A 6000 yr varve record of Holocene climate in Saanich Inlet, British Columbia, from digital sediment colour analysis of ODP Leg 169S cores

Abstract

High-resolution grey-value time series were extracted from digital images of varved sediments in Saanich Inlet, British Columbia (ODP Sites 1033 and 1034). Results allowed reconstruction of a ∼6000 yr long record with annual resolution. Composite records were compiled for Sites 1033 and 1034 by correlation of massive beds, which represent gravity flows, and of characteristic features in the varve patterns. The varve-count age-scale was calibrated with published radiocarbon ages. Results demonstrate that the ODP Leg 169S record is virtually complete. Saanich Inlet varve record has the potential to provide a high-resolution climate record. Temporal variation in varve thickness is interpreted to reflect regional precipitation history, with thick varves representing wet conditions. Long-term changes in varve thickness during the past 6000 yr coincide with known changes in global climate, but without an obvious one to one correlation between wet/dry in Saanich Inlet and warm/cold periods elsewhere. Varve thickness indicates that the climate around Saanich Inlet was wet from the start of the varved sequence at ∼6000 to ∼3250 yr BP, between 2100 and 1750 yr BP (Roman Warm Period) and from 500 yr BP onward (including during Little Ice Age).