Surface formation, preservation, and history of low-porosity crusts at the WAIS Divide site, West Antarctica

Other literature type English OPEN
Fegyveresi, John M. ; Alley, Richard B. ; Muto, Atsuhiro ; Orsi, Anaïs J. ; Spencer, Matthew K. (2018)

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.
  • References (48)
    48 references, page 1 of 5

    Alley, R. B.: Concerning the deposition and diagenesis of strata in polar firn, J. Glaciol., 34, 283-290, https://doi.org/10.3189/S0022143000007024, 1988.

    Alley, R. B. and Fitzpatrick, J. J.: Conditions for bubble elongation in cold ice-sheet ice, J. Glaciol., 45, 147-153, https://doi.org/10.3189/S0022143000003129, 1999.

    Alley, R. B., Saltzman, E. S., Cuffey, K. M., and Fitzpatrick, J. J.: Summertime formation of depth hoar in central Greenland, Geophys. Res. Lett., 17, 2393-2396, https://doi.org/10.1029/GL017i013p02393, 1990.

    Alley, R. B., Shuman, C. A., Meese, D. A., Gow, A. J., Taylor, K. C., Cuffey, K. M., Fitzpatrick, J. J., Grootes, P. M., Zielinski, G. A., Ram, M., and Spinelli, G.: Visual-stratigraphic dating of the GISP2 ice core: basis, reproducibility, and application, J. Geophys. Res.-Oceans, 102, 26367-26381, https://doi.org/10.1029/96JC03837, 1997.

    Anderson, P. S.: A method for rescaling humidity sensors at temperatures well below freezing, J. Atmos. Ocean. Technol., 11, 1388-1391, https://doi.org/10.1175/1520- 0426(1994)011<1388:AMFRHS>2.0.CO;2, 1994.

    Anderson, D. L. and Benson, C. S.: The densification and diagenesis of snow, in Ice and Snow: Properties, Processes and Applications, edited by: Kingery, W. D., MIT Press, Cambridge, MA, 391-411, 1963.

    Andreas, E. L.: A theory for the scalar roughness and the scalar transfer coefficients over snow and sea ice, Bound.-Lay. Meteorol., 38, 159-184, https://doi.org/10.1007/BF00121562, 1987.

    Andreas, E. L.: Parameterizing scalar transfer over snow and ice: a review, J. Hydrometeorol., 3, 417-432, https://doi.org/10.1175/1525- 7541(2002)003<0417:PSTOSA>2.0.CO;2, 2002.

    Banta, J. R., McConnell, J. R., Frey, M. M., Bales, R. C., and Taylor, K.: Spatial and temporal variability in snow accumulation at the West Antarctic Ice Sheet Divide over recent centuries, J. Geophys. Res.-Atmos., 113, D23102, https://doi.org/10.1029/2008JD010235, 2008.

    Battle, M. O., Severinghaus, J. P., Sofen, E. D., Plotkin, D., Orsi, A. J., Aydin, M., Montzka, S. A., Sowers, T., and Tans, P. P.: Controls on the movement and composition of firn air at the West Antarctic Ice Sheet Divide, Atmos. Chem. Phys., 11, 11007- 11021, https://doi.org/10.5194/acp-11-11007-2011, 2011.

  • Metrics
    No metrics available