Using fossil midges from Saltspring Island, British Columbia to infer changes in temperature over the last 14,000 years
Date
2016-09-09
Authors
Lemmen, Jillian
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Abstract
Fossil midge remains from a sediment core from Lake Stowell, Saltspring Island
(48°46’54”N, 123°26’38”W) were used to produce quantitative estimates of mean July
air temperature over the last 14,000 years. Chironomid and Chaoborus remains were
identified, and multiple models of past temperatures based on transfer functions of
northern North American calibration datasets were evaluated. The selected model was
used to create the first quantitative paleotemperature estimates for the Gulf Islands
region.
Inferred paleotemperatures at Lake Stowell varied between 12.1 °C and 18.6 °C
over the last 14,000 calendar years. Several major climate phases were identified based
on changes in paleotemperature. The base of the record is characterised by a cool lateglacial interval with a minimum inferred July temperature of 12.1 °C. Inferred
temperatures generally increased by ~4 °C between ~14,200 and 10,300 cal yr BP but
this warming was interrupted by cooling, coincident with the Younger Dryas
Chronozone, when inferred temperatures drop ~2 °C from the temperatures immediately
preceding this interval. A warm early Holocene extends from ~10,300 to 8100 cal yr BP
with temperatures regularly exceeding 16 °C. Following the early Holocene, inferred
temperatures decreased to approximately 14.9 °C in the mid-Holocene. After a brief
warm peak in the late Holocene, inferred temperatures cooled towards the present.
Inferred changes in paleotemperature from Lake Stowell are consistent with other
paleoenvironmental studies conducted in southern British Columbia and throughout
much of the Northern Hemisphere. Temperature changes at Lake Stowell are muted in
comparison to continental sites, which may be due to the influence of marine conditions.
This research provides context for other studies in the region, and contributes to our
understanding of environmental change since the last glacial maximum.
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Keywords
Chironomids, Fossil midges, Saltspring Island, Gulf Islands, Paleoecology, Paleolimnology, Paleotemperature, British Columbia, Pacific Northwest, Temperature reconstruction, Modern analogue