HR: 1340h
AN: PP33B-0933    [Abstracts]
TI: Diatom Records of Holocene Environmental and Climatic Change in Southeastern British Columbia
AU: * Westover, K S
EM: coyote@unlserve.unl.edu
AF: Department of Geosciences, University of Nebraska-Lincoln, 214 Bessey Hall, P.O. Box 880340, Lincoln, NE 68588-0340 United States
AU: Gavin, D G
EM: dgavin@life.uiuc.edu
AF: Department of Plant Biology, University of Illinois, 265 Morrill Hall, Urbana, IL 61801 United States
AU: Fritz, S C
EM: sfritz2@unl.edu
AF: Department of Geosciences, University of Nebraska-Lincoln, 214 Bessey Hall, P.O. Box 880340, Lincoln, NE 68588-0340 United States
AU: Hu, F
EM: fshu@life.uiuc.edu
AF: Department of Plant Biology, University of Illinois, 265 Morrill Hall, Urbana, IL 61801 United States
AU: Roschen, L A
EM: roschen@uiuc.edu
AF: Department of Plant Biology, University of Illinois, 265 Morrill Hall, Urbana, IL 61801 United States
AB: The sediments of three lakes, spanning a latitudinal gradient and situated within the Interior Cedar-Hemlock biogeoclimatic zone of southeast British Columbia, have been analyzed for independent records of Holocene climate and vegetation history in order to evaluate the role of climate as a control on range expansion of western hemlock and western redcedar. Holocene climate reconstructions are based on multiple proxies, including the diatom and biogenic silica stratigraphies presented here. To our knowledge, these sites provide the first continuous Holocene paleoecological and paleoclimatic records from the region between the Interior Plateau and the Rocky Mountains. Stratigraphic variability in the diatom sedimentary records reflects lake response to changes in water balance, catchment development, and atmospheric inputs of silica (i.e. volcanic ash). At Eleanor Lake, the diatom record shows significant assemblage shifts at $\sim$7500, 6300, and 3700 cal yr BP. Increased abundance of planktonic and tychoplanktonic diatoms and an increase in the abundance of chrysophyte cysts relative to diatoms at 6300 cal yr BP is consistent with an increase in effective moisture at this time. At Mirror Lake, in the south, an assemblage dominated by small benthic species is replaced by a predominantly planktonic assemblage at 6900 cal yr BP, suggesting an earlier increase in lake level. After 6000 cal yr BP, planktonic diatoms further increase in dominance. These dates are consistent with reconstructions of Holocene climate in south-central British Columbia, which suggest a shift to moister conditions ca. 7000 to 6000 cal yr BP. The pollen record indicates the expansion of western hemlock and western redcedar near Mirror Lake at 3550 cal yr BP and 3250 cal yr BP respectively. At Eleanor Lake, hemlock expansion is dated at 4350 cal yr BP. The data indicate a difference of 1950 to $>$ 3000 years between the lacustrine record of increased effective moisture and the vegetation response and suggest that non-climatic factors played a significant role in the Holocene range expansion of these trees.
DE: 3344 Paleoclimatology
DE: 4239 Limnology
DE: 3030 Micropaleontology
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting