Rapid ice sheet retreat triggered by ice stream debuttressing: Evidence from the North Sea

Using high-resolution bathymetric and shallow seismic data from the North Sea, we have mapped hitherto unknown glacial landforms that connect and resolve longstanding gaps in the Quaternary geological history of the basin. We use these data combined with published information and dates from sediment cores to reconstruct the extent of the Fennoscandian and British Ice Sheets (FIS and BIS) in the North Sea during the last phases of the last glacial stage. It is concluded that the BIS occupied a much larger part of the North Sea than previously suggested and that North Sea ice underwent a dramatic disintegration ~18,500 yr ago. This was triggered by grounding-line retreat of the Norwegian Channel Ice Stream, which debuttressed adjacent ice masses, and led to an unzipping of the BIS and FIS accompanied by drainage of a large ice-dammed lake. Our reconstruction of events provides an opportunity to improve understanding and modeling of the disintegration of marine-based ice sheets, and the complex interplay between ocean circulation and the cryosphere

Ocean-ice sheet interaction along the SE Nordic Seas margin from 35 to 15 ka BP

Sediment cores from the south-eastern Nordic Seas simultaneously archive the variability of the Fennoscandian Ice Sheet (FIS), the British-Irish Ice Sheet (BIIS) and the regional oceanic conditions. This study aims to contribute to our understanding of the marine-based section of the FIS and the BIIS between 35,000 and 15,000 years BP, by using cores MD99-2283, MD99-2284 and MD99-2289, retrieved along the upper continental slope between the Faroe-Shetland Channel and the Vøring Plateau. For this, we present a revised, radiocarbon based, Bayesian modelled chronological framework and a compilation of new and published sedimentological, geochemical and micro-paleontological datasets. Our results show a possibly first Weichselian FIS/BIIS confluence at ca. 25,500 years BP in the central North Sea, which buttressed the BIIS to the East, potentially leading to a northwards BIIS deflection via the Shetlands. The Norwegian Channel Ice Stream (NCIS) most likely only reached the shelf edge after 23,300 ± 500 years BP, possibly for the first time during the Weichselian. The NCIS onset directly preceded a pronounced influx of warm Atlantic water to the northern North Sea margin possibly implying forcing through ocean melt. We find a highly variable NCIS, with three ~ 1400 yearlong episodes of increased ice rafted debris flux interrupted by ~ 600 yearlong minima. When compared to other sides of the European Ice Sheet, these episodes appear to correlate well, suggesting a common forcing mechanism. In conclusion, our data supports recent suggestions that the last glacial stage of the BIIS was more extensive in the central North Sea and the confluence later than previously thought

Grain size distribution, Ca/Fe ratios and elemental composition of sediment core GS13-182-CC, Norwegian continental margin

The North Atlantic Oscillation is the dominant atmospheric driver of North Atlantic climate variability with phases corresponding to droughts and cold spells in Europe. Here, we exploit a suggested anti-correlation of North Atlantic Oscillation-phase and north-eastern North Atlantic primary productivity by investigation of south-eastern Norwegian Sea sediment cores spanning the last 8000 years. Age model uncertainties between 2 and 13 years for the period 1992-1850 AD allows for proxy to observational data calibration. Our data suggest that Ca/Fe core-scanning results reflect sedimentary CaCO3-variability in the region. Cross-correlating the Ca/Fe record with nearby phytoplankton counts and dissolved O2 data, suggests that Ca/Fe can be used as a proxy for primary productivity variability in the region. Our data support an anti-correlation of primary productivity to the winter North Atlantic Oscillation index. Hence, we propose a sub-decadally resolved palaeo-North Atlantic Oscillation reconstruction based on an open-ocean record spanning the last 8000 years