Abstract
Today the desert margins of northwest India are dry and unable to support large populations, but were densely occupied by the populations of the Indus Civilization during the middle to late Holocene. The hydroclimatic conditions under which Indus urbanization took place, which was marked by a period of expanded settlement into the Thar Desert margins, remains poorly understood. We measured the isotopic values (δ18O and δD) of gypsum hydration water in paleolake Karsandi sediments in northern Rajasthan to infer past changes in lake hydrology, which is sensitive to changing amounts of precipitation and evaporation. Our record reveals that relatively wet conditions prevailed at the northern edge of Rajasthan from ~5.1 ± 0.2 ka BP, during the beginning of the agricultural-based Early Harappan phase of the Indus Civilization. Monsoon rainfall intensified further between 5.0 and 4.4 ka BP, during the period when Indus urban centres developed in the western Thar Desert margin and on the plains of Haryana to its north. Drier conditions set in sometime after 4.4 ka BP, and by ~3.9 ka BP an eastward shift of populations had occurred. Our findings provide evidence that climate change was associated with both the expansion and contraction of Indus urbanism along the desert margin in northwest India.
Highlights
Today the desert margins of northwest India are dry and unable to support large populations, but were densely occupied by the populations of the Indus Civilization during the middle to late Holocene
Paleolake Karsandi is located in the arid Nohar-Bhadra district in the Indian state of Rajasthan on the Thar Desert margin in northwest India (Fig. 1)
Paleolake Karsandi lies in the semi-arid zone on the NE Thar Desert margin
Summary
Today the desert margins of northwest India are dry and unable to support large populations, but were densely occupied by the populations of the Indus Civilization during the middle to late Holocene. Paleolake Karsandi is located in the arid Nohar-Bhadra district in the Indian state of Rajasthan on the Thar Desert margin in northwest India (Fig. 1). We present the mid-Holocene hydroclimate history from the edge of the northern Thar Desert using the isotopic composition (δ18O and δD) of gypsum hydration water (GHW)[21] deposited in paleolake Karsandi in northwest India (Fig. 1). The paleolakes of the Thar Desert that have been previously investigated lie in different climatic zones, stretching from the arid zone that receives 100–250 mm/year rainfall in the west to regions of increasing rainfall including the semi-arid (250–500 mm) and semi-humid (500–600 mm) zones towards the east[19,20] (Fig. 1) The rainfall in this broad region is derived primarily from the Indian summer monsoon. We measured the stable isotopes of gypsum hydration water (GHW) in samples taken every 2 cm along the sediment section and the chronology was determined using radiocarbon and OSL dates (see Methods for details) (Figs 2, S2 and Table 1)
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