Seasonal Timing of Shellfish Collection and Paleoenvironmental Reconstruction from Archaeological Shells at Blombos Cave, South Africa

The Blombos Cave, located on the southern coast of South Africa, is a key site for understanding the behavioural evolution of modern humans during the Middle Stone Age. This study examines the seasonal timing of shellfish collection and the marine climate's seasonality near Blombos Cave through stable oxygen isotope analysis of the marine gastropod Turbo sarmaticus. By analyzing the δ¹⁸O values in sequential growth increments of T. sarmaticus shells from archaeological layers, we reconstruct past sea surface temperatures (SSTs) and infer patterns of human occupation over the period 100–70 ka. The δ¹⁸O data show distinct seasonal fluctuations in SSTs with an amplitude of approximately 4°C. These fluctuations are consistent with the present-day seasonal variation in sea surface temperatures at Blombos Cave, which is influenced by the interaction between the Agulhas Current (bringing warmer waters from the Indian Ocean) and the Benguela Current (bringing cooler waters from the Atlantic). The isotopic evidence also provides insight into the seasonality of human occupation at Blombos Cave. Preliminary findings suggest that early Homo sapiens primarily inhabited the site during the warmer seasons, likely focusing on marine resource exploitation at that time. Ongoing research will incorporate clumped isotope analysis to provide an independent temperature proxy, improving our estimates of past oxygen isotopic composition in coastal waters and enhancing reconstructions of SST and occupation seasonality.