title: Plant macrofossil evidence for an early onset of the Holocene summer thermal maximum in northernmost Europe.
abstract: 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.
authors: Department of Environmental Sciences, ECRU, University of Helsinki, P.O. Box 65, Helsinki FI-00014, Finland.
authors: M
authors: M
authors: Väliranta
authors: Department of Geosciences and Geography, University of Helsinki, P.O. Box 65, Helsinki FI-00014, Finland.
authors: J S
authors: JS
authors: Salonen
authors: Department of Environmental Sciences, ECRU, University of Helsinki, P.O. Box 65, Helsinki FI-00014, Finland.
authors: M
authors: M
authors: Heikkilä
authors: Institute of Geology, Tallinn University of Technology, Ehitajate tee 5, Tallinn 19086, Estonia.
authors: L
authors: L
authors: Amon
authors: Department of Physical Geography, Stockholm University, Stockholm 106 91, Sweden.
authors: K
authors: K
authors: Helmens
authors: School of Geography, Archaeology and Palaeoecology, Queen's University, Belfast, Northern Ireland BT7 1NN, UK.
authors: A
authors: A
authors: Klimaschewski
authors: Department of Physical Geography, Stockholm University, Stockholm 106 91, Sweden.
authors: P
authors: P
authors: Kuhry
authors: Department of Geosciences and Geography, University of Helsinki, P.O. Box 65, Helsinki FI-00014, Finland.
authors: S
authors: S
authors: Kultti
authors: Institute of Geology, Tallinn University of Technology, Ehitajate tee 5, Tallinn 19086, Estonia.|Department of Physical Geography and Ecosystem Analysis, Lund University, Sölvegatan 12, Lund 223 62, Sweden.
authors: A
authors: A
authors: Poska
authors: Department of Physical Geography, Stockholm University, Stockholm 106 91, Sweden.
authors: S
authors: S
authors: Shala
authors: Institute of Geology, Tallinn University of Technology, Ehitajate tee 5, Tallinn 19086, Estonia.
authors: S
authors: S
authors: Veski
authors: Department of Biology and Bjerknes Centre for Climate Research, University of Bergen, P.O. Box 7803, Bergen N-5020, Norway.
authors: H H
authors: HH
authors: Birks
mesh_terms: D059001:Aquatic Organisms / Q000502:physiology*; D002980:Climate; D003198:Computer Simulation; D005060:Europe; D005580:Fossils; D015233:Models, Statistical; D063148:Plant Dispersal / Q000502:physiology; D011058:Pollen / Q000502:physiology*; D012621:Seasons; D013696:Temperature; D014197:Trees / Q000502:physiology*