Holocene aridification of India

Abstract

Spanning a latitudinal range typical for deserts, the Indian peninsula is fertile instead and sustains over a billion people through monsoonal rains. Despite the strong link between climate and society, our knowledge of the long‐term monsoon variability is incomplete over the Indian subcontinent. Here we reconstruct the Holocene paleoclimate in the core monsoon zone (CMZ) of the Indian peninsula using a sediment core recovered offshore from the mouth of Godavari River. Carbon isotopes of sedimentary leaf waxes provide an integrated and regionally extensive record of the flora in the CMZ and document a gradual increase in aridity‐adapted vegetation from ∼4,000 until 1,700 years ago followed by the persistence of aridity‐adapted plants after that. The oxygen isotopic composition of planktonic foraminiferGlobigerinoides ruberdetects unprecedented high salinity events in the Bay of Bengal over the last 3,000 years, and especially after 1,700 years ago, which suggest that the CMZ aridification intensified in the late Holocene through a series of sub‐millennial dry episodes. Cultural changes occurred across the Indian subcontinent as the climate became more arid after ∼4,000 years. Sedentary agriculture took hold in the drying central and south India, while the urban Harappan civilization collapsed in the already arid Indus basin. The establishment of a more variable hydroclimate over the last ca. 1,700 years may have led to the rapid proliferation of water‐conservation technology in south India.

Indian monsoon variations during three contrasting climatic periods: The Holocene, Heinrich Stadial 2 and the last interglacial–glacial transition

“…The NGHP-01-19B core location is nearest to the Mahanadi River, but may also be influenced by the discharges of other CMZ rivers (Phillips et al, 2014a), thus the variations in the ecological assemblages observed in our study should reflect Indian monsoon variability and magnitude. Lithostratigraphic characteristics indicate that mass transfer events played no role in sedimentation at our sites for the periods considered in our study (Collet et al, 2008;Ponton et al, 2012;Phillips et al, 2014b).…”

“…The portion of core NGHP-01-16A (16°35.59'N / 082°41.00'E, 1265 m water depth, 217 m total length) sampled in this study (0-875 cm) covers the entire Holocene until HS 2. The sediments are composed of smectite-dominated hemipelagic clays commonly bearing calcareous nannofossils, foraminifera, and silt/sand lamina/beds (Phillips et al, 2014a) and terrestrial dominated organic carbon (Johnson et al, 2014) originating from the Godavari River during the last 27,000 years cal BP (Ponton et al, 2012). We also studied samples from core NGHP-01-19B (18°58.66'N / 85°39.52'E, 1,433m water depth, 26 m total length) that was collected close to the Mahanadi River outlet.…”

“…The age model for core NGHP-01-16A was established by Ponton et al (2012) using 11 14 C dates. The measurements were performed on samples composed of mixed planktonic foraminifers >150µm at the National Ocean Sciences Accelerator Mass Spectrometry Facility in Woods Hole (MA, USA) (see supplementary information/auxiliary material in Ponton et al, 2012).…”

“…Identifying its natural rhythmicity, magnitude, and the physical processes involved is a challenge for present-day and future socio-economic policy predictions. Model studies (Broccoli et al, 2006;Chiang et Bits, 2005;Mohtadi et al, 2014;Pausata et al, 2011;Vernekar et al, 1995) and palaeoclimatic observations (Agnihotri et al, 2002;Fleitmann et al, 2007;Gupta et al, 2003;Hahn et al, 1976;Ponton et al, 2012;Sinha et al, 2007) suggest that abrupt changes of Indian monsoon are in phase with North Atlantic climate variations. These studies further show that changes in the Intertropical Convergence Zone (ITCZ), North Atlantic iceberg discharges, Indian Ocean sea surface temperature (SST) gradient and Himalayan snow cover can explain the rapid atmospheric reorganization between the North Atlantic and the Indian region.…”

“…the Core Monsoon Zone (CMZ), and under different climate regimes (e.g. Ponton et al, 2012 for the Holocene Godavari basin and Prasad et al, 2014 for the crater lake Lonar in the Holocene).…”