Sclerochemistry of archaeological mollusc shells from Inqitat (Dhofar, Oman): increasing seasonality and monsoon variability during the Late Holocene

Molluscs from archaeological contexts offer increasing potential for reconstructing past environments, climates, and human-environment interactions, particularly through the geochemical information archived in their shells. Here, we present the first sclerochemical analyses (δ18O, δ13C) conducted on Iron Age molluscs (9th century BCE – 1st century CE) from the Inqitat plateau in the Khor Rori Archaeological Park (Dhofar, Oman), with the aim of assessing changes in seasonal variability during the period of site occupation by the local population. Despite the abundance of archaeological shell assemblages, this region remains sclerochemically understudied due to its complex climatic and oceanographic setting. After selecting the best suitable shells and checking their preservation, we analysed ten specimens belonging to three species: the bivalves Anadara uropigimelana and Tivela stefaninii, and the gastropod Oliva bulbosa. Our results reveal an increase in seawater seasonality over the ∼1000-year interval examined, from ∼4 to ∼8 °C, values exceeding the modern seasonal range along the Dhofar coast, with the most pronounced variability occurring in the last occupation phase. This enhanced seasonality likely reflects a progressive intensification of the summer monsoon and a strengthened upwelling of Indian Ocean waters along the Dhofar coast. Increased monsoon activity, particularly in the latest phase investigated, may have produced longer rainy seasons and more frequent flooding, prompting adaptive responses in the management of meteoric waters and flood-prone areas within the Khor Rori area and beyond. Nevertheless, coastal geomorphology, marine environmental conditions, and upwelling dynamics likely made the coastal area of Dhofar rich in food resources, thereby sustaining its attractiveness to past human communities.