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

Abstract

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 (δ¹³C and δ¹⁸O) of sedimentary carbonates and the associated organic carbon. The alluvial plain from the surface to a depth of ~2 m consists of late-Holocene sediments, deposited during last ~3 kyr, probably by large historic and paleofloods. δ¹³C of both carbonates and organic carbon in the sediments suggest that climate was subhumid throughout the late Holocene (~ 3 kyr) as it is today, and the vegetation was of mixed C₃-C₄ type with little change in their relative proportions. The modern vegetation mostly comprises shrubs and scattered woody plants (C₃) with a little grass (C₄) in some places. The recent change in vegetation is attributable to anthropogenic disturbance: the natural grasslands (C₄) are replaced by shrubs and woody plants (C₃). Two comparatively drier events at ~2.1 ka and ~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 ~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 ~100 cm and 3200–4200 yr at ~200 cm.