Fossil chironomid assemblages and inferred summer temperatures for the past 14,000 years from a low-elevation lake in Pacific Canada

Abstract

Fossil midge remains in a sediment core from Lake Stowell, a low-elevation lake in coastal British Columbia, Canada, were used to assess temporal changes in chironomid communities and to produce quantitative estimates of mean July air temperature (MJAT) for the past 14,000 years based on two different transfer functions. Chironomid assemblages are diverse throughout much of the record, with most taxa present at low relative abundances. The basal portion of the sediment record is characterized by low head capsule concentrations, taxonomic diversity and organic matter content, all of which increase towards the early Holocene. Inferred temperatures suggest a cool late-glacial interval with a minimum MJAT of 12.5 °C, ~2 °C cooler than the inferred modern temperature. Summer temperatures gradually increased from this minimum until a brief cooling of as much as ~3 °C relative to modern that coincides with the Younger Dryas chronozone. An interval of warmer summers with MJAT of ~16-18 °C (2-3 °C warmer than modern) is inferred between ~10,500 and 8000 cal yr BP. This early Holocene warm period was followed by generally cooler inferred temperatures in the middle and late Holocene. The midgeinferred temperature record from Lake Stowell is generally consistent with other temperature reconstructions from the region based on chironomid remains and other climate proxies. This research underscores the potential of low-elevation, mid-latitude sites for chironomid-based temperature reconstructions. In order to maximize the availability of modern analogues for robust temperature reconstructions from similar sites, calibration datasets should be expanded to include more sites from the warm end of the temperature gradient.

Postglacial wetland succession, carbon accumulation, and forest dynamics on the east coast of Vancouver Island, British Columbia, Canada

“…Some paleoecological records from the northeast Pacific coast suggest cooling during the Younger Dryas chronozone (Engstrom et al, 1990; Mathewes, 1993; Lacourse, 2005; Galloway et al, 2007, 2009; Gavin et al, 2013), while others show little evidence of cooling at this time (Brown and Hebda, 2003; Lacourse et al, 2005, 2012; Leopold et al, 2016). A chironomid-based temperature reconstruction from the south coast of BC suggests a decrease of as much as 3°C, relative to modern, during the Younger Dryas (Lemmen and Lacourse, 2018), which is consistent with other paleotemperature records from the northeast Pacific (Kienast and McKay, 2001; Gavin et al, 2013). It is unlikely that the Younger Dryas on the northeast Pacific coast was cool and dry, as it was at many locations around the North Atlantic and in northeast Asia (Björck, 2007).…”

“…Alnus viridis , Salix , and Shepherdia canadensis shrubs were also present, making these early vegetation communities near Grant's Bog similar to those that occurred at about the same time at low elevations on northern Vancouver Island (Lacourse, 2005) and the southeastern BC mainland (Mathewes, 1973). Macroscale climate at this time was cool and likely drier, relative to the present (Heusser et al, 1985; Kienast and McKay, 2001; Lemmen and Lacourse, 2018).…”

“…2) are generally lower. Relative to the early Holocene, climate was cooler, wetter, and less seasonal in the mid- and late Holocene (Walker and Pellatt, 2003; Brown et al, 2006; Lemmen and Lacourse, 2018). The abundance of macroscopic charcoal between ~4800 and 1000 cal yr BP (Fig.…”

Diatom responses to long‐term climate and sea‐level rise at a low‐elevation lake in coastal British Columbia, Canada

“…Mid-to late Holocene increases in taxa indicative of higher DOC and/ or humic-stained waters also indicated potential biogeochemical coupling of terrestrial succession and limnological conditions. Biostratigraphic changes in diatom communities closely matched those of chironomids extracted from the same lake sediments (Lemmen and Lacourse 2018), demonstrating a future avenue for work with respect to comparisons of quantitative reconstructions using both proxies.…”

“…(). In the Lemmen and Lacourse () study, loss on ignition (LOI) was conducted by drying 1 cm 3 sediment samples at 105°C for 20 h, followed by ignition at 550°C for 4 h. Magnetic susceptibility was determined using a Bartington MS2E high‐resolution surface scanner. Six AMS radiocarbon ages (Appendix : Table S1) were obtained on plant macrofossils and were calibrated to calendar years using the IntCal13 data set (Reimer et al.…”