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Brittle ice, which occurs in all intermediate-depth and deep ice cores retrieved from high-latitude regions, presents a challenge for high-resolution measurements of water isotopes, gases, ions and other quantities conducted with continuous flow analysis (CFA). We present a novel method of preserving brittle ice for CFA stable water isotope measurements using data from a new ice core recovered by the Roosevelt Island Climate Evolution (RICE) project. Modest modification of the drilling technique and the accommodation of non-horizontal fractures (‘slanted breaks’) in processing led to a substantial improvement in the percentage of brittle ice analyzed with CFA (87.8%). Whereas traditional processing methods remove entire fragmented pieces of ice, our method allowed the incorporation of a total of 3 m of ice (1% of the 261 m of brittle ice and ~1300 years of climate history) that otherwise would not have been available for CFA. Using the RICE stable water isotope CFA dataset, we demonstrate the effect of slanted breaks and analyze the resulting smoothing of the data with real and simulated examples. Our results suggest that retaining slanted breaks are a promising technique for preserving brittle ice material for CFA stable water isotope measurements.
A robotic submarine was used for the first observations of a grounding-line area of a floating glacier. The site was Mackay Glacier which terminates as a floating glacier tongue in the Ross Sea, at latitude 77°S. Half of the 20 m thick basal debris layers in Mackay Glacier are deposited as subglacial till in the last 1.8 km that the glacier remains grounded. Subglacial till observed at and beyond the grounding line varies rapidly in texture and rheology spatially, occurring as a flat sheet, as flow-parallel flutes, or as bank forms into which it has been pushed at the grounding line. Very little free- flowing subglacial water was present during the observations, and no major subglacial water discharges appear to have occurred in the past. The other half of the basal debris is melted out up to 1.5 km in front of the grounding line, producing a sheet of glacimarine sediment as shelfstone diamicton and mud draped on subglacial till. Both till and glacimarine sediment may be turbated by icebergs. This simple model of till overlain by shelfstone diamicton and mud is a direct contrast to sedimentary depositional systems at tide-water termini of temperate glaciers.
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