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High-resolution Holocene vegetation history and climate from Hole 1034B, ODP leg 169S, Saanich Inlet, Canada

2001; Elsevier BV; Volume: 174; Issue: 1-4 Linguagem: Inglês

10.1016/s0025-3227(00)00151-1

1872-6151

Marlow G. Pellatt, Richard J. Hebda, Rolf W. Mathewes,

Geological formations and processes

High-resolution pollen analysis of laminated marine sediments from ODP Hole 1034B in Saanich Inlet, British Columbia reveals changes in vegetation and inferred climate during the Holocene. Four main pollen zones are discerned using constrained cluster analysis. Although the timing of major vegetation changes at the Saanich Inlet is similar to other study sites in the Pacific Northwest, the composition of pollen assemblage zones is different from the mainland sites. Vegetation assemblages reconstructed from the pollen and spore record include a Douglas-fir (Pseudotsuga menziesii) parkland with abundant grass (Poaceae) and bracken (Pteridium) between 11,450 and 8300 BP (all ages are calibrated calendar years), oak (Quercus) savanna or parkland with high grass and bracken (8300–7040 BP), a mixed deciduous/coniferous forest with oak, western hemlock (Tsuga heterophylla) and Douglas-fir (7040–5750 BP), and the development of modern coastal temperate forest with the marked expansion of cedar (Cupressaceae), western hemlock, spruce (Picea) and Douglas-fir (5750–1050 BP). Climatic periods inferred from the cores include an early Holocene warm/dry interval (11,450–8300 BP), a warm period with mild winters (8300–7040 BP), a period of transitional mid-Holocene climate (7040–5750 BP), and the advent of a relatively cool/wet neoglacial climate after 5750 BP. Modern conifer forests and oak savannas became established by about 3800 BP. The Saanich Inlet pollen record indicates that vegetation and inferred climate change was particularly rapid between 8700 and 8300 BP when grass and bracken abruptly decrease and oak becomes a significant component of the paleovegetation. Because neoglacial conditions have prevailed from 3800 years to present in the Pacific Northwest, factors other than climate, such as anthropogenic modification of the landscape, may be responsible for the persistence of oak savannas.