Early Holocene palaeoseasonality inferred from the stable isotope composition of Unio shells from Çatalhöyük, Turkey

Seasonal δ13C and δ18O data are presented from 14 Unio sub-fossil shells unearthed at the archaeological site of Çatalhöyük in central Turkey, spanning the occupation period ca. 9150–8000 cal years BP. The shells likely lived in the small lakes/wetlands around the site before being gathered and taken to Çatalhöyük. Wet-dry seasonal cycles are clearly apparent in the δ18Oshell profiles with low winter values reflecting winter precipitation and high δ18O in the summer resulting from evaporation. The most striking trend in the δ18O data is the drop in maximum summer δ18O ca. 8300 years BP, which we infer as indicating lower summer evaporation and hence a reduction in seasonality. Previous palaeoclimate records from the area have suggested cooler and more arid conditions, with reduced precipitation, around this time. While the drop in summer δ18O values could be due to reduced summer temperatures reducing summer evaporation, but there was little change in winter δ18O, perhaps suggesting winter growth cessation or reduced influence of winter climate change on δ18O. This shift in seasonal climate could be linked to solar-forced climate change beginning ca. 8600 years BP, and enhanced by the regional expression of the 8·2k event. Changing water balance over the occupation period is likely an important contributory factor behind observed cultural changes at Çatalhöyük in the Late Neolithic/Early Chalcolithic period. Our results might be considered to support the fission-fusion farming hypothesis as we provide additional evidence for wet winter/early spring conditions during the Early Holocene which likely caused flooding of the Çarşamba Fan. The changing water balance after ca. 8300 years BP (i.e. reduced seasonality and potentially reduced local summer evaporation) is also coincidental with the proposed end of this farming system due to multi-decadal drought.