Characterization of the 1966 Camp Century subglacial core: a multiscale analysis

<p>In 1966, drilling at Camp Century, Greenland, recovered 3.44 m of subglacial material from beneath 1350 m of ice. Although prior analysis of this material showed that the core includes glacial sediment, ice, and sediment deposited during an interglacial period, the subglacial material had never been thoroughly studied. To better characterize this material, we analyzed 26 of the 30 core samples remaining in the archive. We performed a multiscale analysis including X-ray diffraction (XRD), micro-computed tomography (<span class="inline-formula"><i>μ</i></span>CT), and scanning electron microscopy (SEM) to delineate stratigraphic units and assign facies based on inferred depositional processes.</p> <p>At the macroscale, quantitative X-ray diffraction revealed that quartz and feldspar dominated the sediment and that there was minimal variation in relative mineral abundance between samples. Mesoscale evaluation of the frozen material, using <span class="inline-formula"><i>μ</i></span>CT scans, showed clear variations in the stratigraphy of the core characterized by the presence of bedding, grading, and sorting. Microscale grain size and shape analysis, conducted using scanning electron microscopy, showed an abundance of fine-grained materials in the lower part of the core and no correspondence between grain shape parameters and sedimentary structures. These multiscale data define five distinct stratigraphic units within the core based on sedimentary process; <span class="inline-formula"><i>k</i></span>-means clustering analysis supports this unit delineation. Our observations suggest that ice retreat uncovered the Camp Century region, exposing weathered basal till (Unit 1), now covered by a remnant of basal ice or firn (Unit 2). Continued ice-free conditions led to till disruption by liquid water causing a mass movement (Unit 3) and deposition of water-worked sediment (units 4–5).</p> <p>Analysis of the Camp Century subglacial material reveals a diverse stratigraphy preserved below the ice that recorded episodes of glaciated and deglaciated conditions in northwestern Greenland. Our physical, geochemical, and mineralogic analyses illuminate the history of deposition, weathering, and sediment transport preserved under the ice and show the promise of subglacial materials to increase our knowledge of past ice sheet behavior over time.</p>