Quantifying climate variability during the past two thousand years using lake sediments from northeast Baffin Island, Arctic Canada

The Arctic is sensitive to climate change because of positive feedbacks, especially those involving the cryosphere. Changes in the Arctic are of scientific and social interest because they have the potential to affect the global climate system via several mechanisms, including the planet's heat budget and sea level rise. High-resolution (i.e. annual to sub-centennial) paleoclimate records increase our spatial and temporal understanding of arctic climate and help to place current changes in a long-term context. Lakes are one of few archives of high-resolution paleoclimate data in the Arctic. This project utilizes two quantitative lacustrine paleoclimate proxies to obtain high-resolution paleotemperature records on northeast Baffin Island, Arctic Canada for recent millennia: a 2400-year-long chironomid (non-biting midge; Diptera: Chironomidae) record and a 1000-year-long varve (annually laminated sediment) record. Dramatic changes in chironomid assemblages during the 20 th century (c.) illustrate that ecological thresholds, unprecedented in the last 5000 years, are being crossed. Stepwise increases in varve thickness during the 19th and 20th c. match regional ice cap melt layer and instrumental temperature records. Although the timing of recent warming differs between the two records, the magnitude of warming is similar: summers during the Little Ice Age (∼15th-19 th c.) are 1-1.5°C cooler than today and pre-20th c. summer temperatures (∼11th and 12th c.) do not exceed present-day summer temperature. Both records also corroborate evidence that the Arctic is particularly sensitive to natural and anthropogenic climate forcing mechanisms. These two independent records provide a unique, detailed understanding of climate during the past two millennia on northeast Baffin Island.