Societal Responses to Holocene Climate Change and Variability in the Eastern Fertile Crescent: A Speleothem Investigation

The Eastern Fertile Crescent (EFC), an area encompassing parts of Iraq, Syria, Turkey and Iran, was an important centre for numerous major societal transformations during the Holocene (11,650 yr BP - Present). Climate change is often cited as an important mechanism that influenced these developments. However, there is an absence of palaeoclimate data in the region with the temporal resolution and chronological precision needed to help support theories regarding human-environmental interactions. Moreover, there are significant discrepancies in the way existing environmental records from Southwest Asia are currently interpreted. Here I address these outstanding problems by producing the first high-resolution palaeoclimate record from the EFC to cover most of the Holocene (c.10,560 yr BP - Present) by geochemically examining a stalagmite (SHC-03) from Iraqi Kurdistan. Stalagmite trace element (Mg/Ca & Sr/Ca) and 87Sr/86Sr data reveal long-term changes in moisture availability, while δ18O, δ13C and Mg/Ca data provide collective evidence for shorter-term climate variability. The stalagmite record indicates climatic conditions between c.10,560 - 7,000 yr BP were relatively dry, while conditions between c.7,000 yr BP - Present were wetter and more stable, consistent with existing pollen studies from the EFC. These long-term hydrological changes were indirectly associated with the evolution of the Indian Ocean Monsoon over the course of the Holocene. Superimposed on these trends, were quasi-cyclical c.1500 yr oscillations between wetter and drier conditions, as well as more abrupt multi-decadal events. The new multi-proxy record reveals that long-term changes in the δ18O composition of the stalagmite were strongly influenced by δ18O changes of the source of moisture, rather than rainfall amount, limiting its effectiveness as a palaeoclimate proxy in the EFC. The stalagmite record allowed the testing of existing hypotheses concerning human-environmental relationships by focusing on two important archaeological case studies. Firstly, I suggest the climate of the early Holocene (c.11,650 - 9,000 yr BP) may not have been as optimum as some previous studies have suggested were necessary for the emergence of Neolithic societies. Secondly, I argue moisture availability was an important influence on the ability to sustain and develop larger, urban settlements in Northern Mesopotamia during the middle Holocene (c.6,350 - 4,200 yr BP).