Geomorphic and climatic interpretations of abrupt changes in glaciolacustrine deposition at Moose Lake, British Columbia, Canada

Sediments deposited in Moose Lake, British Columbia exhibit three abrupt tr ansitions during the Holocene. Basal diamicts are unconformably overlain by coarse sand and silt deposited as turbidity currents in an ice-dammed lake during final retreat of Wisconsinan ice. Rapid withdrawal of the valley gl acier resulted in a fully developed Moose Lake followed by low rates of sed iment input for much of the early and middle Holocene until approximately 4 ,100 years BP. At that time, sediment input doubled and then tripled by 3,1 20 years BP in response to cooling and several phases of regionally documen ted glacier expansions. The transition from the Altithermal dry/warm period to the Neoglacial cooling is coincident with the formation of varves at Mo ose Lake which provide a chronology of changing Neoglacial sediment inputs. The glacier-climate signal recorded in Moose Lake sediments suggests disti nct thresholds for changes in sedimentation style that are dependent on bot h climatic and geomorphic conditions affecting the watershed. Early in the record, direct connection to glaciogenic sediment production produced highl y variable sedimentation rates that ended abruptly as the ice-front retreat ed. In the middle record, climate conditions that led to greatly reduced ic e extent and lower sediment production in the upper Fraser and Moose river watersheds, changed abruptly resulting in varve formation. The change in st yle and increased sedimentation was caused directly by greater seasonal var iations in sediment input due to climate-controlled glacier advances beyond modern limits. While sediment supply is a factor, comparison of the sedime nt record with tree-ring responses to climate change suggest both summer te mperature and winter precipitation are important controls of Holocene varia tions in sediment yield.