Recent Climatic Fluctuations of the Canadian High Arctic and Their Significance for Glaciology

Various measures of the character of ablation season conditions in the Canadian High Arctic (north of 74°N) are discussed based on an analysis of daily climatic data from Alert, Eureka, Isachsen, Resolute, and Thule. Melting degree day totals appear to be the most useful index of summer warmth. An abrupt change in the summer climate of the region occurred around 1963164. Various indices indicate a marked decrease in summer temperature after 1963. During the same period, annual precipitation in the north and northwest has increased. Glacier mass balance is strongly controlled by summer climate; in particular, annual melting degree day totals are highly correlated with long-term mass-balance records. This enabled mass balance on the northwest sector of the Devon Island ice cap to be reconstructed back to 194 7 I 48. Cumulative mass losses on the Devon Island ice cap from 1947148 to 1962163 are estimated to be -3500 kg m-2 • However, from 1963164 to 1973/74 a total of \u3c 350 kg m-2 have been lost. Significant ice-cap growth is presently limited by low precipitation even when mean summer temperatures are very low; an occasional warm summer may therefore obliterate cumulative mass gains over many years. The post-1963 change in summer climate appears to be related to the massive increase of volcanic dust in the upper atmosphere, primarily due to the eruption of Mt. Agung (March 1963). Subsequent eruptions may have caused the cooler conditions to persist. Volcanic dust affects solar radiation receipts and perhaps also influences the general circulation. If the high volcanic dust levels of the 1960s are responsible for reduced mass losses on High Arctic glaciers and ice caps, it is probable that other periods with high atmospheric dust levels (e.g., 1750 to 1880) had summer temperatures at least as cold as the mid to late 1960s. Conversely, the period of very negative balance on the Devon Island ice cap from 1947 to 1963 was probably typical of the period back to 1920 when the atmosphere was relatively free of volcanic dust