Land–sea coupling of Early Pleistocene glacial cycles in the southern North Sea exhibit dominant Northern Hemisphere forcing
Abstract. We assess the disputed phase relations between forcing and climatic response in the Early Pleistocene with a spliced Gelasian (~ 2.6–1.8 Ma) multi-proxy record from the southern North Sea. The cored sections couple climate evolution on both land and sea during the onset of Northern Hemisphere Glaciations (NHG) in NW Europe, providing the first well-constrained stratigraphic sequence of the classic terrestrial Praetiglian Stage. Terrestrial signals were derived from the Eridanos paleoriver, a major fluvial system that contributed a large amount of freshwater to the northeast Atlantic. Due to its latitudinal position, the Eridanos catchment was likely affected by Early Pleistocene NHG, leading to intermittent shutdown and reactivation of river flow and sediment transport. Here we apply organic geochemistry, palynology, carbonate isotope geochemistry, and seismostratigraphy to document both vegetation changes in the Eridanos catchment and regional surface water conditions and relate them to Early Pleistocene glacial–interglacial cycles, and relative sea level changes. Paleomagnetic and palynological data provide a solid integrated timeframe that ties the obliquity cycles, expressed in the borehole geophysical logs, to Marine Isotope Stages (MIS) 103 to 92, independently confirmed by a local benthic oxygen isotope record. Marine and terrestrial palynological and organic geochemical records provide high resolution reconstructions of relative Terrestrial and Sea Surface Temperature (TT and SST), vegetation, relative sea level, and coastal influence. During the prominent cold stages MIS 100, 98 and 96, the record indicates increased non-arboreal vegetation, and low SST and TT, and low relative sea level. During the warm stages MIS 99, 97 and 95 we infer freshwater influx increases causing stratification of the water column together with higher % arboreal vegetation, high SST and relative sea level maxima. The Early Pleistocene distinct warm–cold alterations are synchronous between land and sea, but lead the relative sea level change. The record provides evidence for a dominantly NH driven cooling and glacial build up which is obliquity driven. Timing of southward migration of Arctic surface water masses, indicated by relative SST, are furthermore relevant for the discussion on the relation between the intensity of the Atlantic meridional overturning circulation and ice sheet growth in order to identify lead-lags between forcing and response of Early Pleistocene glaciations.