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More Evidence for Antarctic Ice Sheet Mass Gain
Reference
Van de Berg, W.J., van den Broeke, M.R., Reijmer, C.H. and van Meijgaard, E. 2006. Reassessment of the Antarctic surface mass balance using calibrated output of a regional atmospheric climate model. Journal of Geophysical Research 111: 10.1029/2005JD006495.

What was done
Results of model-simulated Antarctic surface mass balance (SMB) - derived from a regional atmospheric climate model (RACMO2/ANT) for the time period 1980 to 2004 that used ERA-40 fields as lateral forcings - were compared with "all available SMB observations [our italics] from Antarctica (N=1900)" in a recalibration process that ultimately allowed the authors "to construct a best estimate of contemporary Antarctic SMB." The many real-world observations employed in this process came from the studies of Vaughan et al. (1999), Van den Broeke et al. (1999), Frezzotti et al. (2004), Karlof et al. (2000), Kaspari et al. (2004), Magand et al. (2004), Oerter et al. (1999, 2000), Smith et al. (2002) and Turner et al. (2002). Derived by a number of different measurement techniques - such as stake arrays, bomb horizons and chemical analyses of ice cores - the various observations covered time periods that ranged from a few years to more than a century.

What was learned
Van de Berg et al. report that "the SMB integrated over the grounded ice sheet (171 3 mm year-1) exceeds previous estimates by as much as 15%." The largest differences between their results and those of others, according to them, are "up to 1 m year-1 higher in the coastal zones of East and West Antarctica, which are without exception in areas with few observations."

What it means
Because of their blending of climate modeling with the employment of massive amounts of real-world data to constrain the results, the four Dutch researchers rightly conclude that their "new estimate of Antarctic SMB is as reliable as the reliability that is credited to atmospheric models." Hence, they further conclude that "support or falsification of this result can only be found in new SMB observations from poorly covered high accumulation regions in coastal Antarctica," which is indeed reasonable. Until such time as new data might indicate otherwise, therefore, we have no reason to believe anything different from what they have concluded, i.e., that the mass of Antarctica's grounded ice sheet has been steadily growing over the past quarter-century.

References
Frezzotti, M., Pourchet, M., Flora, O., Gandolfi, S., Gay, M., Urbini, S., Vincent, C., Becagli, S., Gragnani, R., Proposito, M., Severi, M., Traversi, R., Udisti, R. and Fily, M. 2004. New estimations of precipitation and surface sublimation in East Antarctica from snow accumulation measurements. Climate Dynamics 23: 803-813.

Karlof, L., Winther, J.-G., Isaksson, E., Kohler, J., Pinglot, J. F., Wilhelms, F., Hansson, M., Holmlund, P., Nyman, M., Pettersson, R., Stenberg, M., Thomassen, M. P. A., van der Veen, C. and van de Wal, R. S. W. 2000. A 1500-year record of accumulation at Amundsenisen western Dronning Maud Land, Antarctica, derived from electrical and radioactive measurements on a 120-m ice core. Journal of Geophysical Research 105: 12,471-12,483.

Kaspari, S., Mayewski, P.A., Dixon, D.A., Spikes, V.B., Sneed, S.B., Handley, M.J. and Hamilton, G.S. 2004. Climate variability in West Antarctica derived from annual accumulation rate records from ITASE firn/ice cores. Annals of Glaciology 39: 585-594.

Magand, O., Frezzotti, M., Pourchet, M., Stenni, B., Genoni, L. and Fily, M. 2004. Climate variability along latitudinal and longitudinal transects in East Antarctica. Annals of Glaciology 39: 351-358.

Oerter, H., Graf, W., Wilhelms, F., Minikin, A. and Miller, H. 1999. Accumulation studies on Amundsenisen, Droning Maud Land, by means of tritium, dielectric profiling and stable-isotope measurements: First results from the 1995-96 and 1996-97 field seasons. Annals of Glaciology 29: 1-9.

Oerter, H., Wilhelms, F., Jung-Rothenhausler, F., Goktas, F., Miller, H., Graf, W. and Sommer, S. 2000. Accumulation rates in Dronning Maud Land, Antarctica, as revealed by dielectric-profiling measurements of shallow firn cores. Annals of Glaciology 30: 27-34.

Smith, B.T., van Ommen, T.D. and Morgan, V.I. 2002. Distribution of oxygen isotope ratios and snow accumulation rates in Wilhelm II Land, East Antarctica. Annals of Glaciology 35: 107-110.

Turner, J., Lachlan-Cope, T.A., Marshall, G.J., Morris, E.M., Mulvaney, R. and Winter, W. 2002. Spatial variability of Antarctic Peninsula net surface mass balance. Journal of Geophysical Research 107: 10.1029/JD000755.

Van den Broeke, M.R., Winther, J.-G., Isaksson, E., Pinglot, J.F., Karlof, L., Eiken, T. and Conrads, L. 1999. Climate variables along a traverse line in Dronning Maud Land, East Antarctica. Journal of Glaciology 45: 295-302.

Vaughan, D.G., Bamber, J.L., Giovinetto, M. and Cooper, A.P.R. 1999. Reassessment of net surface mass balance in Antarctica. Journal of Climate 12: 933-946.

Reviewed 30 August 2006