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We reconstruct centennial scale quantitative changes in surface seawater temperature (SST), evaporation-precipitation (from Mg/Ca and δ18O of surface dwelling planktic foraminifera), productivity (from relative abundance of Globigerina bulloides), carbon burial (from %CaCO3 and organic carbon [%Corg]) and dissolved oxygen at sediment-water interface, covering the entire Holocene, from a core collected from the eastern Arabian Sea. From the multi-proxy record, we define the timing, consequences and possible causes of the mid-Holocene climate transition (MHCT). A distinct shift in evaporation-precipitation (E-P) is observed at 6.4 ka, accompanied by a net cooling of SST. The shift in SST and E-P is synchronous with a change in surface productivity. A concurrent decrease is also noted in both the planktic foraminiferal abundance and coarse sediment fraction. A shift in carbon burial, as inferred from both the %CaCO3 and %Corg, coincides with a change in surface productivity. A simultaneous decrease in dissolved oxygen at the sediment-water interface, suggests that changes affected both the surface and subsurface water. A similar concomitant change is also observed in other cores from the Arabian Sea as well as terrestrial records, suggesting a widespread regional MHCT. The MHCT coincides with decreasing low-latitude summer insolation, perturbations in total solar intensity and an increase in atmospheric CO2.

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Dholavira is a Harappan city in Gujarat, India whose fortification, with maximum wall thickness of up to 18 m is extraordinary. The probable cause of such a massive protective wall is yet to be addressed. Based on (i) the location of Dholavira along tsunami/stormprone coast; (ii) climatic scenario during the midHolocene with special reference to higher sea level and (iii) lack of proto-historic military evidences, we hypothesize that the walls may have acted as defence against tsunami/sea storm. The presence of extremely thick protective walls thus implies that the Dholavirans were probably aware of the magnitude of destruction caused by tsunami waves/storms.