Glacial geology and glaciology of the Younger Dryas ice cap in Scotland

摘要

This thesis uses geological field data and numerical ice sheet modelling to study the YoungerudDryas ice cap in Scotland. The Younger Dryas stadial is important because it represents theudmost recent period of high-magnitude global climate change, and was marked by the expansionudof ice sheets in North America and Scandinavia, and the regrowth of glaciers in the BritishudIsles. An integrated methodology linking field results and modelling is developed and appliedudhere, specifically focussing on the deposits, landforms, and palaeoglaciology of Younger Dryasudglaciers in western Scotland. This combined approach enables data of different scales to beudcompared, and connected, from local sedimentological investigations and empirically derivedudreconstructions, to regional ice-sheet simulations from a high-resolution numerical model. Previousudgeological mapping in western Scotland resulted in contradictory views of the thicknessudand extent of ice during the Younger Dryas, consequently leading to uncertainty about theuddynamics of the former ice cap. By using a ‘landsystem’ method to characterise the terrain, itudis argued here that geological evidence in the study area implies a relatively thick central iceudcap that fed steep outlet glaciers around its margins. These glaciers oscillated throughout theudstadial, and during deglaciation produced suites of moraines that marked successive positionsudof glacier retreat. Widespread preservation of superimposed landforms, and of sedimentudsequences pre-dating the Younger Dryas, suggest that, despite being active, the Younger Dryasudice cap was not particularly erosive in its central area and only subtly modified its bed. Theseudgeological interpretations are supported by high-resolution numerical modelling of the iceudcap, which reveals clear spatial variability in the velocity structure, thermal regime, and flowudmechanism of the ice cap; patterns that led to local contrasts in basal processes and diversityudin the geological imprint. These model experiments also highlight the non-linear relationshipudbetween climate forcing and glacier response, identifying evidence of ice sheet hysteresis andudclimatically decoupled glacier oscillations – concepts as relevant to geological investigations ofudformer ice masses as they are to the prediction of glacier response under future climate changes.