Provenance and transport of terrigenous sediment in the South Atlantic Ocean and their relations to glacial and interglacial cycles: Nd and Sr isotopic evidence

Sr and Nd isotopic compositions of Late Quaternary surface sediment and sed iment cores from the south Atlantic and southeast Pacific sectors of the So uthern Ocean are used to constrain the provenance and transport mechanisms of their terrigenous component. We report isotopic and mineralogical data f or core samples from three localities, the Mid-Atlantic Ridge at 41 degrees S and the northern and southern Scotia Sea. In addition, data for surface s ediment samples from the south Atlantic and southeast Pacific sectors of th e Southern Ocean are presented. The variations of Sr and Nd isotopic compos itions of the bulk sediment samples in all cores were correlated with the m agnetic susceptibility of the sediment and with the inferred glacial-interg lacial stages. The isotopic data indicate that, during glacial periods, sed iment was delivered from continental crust with a shorter residence time th an that supplying material during interglacial periods. At the core site ne ar the Mid-Atlantic Ridge, Nd isotopic, combined with mineralogical evidenc e indicates interglacial period deposition of a relatively high amount of k aolinite and silt with low epsilon (Nd) values < -8. The material was proba bly supplied by North Atlantic Deep Water from low latitudes. For glacial p eriods, a high contribution of silt and clay with <epsilon>(Nd) > -4.5, pro bably derived from southern South America, was indicated. The glacial-inter glacial shift in sources may be due to either a decreasing influence of Nor th Atlantic Deep Water during glacial times or by a larger contribution of glaciogenic detritus from southern South America. At the core site in the n orthern Scotia Sea, sediment of interglacial periods is dominated by smecti te with epsilon (Nd) < - 6 and silt with <epsilon>(Nd) > -4. We suggest tha t smectite was derived from the Falkland shelf and silt was derived from th e Argentinian shelf. During glacial periods, the Argentinian shelf was an i mportant source for silt and chlorite with epsilon (Nd) > -4. The contribut ion from the Falkland shelf seems to have remained similar during glacial a nd interglacial periods. Hydrographic transport by bottom currents and turb idites could account for the high glacial detrital flux. An evaluation of t he significance of an aeolian contribution to deep sea sediment suggests th at it plays only a minor role. In the southern Scotia Sea, the Antarctic Pe ninsula is considered an important source for young material with epsilon ( Nd) > -4, in particular during glacial periods. During interglacial periods , sediment supply from the Antarctic Peninsula was lower than during glacia l times, resulting in a relatively high contribution of old material (epsil on (Nd) < -8) from East Antarctica. Deep water currents and icebergs could account for the transport of the old component to the southern Scotia Sea. The accumulation rates of material from the various source regions for glac ial times are in agreement with an increase in the strength of the Antarcti c Circumpolar Current. The production rate and the circulation pattern of b ottom water in the Weddell Sea appear to have remained similar over most of the last 150 kyr. Copyright (C) 2000 Elsevier Science Ltd.