Late-Holocene climate in the Lower Narmada valley, Gujarat, western India, inferred using sedimentary carbon and oxygen isotope ratios

We report the late-Holocene climate and vegetation of the Lower Narmada valley, Gujarat, western India as inferred from the stable carbon and oxygen isotopic composition (delta C-13 and delta O-18) of sedimentary carbonates and the associated organic carbon. The alluvial plain from the surface to a depth of similar to 2 m consists of late-Holocene sediments, deposited during last similar to 3 kyr, probably by large historic and paleofloods. delta C-13 of both carbonates and organic carbon in the sediments suggest that climate was subhumid throughout the late Holocene (similar to 3 kyr) as it is today, and the vegetation was of mixed C-3-C-4 type with little change in their relative proportions. The modern vegetation mostly comprises shrubs and scattered woody plants (C-3) with a little grass (C-4) in some places. The recent change in vegetation is attributable to anthropogenic disturbance: the natural grasslands (C-4) are replaced by shrubs and woody plants (C-3). Two comparatively drier events at similar to 2.1 ka and similar to 1.3 ka are observed, consistent with widespread proxy paleoclimatic records and are attributed to a weaker southwest monsoon rain. Marine influence on the isotopic compositions is observed in a cliff section of the Narmada estuary throughout its depositional history of similar to 4.2 kyr. The radiocarbon ages of the sediments are of the order of decades to a century at the surface and increase almost linearly with depth, being 1000-3000 yr at similar to 100 cm and 3200-4200 yr at similar to 200 cm.