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Between the second urbanisation of late Iron Age/Early historic and medieval period Indian subcontinent experienced repeated invasion/human migration of central Asian warriors from Greco-Bactrian conquests till Sultanate-Mughals of sixteenth century. Historians often argue whether such invasions/migrations in the past were driven by change in climate and/or social dynamics. We present results of first detailed archaeological excavation and chronology from a multi-cultural site of Vadnagar, Gujarat state, Western India. We document records of seven cultural stages of continuous human settlement from ca. 2754 calibrated (cal) years B.P. (contemporary to Late-Vedic/pre-Buddhist Mahajanapadas or oligarchic republics), Mauryan, Indo-Greek, Indo-Scythian or Shaka-Kshatrapas (AKA 'Satraps', descendants of provincial governors of ancient Achaemenid Empires), Hindu-Solankis, Sultanate-Mughal (Islamic) to Gaekwad-British colonial rule (∼318 years B.P.) and recent. We constrain the climate (Indian summer monsoons or ISM) at Vadnagar by both bulk and isotope sclerochronology (seasonality) of molluscan shells and show that each of these periods flourished during a good ISM phase. Conversely, the arid/hyper-arid phases witnessed decline in material culture, craftsmanship, and/or increased social instability yet the settlement was never abandoned thus making Vadnagar the oldest living city within a single fortification unearthed so far in India. We also compare the proxy climate data with the coupled General Circulation Climate (Earth system) model-generated precipitation over western India that is in anti-phase with Arid Central Asia (ACA). We suggest that the seven major phases of invasions/migration to India over the past 2200 years occurred during periods when the ACA was hyper-arid and uninhabitable, but the agrarian subcontinent was prosperous with relatively stronger ISM. • Deep excavation at Vadnagar, India records human settlement for last three millennia. • Seven multicultural periods found from Late Vedic/Pre-Buddhist till British period. • Palaeomonsoon is reconstructed using isotope schlerochronology of molluscan shells. • Archaeological/isotope data shows rise/fall of cultures linked to monsoon change. • Seven human migration from central Asia to India were climate driven. [ABSTRACT FROM AUTHOR]

Despite several attempts, the effects of volcanism and greenhouse gas emission on climate (e.g., rainfall) over India across the Cretaceous/Palaeogene Boundary (66.1 ± 0.01 Ma) remain a contentious issue. Inferences from conventional isotopic, palaeosol, floral analysis, and palaeoclimate models are contradictory ranging from much lower- to higher-than-today rainfall during this high CO 2 atmosphere. To resolve this, robust tracer of triple oxygen isotopic ratios (ẟ18O-∆′17O) of silicified fossil woods from Deccan intertrappean lacustrine sediments, central India were analysed for retrieving the silicification temperature and ambient fluid (water) isotopic composition. Under certain assumptions and uncertainty, triple oxygen isotope data indicate that the fluids were derived from a mixture of meteoric and hydrothermal water. The meteoric water end member possibly had a low ẟ18O VSMOW value (∼− 12 ± 2‰) compared to the modern mean monsoon rainwater (∼− 5‰) which implies a substantially higher rainfall than today (∼1760 ± 200 to 1860 ± 200 mm/year) in the terminal Cretaceous India. This result supports the prediction of elevated precipitation by the recent new generation of global coupled models that consider various feedbacks and ocean dynamics, at a high CO 2 atmosphere. It is also consistent with the paleo-botanical evidence but far exceeds the amount predicted by the older paleoclimate models pertaining to the Cretaceous period. • The ẟ18O-∆′17O values of silicified woods from Deccan intertrappeans were measured to estimate fluid composition. • Depleted δ18O fluid (∼ -12 ± 2‰) values suggest a higher tropical rainfall (1760 − 1860 mm/y) in terminal Cretaceous period. • The change in rainfall during Cretaceous-Palaeogene transition closely follows the change in atmospheric CO 2 concentration. • The inferred rainfall increase is consistent with palaeobotanical evidence and recent coupled climate models. [ABSTRACT FROM AUTHOR]

Groundwater resources in tropical regions are largely dependent on recharge by rainwater infiltration through soil layers with variable time. However, the rainwater infiltration through soil is a serious concern in urban tropics where it interacts with landfills at the dumpsites, potentially contaminating adjoining groundwater. In this study, the stable isotopic compositions of oxygen and hydrogen (δ 18 O and δ 2 H, respectively) in groundwater and leachates, adjoining municipal dumpsites in urban tropics (Bangalore, Kolkata and Durgapur located in diverse rainfall zonation of India), were analyzed to investigate their recharge sources and trace the possible mixing of leachate contaminants under three diverse climatology. The measured values of δ 18 O and δ 2 H suggested that the groundwater in these sites reflects higher recharge by rainwater. However, the d-excess values indicated secondary effects suggesting the groundwater has experienced significant modifications. The end member analysis using δ 18 O-d-excess relation pinpointed an additional leachate contribution from adjoining dumpsites. The critical fraction of leachate infiltration to groundwater quantified using two component mixing model ranged between (i) 1 and 33% in Bangalore, (ii) 5 and 13% in Kolkata and (iii) 18 and 76% in Durgapur, with its variability dependent on seasonality and aquifer connectivity. This information is crucial for groundwater management to secure water quality and to quantify potential hydrological contaminants particularly in drier seasons and drier regions, when and where the demand for groundwater is high, respectively., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Air quality in the megacity Delhi is affected not only by local emissions but also by pollutants from crop residue burning in the surrounding areas of the city, particularly the rice straw burning in the post monsoon season. As a major burning product, gaseous CO 2 , which is rather inert in the polluted atmosphere, provides an alternative solution to characterize the impact of biomass burning from a new perspective that other common tracers such as particulate matters are limited because of their physical and chemical reactiveness. Here, we report conventional ([CO 2 ], δ 13 C, and δ 18 O) and unconventional (Δ 17 O) isotope data for CO 2 collected at Connaught Place (CP), a core area in the megacity Delhi, and two surrounding remote regions during a field campaign in October 18-20, 2017. We also measured the isotopic ratios near a rice straw burning site in Taiwan to constrain their end member isotopic compositions. Rice straw burning produces CO 2 with δ 13 C, δ 18 O, and Δ 17 O values of -29.02 ± 0.65, 19.63 ± 1.16, and 0.05 ± 0.02‰, respectively. The first two isotopic tracers are less distinguishable from those emitted by fossil fuel combustion but the last one is significantly different. We then utilize these end member isotopic ratios, with emphasis on Δ 17 O for the reason given above, for partitioning sources that affect the CO 2 level in Delhi. Anthropogenic fraction of CO 2 at CP ranges from 4 to 40%. Further analysis done by employing a three-component (background, rice straw burning, and fuel combustion) mixing model with constraints from the Δ 17 O values yields that rice straw burning contributes as much as ∼70% of the total anthropogenic CO 2 , which is more than double of the fossil fuel contribution (∼30%), during the study days., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)