The importance of effective moisture and landscape controls on diatom assemblages and primary production in Roche Lake, British Columbia, Canada over the past ca. 1800 years

Abstract

Lakes in the semiarid Southern Interior Plateau of British Columbia, Canada are vulnerable to future climate-driven changes in water quantity and quality. However, few long-term monitoring records exist to assess the effects of varying hydroclimate conditions on lake function. We present a high-resolution multiproxy paleolimnological record containing subfossil diatoms, μXRF via ITRAX, and chlorophyll-a that spans the past 1800 years from Roche Lake in south-central British Columbia. Generalized additive models indicate that the diatom assemblages were associated with changes in lake level and the accompanying effects of atmospheric forcing on lake thermal structure, and that these forcing mechanisms had a weak relationship with primary production. We infer two pronounced arid periods between ca. AD 600–950 and ca. AD 1730–1950 that correspond to evidence of reduced lake mixing and enhanced anoxia, but variable patterns in primary production. Synthesis of regional proxy records suggests that inferences of moist but possibly warm conditions during the Medieval Climate Anomaly may have occurred because of a complex interaction between prolonged La Niña-like conditions and higher radiative forcing. Overall, lakes in this region are sensitive to changes in hydroclimate generated by interactions between external forcing and Pacific Ocean–atmosphere processes, and the resulting changes in aridity may have potentially negative consequences on salmonid habitat.

A Link Between Hydroclimate Variability and Biomass Burning During the Last Millennium in the Interior Pacific Northwest

“…Charcoal accumulation rates in Castor, Round, Fish, and Doheney lakes (Walsh et al, 2018(Walsh et al, , 2023 were low in the MCA and increased during the LIA, when winter conditions were generally drier than before (e.g., MacDonald & Case, 2005;Mushet et al, 2023;Steinman et al, 2012;Steinman et al, 2014) and multidecadal hydroclimate variability was high (Figure 3 and Figure S10 in Supporting Information S1). Nearby sites in northern Idaho (Baker Lake, 2,300 m a.s.l, Hoodoo Lake, 1770 m a.s.l, Burnt Knob Lake, 2,250 m a.s.l Figure 1) and Montana (Foy Lake 1006 m a.s.l Figure 1), also show increased charcoal accumulation during the LIA compared to the MCA (Brunelle & Whitlock, 2003;Brunelle et al, 2005;Power et al, 2006).…”