LES DUNES DU QUEBEC MERIDIONAL: CONTRIBUTION A L'ETUDE DES VENTS DOMINANTS DURANT L'HOLOCÈNE

Les donnees disponibles sur 67 sites de dunes au Quebec meridional ont permis d'esquisser l'histoire des vents dominants durant l'Holocene. En se basant sur la chrono-logie du recul du front glaciaire et sur la regression des mers postglaciaires, il apparaǐt que le regime des vents fut relativement stable entre 11000 et 7500 ans bp, bien qu'entre 9500 et 8500 ans bp la plaine au sud du Saint-Laurent ait connu un episode pendant lequel la provenance des vents dominants etait changeante. La provenance des paleovents dominants montre les měmes variations regionales que celle des vents actuels. Ainsi, independamment de leur ǎge, les paleovents dominants provenaient du NE dans la plaine sud du Saint-Laurent, de l'O et du NE sur le rebord des Laurentides, de l'O, du SO, du NO et du N au Lac-Saint-Jean et de l'O a l'OSO sur la Cǒte-Nord du Saint-Laurent. Les vents qui ont edifie les dunes provenaient d'une circulation d'air anticyclonique provoquee par le retrait de l'Inlandsis laurentidien. Available data on the sand dunes of southern Quebec has permitted the historic reconstitution of prevailing wind patterns during the Holocene. From age data derived from the chronology of glacial front retreat and postglacial sea recession, it appears that the wind regime was relatively stable between 11000 and 7500 years bp, although during the period between 9500 and 8500 bp, the plain located south of the St. Lawrence underwent an episode during which the direction of the dominant winds was variable. The direction of the prevailing winds during the latter period shows the same regional variations as the actual winds. Thus, regardless of their age, the prevailing winds at that time were from the NE in the southern plain of the St. Lawrence, from the W and NW in the Laurentian foothills, from the W, SW, NW and N in the Lac-Saint-Jean area, and from the W to WSW for the North Shore of the St. Lawrence. Winds which produced the dunes came from anticyclonic circulation induced by the retreat of the Laurentide Ice Sheet.