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Climate of the Past An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/cp-2018-60
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
12 Jun 2018
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Climate of the Past (CP).
The role of elevated atmospheric CO2 and increased fire in Arctic amplification of temperature during the Early to mid-Pliocene
Tamara Fletcher1,*, Lisa Warden2,*, Jaap S. Sinninghe Damsté2,3, Kendrick J. Brown4,5, Natalia Rybczynski6,7, John Gosse8, and Ashley P. Ballantyne1 1College of Forestry and Conservation, University of Montana, Missoula, 59812, USA
2Department of Marine Microbiology and Biogeochemistry, NIOZ Royal Netherlands Institute for Sea Research, Den Berg, 1790, Netherlands
3Department of Earth Sciences, University of Utrecht, Utrecht, 3508, Netherlands
4Natural Resources Canada, Canadian Forest Service, Victoria, V8Z 1M, Canada
5Department of Earth, Environmental and Geographic Science, University of British Columbia Okanagan, Kelowna, V1V 1V7, Canada
6Department of Palaeobiology, Canadian Museum of Nature, Ottawa, K1P 6P4, Canada
7Department of Biology & Department of Earth Sciences, Carleton University, Ottawa, K1S 5B6, Canada
8Department of Earth Sciences, Dalhousie University, Halifax, B3H 4R2, Canada
*These authors contributed equally to this work.
Abstract. The mid-Pliocene is a valuable time interval for understanding the mechanisms that determine equilibrium climate at current CO2 concentrations. One intriguing, but not fully understood, feature of the early to mid-Pliocene climate is the amplified arctic temperature response. Current models underestimate the degree of warming in the Pliocene Arctic and validation of proposed feedbacks is limited by scarce terrestrial records of climate and environment, as well as discrepancies in current CO2 proxy reconstructions. Here we reconstruct the CO2 and summer temperature from a re-dated 3.9 +1.5/−0.5 Ma sub-fossil fen-peat deposit on west-central Ellesmere Island, Canada, and investigate fire as a potential feedback to Arctic amplification of warming during the mid-Pliocene.

Average CO2 was determined using isotope ratios of mosses to be 440 ± 50 ppm. The estimate for average mean summer temperature is 15.4 ± 0.8 °C using specific bacterial membrane lipids, i.e. branched glycerol dialkyl glycerol tetraethers. Macro-charcoal was present in all samples from this Pliocene section with notably higher charcoal concentration in the upper part of the sequence. This change in charcoal was synchronous with a change in vegetation that saw fire promoting taxa increase in abundance. Paleovegetation reconstructions are consistent with warm summer temperatures, relatively low summer precipitation and an incidence of fire comparable to fire adapted boreal forests of North America, or potentially central Siberia.

To our knowledge, this study represents the furthest northern evidence of fire during the Pliocene and highlights the important role of forest fire in the ecology and climatic processes of the Pliocene High Arctic. The results provide evidence that terrestrial fossil localities in the Pliocene High Arctic were probably formed during warm intervals that coincided with relatively high CO2 concentrations that supported productive biotic communities. This study indicates that interactions between paleovegetation and paleoclimate were mediated by fire in the High Arctic during the Pliocene, even though CO2 concentrations were only ~ 30 ppm higher than modern.

Citation: Fletcher, T., Warden, L., Sinninghe Damsté, J. S., Brown, K. J., Rybczynski, N., Gosse, J., and Ballantyne, A. P.: The role of elevated atmospheric CO2 and increased fire in Arctic amplification of temperature during the Early to mid-Pliocene, Clim. Past Discuss., https://doi.org/10.5194/cp-2018-60, in review, 2018.
Tamara Fletcher et al.
Tamara Fletcher et al.
Tamara Fletcher et al.

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Short summary
3–4 million years ago was the last time atmospheric CO2 was similar to present. The Arctic was warmer compared to the global average and the causes are not fully known. To investigate this, we reconstructed CO2, summer temperature and forest fire at a 3.9 Ma peat in arctic Canada. Mean CO2 was ~ 440 ppm, summer temperature was ~ 15.4 °C and charcoal was abundant. Interactions between vegetation and climate were mediated by fire and may contribute to high Arctic temperatures during the Pliocene.
3–4 million years ago was the last time atmospheric CO2 was similar to present. The Arctic was...
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