Shifting shorelines and hydroclimate changes in southern South Africa: Insights from sediment provenance during the Middle Stone Age (90-50 ka)

Abstract

Southern South Africa houses some key archaeological sites, which document the behavioural and technological development of Homo sapiens . During Marine Isotope Stages (MIS) 5 and 4, this region experienced marked climate variability, particularly in temperature and precipitation. Therefore, this study advances on the region's past climate reconstructions to provide an environmental context for the archaeological findings. Radiogenic strontium (Sr) and neodymium (Nd) isotope, grain size and X-ray fluorescence (XRF) core scanning records from marine sediment core MD20-3591, located offshore the Palaeo-Agulhas Plain (PAP), southern Africa, document changes in sediment provenance between 90 and 50 ka, an interval within the Middle Stone Age period (MSA; 300 - 40 ka). The Nd isotope record reflects a combination of alternating riverine material from South African sources and that transported southwards by the Agulhas Current. Shifts in river discharge from the northern Limpopo to the southern South African endmembers likely resulted from local insolation changes, which caused latitudinal shifts in the Intertropical Convergence Zone (ITCZ). The Sr isotopes highlight additional contributions from southern South African sources on shorter timescales, reflecting local hydroclimate sensitivity. The XRF and Nd isotope record, together with climate model results, indicate an increased sediment contribution from the Limpopo River catchment during Southern Hemisphere (SH) summer insolation maxima, likely driven by southward shifts in the subtropical rain belts leading to increased runoff from this basin. Conversely, during SH summer insolation minima, sediment supply from the Limpopo River decreases. During MIS 4 (71-57 ka), a consistent pattern emerges of greater local South African sediment input at marine sediment core site MD20-3591, with coarser sediments likely being sourced from Southern Cape rivers due to a reduced distance from the palaeoshoreline at the sea-level low-stand, and enhanced sediment availability from the exposed continental shelf. This study is of interest for the regional anthropological record, as pulses of technological innovation may have been linked to fluctuations in hydroclimate and in exposure of the PAP, including the elaboration of complex toolkits and subsistence strategies by Homo sapiens .