Articles | Volume 12, issue 4
Clim. Past, 12, 1043–1060, 2016
Clim. Past, 12, 1043–1060, 2016

Research article 21 Apr 2016

Research article | 21 Apr 2016

Climate variability and long-term expansion of peatlands in Arctic Norway during the late Pliocene (ODP Site 642, Norwegian Sea)

Sina Panitz1, Ulrich Salzmann1, Bjørg Risebrobakken2, Stijn De Schepper2, and Matthew J. Pound1 Sina Panitz et al.
  • 1Department of Geography, Faculty of Engineering and Environment, Northumbria University, Newcastle upon Tyne NE1 8ST, UK
  • 2Uni Research Climate, Bjerknes Centre for Climate Research, Allégaten 55, 5007 Bergen, Norway

Abstract. Little is known about the terrestrial response of high-latitude Scandinavian vegetation to the warmer-than-present climate of the late Pliocene (Piacenzian, 3.60–2.58 Ma). In order to assess Piacenzian terrestrial climate variability, we present the first high-resolution reconstruction of vegetation and climate change in northern Norway between 3.6 and 3.14 Ma. The reconstructions are derived from pollen assemblages in the marine sediments of ODP Hole 642B, Norwegian Sea (67° N). The palynological assemblages provide a unique record of latitudinal and altitudinal shifting of the forest boundaries, with vegetation alternating between cool temperate forest during warmer-than-present intervals and boreal forest similar to today during cooler intervals. The northern boundary of the nemoral to boreonemoral forest zone was displaced at least 4–8° further north, and warmest-month temperatures were 6–14.5 °C higher than at present during warm phases. Warm climatic conditions persisted during the earliest Piacenzian (ca. 3.6–3.47 Ma) with diverse cool temperate nemoral to boreonemoral forests growing in the lowlands of the Scandinavian mountains. A distinct cooling event at ca. 3.47 Ma resulted in a southward shift of vegetation zones, leading to the predominance of boreal forest and the development of open, low alpine environments. The cooling culminated around 3.3 Ma, coinciding with Marine Isotope Stage (MIS) M2. Warmer climate conditions returned after ca. 3.29 Ma, with higher climate variability indicated by the repeated expansion of forests and peatlands during warmer and cooler periods, respectively. Climate progressively cooled after 3.18 Ma, resembling climatic conditions during MIS M2. A high variability of Norwegian vegetation and climate changes during the Piacenzian is superimposed on a long-term cooling trend. This cooling was accompanied by an expansion of Sphagnum peatlands that potentially contributed to the decline in atmospheric CO2 concentrations at the end of the Piacenzian warm period and facilitated ice growth through positive vegetation–snow albedo feedbacks. Correlations with other Northern Hemisphere vegetation records suggest hemisphere-wide effects of climate cooling.

Short summary
This paper presents the first late Pliocene high-resolution pollen record for the Norwegian Arctic, covering the time period 3.60 to 3.14 million years ago (Ma). The climate of the late Pliocene has been widely regarded as relatively stable. Our results suggest a high climate variability with alternating cool temperate forests during warmer-than-presen periods and boreal forests similar to today during cooler intervals. A spread of peatlands at the expense of forest indicates long-term cooling.