Plant macrofossil evidence for an early onset of the Holocene summer thermal maximum in northernmost Europe

• Published in: Nature communications Vol. 6; no. 1; p. 6809
• Main Authors: Väliranta, M, Salonen, J S, Heikkilä, M, Amon, L, Helmens, K, Klimaschewski, A, Kuhry, P, Kultti, S, Poska, A, Shala, S, Veski, S, Birks, H H
• Format: Journal Article
• Language: English
• Published: England Nature Publishing Group 10.04.2015; Nature Pub. Group
• Subjects: Aquatic Organisms - physiology; Aquatic plants; Climate; Computer Simulation; Earth and Related Environmental Sciences; Europe; Fossils; Geography; Geovetenskap och miljövetenskap; Hypotheses; Models, Statistical; Natural Sciences; Naturgeografi; Naturvetenskap; Physical Geography; Plant Dispersal - physiology; Pollen - physiology; Seasons; Temperature; Trees; Trees - physiology; Europe; Sweden; Lapland; Finland
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms7809

Holocene summer temperature reconstructions from northern Europe based on sedimentary pollen records suggest an onset of peak summer warmth around 9,000 years ago. However, pollen-based temperature reconstructions are largely driven by changes in the proportions of tree taxa, and thus the early-Holocene warming signal may be delayed due to the geographical disequilibrium between climate and tree populations. Here we show that quantitative summer-temperature estimates in northern Europe based on macrofossils of aquatic plants are in many cases ca. 2 °C warmer in the early Holocene (11,700-7,500 years ago) than reconstructions based on pollen data. When the lag in potential tree establishment becomes imperceptible in the mid-Holocene (7,500 years ago), the reconstructed temperatures converge at all study sites. We demonstrate that aquatic plant macrofossil records can provide additional and informative insights into early-Holocene temperature evolution in northernmost Europe and suggest further validation of early post-glacial climate development based on multi-proxy data syntheses.