Ice-push disturbances in high-Boreal and Subarctic lakeshore ecosystems since AD 1830,northern Québec,Canada

Abstract

Ice scars on lakeshore trees were surveyed on the islands of two large lakes in northern Québec: Clearwater Lake (1270 km²) and Bienville Lake (900 km²), respectively at the southern edge of the Subarctic and at the northern limit of the Boreal zones. Correspondence of ice-scar chronologies with hydrological and climatological instrumental registers indicated that shore ice pushes are due to lake floods. In the AD 1930s, a shift in the flood regimes occurred. In the high Boreal, ice-push activity was much more frequent prior to 1930 than in the Subarctic. Major regional ice pushes occurred in AD 1854, 1903, 1914, 1936, 1947, 1954,1959-60, 1970 and 1979. Prior to 1930, local major events were concentrated south of the Subarctic zone, but the situation inverted after 1930. A northward shift in the average position of the Arctic front is postulated as having been the driving force of local hydrologic regimes that allowed ice disturbances to occur, especially A in controlling the amount of snowfall. Ice scars provide proxy indicators of an increase in the frequency of snowy winters between the mid-1930s and 1980. The recent period of low levels represents an anomalous incursion in the century trend, but equivalent long episodes of low seasonal lake levels occurred prior to 1930.