A Holocene record of diatom and silicoflagellate microfossils in sedimentsof Saanich Inlet, ODP Leg 169S

ODP Leg 169S laminated sediment cores provided a unique opportunity to exam ine changes in the siliceous phytoplankton community of Saanich Inlet. Thes e laminated sediments are rich in diatom and silicoflagellate remains as a result of the inlet's high production and excellent preservation. Our resul ts suggest that species composition and abundance of diatoms and silicoflag ellates in the inlet have changed very little since the inlet's formation. Carbon and opal data indicate an increase in primary productivity with time which is not apparent in the fossil data. However, the discrepancy between data sets may be due to changes in grazer activity which could have reduce d the number of identifiable fossils. Individual species were useful for id entifying changes in the inlet, Some planktonic diatoms suggest that nutrie nt supply was highest in the early-mid Holocene. Increases in the abundance of a partially benthic diatom, Paralia sulcata, follow variations in sea l evel and availability of benthic habitat in the inlet. A large peak of the silicoflagellate, Dictyocha fibula, corresponds to a catastrophic hood even t in the early Holocene, which probably washed terrestrial material and low salinity water from the British Columbia mainland into Saanich Inlet. Foss il data were also analyzed to infer past changes in the environment using a weighted averaging calibration and regression technique. These data sugges t that only minor variations in sea surface temperature have occurred. (C) 2001 Elsevier Science B.V. All rights reserved.