TREE-RING BASED ESTIMATES OF PEYTO GLACIER MASS BALANCE, 1673-1995

Point estimates of mass balance have been reconstructed for Peyto Glacier in the Canadian Rocky Mountains from 1673-1995. Summer mass balance was reconstructed from tree-ring estimates of summer temperature and precipitation in the Canadian Rockies. The winter balance was calculated from tree-ring chronologies in the Gulf of Alaska and western British Columbia using the strong documented teleconnection between winter climate in these areas and the Canadian Rockies. The models for winter and summer balance explain over 40% of the variance in each measured mass balance series and pass conventional verification tests. The resulting net balance is significantly correlated with the measured net balance figures (r=0.69, 1966-1995). Two major intervals of strongly positive mass balance are reconstructed (1695-1720 and 1810-1825), both periods of increased winter precipitation and reduced summer ablation. The cumulative and net mass balance series agree with the independently- derived LIA regional moraine record and show that major moraine building episodes (ca. 1700-1725, 1825-1850) followed the periods of reconstructed positive mass balance. Mass balances in the latter half of the 18th century (1760-1805) were generally negative. Positive mass balances in the 1845-1880 period correspond with several intervals of glacier readvance. These results indicate a significant change in the mass balance regime in the 1880s. Prior to 1883 the mean net balance is zero but subsequently the glacier has an almost continuously negative balance with an average loss of 378mm w.e./yr. This reconstructed mass balance history provides a more continuous and complete record of glacier changes than the previously available record of glacier fluctuations and allows examination of relationships with climatic forcing from the Pacific (PDO and ENSO) that may significantly control winter balances.