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Ice-push disturbances in high-Boreal and Subarctic lakeshore ecosystems since AD 1830, northern Québec, CanadaCentre d'études nordiques and département de géographie, Université Laval, Sainte-Foy, Québec G1K 7P4, Canada 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.
Key Words: Ecosystem disturbance • Ice Push • Lake Shoreline • Flood • Snow • Tree-ring • Ice scar • Boreal • Subarctic • Québec • Canada
The Holocene, Vol. 10, No. 2,
179-189 (2000) |
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