Postglacial hydroclimate in the southern interior of British Columbia (Canada): Lake ecosystem response to the Holocene Thermal Maximum and drivers of mid-to-late Holocene climate variability

Abstract

The Holocene Thermal Maximum (HTM) is relatively well-understood both in terms of its external drivers and timing of its expression in different regions across the globe, and has previously been used to investigate lake ecosystem response to a warm and drier climate. However, connections between mid-to-late Holocene climate, associated drivers, and lake response are less understood, particularly in western North America (WNA) where complex topography and differences in proximity to the Pacific coast result in spatially variable responses to ocean-atmosphere processes. Here, we present a multi-proxy paleolimnological record spanning 11,000 years from a small lake in the semi-arid southern Interior Plateau (SIP) of British Columbia. Sub-fossil diatom, trace element (μXRF via ITRAX), and pollen data indicate that our study lake was shallow, nutrient-poor, and poorly oxygenated during the HTM. High effective moisture (EM) is inferred throughout the mid-Holocene (∼6500–2000 calibrated years before present (cal yr BP)), followed by a return to low EM after 2000 cal yr BP. Synthesis of additional SIP diatom records show similarities in EM throughout the Holocene, but most notably, the decline in EM at ∼2000 cal yr BP. Comparison of patterns in the SIP with additional climate proxy data across WNA, including lake sediment δ18O records that are interpreted to represent changes in Pacific ocean-atmosphere processes, suggest that shifts in the mean state of the Pacific Decadal Oscillation (PDO) and the El Niño Southern Oscillation (ENSO), and associated strength and position of the Aleutian Low, are linked with late Holocene declines in EM throughout the SIP.