Climatic Control on Variations of Terrigenous Particle Provenance and Transport in the Scotia Sea (Southern Ocean): Evidence from Nd, Pb, and Sr Isotopes

Abstract

Terrigenous matter constitutes a considerable proportion of total sediment accumulation in Late Quaternary deposits of the Atlantic sector of the Southern Ocean. Input of lithogenic debris from land to sea, mainly to the shelf, is driven by glaciogenic supply from Antarctica, the river systems of South America, and wind transport through the southern westerlies. Deep and bottom water circulation most effectively control the distribution of terrigenous particles in the pelagic realm (Petschick et al., 1996). Variations of terrigenous sediment accumulation rates, grain size properties, and mineralogical composition, as inferred from sediment core studies, support the important role of ocean currents as major particle carriers throughout the late Quaternary (Diekmann et al., 1996; Diekmann and Kuhn, 1997). Clues exist for increased long-distance influxes of air-borne dust from Patagonia to both the Southern Ocean (Kumar et al., 1995) and Antarctica (Petit et al., 1990) during cold climatic stages. A Patagonian provenance of dust particles in ice cores from East Antarctica has been proposed from 143Nd/144Nd isotope data (Basile et al., 1997). This finding documents the importance of an atmospheric pathway during glacial periods, which has also been inferred from deep-sea sediments of the South Atlantic (Kumar et al., 1995). The authors postulated that the increase in primary productivity in the Southern Ocean during glacial periods has resulted from a relief of today's iron limitation by a greater supply of iron-rich aeolian dusts from dry areas of Patagonia. Nevertheless, their interpretation may be challenged because the aeolian dust component of the deep-sea sediments has not been isolated and analysed. Significant dust deposition in deep-sea sediments probably occurred in the southern Scotia Sea (sediment core location PS2319), indicated by down-core fluctuations of grain size parameters and magnetic susceptibility (Fig. 1). The latter may be correlated with dust records in Antarctic ice cores (Hofmann, in press). Maxima of magnetic susceptibility correspond to dust peaks in ice cores. Similar variations of magnetic susceptibility appear in sediment core PS2515 from the northern Scotia Sea (Fig. 1). However, little is known about provenance and proportions of primary aeolian dust components deposited directly on the sea floor. In order to investigate the hypothesis of an increased supply of aeolian dust into the Southern Ocean during glacial times, we have analysed the Nd, Pb, and Sr isotope compositions in bulk samples from sediment cores PS2515 and PS2319 of the Scotia Sea located at 53~ 45~ and 60~ 43~ respectively. Both sediment cores span the climate cycles of the last 140 ka, representing marine isotope stages 1 through 6 (Figs. 1). The isotope data of bulk sediments delineate systematic down-core variations in accordance with signatures of magnetic susceptibility (Fig. 1). In core intervals representing cold stages (marked by maxima of magnetic susceptibility) Nd and Sr isotopes exhibit a higher proportion of a mantle-