Abrupt climate change in the late third millennium BCE and the demise of the Jiroft Civilization

The Jiroft Valley, southeastern Iran, was a West Asian hub for human settlement during the Chalcolithic and the Early Bronze Ages, ca. ۷۰۰۰-۲۲۰۰ BCE. The absence of detailed regional Holocene paleoclimate records, however, has obscured regional hydroclimate variability and its effects on Jiroft and adjacent region societal trajectories. Here, we present a high-resolution Holocene hydroclimatic record, including plant leaf-wax hydrogen isotope (δDwax), grain size, and elemental geochemistry, from a sediment core retrieved from the Konar Sandal peat bog (KSB), located near the major Chalcolithic and Early Bronze Age settlements along the Halil River within the Jiroft Valley. Our results suggest that the region was influenced by the Indian Summer Monsoon between ~۱۰,۵۰۰ and ~۶,۰۰۰ cal. yr BP when coarse sediment deposits indicate that intense monsoon rainfall conditioned Neolithic settlement at higher elevations. A regional reorganization of atmospheric circulation at ~ ۶۰۰۰ BP shifted precipitation to the Midlatitude Westerlies and promoted Chalcolithic settlement along the Halil River. The succeeding Early Bronze Age urban growth, beginning ca. ۳۰۰۰ BCE, made Konar Sandal and the Jiroft Valley the well-documented center for the Iranian plateau and West Asian urban settlement, craft. specialization, and inter-regional trade in exotic materials. The proxy isotope records from the Konar Sandal peat bog (sampling resolution ۳۲ years) now document a regional abrupt, two-stage, aridification event at ca. ۴۲۰۰ BP (۲۲۰۰ BCE) that extended until ۳.۹ ka BP (۱۹۰۰ BC), synchronous with the ۴.۲ ka BP megadrought documented from Spain to China, and elsewhere on the Iranian Plateau, that severely displaced the Midlatitude Westerlies, Indian Summer Monsoon and East Asian Summer Monsoon precipitation systems which sustained both rain-fed and irrigation cereal agriculture economies. The abandonment of Konar Sandal and the region-wide Jiroft Valley settlement collapse at the ۴.۲ ka BPmegadrought was coincident with the adjacent regional abandonments and socio-political collapses of Old Kingdom Egypt, Akkadian Mesopotamia, Harappan Indus Valley and Longshan Yangtze River societies.

کلیدواژه ها:

Climate change ، Bronze Age ، Jiroft Civilization ، ۴.۲ ka event