From the melting sea ice and dead polar bears department comes this new study:

Multiproxy paleoecological evidence of Holocene climatic changes on the Boothia Peninsula, Canadian Arctic

Marie-Claude Fortin, Konrad Gajewski, Ottawa-Carleton Institute of Biology, Laboratory for Paleoclimatology and Climatology, University of Ottawa, Ottawa, ON K1N 6N5, Canada

Received 20 September 2015, Available online 22 March 2016

doi:10.1016/j.yqres.2016.02.003

Abstract

A study of chironomid remains in the sediments of Lake JR01 on the Boothia Peninsula in the central Canadian Arctic provides a high-resolution record of mean July air temperatures for the last 6.9 ka. Diatom and pollen studies have previously been published from this core. Peak Holocene temperatures occurred prior to 5.0 ka, a time when overall aquatic and terrestrial biological production was high. Chironomid-inferred summer air temperatures reached up to 7.5°C during this period. The region of Lake JR01 cooled over the mid- to late Holocene, with high biological production between 6.1 and 5.4 ka. Biological production decreased again at ~ 2 ka and the rate of cooling increased in the past 2 ka, with coolest temperatures occurring between 0.46 and 0.36 ka, coinciding with the Little Ice Age. Although biological production increased in the last 150 yr, the reconstructed temperatures do not indicate a warming during this time. During transitions, either warming or cooling, chironomid production increases, suggesting an ecosystem-level response to climate variability, seen at a number of lakes across the Arctic.

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Mean July air temperatures inferred from the fossil chironomid assemblages based on the WAPLS 2-component model and using the modern calibration dataset of Fortin et al. (2015) show a long-term cooling over the record (Fig. 7). Starting at ~ 0.6 ka, inferred temperatures abruptly decreased, with the coldest temperature occurring between 0.46 and 0.36 ka, then increased at 0.3 ka and then decreased until recent times.

Conclusions At Lake JR01 from the Boothia Peninsula, Nunavut, chironomid-inferred mean July air temperatures were warmest in the mid-Holocene, reaching as high as 7.5°C. Temperatures decreased over the course of the mid- to late-Holocene. Overall terrestrial and aquatic production, as indicated by chironomid, pollen and diatom concentrations and accumulation rates, as well as sediment organic and biogenic content, were higher prior to 5.0 ka than at any other time in the Holocene. The diatom community assemblages during the mid-Holocene also indicate that this was a warm period in the lake’s history. Between 5.0 and 1.0 ka, the lake was cooler and less productive. Inferred temperatures, based on both the chironomid and the pollen records, indicate additional cooling between 0.46 and 0.36 ka that corresponds to the Little Ice Age (LIA). Interpretation of changes in the diatom assemblages offers further evidence of a cooling at this time. Indices of both aquatic and terrestrial biological production increased in the last 150 yr, although the reconstructions do not indicate warming. Modern inferred temperatures based on both pollen and chironomids are up to 3°C cooler than those inferred for the mid-Holocene. The overall climatic trends recorded by both the pollen and the chironomids at Lake JR01 are comparable to those observed at other sites across the Arctic, offering further evidence that regional-scale climates have influenced Arctic aquatic and terrestrial ecosystems over the Holocene.

Brief periods of greater chironomid production of both warm- and cold-tolerant taxa occurred at Lake JR01 at the onset of periods of climatic and environmental change, regardless of the direction of these changes. Elevated chironomid production is also seen during environmental transitions in the Holocene record of other lakes from across the Arctic. A temporary increase in production may be a consequence of the chironomid community adjustment during environmental transitions.

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