Recent deep-water sedimentation, trace metal and radioisotope geochemistry across the Southern Ocean and Northern Weddell Sea, Antarctica

A wide variety of deep-water depositional environments were examined across 12 sampling stations in the Southern Ocean and northern Weddell Sea, Antarctica in order to provide a depositional context for the benthic biodiversity studies of ANDEEP (Antarctic Benthic Deep-Sea Biodiversity: colonisation history and recent community patterns). Here we present a diverse dataset comprising sub-bottom profiles, seabed photographs, sediment profile images, and box and multicore samples in order to investigate the recent depositional environments across the region. The sediments were investigated using texture, structure, trace metal (Mn, Fe, U, Mo, Ba, and Pb), stable (206Pb/207Pb) and radionuclide (excess 210Pb) isotopes. The sediments of the Agulhas Basin are interpreted as siliceous pelagites, the product of enhanced surface productivity. The eastern Weddell continental rise is characterised by diverse depositional environments with hemipelagic, turbiditic and contouritic sedimentation. In contrast, the northern Weddell Abyssal Plain is dominated by hemipelagites with fine-grained turbidites. A single sampling station from the central Powell Basin contained hemipelagites and a fine-grained turbidite. A core from the central Bransfield Strait recovered hemipelagites with a silt turbidite. The seabed photographs display a seabed dominated by biogenic mud balls formed by cirratulid polychaetes. Trace metal, Pb-isotope, and excess 210Pb data all reveal the central Bransfield Strait to be a region of enhanced productivity with a mass accumulation rate of 0.073 g/cm2. Two stations in the Bellingshausen Sea recovered hemipelagites and turbidites. Mn, Fe and Mo data suggest a degradation of organic matter in the sediments leading to redox cycling.