Lake sediment oxygen isotope records of Holocene climate variability in the Southern Canadian Rocky Mountains

Oxygen isotope ratios in authigenic carbonate sediment from South Hogarth Lake and Marl Lake (Alberta) provide a ~10,000 year record of variations in precipitation-evaporation balance in the southern Canadian Rocky Mountains. SEM and XRD analyses of the carbonate sediment from each lake indicate authigenic calcite (CaCO₃) throughout. The age models are based on radiocarbon and tephra dates and indicate that sediment has been continuously deposited since deglaciation. The sequences were sampled at 1mm to 5cm intervals, and the isotopic composition (δ¹⁸O) of the fine-grained, authigenic CaCO₃ was measured. Water isotope values from both lakes are isotopically enriched relative to local meteoric water, indicating that evaporation is a substantial component of their water budgets. In closed-basin lakes, low δ¹⁸O values in both water and sediment generally indicate wetter conditions, and high δ¹⁸O values indicate drier conditions. The South Hogarth and Cleland (British Columbia) lake records exhibit higher δ¹⁸O values during the late Holocene, suggesting a decline in lake levels and a reduction in cold season precipitation. Previous work on Shark Lake (Alberta) and Cleland Lake suggests that mid-Holocene climate was drier than present overall, but wetter conditions persisted during the cold season. Several climate model simulations from the Paleoclimate Modeling Intercomparison Project Phase 3 (PMIP3) support the idea that the mid-Holocene in the Pacific Northwest was characterized by enhanced hydroclimatic seasonality, although this result is not consistently expressed by all models. Oxygen isotope measurements from South Hogarth Lake and Marl Lake provide insight on climate change in an underrepresented region of western North America and thus provide a new spatial perspective for testing hypotheses on ocean-atmosphere control of precipitation-evaporation balance variability during the middle through late Holocene. The development of such paleoclimate proxy records provides a more thorough understanding of the full range of hydroclimate variability, in turn allowing for the development of better water resource management strategies.