Surface formation, preservation, and history of low-porosity crusts at the WAIS Divide site, West Antarctica
Other literature type
Fegyveresi, John M.
Alley, Richard B.
Orsi, Anaïs J.
Spencer, Matthew K.
(issn: 1994-0424, eissn: 1994-0424)
Observations at the West Antarctic Ice Sheet (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 <q>glazed</q> 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 2008–2009 to 2012–2013, supplemented
by automated weather station (AWS) data with short- and longwave radiation
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 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 show that daytime solar
heating often warmed the near-surface snow above the air temperature,
contributing to upward mass transfer, favoring crust formation from below,
and then surface hoar formation. A simple surface energy calculation supports
this observation. Subsequent examination 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.