Expedition | 507

Intensification of global glacial-interglacial cycles, marked by the onset of the Pleistocene (~2.6 Ma), was a critical climate transition as progressively more severe cold conditions triggered continental-scale Northern Hemisphere glaciation. While the last glacial cycle is increasingly well-understood, prior glaciations have little information about ice sheet margins, the underlying glacial- and morpho-dynamic controls, and how glacial variability was linked with climate and ecosystem changes. There is piecemeal evidence for some of these unknowns – e.g., landforms on the glaciated terrains of northwest Europe and North America suggest that, in some instances, Early Pleistocene ice sheets may have been comparable in size to those in the Late Pleistocene. However, with Early Pleistocene sea level lowstand estimates generally, but not always, ~50-60% of those in the Late Pleistocene, such observations provide uncertainty on how they match up and, more broadly, the nature of Pleistocene climate-cryosphere evolution and its feedbacks relative to the preceding Pliocene global warmth. If we cannot fully understand the nuances of such discrepancies then it provides a limit on how effectively the past can be used as an analogue for the future.

The 600-km long North Sea Basin (NSB) transitioned through ~50 glacial-interglacial cycles – of varying lengths between the 41-kyr and 100-kyr worlds – as it was infilled by an offset-stacked succession of largely muddy deep-to-shallow marine and terrestrial sediments. Ample accommodation and high sediment fluxes combined to preserve a unique ~1.2-km-thick late Plio-Pleistocene succession that captures the co-evolution of glaciation and Europe’s largest river systems in a shallow marine basin. These sediments record palaeo-environment signatures from all over northwest Europe as they were sourced by multiple rivers and ice sheets connecting mid- and high-latitudes. The interval also benefits from near-complete 3D- and 2D-seismic coverage and these data have revolutionised our understanding, providing paradigm shifts on patterns of basin infill and process dominance.  The northwest European Pleistocene ice sheets likely generated global-scale feedbacks that impacted the climate system, and nutrient/carbon exchange in the North Atlantic. Thus, the NSB Pleistocene sequence and the late Pliocene succession capturing the transition into it, provide a unique land-to-sea-to-ocean palaeo-climate archive across millions of years. Despite thousands of successfully-drilled exploration wells, industry operations rarely collected materials from the upper ~1.5 km, meaning this climate archive lacks samples to date and corroborate hypotheses, something that GLACE-NS hopes to resolve.