Evolution of the Indian summer monsoon: synthesis of continental records

Abstract

Fluvial sediments of the Siwalik succession in the Himalayan Foreland Basin form the most important continental archive for reconstructing monsoonal fluctuations during the Late Miocene to Late Pleistocene. A number of proxy records suggest multiple phases of monsoonal intensification with peaks at 10.5, 5.5 and 3 Ma after which the strength of the monsoon decreased to modern day values with minor fluctuations. Detailed evaluation of Late Quaternary interfluve stratigraphic development in the Ganga plains shows that interfluve areas near the major rivers aggraded periodically between 27 and 90 ka. They subsequently degraded or accumulated sediment only locally, probably reflecting decreased monsoonal precipitation around the Last Glacial Maximum. Increased precipitation during the 15 to 5 ka period of monsoon recovery probably increased discharge and promoted incision and widespread badland formation. In western India, the fluvial records back to c. 128 ka suggest a stronger monsoon around 80 ka followed by periods of weakened monsoon around 70 to 30 ka and progressive desiccation in the glacial period. Holocene lacustrine records from western Rajasthan suggest maximum lake levels at c. 6 ka and complete desiccation between c. 3 and 4 ka.

Rapid response of silicate weathering rates to climate change in the Himalaya

“…2; Thompson et al, 1997). This oxygen isotope record is consistent with an intensification of the monsoon between 25 and 10 ka ago, as suggested by most studies (Goodbred and Kuehl, 2000;Sanyal and Sinha, 2010;Beukema et al, 2011 (Blum et al, 1993;Colin et al, 1999). For instance, Blum et al (1993) 18 O values suggest that the response of transport and storage of weathering products to climate change was rapid (< a few thousand years).…”

“…Thus, the observed increase in 87 Sr/ 86 Sr between 25 and 10 ka could be interpreted as an increasing contribution of sediments from the LH. However, as the monsoon intensified between 25 and 10 ka ago (Sanyal and Sinha, 2010), moisture penetrated further north, promoting erosion in the HHC, as demonstrated for the Sutlej River (Bookhagen et al, 2005). More sediments from the HHC would have resulted in a decrease of sediment 87 Sr/ 86 Sr ratios, at odds with the data presented here (Fig.…”

Indian monsoons shape dispersal phenology of plants

“…Considering that the Indian monsoons stretch back around 15 -20 Myr [1], it is possible that differences in fruiting time among populations of different regions reflect adaptive genetic differences. These observed shifts in phenology could also be a consequence of phenotypic plasticity, which itself might have been selected for.…”

“…The Indian monsoons, estimated to be about 15-20 million years old, are a major annual climatic event, bringing rainfall to the Indian subcontinent [1]. During the monsoons, there is a seasonal reversing of wind currents accompanied by corresponding changes in precipitation over the Indian land mass [2].…”

Alluvial stratification styles in a large, flash‐flood influenced dryland river: The Luni River, Thar Desert, north‐west India

“…) due to transmission losses (Sharma et al ., ; Kale et al ., ). The bed sediment is predominantly fine to medium sand ( D 50 = 0·26 to 0·31 mm; Chitale, ; D 50 = 0·16 to 0·55 mm; Sharma & Murthy, ), with less than 1% silt, 3 to 4% clay (Dhir et al ., ), and with a little fine gravel and calcrete nodules (Sanyal & Sinha, ). Suspended load is not measured routinely, but for the 1979 flood Sharma & Vangani () and Sharma () reported a maximum measured concentration of 40·2 gl −1 .…”