Northeast monsoon variations during the Holocene inferred from palaeochannels and active channels of the Palar River basin, Southern Peninsular India

Abstract

The present-day Palar River and its palaeochannel located in the Southern Peninsular India were investigated with a multidisciplinary approach. The main aim of the study was to reconstruct the palaeoenvironment history of the Palar River basin and to delineate the role of Holocene fluctuations that played a major role in the geomorphological evolution of the region since the Holocene period. The results obtained based on sedimentary facies analysis supported by elemental concentrations and optically stimulated luminescence (OSL) dates reveal distinct seven climatic phases since the past ~10 ka. Phase 1 signifies a very high precipitation as attested by the low CWI with high Rb/Sr ratio. Subsequent to Phase 1, a decreasing trend in the northeast monsoon rainfall (NEMR) is observed (Phase 2). Phase 3 (~4.83–3.59 ka) reflects a decrease in NEMR further supported by low Mn/Al, Mg/Al and Chemical Index of Alteration (CIA) values. Phase 4 (~3.59 ka) is marked by high sand flux, higher K/Al, Ti/Al, Rb/Sr and Ba/Sr ratios coupled with lower values of CaO/MgO, Mn/Al and Fe/Al indicating wetter conditions in the catchment area resulting in the intense weathering of the bedrocks caused owing to the increase in NEMR precipitation. Phase 5 (3.26–2.42 ka) reveals a decline in NEMR precipitation coupled with rapid upstream avulsion because of neotectonic activity that occurred in an intense dry phase. Phase 6 (~1.88–1.44 ka) is marked by an augment NEMR causing higher K/Al, Mg/Al, Ti/Al ratios, CIA and CWI values. Finally, Phase 7 (~1.44 ka–present) is marked by lowered elemental solubility and mobility reflecting short periods of weaker or deteriorated NEMR. The documented record of the Palar River and palaeochannels suggests Holocene NEMR variability in the study region and is synchronous with the various proxy records of NEMR-dominated regions, however, revealing an inverse coupling with southwest monsoon rainfall (SWMR) during the Holocene period.

An overview of Holocene monsoon variability of Sri Lanka and its association with Indian subcontinent climate records

“…A colder phase with suppressed monsoon activities from 0.60-0.25 kyr BP (Srivastava et al, 2017), decreased winter monsoon precipitation from ca. 1.44 kyr BP to present (Resmi and Achyuthan, 2018) and wetter to drier transition around ~0.68 kyr BP which was continued till 0.34 kyr BP as identified in Kedarnath peat records, from Central Himalayas, river sediments of Palar River basin, South India and in a Cave Stalagmite record from Southern Oman, respectively (Fleitmann et al, 2004).…”

“…Significant weakening of the Indian summer monsoon was recorded from 11.1 to 10.7 kyr BP as identified in the Shantiasgara lake record (Sandeep et al, 2017) South India (Resmi and Achyuthan, 2018). Apart from that, significantly weak monsoon phases from 10.8 to 10.2 kyr BP, 9.8 to 8.8 kyr BP, and 8.4 to 8.0 kyr BP were also recorded in marine sediments from the Arabian Sea.…”

“…Climate variations were important during the late Holocene period since expansion of human settlements was expanded during this period. An extremely strong south-west monsoon phase was recorded in hydrological conditions observed during 1.8-1.0 kyr BP in higher central Himalayas (Bhushan et al, 2018) and increased winter monsoon precipitation was recorded from 1.88 to 1.44 kyr BP in South India (Resmi and Achyuthan, 2018). In contrast, a weakening of the southwest monsoon was recorded in central Sri Lanka from ca.…”

Holocene Monsoonal Variations Over Southern India: Looking Into Its Antecedents

“…Intensity of Chemical weathering (CWI) is also a proxy for understanding precipitation (Sun et al, 2010). In this review, CWI records from the Palar River (Resmi and Achyuthan, 2018) and Kukkal Lake (Rajamanickam et al, 2016) are also included. CWI is often higher in warm and humid climates than in cold and dry climates.…”

“…From the Indian subcontinent, various records viz. lacustrine (Rajagopalan et al, 1997;Juyal et al, 2004;Prasad et al, 2014;Sarkar et al, 2015;Rajaminkam et al, 2016), marine (Gupta et al, 2003;Thamban et al, 2007;Achyuthan et al, 2014), and fluvial records (Kale, et al, 2010;Resmi et al, 2016;Resmi and Achyuthan, 2018) have been used to reconstruct the paleomonsoon variability during the Holocene period.…”