Quantitative reconstruction of Younger Dryas to mid-Holocene paleoclimates at Le Locle, Swiss Jura, using pollen and lake-level data
Résumé
Pollen and lake-level data from Le Locle in the Swiss Jura were used to quantitatively reconstruct climatic parameters for the Younger Dryas event and the first half of the Holocene period. The Younger Dryas cold event at Le Locle was characterized by (i) a general trend toward a slight increase in summer temperature and a decrease in annual precipitation and (ii) a marked drying phase at ca. 11,900 cal yr B.P. that occurred between two wetter ones. Further phases of major deficit in moisture occured at ca. 11,500 cat yr B.P. (Younger Dryas-Holocene transition), 10,800 cat yr B.P., 8700 cat yr B.P., and 6500 cat yr B.P. Climatic parameters reconstructed here suggest that phases of higher lake level developing at ca. 12,500-12,000, 11,750-11,600, 11,200-10,900 (synchronous with the Preboreal oscillation), 10,400-8900, 8400-8300 (possibly related to the 8200 yr event), and 7800-7000 cat yr B.P. coincided with an increase in annual precipitation, a decrease in summer temperature, and a shorter growing season. Conversely, periods of low lake level corresponded to a decrease in annual precipitation, an increase in summer temperature, and a longer growing season. This general pattern could have resulted from alternate southward-northward displacements of the Atlantic Westerly Jet. (C) 2001 University of Washington.