The antiquity and decline of the Bronze Age Harappan civilization in the Indus-Ghaggar-Hakra river valleys is an enigma in archaeology. Weakening of the monsoon after ~5 ka BP (and droughts throughout the Asia) is a strong contender for the Harappan collapse, although controversy exists about the synchroneity of climate change and collapse of civilization. One reason for this controversy is lack of a continuous record of cultural levels and palaeomonsoon change in close proximity. We report a high resolution oxygen isotope (δ18O) record of animal teeth-bone phosphates from an archaeological trench itself at Bhirrana, NW India, preserving all cultural levels of this civilization. Bhirrana was part of a high concentration of settlements along the dried up mythical Vedic river valley ‘Saraswati’, an extension of Ghaggar river in the Thar desert. Isotope and archaeological data suggest that the pre-Harappans started inhabiting this area along the mighty Ghaggar-Hakra rivers fed by intensified monsoon from 9 to 7 ka BP. The monsoon monotonically declined after 7 ka yet the settlements continued to survive from early to mature Harappan time. Our study suggests that other cause like change in subsistence strategy by shifting crop patterns rather than climate change was responsible for Harappan collapse.

Radiocarbon dating of archaeological carbonates from seven cultural stages of Dholavira, Great Rann of Kachchh (GRK), the largest excavated Harappan settlement in India, suggests the beginning of occupation at ~5500 years BP (pre‐Harappan), and continuation until ~3800 years BP (early part of the Late Harappan period). The settlement rapidly expanded under favourable monsoonal climate conditions when architectural elements such as the Citadel, Bailey, Lower and Middle Town were added between the Early and mid‐Mature Harappan periods. Abundant local mangroves grew around the GRK sustaining prolific populations of the edible gastropod Terebralia palustris. Oxygen isotope (δ18O) sclerochronology of Early Harappan gastropod shell suggests seasonal mixing of some depleted (δ18O ~ −12‰) river water in summer/monsoon months (through ancient Saraswati and/or Indus distributary channels) with seawater that periodically inundated the GRK. Evaporation from this semi‐enclosed water body during the non‐monsoon months enriched the δ18O of water/shell carbonates. The humid fluvial landscape possibly changed due to a catastrophic drought driving the final collapse of the settlement of Dholavira exactly at the onset of the Meghalayan (Late Holocene) stage (~4300–4100 years BP). Indeed, Dholavira presents a classic case for understanding how climate change can increase future drought risk as predicted by the IPCC working group. Copyright © 2019 John Wiley & Sons, Ltd.

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Rationale The stable isotopic compositions of biogenic carbonates like fish otoliths (ear bones) are widely used for palaeoclimatic reconstruction. The conventional method using acid‐digestion of micro‐milled samples is a multi‐step time‐consuming process. Here we report a fast method based on laser heating of otolith carbonates to obtain accurate and high‐resolution stable isotopic compositions. Method Otoliths of catfish from the Gulf of Kutch were analysed to check the precision, accuracy and time‐resolution of the isotope ratios. The CO2, generated by heating otoliths with a 50 W CO2 laser, was analysed for its oxygen and carbon isotope ratio [δ18O and δ13C, with precision: 0.12 and 0.17‰ (1σ), accuracy: 0.13 and 0.25‰, respectively] using a continuous‐flow isotope ratio mass spectrometer. The effect of laser power (0.7–2 W) was assessed for reproducible data. Samples were roasted and analysed to account for the effect of the inherent organic matter on the isotopic values. Results Roasting did not alter the δ18O of the otoliths but increased the δ13C slightly. High‐resolution (125 μm) analysis of the right and left otolith of a fish yielded similar δ18O and δ13C values, suggesting the suitability of either of them for deriving the climate signal. An increase in δ18O values from ~ −2‰ to ~ −1‰, observed across the ontogeny, is consistent with the known migratory behaviour of the catfish between freshwater and the sea. Conclusions The otolith δ18O value of an adult fish records the sea surface temperature (with ~3°C uncertainty) on a monthly scale. The otolith δ13C values, with the knowledge of dietary δ13C, provide the mean annual δ13C value of dissolved inorganic carbon. The study provides a rapid method for retrieving high‐resolution seasonal climate data from otoliths found aplenty in geological/archaeological records.