Changes in current patterns in the Fram Strait at the Pliocene/Pleistocene boundary

Seismic reflection profiles from the northwestern and central part of the Fram Strait show thick packages of drift type sediments mainly along the western Yermak Plateau flank, but also in the central, flat part of the Fram Strait. North of 80.5°N, a large-scale field of sediment waves along the Yermak Plateau rise separates a western, lower from an eastern, upper drift body. These drift bodies were deposited by bottom currents, most likely the northbound Yermak Branch of the West Spitsbergen Current, but we cannot rule out that the western drift body may also have been influenced by southbound bottom currents. A stratigraphic boundary is clearly visible within the drift bodies and even more pronounced within the sediment waves, separating a lower package of waves migrating upslope at low angle (∼5°) from an upper package with significantly increased wave crest migration (∼16.5°). This stratigraphic boundary could be tracked along the seismic network and corresponds to the lithostratigraphic boundary between units IA and IB at ODP Leg 151, Site 911 that was dated to 2.7 Ma. The increase in wave-crest migration angle indicates a shift towards higher sedimentation rates at 2.7 Ma, which corresponds to the intensification of the Northern Hemisphere glaciation with a major expansion of the Greenland, Scandinavian, northern Barents Sea and North American ice sheets. The subaerially exposed Barents shelf and the expansion of the northern Barents Sea ice sheet (as well as Svalbard) are likely sources for enhanced erosion and enhanced fluvial input along the pathway of the West Spitsbergen Current, resulting in higher sedimentation rates in the Fram Strait.