Climate, fine-sediment transport linkages, Coast Mountains, British Columbia

The relation between climate and sediment yield remains poorly defined in regions of high relief and where sediment sources are numerous. This study examines the climatic controls associated with fine sediment production and yield for six glacierized watersheds in the Coast Mountains, British Columbia, Canada. Contemporary monitoring of suspended sediment transport was undertaken to detail the hydrologic conditions responsible for the entrainment and production of fine-grained sediment production and transport. The analysis of lake sediments recovered from outlet lake basins provided a means of documenting changes in sediment delivery over century to millennia time scales. Four of the lake basins contain finely laminated sediments which are interpreted to be clastic varves and so detail lake sedimentation at annual to event time scales.; The results indicate that much of the variance in sediment transport records can be attributed to hydro-climatic variability at all time scales under consideration and much like other geophysical time series, a 1/frequency-variance scaling is apparent within the yield proxies of this study. Climatological conditions important for sediment production and entrainment at event to annual scales include those processes responsible for high flow events in the study area. Decadal-scale variations in sediment delivery coincide with sustained periods of ice melt. Sediment delivery from the watersheds at century to millennial time scales reflects major changes in ice cover. The correspondence between long records of lake sedimentation and air-temperature proxies developed from tree rings and ice cores suggests that changes in sediment yield from the watersheds reflects changes in air temperatures in the study area. Variations in air temperature appear to influence sediment transfers by controlling the intensity of glacial runoff during the ablation season. Highest sensitivity (i.e. those records where geomorphic filtering of the climate signal has not occurred) is noted for those basins which have active glaciers and the opportunity for sediment storage of fine-grained sediment in the fluvial system is low.