The importance of plant macrofossils in late-glacial climatic reconstructions: An example from western Norway: A contribution to the ‘North Atlantic seaboard programme’ of IGCP-253, ‘Termination of the Pleistocene’

Abstract

Late-glacial pollen diagrams from two sites on the outermost coast of western Norway are discussed; on the islands of Utsira (Paus, 1990) and Blomøy (Mangerud, 1970). During the Allerød chronozone (12,000-11,000 BP), their climatic reconstructions depend on the assumed local occurrence of tree Betula (B. pubescens) at Blomøy, and on the presence of pollen of thermophilous taxa at Utsira. The plant macrofossil analyses at these same sites do not indicate the presence of Betula at either during the Allerød. Reconstruction of the local vegetation is of willow shrubs and Empetrum dwarf-shrub heath at Utsira, and of Salix herbacea-dominated vegetation at Blomøy. These reconstructions accord well with modern analogues above the tree line in the west Norwegian mountains. The inferred summer temperatures during the Allerød are thus 2–6°C lower than had been proposed from pollen evidence alone. Late-glacial plant macrofossil assemblages can generally be easily matched with modern vegetation analogues. On the west Norwegian coast, it would appear that the pollen of Betula and thermophilous indicators arrived by long-distance dispersal, facilitated by the strong winds during the late-glacial. The frequently found ‘no analogue’ pollen assemblages of the late-glacial period may therefore be due to their previously unsuspected content of extra-regional pollen, dispersed by strong winds. This emphasises that climatic reconstructions should only be made using taxa that were certainly growing locally. It demonstrates the importance of using locally derived, ecologically sound, vegetational reconstructions for the reconstruction of late-glacial climates, and for this, plant macrofossil analysis is invaluable.