Short communication: Massive erosion in monsoonal central India linked to late Holocene land cover degradation

Abstract

Abstract. Soil erosion plays a crucial role in transferring sediment and carbon from land to sea, yet little is known about the rhythm and rates of soil erosion prior to the most recent few centuries. Here we reconstruct a Holocene erosional history from central India, as integrated by the Godavari River in a sediment core from the Bay of Bengal. We quantify terrigenous fluxes, fingerprint sources for the lithogenic fraction and assess the age of the exported terrigenous carbon. Taken together, our data show that the monsoon decline in the late Holocene significantly increased soil erosion and the age of exported organic carbon. This acceleration of natural erosion was later exacerbated by the Neolithic adoption and Iron Age extensification of agriculture on the Deccan Plateau. Despite a constantly elevated sea level since the middle Holocene, this erosion acceleration led to a rapid growth of the continental margin. We conclude that in monsoon conditions aridity boosts rather than suppresses sediment and carbon export, acting as a monsoon erosional pump modulated by land cover conditions.

Land use and land cover changes in the Haean Basin of Korea: Impacts on soil erosion

“…The water turbidity crosses the guideline value of 30 NTU, specifically during the period of monsoon rainfall due to heavy runoff. In contrast to this study, a study of a plain area in India revealed an increase in the soil erosion with the decline of the monsoon rainfall (Giosan et al, 2017). The elevation and mountain slope in the Haean Basin increases the soil erosion and runoff during the monsoon season.…”

Response AE

“…In this study we use the feldspar IR50 and pIRIR150 age data to provide insights into the completeness of bleaching of the quartz OSL signal (e.g., Murray et al, 2012;Rémillard et al, 2016). This is based on the observation that feldspar signals bleach much more slowly than quartz OSL (Godfrey-Smith et al, 1988;Thomsen et al, 2008): IR50 signals bleach approximately 1 order of magnitude slower than quartz OSL, and pIRIR signals bleach even more slowly than IR50 signals (e.g., Kars et al, 2014;Colarossi et al, 2015). We are confident that the quartz signal is well bleached when the pIRIR150 age agrees within uncertainty with the quartz age; this is the case for sample 177 204.…”

Reconciling drainage and receiving basin signatures of the Godavari River system

“…Draining central peninsular India, the river integrates rainfall within the core monsoon zone of central India, both reflecting the mean monsoon regime and capturing fluctuations in monsoonal rains over the sub-continent. With over 90 % of discharge from the Godavari deriving from summer monsoon precipitation (Rao et al, 2005), corresponding offshore sedimentary sequences record past variations in continental climate as well as anthropogenic activity within the drainage basin (Cui et al, 2017;Giosan et al, 2017;Ponton et al, 2012;Zorzi et al, 2015).…”

“…Prior studies, spanning the Holocene, of a Godavari Riverproximal sediment core NHGP-16A from the Bay of Bengal (BoB) have revealed marked geochemical and sedimentological variations that have been interpreted in the context of both evolving regional hydroclimate and accompanying changes in land use within the Godavari catchment (Giosan et al, 2017;Ponton et al, 2012). Specifically, a distinct change in the stable carbon isotopic (δ 13 C) composition of molecular markers of terrestrial vegetation implies an increase in the proportion of aridity-adapted C 4 vegetation beginning around 4.5 kyr BP (Ponton et al, 2012).…”