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Climate of the Past An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/cp-2020-84
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/cp-2020-84
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  26 Jun 2020

26 Jun 2020

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This preprint is currently under review for the journal CP.

Cold season warming in the North Atlantic during the last 2000 years: Evidence from Southwest Iceland

Nora Richter1,2, James M. Russell1, Johanna Garfinkel1, and Yongsong Huang1 Nora Richter et al.
  • 1Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI 02912, USA
  • 2The Josephine Bay Paul Center for Comparative Molecular Biology and Evolution, Marine Biological Laboratory, Woods Hole, MA, 02543, USA

Abstract. Temperature reconstructions from the Northern Hemisphere (NH) generally indicate cooling over the Holocene which is often attributed to decreasing summer insolation. However, climate model simulations predict that rising atmospheric CO2 concentrations and the collapse of the Laurentian ice sheet caused mean annual warming during this epoch. This contrast could reflect a bias in temperature proxies, and particularly a lack of proxies that record cold (late fall–early spring) season temperatures, or inaccuracies in climate model predictions of NH temperature. We reconstructed winter–spring temperatures during the Common Era (i.e. the last 2000 years) using alkenones, lipids produced by Isochrysidales haptophyte algae that bloom during spring ice-off, preserved in sediments from Vestra Gíslholtsvatn (VGHV), southwest Iceland. Our record indicates cold-season temperatures warmed during the last 2000 years, in contrast to NH averages. Sensitivity tests with a lake energy balance model show that this warming is likely driven by increasing winter–spring insolation. We also found distinct seasonal differences in centennial-scale, cold-season temperature variations in VGHV compared to existing records of summer and annual temperatures from Iceland. Sustained or abrupt cooling in VGHV temperatures are associated with the cumulative effects of solar minima and volcanic eruptions, and potentially ocean and sea-ice feedbacks associated with cooling in the broader Arctic. However, multi-decadal to centennial-scale changes in cold season temperatures were strongly modulated by internal climate variability, i.e. the North Atlantic Oscillation, which can result in winter warming in Iceland even after a major negative radiative perturbation.

Nora Richter et al.

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Nora Richter et al.

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Latest update: 26 Oct 2020
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Short summary
We present a reconstruction of winter–spring temperatures from lake sediments in Iceland over the last 2000 years to improve our understanding of seasonal temperature changes in the North Atlantic region. We observe warming in winter–spring temperatures that is likely driven by increasing winter–spring insolation. On multi-decadal to centennial timescales, changes in cold season temperatures are associated with solar minima and volcanic eruptions but also internal climate variability.
We present a reconstruction of winter–spring temperatures from lake sediments in Iceland over...
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