection. In 2021 CE, we documented, described, and then cut each of the remaining frozen archived segments (n=26). We saved an archival half and cut the working half into eight oriented sub-samples under controlled temperature and light conditions for physical, geochemical, isotopic, sedimentological, magnetic, and biological analyses. Our approach was designed to maximize sample usage for multiproxy analysis, minimize contamination, and preserve archive material for future analyses of this legacy subglacial material. Grain size, bulk density, sedimentary features, magnetic susceptibility, and ice content, as well as pore ice pH and conductivity, suggest that the basal sediment contains five stratigraphic units. We interpret these stratigraphic units as representing different depositional environments in subglacial or ice-free conditions: from bottom to top, a diamicton with subhorizontal ice lenses (Unit 1), vertically fractured ice with dispersed fine-grained sediments (<20 % in mass) (Unit 2), a normally graded bed of pebbles to very fine sand in an icy matrix (Unit 3), bedded very fine to fine sand (Unit 4), and stratified medium to coarse sand (Unit 5). Plant macrofossils are present in all samples and are most abundant in Units 3 and 4; insect remains are present in some samples (Units 1, 3, and 5). Our approach provides a working template for future studies of ice core basal materials because it includes intentional planning of core sub-sampling, processing methodologies, and archiving strategies to optimize the collection of paleoclimate, glacial process, geochemical, geochronological, and sediment properties from archives of limited size. Our work benefited from a carefully curated and preserved archive, allowing the application of analytical techniques not available in 1966 CE. Preserving uncontaminated core material for future analyses that use currently unavailable tools and techniques is an important consideration for rare archive materials such as these from Camp Century. [ABSTRACT FROM AUTHOR]

Basal materials in ice cores contain information about paleoclimate conditions, glacial processes, and the timing of past ice-free intervals, all of which aid understanding of ice-sheet stability and its contribution to sea-level rise in a warming climate. Only a few ice cores have been drilled through ice sheets to the underlying sediment and bedrock, producing limited material for analysis. The Camp Century ice core, which the US Army drilled in northwest Greenland from 1960-1966 CE, recovered about 3.5 meters of sub-glacial sediment. Here, we document the scientific history of the Camp Century sub-glacial sediment, and present our recent core-cutting, sub-sampling, and processing methodology and results for what remains of this unique archive. In 1972, curators in the Buffalo Ice Core Laboratory cut the original core segments into 32 segments each about 10-cm long. Since then, two segments are unaccounted for, two were thawed, and two were cut as pilot samples in 2019. With the exception of the two thawed segments, the rest of the extant core remained frozen since collection. In fall 2021, we documented, described, and then cut each of the remaining frozen archived segments (n=26). We saved an archival half and then cut the working half into eight oriented sub-samples under controlled temperature and light conditions for physical, geochemical, isotopic, sedimentological, magnetic, and biological analyses. Our approach maximized sample usage for multi-proxy analysis, minimized contamination, and preserved archive material for future analyses of this legacy sample material. Grain size, bulk density, sedimentary features, magnetic susceptibility, ice content, as well as pore-ice pH and conductivity, suggest that the basal sediment contains five stratigraphic units We interpret these stratigraphic units as representing different depositional environments in sub-glacial or ice-free conditions: from bottom to top, a diamicton with sub-horizontal ice lenses (Unit 1); vertically-fractured ice with dispersed fine-grain sediments (< 20% in mass) (Unit 2); a normally graded bed of pebbles to very fine sand in an icy matrix (Unit 3); bedded very fine to fine sand (Unit 4); and stratified medium to coarse sand (Unit 5). Plant macrofossils are present in all samples and most abundant in Units 3 and 4; insect remains are present in some samples (Units 1, 3, and 5). Our approach provides a working template for future studies of ice-core basal sediment because it includes intentional planning of core sub-sampling, processing methodologies, and archiving strategies in order to optimize the collection of paleoclimate, glacial process, geochemical, geochronological, and sediment properties from archives of limited size. Our work benefited from a carefully curated and preserved archive, allowing for the application of techniques not available in 1966. Preserving uncontaminated core material for future analytical capabilities is an important consideration for rare archive materials such as these from Camp Century. [ABSTRACT FROM AUTHOR]

The mechanics of snow friction are central to competitive skiing, safe winter driving and efficient polar sleds. For nearly 80 years, prevailing theory has postulated that self-lubrication accounts for low kinetic friction on snow: dry-contact sliding warms snow grains to the melting point, and further sliding produces meltwater layers that lubricate the interface. We sought to verify that self-lubrication occurs at the grain scale and to quantify the evolution of real contact area to aid modeling. We used high-resolution (15 µm) infrared thermography to observe the warming of stationary snow under a rotating polyethylene slider. Surprisingly, we did not observe melting at contacting snow grains despite low friction values. In some cases, slider shear failed inter-granular bonds and produced widespread snow movement with no persistent contacts to melt (μ < 0.03). When the snow grains did not move and persistent contacts evolved, the slider abraded rather than melted the grains at low resistance (μ < 0.05). Optical microscopy revealed that the abraded particles deposited in air pockets between grains and thereby carried heat away from the interface, a process not included in current models. Overall, our results challenge whether self-lubrication is indeed the dominant mechanism underlying low snow kinetic friction. [ABSTRACT FROM PUBLISHER]

A firn air cooling system that utilized the natural reservoir of cool air at depth in polar ice sheets was tested at Summit Station, Greenland during the summer of 2010. Cooling is required on station to meet the requirements for food safety and scientific core storage. Firn air cooling is a potential replacement for traditional mechanical cooling systems. The system design, installation, and results of several experiments are presented. The system cooled a enclosed, insulated structure from to using a 10-m borehole and a fan pumping the naturally cool air. The system was easy to install in a short time frame and was low cost from an equipment and operating perspective. [ABSTRACT FROM AUTHOR]