Century- to milliennial-scale sedimentological-geochemical records of glacial-Holocene sediment variations from the Barra Fan (NE Atlantic).

The Barra Fan, located at the continental margin of NW Scotland, offers a unique possibility to retrieve records of exceptional high resolution to obtain climate records on a century-millennial timescale. We used a sedimentological-geochemical approach to examine the sediment variations that reflect the palaeoceanography and climate history of the area. Inorganic chemistry combined with micropalaeontology reveals trends and changes in NE Atlantic palaeoceanography and northwest European climate at the sub-Milankovitch frequency. This study builds on results from two British Geological Survey cores and one giant piston core (Core 57/-11/59, Core 56/-10136 and Images Core MD95-2006) that were obtained during the NEAPACC (NE Atlantic Palaeoceanography, Special Topic NERC) phase. Geochemical records of lithogenic input fluctuate rapidly and their patterns parallel sea surface temperature and particle size records. The cold periods are characterized by increased clay input compared to the warm periods. The Younger Dryas period and other prominent periods such as the equivalent of Heinrich Event 1, show extremely expanded sections up to several metres in thickness. Enhancement of accumulation rates in the glacial section is due to the influence of downslope sedimentation, meltwater deposition; and large-scale currents redistributing the sediment along the upper slope. The radiochemical tracer (excess Th-230) shows that major shifts in terrigenous sediment supply were extremely rapid over the last 15 ka. The shifts in terrigenous supply occurred over time-spans of less than a century. Century-scale events of lithogenic input can be visually correlated to other North Atlantic climate records such as the GISP2 Greenland ice core delta(18)O record for the last 15 ka, although the resolution of radiocarbon dating of these events in the sediments is not sufficiently precise to verify that the visual correlations are correct. The particle flux and biogenic records show sawtooth-shaped cycles opposite to the Dansgaard-Oeschger cycles.