RECONSTRUCTION OF HOLOCENE PALEOCLIMATE IN THE NORTHERN ROCKY MOUNTAINS, ALBERTA, CANADA, USING OXYGEN ISOTOPE ANALYSIS OF LACUSTRINE CARBONATE SEDIMENT

Research on Holocene patterns of drought/pluvial variability is useful because it provides a long-term perspective for assessing observed climate change. Variations in precipitation timing, amount, and phase affect water availability in the Rocky Mountains and the nearby Great Plains, with implications for agriculture and industry. Previous research supports the use of oxygen isotopes in lake sediments as an effective proxy for either changes in precipitation source or precipitation-evaporation balance (depending on lake hydrologic characteristics). This goal of this research is to add to the existing database of paleoclimate data in the Rocky Mountains, which will ultimately inform on hydroclimate variability in a topographically complex region.

We collected sediment cores from South Hogarth Lake and Shark Lake located in Peter Lougheed Provincial Park in the Spray Lakes Valley of Alberta, Canada. Shark Lake is an open-basin lake with small, ephemeral inflows, one large outflow, and water isotope values consistent with local meteoric water. South Hogarth Lake is the highest lake in a chain of three lakes with water isotope values that are enriched relative to the local meteoric water line. Authigenic carbonate minerals form in the water column of both lakes and record the isotopic composition of water at the time of mineral formation (with a secondary influence by lake water temperature). We used IRMS to measure the oxygen (δ¹⁸O) and carbon (δ¹³C) isotopic composition of calcite in sediment from both lakes. Sediment texture, mineral, and elemental composition was determined using general core description, LOI, XRF, and XRD.

Calibrated basal ¹⁴C ages of the Shark Lake and South Hogarth Lake sediment cores are between 9630 to 10171 years before present (BP). The δ¹⁸O results reveal changes in regional hydroclimate that likely reflect century to millennium scale variations in Pacific ocean-atmosphere dynamics through the middle to late Holocene in combination with a local signal that reflects atmospheric interactions with local topography. The development of many climate proxy records from sites spanning a wide spatial distribution is essential for reconstructing past precipitation/drought variability in regions with complex orography and spatial/temporal responses to synoptic scale events.