Mid-Holocene hydroclimatic optimum recorded in a stalagmite from Shalaii Cave, northern Iraq

In Mesopotamia, climate is regarded as an important contributing factor to major socio-cultural transformations. However, the scarcity of Holocene paleoclimate reconstructions in this region impedes analysis of potential climate-human interactions. Furthermore, current hydroclimatic scenarios for Mesopotamia are predominantly based on oxygen isotope (δ18O) proxy records from the eastern Mediterranean, whereas the paleoclimatic significance of δ18O remains debated. Here, we present a Holocene stalagmite multi-proxy record from Shalaii Cave in northern Mesopotamia. Based on stable isotope, trace element and strontium isotope measurements, our new Shalaii Cave record suggests that long-term changes in δ18O were influenced by multiple factors, such as δ18O changes of the source of moisture, amount and seasonality of rainfall. The Shalaii Cave trace element and strontium isotope records indicate rather dry conditions during the early Holocene and wettest conditions during the mid-Holocene. This mid-Holocene hydroclimate optimum at Shalaii Cave is in good agreement with other non-isotopic records from SW-Asia, such as pollen evidence for concurrent rapid forest expansion and peaking lake levels. The mid-Holocene hydroclimatic optimum is most likely related to an increase in the amount of spring precipitation related to the remote influence of the Indian summer monsoon (desert-monsoon mechanism) and spring insolation-driven weakening of the Arabian anticyclone. In particular the latter northward migration of the Arabian anticyclone in spring promoted a longer spring rainfall season.