Flora, fauna and climate of Scotland during the Weichselian Middle Pleniglacial ^ palynological, macrofossil and coleopteran investigations

Abstract Thin lenses of organic-rich material, on the upper surface of a layer of glacio-fluvial deposits have been studied in an open cast coal-mine near Sourlie, western Scotland. Radiocarbon dates on antler fragments, plant debris and bulk organic matter from silt, showed that the sediments accumulated between ca. 33 500 and 29 000 14 C yr BP, during a period when this part of western Scotland was free of glaciers. The organic-rich sediments yielded a very rich flora and fauna and in total about 160 plant taxa and 61 coleopteran taxa were recorded together with other invertebrates. The Sourlie flora is one of the richest late Middle Weichselian floras yet studied within the British Isles. Leg bones of Coelodonta antiquitatis (woolly rhinoceros) and Rangifer tarandus (reindeer) were also found at the site. During this period, the landscape was treeless and the vegetation could be characterised as an intermediate between a low shrub tundra and sedge–grass–moss tundra. Both the flora and arthropod fauna suggest that during formation of the organic-rich layers at Sourlie, mean July temperatures were 9–10°C. The flora suggests also that at the beginning of formation of these layers, minimum mean July temperatures increased from 7 to 9–10°C, but later dropped again to 7–8°C. A possible time correlation with one of the warmer periods of the Dansgaard–Oeschger cycles in the stable oxygen isotope record of the Greenland ice cores during this period is proposed. The arthropod fauna suggests that mean January temperatures were somewhere between −34 and −11°C. Mean annual temperatures lay probably between −1 and −10°C, which implies the possible presence of discontinuous or continuous permafrost in the area. During winter, a protective snow cover of varying thickness probably enabled perennial plants, especially shrubs, to survive.