British-Irish Ice Sheet dynamics during the last glaciation and deglaciation and its influence on sedimentary processes in deep-water along the North Atlantic Passive Margin, North-West Ireland.

The last British-Irish ice sheet (BIIS) during its maximum extension covered Ireland and part of Britain. Recently the BIIS has been defined as partially marine-based and highly dynamic with several advances and retreats on the continental shelf. The sedimentary processes in deep-water have been strongly influenced by the presence of the ice sheet on the outer shelf. Recent studies along the North Atlantic margin show that mass transport deposit, turbidites, plumites and Ice Rafted Debris (IRD) are all characteristic of a growing ice shelf and ice at its maximum extent, whilst contouritic and hemipelagic deposition are more
common during interglacials. In this project, over 20 deep-sea sediment cores from the North Atlantic passive margin are investigated. The cores, retrieved from the Donegal Barra Fan, the Rockall Trough and along three transects on the Irish continental slope are used to reconstruct and chronologically constrain the variability of the BIIS in this specific deep-water sector. Microfossil and IRD contents will provide a reconstruction of BIIS dynamics; these proxies are strongly influenced by the location of the ice sheet margin. Moreover, the
investigation of the sortable silt fraction (10-63 μm) will supply information about paleocurrents and the effects of the waxing and waning BIIS on the oceanic circulation. Sedimentological analysis, x-radiographs, interpretation of physical properties (including shear strength, magnetic susceptibility, density and P-wave velocity), and microfossil and IRD counts provide information the depositional processes represented by the cores. Four different lithofacies, interpreted as contourites, turbidites, mass transport deposits and plumites, have been identified. The abundance of Neogloboquadrina pachyderma left coiling (NPS) and IRD concentration calculated at 20 cm sampling interval show the alternation of colder and warmer periods that can possibly be linked to a fluctuating BIIS margin. NPS and IRD contents show a direct relationship: high NPS abundance correspond to high IRD concentrations, suggesting an environment characterized by cold surface water temperature and floating icebergs. The NPS-IRD relationship will also be graphically tuned with the δ 18O from the Greenland Ice Core Record (GISP2) to set up a regional age model for the study area. Radiocarbon dates based on monospecific and mixed pick of foraminifera will provide a more robust chronology of the dynamism of the BIIS.