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Fegyveresi, John M.; Alley, Richard B.; Muto, Atsuhiro; Orsi, Anaïs J.; Spencer, Matthew K. (2016)
Languages: English
Types: Article
Subjects:
Observations at the WAIS Divide site show that near-surface snow is strongly altered by weather-related processes such as strong winds and temperature fluctuations, producing features that are recognizable in the deep ice core. Prominent "glazed" surface crusts develop frequently at the site during summer seasons. Surface, snow pit, and ice core observations made in this study during summer field seasons from 2008–09 to 2012–13, supplemented by Automated Weather Station (AWS) data with insolation sensors, revealed that such crusts formed during relatively low-wind, low-humidity, clear-sky periods with intense daytime sunshine. After formation, such glazed surfaces typically developed cracks in a polygonal pattern with few-meter spacing, likely from thermal contraction at night. Cracking was commonest when several clear days occurred in succession, and was generally followed by surface hoar growth; vapor escaping through the cracks during sunny days may have contributed to the high humidity that favored nighttime formation of surface hoar. Temperature and radiation observations showed that daytime solar heating often warmed the near-surface snow above the air temperature, contributing to mass transfer favoring crust formation and then surface hoar formation. Subsequent investigation of the WDC06A deep ice core revealed that crusts are preserved through the bubbly ice, and some occur in snow accumulated during winters, although not as commonly as in summertime deposits. Although no one has been on site to observe crust formation during winter, it may be favored by greater wintertime wind-packing from stronger peak winds, high temperatures and steep temperature gradients from rapid midwinter warmings reaching as high as −15 °C, and perhaps longer intervals of surface stability. Time-variations in crust occurrence in the core may provide paleoclimatic information, although additional studies are required. Discontinuity and cracking of crusts likely explain why crusts do not produce significant anomalies in other paleoclimatic records.
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