Is the 4.2-ka event visible in speleothem records from southwest Asia?

The ‘4.2 ka event’ (~4200–3900 yr BP) is now a globally-recognised Holocene chronostratigraphic marker, delineating the boundary of the middle-to-late Holocene¹. First identified as a drought signal corresponding to ~2200 BCE in the Tell Leilan stratigraphy (Syria), correspondence between this signal and the collapse of the Akkadian empire was interpreted as sign of a causal association, and one of the first explicit links made between a major climate shift and civilizational transformation². Several studies have more recently presented evidence suggesting this drought was in fact a globally-pervasive phenomenon, linked to the decline of the ancient Egyptians, the de-urbanization of the Harappans, and the demise of the Neolithic Culture of China^3,4,5. However, no clear consensus exists on whether the 4.2-kyr event was truly global in scale, nor whether the event was consistently marked by aridity^6,7. But perhaps most critically, it is unclear whether a clear drought signal at 4.2-ka² occurs consistently in paleoclimate records across southwest Asia⁸. Without a clear perspective on if, and how, regional climate signals relate to one another across this interval, it is difficult to ascertain whether changes occurring at ~4.2 ka are mechanistically distinguishable from internal noise in a highly sensitive, and complex climate system⁹. To address this uncertainty, we present a first look at new stable isotope, trace element, and fluid inclusion measurements from speleothems grown in Kuna Ba and Shalaii Caves (~400 km SE of Tell Leilan) in Iraqi-Kurdistan. By combining these results with published geochemical data from paleoclimate archives across southwest Asia, we will assess whether the hydro climatic changes recorded in these archives capture a distinct anomaly corresponding to the 4.2-ka event.  Hence, providing a chronologically-robust framework with which to assess the regional-scale timing, expression, and coherence of climate variability before, during, and after the proposed 4.2-ka event.

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¹Walker et al. (2018) Episodes 41(4): 213-223 ; ²Weiss et al. (1993) Science 261 (5124): 995-1003 ; ³Weiss & Bradley (2001) Science 291(5004): 609-610 ; ⁴Carolin et al. (2019) PNAS USA 116(1): 67-72 ; ⁵Zhang et al. (2021) Science Advances 7(48): 1-9 ; ⁶McKay et al. (2024) Nature Communications 15: 6555 ; ⁷Nan et al. (2025) Earth-Science Reviews 265: 105128 ; ⁸Finné et al. (2011) Journal of Archaeological Science 38: 3153-3173 ; ⁹Zittis et al. (2022) Reviews of Geophysics 60: e2021RG000762.