Fossil chironomid assemblages and inferred summer temperatures for the past 14,000 years from a low-elevation lake in Pacific Canada
Lemmen, J. | Lacourse, T.
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 to 18 °C (2–3 °C warmer than modern) is inferred between ~10,500 and 8000 cal year BP. This early Holocene warm period was followed by generally cooler inferred temperatures in the middle and late Holocene. The midge-inferred 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.
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