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ABSTRACT
Palaeoclimatic information is still sparse for South-east Asia, despite the fact that this region contains numerous lakes and wetlands that may hold potential sedimentary archives. Pollen analysis of sediment samples from a 100-cm-deep sedimentary core from Loktak Lake, the biggest freshwater lake in Manipur state, north-east India, has provided insight into the changing vegetation and climate of the region during the Late Holocene. The palyno-investigation has revealed that between 2330 and 1460 cal yr BP (LL-I zone), an open vegetation consisting mostly of grasses and heathland taxa, namely Xanthium, Artemisia, Asteraceae and Amaranthaceae, with scattered tree elements, viz. Fabaceae, Terminalia, Schleichera, Syzygium, Elaeocarpus, Meliaceae and Sapotaceae, existed near the lake under a warm and relatively dry climate. Between 1460 and 560 cal yr BP (LL-II zone), the consolidation of core forest constituents was noticed, with relative enhancement of major arboreal taxa along with marshy and aquatic taxa such as Cyperaceae, Polygonum and Lemna during 1460 to 1150 cal yr BP (LL-IIa subzone), indicating a humid climate attributable to a strong south-west monsoon. Evidence of agricultural practices showed the presence of cereal and other cultural pollen taxa. Later, a more humid climate persisted during the period 1150 to 560 cal yr BP (LL-IIb subzone) as indicated by an exceptional increase in a major arboreal group (Syzygium-Schleichera-Lagerstroemia-Dipterocarpaceae-Moraceae), suggesting the consolidation of vegetation around the lake under warm and increasingly humid climate conditions, and this occurs during the Medieval Warm Period (MWP). From 560 cal yr BP to the present (LL-III zone), a rise in cereal and heathland taxa indicates a relatively less humid climate; reduction in south-west monsoon precipitation is invoked to explain this which is supported by a steep fall in woodland, consistent with an anthropogenic influence.
Acknowledgements
We thank Prof. Sunil Bajpai, Director, Birbal Sahni Institute of Palaeosciences, for providing laboratory facilities and permission to publish the manuscript (BSIP/RDCC/Publication no. 63/2016-17). We are very grateful to SERB, New Delhi, for providing financial assistance under SERB Fast Track Young Scientist project no. ‘SR/FTP/ES-141/2014’ for carrying out the research. Thanks are also due to Mr Satyendra Tripathi for his help during the collection of sedimentary core from Loktak Lake. ST sincerely thanks her mother, Mrs Seema Dixit, for her kind cooperation during the work.
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Notes on contributors
Swati Tripathi
SWATI TRIPATHI is currently working as a Scientist-C in the Quaternary Laboratory of the Birbal Sahni Institute of Palaeosciences. Her research interests include Quaternary vegetation and climate change through pollen and non-pollen palynomorphs, examining pollen morphology of living plants, and melissopalynology. She was awarded a BSc from Lucknow University in 2005. She received three gold medals for obtaining the highest percentage of marks in MSc (Botany), Lucknow University in 2007. She received her PhD in 2011 from the Department of Botany, Lucknow University. Swati worked as a research fellow, Birbal Sahni Research Associate and Scientist-B before joining as a Scientist-C. She is also the recipient of the Dr B.S. Venkatachala Memorial Medal (2012) and the Dr Chunni Lal Khatiyal Medal (2016) for her outstanding research work in palaeosciences. She is an Associate of the Indian Academy of Sciences, Bangalore. She has 30 research papers published in peer-reviewed journals. She has trained three MSc students and is currently running a SERB-fast track young scientist project dealing with past vegetation and palaeoclimatic changes in Manipur.
Yengkhom Raghumani Singh
YENGKHOM RAGHUMANI SINGH is currently working as an assistant professor (S-3) in the Department of Earth Sciences, Manipur University, India. After finishing his PhD, he was appointed as lecturer in the Department of Geology, Jammu University, India in 2004. He joined Manipur University as a faculty member in the year 2007. He received a BSc in geology from Manipur University in 1993, an MSc in applied geology from Kurukshetra University in 1995 and a PhD in palynostratigraphy from Kurukshetra University in 2002. His research interests include Palaeogene palynology and hydrocarbon source evaluation of the north-west and north-east Himalayas. Yengkhom has 18 years’ research experience, and has published 30 research papers in peer-reviewed journals. He has supervised several research students.
Chandra Mohan Nautiyal
CHANDRA MOHAN NAUTIYAL, after achieving a BSc (Hons.) in physics, received a master’s degree in physics from the University of Roorkee (now IIT – Roorkee) in 1977, followed by a PhD at the Physical Research Laboratory, Ahmedabad. He won three scholarships and later opst-doctoral fellowships at PRL, and also an INSA-DFG Fellowship to visit Germany. He received a travel grant award from The Meteoritical Society (1984), a prize from the Indian Society for Mass Spectrometry (1988), the INSA Medal for Young Scientists (1988), a Consultancy Medal from BSIP (2008), and several recognitions for science communication. He has been a member of several national committees for science and science communication. He has about 50 research publications to his credit. He is a fellow of the NCSTC- Network, the Society of Earth Scientists and the Geological Society of India. He has organised several national and international conferences. He was formerly the scientist in charge of the Radiocarbon Lab of Birbal Sahni Institute of Palaeosciences, Lucknow.
Biswajeet Thakur
BISWAJEET THAKUR is presently working as a Scientist-D at the Birbal Sahni Institute of Palaeosciences, Lucknow, India. He is currently engaged in palaeobiological studies of Quaternary sediments of western coastal margins and offshore regions of the Indian subcontinent (Arabian Sea). His fields of specialisation include micropalaeontology and stratigraphy of Quaternary sediments of the Indian subcontinent, and remote sensing and GIS applications for the development of microfossil domains. He is currently running two DST-sponsored projects as Principal Investigator. He has published about 15 research papers in peer-reviewed journals, and has participated in various national and international conferences and training programmes. He is the recipient of a Best Poster award at the XXIII Indian Colloquium on Micropalaeontology and Stratigraphy and International Symposium on Global Bioevents in the Earth History. He has trained several MSc students and is currently supervising one PhD scholar.