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Increase in rainfall during the early Holocene has been reported from different regions of Indian subcontinent, although the magnitude shows spatial variability with lower change in higher rainfall regions and vice versa. While the early-Holocene rainfall records are available from lowland areas of the Indian sub-continent, the record is poorly documented from the high-altitude Central Himalayan region where orography plays an important role in the spatial variability in the rainfall pattern. For the first time, δDC29, δ13CC29 values of alkane and δ13C values of organic matter from a relict lake of Benital area in the Central Himalaya have been used to reconstruct monsoonal rainfall and contemporary vegetation for last 10.5 ka with an emphasis on the early Holocene. The δDC29 values suggest that the early Holocene was characterized by a wet phase at ca. 9 ka with 25% higher rainfall compared to present while the middle-late-Holocene was relatively arid. The estimated increase in monsoonal rainfall for the early Holocene is the highest compared to the previous report from elsewhere. The magnitude of early-Holocene rainfall estimated in this study suggests that in addition to erosion of the bed-rocks at the head-water region, increased stream power reworked the older floodplain and resulted in 2.3 times higher sediment discharged into the Ganges-Brahmaputra (GB) delta compared to the present discharge. The δ13CC29 values of the lake sediments suggest a transition from woody to non-woody plant assemblages occurred at 7 ka. The poor correlation between δDC29 and δ13CC29 values suggests at higher rainfall, the δ13CC29 values of catchment vegetation were less responsive. [ABSTRACT FROM AUTHOR]

Millennial-scale climate cycles have been meagerly discussed in the terrestrial records from the Indian subcontinent, particularly the wetlands of the Ganga Plain. The mineral magnetic and textural analyses, along with chronology, distinctly record variation in the monsoon intensity since 15000 cal yrs BP in the sediment core collected from the Kanwar Lake in the Central Ganga Plain (CGP) of India. This unique high-resolution data allowed us to analyse monsoon fluctuation in the CGP with respect to changes in the North Atlantic process (internal) and external (solar cycles) forcing. During this period, several palaeoclimatic events, such as the Bølling-Allerød (B/A), Older and Younger Dryas, and the high-frequency fluctuations in the Holocene viz., Greenlandian, Northgrippian, and Meghalayan stages, were observed. The B/A event is correlated with the Indian Summer Monsoon (ISM) intensification period of the CGP. Eleven dry events are recorded at 13600–13200, 13000–11700, 11000, 10600, 9800–9000, 8200, 6100–5300, 4300–4200, 3800, 1800–900 and 300 cal yrs BP. During the Holocene, the sustained episodes of weaker monsoon centered around 10600, 9600, 8200, 6000, 4200, 2800, 1400 and 600 cal yrs BP, where the variability of the proxy data is mostly synchronous with the reduced upwelling intensity in the western Arabian Sea as well as roughly align with ∼1500 years cyclic signals in the drifted ice proxy recorded Bond Events indicating weakened ISM circulation during colder North Atlantic. Two distinct short cycles, spanning 172–344 and 172–688 years, are evident around 12,000 and 14,000 cal yrs BP with an additional occurrence from 86 to 344 years during 2000 and 6000 cal yrs BP, affirming the significance of external forcing, particularly solar activity. For the 1492 years cycle in ISM fluctuation, we postulate it may represent a combined forcing of external (solar) and internal (Atlantic Meridional Overturning Circulation (AMOC)) factors during the Holocene. This is the first high-resolution record available in the CGP, which brings out crucial monsoon reconstruction during the last 15000 years. • Fifteen millennia monsoon variability record from Ganga Plain, India. • The B/A event records ISM intensification and enhanced solar insolation. • Short and long cyclicity is observed in the record. • A combined forcing of external and internal factors seen during the Holocene. • The wetland shrinkage since the last 300 years i.e after the LIA. [ABSTRACT FROM AUTHOR]

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]