Implications of a late-glacial pollen record for the glacial and climatic history of the Fraser Lowland, British Columbia

Late-glacial sediments at Mike Lake in the Fraser Lowland of southwestern British Columbia shed light on the timing and significance of the Younger Dryas and Sumas events on the west coast of Canada. Five pollen zones span the period from about 11 700 to 9700 radiocarbon years before present (yr BP) or 13 700 to 11 200 calibrated calendar years before present (cal BP). Climate during this interval is inferred to have ranged from cool continental to warm and dry. Changes in pollen assemblages, lithology, and loss on ignition in Mike Lake sediments deposited prior to 11 000 yr BP (13 000 cal BP) may signal the Sumas glacial advance, which has been dated elsewhere in the Fraser Lowland to this time. Palynologic and sedimentological data indicate that there was much climatic and ecological variability in southwestern British Columbia during the Younger Dryas chronozone. Detrended correspondence analysis of modern pollen from lake-sediment surface samples collected throughout British Columbia is used to compare Mike Lake fossil pollen assemblages to modern vegetation zones. The inferred vegetation assemblage during most of the Younger Dryas chronozone indicates a progressively warming climate with a cool interval between 10 400 and 10 000 yr BP. The pollen assemblage in this interval is similar to that of present subalpine forests on the west coast of Canada. The cooling coincides with the later part of the Younger Dryas chronozone and occurred too late to be the driving mechanism for the final Sumas advance, which peaked around 11 300 C-14 yr BP (13 200 cat BP). (C) 2002 Elsevier Science B.V. All rights reserved.