Deriving mass balance and calving variations from reanalysis data and sparse observations, Glaciar San Rafael, northern Patagonia, 1950–2005

摘要

Mass balance variations of Glaciar San Rafael, the northernmost tidewaterglacier in the Southern Hemisphere, are reconstructed over the period1950–2005 using NCEP-NCAR reanalysis climate data together with sparse,local historical observations of air temperature, precipitation,accumulation, ablation, thinning, calving, and glacier retreat. The combinedobservations over the past 50 yr indicate that Glaciar San Rafael hasthinned and retreated since 1959, with a total mass loss of ~22 km3of ice eq. Over that period, except for a short period of coolingfrom 1998–2003, the climate has become progressively warmer and drier, whichhas resulted primarily in pervasive thinning of the glacier surface and adecrease in calving rates, with only minor acceleration in retreat of theterminus. A comparison of calving fluxes derived from the mass balancevariations and from theoretical calving and sliding laws suggests thatcalving rates are inversely correlated with retreat rates, and that terminusgeometry is more important than balance fluxes to the terminus in drivingcalving dynamics. For Glaciar San Rafael, regional climate warming has notyet resulted in the significant changes in glacier length seen in othercalving glaciers in the region, emphasizing the complex dynamics betweenclimate inputs, topographic constraints and glacier response in calvingglacier systems.