A multi-proxy lake-sediment record of middle through late Holocene hydroclimate change in southern British Columbia, Canada

Analysis of the oxygen isotopic composition (δ¹⁸O) of sedimentary carbonates in Turquoise Lake (N50.83°, W121.69°, 807 m), southwestern British Columbia, provides information on middle through late Holocene hydroclimate variability at decadal-scale temporal resolution. Turquoise Lake water balance is strongly influenced by cold season precipitation and to a lesser extent by warm season evaporation. The lake water isotopic signature falls along the local evaporation line and is slightly enriched relative to local meteoric water, indicating that water losses from the lake occur principally through overflow and groundwater outseepage. An age model was developed using ²¹⁰Pb, ¹³⁷Cs, twelve ¹⁴C measurements, and one tephra layer. 375 samples of authigenic carbonate (< 63 µm-fraction), collected at 2–10 mm intervals over a 3 m long sediment sequence, were analyzed to produce the δ¹⁸O record. Multiple turbidite sequences that complicate the δ¹⁸O signal were identified via X-ray fluorescence, magnetic susceptibility, scanning electron microscopy, and powder x-ray diffraction analysis and were removed from the record. The Turquoise Lake δ¹⁸O record exhibits anomalously high values at ~ 7.6–6.5 ka, implying a dry middle Holocene and a transition to a wetter climate in the late-middle through late Holocene, with substantial variability on decadal and longer timescales. This result is consistent with other records from the Pacific Northwest, but the magnitude and timing of the transition from dry to wet conditions exhibited by the Turquoise δ¹⁸O record is unusual, with only the Castor Lake δ¹⁸O record exhibiting a somewhat similar pattern. Differences in hydroclimate signals from δ¹⁸O and other records in the Pacific Northwest point to complex intra-regional responses to Pacific ocean–atmosphere dynamics likely related to disparity in the orographic settings of the paleoclimate archives.