The drivers and responses of North Atlantic climatic variability during the Younger Dryas

To understand the mechanisms behind the climatic variations during the Younger Dryas in the North Atlantic region, it is vital to effectively understand how the climate varied spatially during this period. This thesis involved a systematic review of of the Polar Front indicator N. pachyderma and other sea-surface proxies, to reconstruct sea-ice fluctuations and more indirectly, North Atlantic surface water changes. This synthesis was then used to identify the regions with sparser data for future work and to explore how sea-ice varied during the Younger Dryas. Where possible, the Vedde Ash (VA) tephra layer was used to constrain the timing of variability, but this is not found ubiquitously across the North Atlantic. It is hoped that this synthesis will also be useful for comparing with model-output data of sea-ice changes in relation to AMOC variability and atmospheric conditions associated with high/low sea-ice maximum years from the modern day. Alongside the synthesis of N. pachyderma records, several sites were selected from around the North Atlantic to plug these data-poor regions and reveal heterogeneous oceanic changes occurred across the NW Atlantic, with tephrochronological and radiocarbon-based chronologies constructed to ensure sites could be robustly linked to existing regional records. Parallel to these marine and tephrostratigraphic investigations, a number of sedimentological experiments were established to assess the degree to which lacustrine records in different environmental contexts can reflect broader climatic change. These experiments combined with the final spatial synthesis of a network of sites should allow for an assessment of the optimal lake contexts for retrieving climatically sensitive records for sedimentological analysis.
A network of terrestrial sites were analysed for their physical and geochemical properties from a range of different catchment contexts to investigate both the spatial propagation of environmental change during the Younger Dryas within the UK, but also to assess how the different contexts may have affected their environmental sensitivity. The findings of both marine and terrestrial archives were then incorporated into a synthesis of changes within the Younger Dryas, to enable the examination of the different climatic controls on the North Atlantic region that may have evolved during this stadial period. This thesis has highlighted those current hypotheses of change, which hinge on a simple sea-ice expansion and contraction are insufficient to explain the complexity of changes seen within the period.