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Two Millennia of Snowfall Accumulation in Antarctica

Paper Reviewed
Roberts, J., Plummer, C., Vance, T., van Ommen, T., Moy, A., Poynter, S., Treverrow, A., Curran, M. and George, S. 2015. A 2000-year annual record of snow accumulation rates for Law Dome, East Antarctica. Climate of the Past 11: 697-707.

Providing the rational for their work, Roberts et al. (2015) write that "the short and sparse instrumental record in the high latitudes of the Southern Hemisphere means investigating long-term precipitation variability in this region is difficult without access to appropriate proxy records." Thus, it was the objective of this team of nine researchers to extend the duration of the Law Dome, East Antarctica, snowfall accumulation record back in time an additional 750 years such that it would encompass over two millennia of time.

The resultant 2035 year-long proxy (22 BC to 2012 AD) is presented in the figure below. As reported by the authors, the average long-term snow accumulation rate was calculated as 0.686 m yr-1 ice equivalent, which rate they say "is in agreement with previous estimates, and further supports the notion that there is no long-term trend in snow accumulation rates, or that any trend is constant and linear over the [2035-year] period of measurement." Despite this fact, there were several decadal-scale oscillations in the record, described by the authors as "common," with "74 events (33 positive and 41 negative) of at least a 10-year duration in the record." The three longest periods of above average integrated snowfall occurred over the intervals 380-442, 727-783, and 1970-2009, while the three longest periods of below average integrated snowfall occurred during 663-704, 933-975, and 1429-1468.

Annual (grey) and smoothed (green) snow accumulation rate history for Law Dome, East Antarctica over the period 22 BC-2012 AD based on a power law vertical strain rate model to correct for thinning as the annual snowfall layers compacted and thinned due to vertical strain over time. Adapted from Roberts et al. (2015).

With respect to the cause of the interannual and decadal variability in the record, Roberts et al. report they found no significant correlation between snowfall accumulation and (1) the Southern Oscillation Index, (2) volcanic activity, (3) the Southern Annular Mode or (4) the Law Dome CO2 record. Spectral analysis, however, revealed periodicities that "may be related to El Niño-Southern Oscillation (ENSO) and Interdecadal Pacific Oscillation (IPO) frequencies."

In considering the above, it is abundantly clear there is nothing unusual, unnatural or unprecedented about present snowfall accumulation rates in this region of the Antarctic. Furthermore, there is nothing to suggest a global warming/CO2-induced influence on this record across the entire time span of the Industrial Revolution, despite a 40% increase in atmospheric CO2. And, lastly, there is no indication the great millennial-scale temperature oscillations that brought the Roman Warm Period, the Dark Ages Cold Period, the Medieval Warm Period, the Little Ice Age, and the Current Warm Period, had any effect on the snowfall record either. Thus, it seems safe to conclude that, in the future, annual snowfall accumulation totals will likely continue much as they have for the past 2035 years, never straying too far (or too long) from their long-term mean, unaffected by changes in CO2 or temperature.

Posted 22 October 2015