PEATLAND INITIATION DURING THE HOLOCENE IN CONTINENTAL WESTERN CANADA

Today, the southern limit of peatlands in continental western Canada i s largely limited by thermal seasonal aridity, although physiographic parameters of substrate texture, topography, and salinity also exsert important controls on the presence and absence of peatlands. Factors t hat control peatland distribution today also operated in the past, thu s the initiation of peatlands during the Holocene was mainly limited b y aridity and physiography. Calibrated radiocarbon dates of basal peat deposits from 90 locations across continental western Canada indicate that peat formation began approximately 8,000 to 9,000 years BP in nu cleation zones along the upper elevations of the Montane region of Alb erta and in northern Alberta uplands after an initial deglacial lag. P redictions of maximum early Holocene summer insolation by climate simu lations provide a mechanism for limiting peatland establishment during the early Holocene. From 6,000 to 8,000 years ago, peat formation in continental western Canada expanded eastwards into Manitoba responding to decreases in summer insolation. Peatland expansion during the earl y Holocene was more extensive in Alberta than in Manitoba in response to a southwesterly shift in the Arctic front. The displacement of the Arctic front allowed for more frequent incursions of moist Pacific air into Alberta while limiting it in Manitoba After 6,000 years BP, the trend of southeasterly peatland expansion continued. Peatlands are you ngest in the southern Boreal Forest and Aspen Parkland Region as well as in the lower elevations of the Peace-Wapiti River drainage basin, f orming over the last 3,000 to 4,000 years. Peatlands are also young in the lower elevations of the Hudson Bay Lowlands where peat initiation has been limited by timing of emergence from glacial rebound. The spa tial and temporal distribution of peatland initiation during the Holoc ene is verified by existing pollen records and corroborates some simul ated climate models.