Outflow of the Western Boundary Undercurrent vs 230Th-Excesses in the Late Quaternary Sediments of the NW Atlantic Marginal Basins

Abstract

Late Quaternary sedimentary sequences collected during two campaigns of the CSS Hudson (90-013 and 91-045) in the North Atlantic marginal basins (30-60~ 50-60~ were analysed for their Th and U isotope contents. They include 21 box cores selected along three transects: i) in the Labrador Sea, from Hamilton Inlet on the Labrador coast, to Cape Farewell, south Greenland, ii) in the Irminger and western Iceland basins, along the 60th parallel, and iii) along the northern edge of the Charlie Gibbs Fracture zone. Five long cores spanning at least the Last Glacial Maximum (LGM)-Present, were also used. They were raised respectively, from the Greenland lower slope (PC-012) and upper rise (PC-013), the Orphan Knoll area (PC-094) and the Iceland basin (P-072; TWC-074). Sedimentological, geochemical, and isotopic studies provided independent chronologies. During the Holocene, very low Holocene sedimentological rates (2 to 5 cm/ka) are observed on the lower slope, i.e. along the high velocity core of the Western Boundary Undercurrent (WBUC) as well as in central parts of the major gyres. They contrast with the much higher rates observed below, on the rise (~> 20 cm/ka) (HillaireMarcel et al. , 1994). A reverse situation prevailed during the Last Glacial Maximum (LGM), when a weaker WBUC resulted in higher sedimentation rates