Multiple drivers of Late Holocene paraglacial sediment reworking in Ireland

Abstract

On the east coast of Ireland, glacigenic sediments and landforms reflect both phases of late Devensian ice retreat, and postglacial slope readjustment under a paraglacial process regime. These different phases of landscape development are commonly difficult to identify in the absence of geomorphological, sedimentary and dating evidence for the style, magnitude and timing of postglacial landscape change. Here, sediments and radiocarbon dates on raised coastal sediments adjacent to a prominent retreat moraine of the late Devensian Irish ice sheet provide evidence for one such extended phase of paraglacial sediment reworking, in the 8th and 10th centuries CE. The timing of this phase of sediment reworking provides evidence for climatic deterioration during the European late Dark Ages/early Medieval Warm Period, and is consistent with evidence across northwest Europe for enhanced landscape geomorphic change at this time. From this evidence it is inferred that landscape morphological change dominantly reflects climatic rather than anthropogenic forcing, although the latter cannot be wholly discounted. Further, this evidence highlights the sensitivity to Holocene climate forcing of coastal paraglacial systems that contain abundant glacigenic sediment supply.