Journal of Paleolimnology

, Volume 48, Issue 1, pp 275–286

Fusing pollen-stratigraphic and dendroclimatic proxy data to reconstruct summer temperature variability during the past 7.5 ka in subarctic Fennoscandia

  • Samuli Helama
  • Heikki Seppä
  • Anne E. Bjune
  • H. John B. Birks
Original paper


A new palaeoclimatic reconstruction of mid-summer (July) temperatures for the last 7.5 ka in northern Fennoscandia is presented. It is based on two botanical proxies: spectra of fossil pollen and tree rings of Scots pine logs recovered from lacustrine sediments in the Arctic tree-line region. A newly developed method of proxy fusion is used to integrate the proxy-specific reconstructions of past summer temperature variability based on the pollen-stratigraphic and dendroclimatic data. The rationale behind the method is that the two proxies are likely to be connected to climate variability in a timescale-dependent fashion and, accordingly, the new reconstruction makes use of the low- and high-frequencies from pollen-stratigraphic and tree-ring data, respectively. The most prominent features of the new reconstruction are: (1) the long-term decline of temperatures by 2.0 °C over the past 7.5 ka, (2) the mid-Holocene warmth culminating between 5 and 4 ka as a deviation from the cooling trend, (3) the Little Ice Age cool phase between 0.7 and 0.1 ka, and (4) the subsequent warming during the past century. These periods are superimposed on year-to-year variations in climate as dated to calendar-year accuracy by dendrochronology. Within the modern period, the years 1934 and 1937 are among the warmest, and the years 1903 and 1910 are among the coldest summers in the context of the past 7.5 ka. On average, the reconstructed Holocene climate was approximately 0.85 °C warmer than the twentieth century.


Climate variability Climatic change Dendrochronology Paleoclimatology Paleolimnology Pollen data Proxy fusion 

Supplementary material

10933_2012_9598_MOESM1_ESM.xls (340 kb)
Supplementary material 1 (XLS 340 kb)
10933_2012_9598_MOESM2_ESM.xls (994 kb)
Supplementary material 2 (XLS 993 kb)

Copyright information

© Springer Science+Business Media B.V. 2012

Authors and Affiliations

  • Samuli Helama
    • 1
  • Heikki Seppä
    • 2
  • Anne E. Bjune
    • 3
  • H. John B. Birks
    • 3
    • 4
    • 5
    • 6
  1. 1.Arctic CentreUniversity of LaplandRovaniemiFinland
  2. 2.Department of Geosciences and GeographyUniversity of HelsinkiHelsinkiFinland
  3. 3.Bjerknes Centre for Climate ResearchUniversity of BergenBergenNorway
  4. 4.Department of BiologyUniversity of BergenBergenNorway
  5. 5.Environmental Change Research CentreUniversity College LondonLondonUK
  6. 6.School of Geography and the EnvironmentUniversity of OxfordOxfordUK

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