Late Quaternary variability of ocean circulation in the southeastern South Atlantic inferred from the terrigenous sediment record of a drift deposit in the southern Cape Basin (ODP Site 1089)

Abstract

During Leg 177 of the Ocean Drilling Program, an expanded sequence of Pliocene to Holocene calcareous muds was recovered at Site 1089 on a drift deposit in the southern Cape Basin (SE South Atlantic). The reconstruction of detrital sources and modes of sediment transport gives insight into the operational modes of regional current systems in response to climate variability over the last 590 kyr, as inferred from sedimentological and mineralogical parameters of the terrigenous sediment fraction. Terrigenous sediments mainly originate from African sources with minor contributions from distant southern sources (South America and Antarctica) and are supplied by circumpolar water masses, North Atlantic Deep Water (NADW), and surface currents of the Agulhas Current. Changes in clay mineralogy as tracers of deep and shallow ocean circulation, best displayed by variations in quartz/feldspar ratios and kaolinite/chlorite ratios of clay, reflect both the northward displacement of NADW injection into the Antarctic Circumpolar Current and a weakening of Agulhas Current leakage from the Indian Ocean around South Africa to the South Atlantic during glacial stages, sub-stages, and stadials. Modifications of these regional current patterns are consistent with perturbations in global conveyor circulation and climate variability on Milankovitch and subMilankovitch time scales. Elevated mass-accumulation rates of terrigenous matter generally document high particle fluxes and focusing effects by bottom-current action throughout the late Quaternary. Current sorting and coarsening of terrigenous mud, independently of its source signals, prevails during interglacial periods and is linked to a stronger flow of Antarctic Bottom Water and the invigoration of deep contour currents in response to long-term changes (100-kyr cyclicity) in Antarctic ice-sheet dynamics, high-amplitude fluctuations in global sea level, and increased bottomwater formation. ß

Terrigenous Sediment Supply in the Polar to Temperate South Atlantic: Land-Ocean Links of Environmental Changes during the Late Quaternary

“…Time-series of IRD flux are expressed as clast abundances per area and time unit [# cm-2 kyr-I ] , by integrating counted IRD abundances at equal time increments of 1 kyr. The proportions of non-carbonate silt and clay (referred to as terrigenous mud) were determined by grain-size separation in settling tubes, after sieving the bulk samples through a 63-llm mesh for separation of the sand fraction and dissolution of carbonate with 10-% acetic acid (Brehrne 1992;Kuhn and Diekmann 2002a, b). Silt grain-size analyses were conducted on sediment cores from the southern Cape Basin (Site 1 089/PS2821) and the northwestern Weddell Sea (PS2515).…”

“…The non-carbonate silt fraction was dispersed in sodium-polyphosphate solution and measured with a 'Micromeritics SediGraph 5000E' to determine the grain-size distribution in lilO-Phi steps and hence the proportion of sortable silt (particle sizes 63-10 Ilm) in the mud fraction (McCave et al 1995). The bias of the terrigenous grain-size signal caused by biosiliceous particles in the non-carbonate mud fraction is negligible, because of relatively low opal concentrations that range between 3% and 7% in sediment core PS1575 (Bonn et al 1998) and are ~15 % in the record of Site 1989IPS2821 (Kuhn and Diekmann 2002a, b). Moreover, no correlation exists between opal concentrations and grain-size variability for the latter record with the slightly elevated opal concentrations (Kuhn and Diekmann 2002b).…”

“…Sediment accumulation is focused and restricted to current-sheltered depressions, like at core locations PS2319 and PS2515. High accumulation rates also ~har acterize drift deposits in the southern Cape Basin (pS28211Site 1089), which are influenced by bottom contour currents (Kuhn and Diekmann 2002a). MARTs in the remote eastern ACC region are variable and mostly low «1.0 g cm-2 kyr-1), with slightly increased values at core location PS2498 (>2.0 g cm-2 kyr-l) on the Mid-Atlantic Ridge.…”

Opal burial in the equatorial Atlantic Ocean over the last 30 ka: Implications for glacial‐interglacial changes in the ocean silicon cycle

“…[49] Several studies of the Southeast Atlantic have concluded that the supply of Agulhas water to the Atlantic was reduced substantially during glacial times [Flores et al, 1999;Kuhn and Diekmann, 2002;Peeters et al, 2004;Franzese et al, 2006]. Furthermore, as the Agulhas system and the Drake Passage are the two primary avenues for return flow to the North Atlantic [Gordon et al, 1992], the glacial reduction in supply of Agulhas water may have been compensated for by increased supply via the Drake Passage.…”

Late Oligocene obliquity-paced contourite sedimentation in the Wilkes Land margin of East Antarctica: implications for paleoceanographic and ice sheet configurations

“…In addition to the elemental analyses of the XRF-scanned data, we use the detrital Al/Ti ratio in discrete XRF bulk sediment samples to reflect changes in terrigenous provenance (Kuhn and Diekmann, 2002;Scher et al, 2015). Al/Ti ratio varies between 17-21, with the highest values found within F1 and the lowest in F2 (Fig.…”