Early Pleistocene British-Irish ice rafting: Was the onset of Northern Hemisphere glaciation more widespread than previously assumed?

The late Pliocene - early Pleistocene onset and intensification of Northern Hemisphere glaciation marks an important threshold in Earth's climate system. Unravelling the extent and dynamics of early ice-sheet development is crucial to our understanding of the processes driving Quaternary glaciations and hence, affecting global climate and its variability[1]. In the North Atlantic Ocean, ice-rafted detritus (IRD) layers attest to the development of marine-terminating ice sheets, discharging sediment-loaded icebergs into the ocean. So far, Early-Pleistocene IRD deposition has been predominantly linked to the intensified glaciation of high-latitudinal regions surrounding the North Atlantic (Canada, Greenland, Iceland and Scandinavia), while the extent and role of early ice build-up in more temperate mid-latitudinal regions is still poorly understood. Here we present results from a multiproxy provenance analysis of the unique, Pleistocene IRD record that has been preserved in the Challenger Mound sequence (IODP Expedition 307; Irish NE Atlantic continental margin). This archive has, recently, revealed the first evidence supporting substantial and repeated ice build-up on the British-Irish Isles (57° - 52°N) since the earliest Pleistocene (ca 2.6 Ma) [2]. Nd-Sr isotopic analysis of multiple IRD intervals throughout the sequence show a dominant sediment input from the adjacent British-Irish Isles, even for the early Pleistocene IRD deposits. Furthermore, the Pb isotopic composition of detrital, and apparently ice-rafted, K-feldspar grains shows excellent correspondence to a NW Irish Mainland source, definitively ruling out more far-travelled, northern sources for these grains. The long-term development of an ice sheet on NW Ireland, even in the early stages of Northern Hemisphere glacial expansion, is evidenced and discussed in this study. Overall, widespread circum-Atlantic ice-sheet development at more temperate, mid-latitudes appears to be a persistent feature of the Pleistocene climate system and, hence, should be accounted for. References [1] e.g. Raymo, M.E., Huybers, P., 2008. Unlocking the mysteries of the ice ages. Nature 451, 284-285. [2] Thierens, M., Pirlet, H., Colin, C., et al. 2011. Ice-rafting from the British-Irish ice sheet since the earliest Pleistocene (2.6 million years ago): implications for long-term mid-latitudinal ice-sheet growth in the North Atlantic region. Quaternary Science Reviews, 10.1016/j.quascirev.2010.12.020.