Vegetational and climatic variations during the past 3100 years in southern India: evidence from pollen, magnetic susceptibility and particle size data

Abstract

Vegetational history vis a vis climate change during the past 3100 cal. years BP was deciphered from pollen data supplemented with magnetic susceptibility and particle size data for a 2.5 m long sediment core from Pookot Lake, Kerala, southern India. Pollen data suggest a mixed assemblage of upland tropical elements and wetland mangrove taxa. The presence of trace amounts of pollen grains of montane taxa like Betula, Pinus and Alnus points to their long distance dispersal. Pollen grains of Ixora, Syzygium, Symplocos, Moraceae and Arecaceae that represent tropical vegetation were also recovered, indicating modern vegetation in and around Pookot Lake. Mangrove elements are mostly represented by species of Rhizophora and Ceriops decandra along with other taxa. High-rainfall periods are characterised by high sand % and low clay % and vice versa. The pollen data correspond well with magnetic susceptibility and particle size data. The data obtained suggest three broad phases of climate, with minor oscillations, during the past 3100 cal. years BP: (1) wet climate during 3100-2500 cal. years BP; (2) dry climate spanning a long period that ended around 1000 cal. years BP; (3) amelioration in climate after 1000 cal. years BP, reflected in the presence of luxuriant vegetation and high magnetic susceptibility values.

Holocene climate variability and Indian Summer Monsoon: An overview

“…During the last 3 million years, the eccentricity of the earth has remained less than 0.07 (Berger and Loutre, 1994) while it becomes nearly zero in every 400,000 years (Loutre, 2009a). The (Agnihotri et al, 2002(Agnihotri et al, , 2008Bhattacharyya et al, 2015;Kumaran et al, 2005;Limaye and Kumaran, 2012) with the other continental records from the Indian subcontinent (Banerji et al, 2017(Banerji et al, , 2019Dixit et al, 2014a;Joshi et al, 2015;Kotlia et al, 2012;Phadtare, 2000;Prasad et al, 2014a;Quamar and Chauhan, 2014) earth's obliquity varied between 22° and 25° during the last 300,000 years with a quasi-periodic oscillation of 41,000 years (Berger, 1978;Loutre, 2009b). Larger obliquity enhances the energy received by each of the Hemisphere during local seasonal warming.…”

“…Thus, the LIA became a frontier in understanding the present and future climatic trends. The LIA over Indian subcontinent has been recognised as weakened ISM (Agnihotri et al, 2002(Agnihotri et al, , 2008Bhattacharyya et al, 2015) resulting in dry climate (Figure 6) or wet climate because of winter precipitation (Banerji et al, 2017(Banerji et al, , 2019Kotlia et al, 2012;Rühland et al, 2006). Most of the marine and continental records from the Arabian Sea and peninsular India demonstrated a dry climate as a result of ISM weakening (Agnihotri et al, 2002;Menzel et al, 2014).…”

Paleoenvironmental shifts spanning the last ~6000 years and recent anthropogenic controls inferred from a high-altitude temperate lake: Anchar Lake, NW Himalaya

“…Mineral magnetic techniques have also been employed in recent decades to study paleoclimate and paleolimnological processes (Bhattacharyya et al, 2015; Foster et al, 2008; Geiss et al, 2003; Oldfield et al, 1983; Peck et al, 2004; Shankar et al, 2006; Thompson et al, 1975; Warrier et al, 2017). These techniques offer information on the concentration, grain size, and mineralogy of magnetic minerals associated with sediments.…”

A multi-proxy lake sediment record of Indian summer monsoon variability during the Holocene in southern India

“…There have been studies on many lake and palaeolake deposits from western India (Prasad et al, 2014), northwestern India (Dixit et al, 2014a,b) and the Himalaya (Rawat et al, 2015a,b;Mishra et al, 2015) to reconstruct the ISM variability. However, very few lakes from southern India have been investigated for the reconstruction of Holocene ISM variability (Shankar et al, 2006;Warrier and Shankar, 2009;Warrier et al, 2014;Sandeep et al, 2015;Bhattacharyya et al, 2015) most of them provide monsoonal history of only the Late Holocene. Hence, it needs to be verified whether major monsoonal events, reported by many researchers, like the strengthening of ISM during the Early Holocene (Prasad et al, 2014), its weakening after ~ 7 ka BP (Fleitmann et al, 2007;Demske et al, 2009), dry episodes or abrupt weakening of ISM around 8.2 ka BP and 4.2 ka BP (Staubwasser et al, 2003;Dixit et al, 2014a, b) were widespread phenomena and prevalent in southern India too.…”