Abstract
ABSTRACTBrittle 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.
Highlights
Ice cores retrieved from high-latitude regions are an important archive of past climate (Taylor and others, 2005; Brook and others, 2006)
We focus on (a) our drilling system, designed to minimize fractures at the time of core recovery, and (b) a novel approach used to process the ice from the Roosevelt Island Climate Evolution (RICE) ice core, which allowed us to successfully conduct continuous flow analysis (CFA) water-stable isotope measurements on 94.2% of the total length of the core, including 87.8% of the brittle ice zone (BIZ)
We focus our discussion on the CFA water-stable isotope data from the RICE core because they are a fundamental part of any ice core study (Grootes and Stuiver, 1997; Legrand and Mayewski, 1997; Petit and others, 1999; EPICA Community Members, 2004), and the detailed record obtained with the high resolution of laser spectroscopy (Emanuelsson and others, 2015) allows us to more readily evaluate and detect subtle changes in the ice core quality
Summary
Ice cores retrieved from high-latitude regions are an important archive of past climate (Taylor and others, 2005; Brook and others, 2006). All intermediate-depth and deep cores face the challenge of ‘brittle ice’ (Gow, 1968; Gow, 1971), generally occurring at a depth of 500–1100 m from the surface (Neff, 2014) At these depths, the overburden of pressure on air bubbles trapped in the ice leads to rapid decompression once the ice is brought to the surface and is exposed to ambient air pressure (Uchida and others, 1994; Taylor and others, 2005). Fractured pieces usually need to be removed in their entirety before analysis to create a clean, flat surface and prevent contamination, potentially representing a loss of important climate history.
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