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, 8 (1), 4225

Intensified Summer Monsoon and the Urbanization of Indus Civilization in Northwest India

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Intensified Summer Monsoon and the Urbanization of Indus Civilization in Northwest India

Yama Dixit et al. Sci Rep.

Erratum in

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.

Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Map of NW India showing the location of paleolake Karsandi (white triangle) and other paleolake records (black triangles). Orange circles denote the Indus settlements in northwest India and the red dots are the urban Indus centres. White lines are isohyets (mm) between 1900 and 2008. Inset shows location of the main map in relation to the limits of the Indian subcontinent. Rainfall isohyets were extracted from the University of Delaware monthly global gridded high resolution station (land) data set of precipitation from 1900–2008 (v2.01). Data available for free from: http://www.esrl.noaa.gov/psd/data/gridded/data.UDel_AirT_Precip.html UDel_AirT_Precip data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA, from their Web site at https://www.esrl.noaa.gov/psd/. NASA Blue Marble: Next Generation satellite imagery data freely available at NASA's Earth Observatory (NASA Goddard Space Flight Center http://earthobservatory.nasa.gov/Features/BlueMarble/). Maps composed using Esri ArcGIS 10.2.0.3348.
Figure 2
Figure 2
Lithostratigraphy of the sediment section and δD, δ18O, d-excess of paleolake Karsandi water obtained after correction of GHW isotopes for fractionation factors. Detrital content (% detrital) is shown in brown. Black vertical line denotes the mean isotopes across the section. The calibrated radiocarbon ages (ka BP) are shown in black with red arrows pointing to their respective depths. OSL dates and depth of sand collection for dating are shown in blue. Grey bands denote the nearly pure gypsum deposits indicating periods of relatively lower rainfall. Roman numerals denote lithologic units.
Figure 3
Figure 3
δ18O and δD of gypsum hydration water as measured from Karsandi paleolake (open blue diamonds), and predicted paleo-lake water values for Karsandi (closed blue diamonds) after correction for fractionation factors. The local meteoric water line (LMWL) is based on GNIP data from Delhi. The solid blue line represents the evaporative line estimated from the corrected Karsandi data. Surface water samples (red filled circles) from nearby Riwasa village, are plotted for comparison.
Figure 4
Figure 4
Correlation of climatic variability recorded in the lithostratigraphy, δD (orange), δ18O (blue), of paleolake Karsandi water and ostracod abundance with Indus cultural changes. The calibrated radiocarbon ages (ka BP) are shown in black with red arrows pointing to their respective depths. OSL dates and depth of sand collection for dating are shown in blue. Grey bands denote the nearly pure gypsum deposits indicating periods of relatively lower rainfall and blue band denotes wetter periods. Roman numerals denote lithologic units. The Early phase of the Indus Civilization developed during increased monsoon intensity as indicated by lower GHW isotopes and high shell abundance after ~5.1 ± 0.2 ka BP. The Mature Harappan phase and peak in urbanism coincides with the lowest GHW isotopes and highest shell abundance between ~5.0 and ~4.4 ka BP. Note that the subsequent decline in urbanism and disappearance of Post-urban Harappan sites in this region is coincident with drying conditions suggested by reappearance of massive gypsum with increasing GHW isotopes and complete absence of ostracod and gastropod shells.
Figure 5
Figure 5
Location of (A) Urban Harappan sites at ∼4.6–4.5 ka BP and (B) Post- Urban Harappan after ~4.1–4.0 ka BP sites in NW India as denoted by the orange dots in each case. Note that the urban-Harappan sites are located on the margin of the Thar Desert and the post-urban Harappan sites are clustered to the right of paleolake Karsandi on the Indo-Gangetic plains. The location of Karsandi shown by the white triangle and other reported paleolakes in black triangles. Rainfall isohyets were extracted from the University of Delaware monthly global gridded high-resolution station (land) data set of precipitation from 1900–2008 (v2.01). Data available for free from: http://www.esrl.noaa.gov/psd/data/gridded/data.UDel_AirT_Precip.html. UDel_AirT_Precip data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA, from their Web site at https://www.esrl.noaa.gov/psd/. NASA Blue Marble: Next Generation satellite imagery data freely available at NASA's Earth Observatory (NASA Goddard Space Flight Center http://earthobservatory.nasa.gov/Features/BlueMarble/). Maps composed using Esri ArcGIS 10.2.0.3348.

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