Sediment delivery and depositional patterns off Adelie Land (East Antarctica) in relation to late Quaternary climatic cycles

This study focuses on the understanding of depositional patterns over late Quaternary glacial/interglacial cycles and of the influence of diagenesis on geochemical sedimentary records from the continental margin off Adelie Land (East Antarctica). We provide a complete analysis of the 30-m-long sediment core MD03-2603, collected on a deep-sea sediment mound deposit. The LR04 benthic oxygen isotope stack vs. down-core records of Ba/Al and Ba/Ti atomic ratios, reflectance data and micropaleontological evidence, allow to determine a detailed chronology back to similar to 490 ka BP. Long-lived Uranium and Thorium (U-238, U-234, Th-232, and Th-230) provide an assessment of lateral vs. vertical sediment advection, by constraining the sediment focusing factor (Phi). Phi is high in most glacial intervals, when mostly detrital material was transported down-slope and focused to the core area. Interglacials display highs in Ba/Al and Ba/Ti, coupled to low Phi values, related to stronger contour current flow. Biogenic fractions are more abundant during interglacials and more diluted by detrital fractions during glacials. The diatom assemblage is dominated by the open-ocean species Fragilariopsis kerguelensis, but glacial intervals display an increase of sea-ice related and coastal species. The integrated approach (high-resolution record of major and minor elements, U-auth, delta N-15, N-org, delta C-13, and C-org) provides key insights into how redox conditions affect glacial/interglacial sedimentation processes. Our evidence shows that diagenetic effects, due to development of reducing conditions and consequent higher preservation of organic matter, may overprint the paleoclimatic significance of some proxies involved into a sequence of diagenetic remineralization pathways. Comparison of the marine record to ice-core data (EPICA Dome C-EDC) allows to extend the information to the whole East Antarctic margin. Sediment proxies of increased burial of biogenic material, or increased preservation of organic matter, are linked to climatic amelioration on the continent. Highs in EDC dust flux correlate with high Mn/Al and Mo/Al ratios within the sediment record, confirming that establishment of colder conditions on the continent triggered changes in sedimentation rates at the glacial/interglacial transition, which in turn affected the development of reducing redox fronts within the sediment. (C) 2011 Elsevier B.V. All rights reserved.