Diatom, pollen, and chemical evidence of postglacial climatic change at Big Lake, south-central British Columbia, Canada

Postglacial climatic conditions were inferred from cores taken from Big Lak e in southern British Columbia. Low concentrations of nonarboreal pollen an d pigments near the base of the core suggest that initial conditions were c ool. Increases in both aquatic and terrestrial production suggest warmer an d moister conditions until similar to 8500 cal yr B.P. Hyposaline diatom as semblages, increases in nonarboreal pollen, and increased concentrations of pigments suggest the onset of arid conditions from similar to 8500 to simi lar to 7500 cal yr B.P. Slightly less arid conditions are inferred from sim ilar to 7500 until similar to 6660 cal yr B.P. based on the diatoms, small increases and greater variability in biogenic silica and pigments, and high er percentages of arboreal pollen. At similar to 6600 cal yr B.P., changes in diatoms, pigments, biogenic silica, and organic matter suggest that Big Lake became fresh, deep, and eutrophic until similar to 3600 cal yr B.P., w hen water levels and nutrients decreased slightly. Our paleoclimatic infere nces are similar to pollen-based studies until similar to 6600 cal yr B.P. However, unlike these studies, our multiple lines of evidence from Big Lake imply large changes in effective moisture since 6000 cal yr B.P. (C) 2001 University of Washington.