The Devensian (Weichselian) Lateglacial palaeoenvironmental record from Gransmoor, East Yorkshire, England: A contribution to the ‘North Atlantic seaboard programme’ of IGCP-253, ‘Termination of the Pleistocene’

Abstract

Palynological and coleopteran data are described from a section through Late Devensian (Weichselian) deposits at Gransmoor, East Yorkshire, England. The pollen evidence shows that, following an initial open-habitat episode, first Juniperus scrub and later Betula woodland became established in the area during the Lateglacial Interstadial. This woodland was replaced during the Loch Lomond (Younger Dryas) Stadial by a predominatly herbaceous flora with arctic/alpine, steppe and halophytic elements. The coleopteran evidence indicates a similar local environment and that the thermal maximum of the Interstadial, when mean July temperatures may well have exceeded 18°C, occurred prior to the deposition of the earliest polleniferous sediments. By the time of the Juniperus expansion, summer temperatures had fallen by 2–4°C to levels comparable with those of the present day. A further temperature decline followed the expansion of Betula during the later Interstadial and another fall occurred at the Lateglacial Interstadial/Loch Lomond Stadial boundary. During the Loch Lomond Stadial mean July temperatures of 9–11°C are implied, with winter temperatures as low as −15 to −20°C. Collectively the evidence reemphasises the point that for the first 1000 years or so of the Lateglacial Interstadial, there was a disequilibrium between the palynological and coleopteran records in terms of climatic signal. During the later Interstadial, however, a closer relationship is apparent between both proxy data sources. Of particular significance in this respect is the fluctuation in reconstructed summer and winter temperatures, and a rise and subsequent fall in Betula pollen frequencies. This may be the correlative of one of the pre-Younger Dryas climatic oscillations recorded in other proxy data sources including palynological records from Britain and eastern Canada, oxygen isotope traces from Swiss lake sediments, isotopic and electrical conductivity profiles from the Greenland ice sheet, and diatom and foraminiferal records in cores from the Norwegian Sea and the North Atlantic Ocean.