GLACIAL-INTERGLACIAL VARIABILITY IN SEDIMENT PROVENANCE OF NORTH ATLANTIC MARINE SEDIMENTS CARRIED BY THE WESTERN BOUNDARY UNDERCURRENT

The Nd, and Pb isotopic composition of detrital phases is a useful tool for constraining the provenance of marine sediments, thus enabling identification of changes in sediment supply and pathways of deep oceanic currents. Previously published studies of detrital Nd and Pb isotopic records from Eirik Drift reconstructed the evolution of the Western Boundary Undercurrent (WBUC) in the North Atlantic Ocean since the last glaciation (~26 ka). This study expands these records by incorporating data from six different Marine Isotope Stages (MIS) over the last 140 ka to better understand the long-term, climate-driven variability of the geologic and oceanographic processes influencing sedimentation on Erik Drift. We analyzed the Nd and Pb isotopic compositions of four-grain size fractions (<3 μm, 3-10 μm, 10-32 μm, and 32-63 μm) of detrital sediment sampled from IODP sites U1305 (3459 mwd) and U1306 (2272 mwd). The Nd isotopic data suggest the supply and delivery of the sediments at site U1305 are influenced by three distinct climatic regimes: 1) a glacial regime characterized by unradiogenic values for all grain size fractions, suggesting a predominance of local Greenlandic sources, 2) an early interglacial regime characterized by a larger range of isotopic values with more radiogenic finer particles indicating a relative increase in the deposition of distal materials including Icelandic sources carried by the WBUC, and 3) a later interglacial regime with a moderate isotopic spread created by a large shift towards more radiogenic values in the coarser fractions, suggesting a restricted supply of local Greenlandic sediments. Similar distribution patterns are present in the Pb isotopic data; however, a greater distribution of isotopes between fractions is likely associated with mineralogical sorting. At the shallower site U1306, the contrast between distinct climatic phases is manifested as a general shift towards more radiogenic values from the glacial to the interglacial interval without significative changes in the isotopic sorting by grain size, suggesting that changes in the position and strength of the WBUC have unique effects on sediment delivery to these sites.