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Evaluating Geochemical Proxies for Paleoclimate Reconstruction in Tropical Montane Peat : A Case Study from the Nilgiris, Southern India

Electronic Theses of Indian Institute of Science

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Title Evaluating Geochemical Proxies for Paleoclimate Reconstruction in Tropical Montane Peat : A Case Study from the Nilgiris, Southern India
 
Creator Bala, P Ramya
 
Subject Tropical Montane Peat
Palaeoclimatology
Inorganic Geochemistry
Paleoenvironmental Reconstruction
High Resolution Chronology
Geochemical Proxies
Nilgiris Montane Peat Bogs
Environmental Reconstruction Proxies
Abrupt Climate Shifts
Peat Chronology
Earth Science
 
Description Peat from the temperate regions has been used for paleoenvironmental reconstruction using diverse proxies for over a century now. Peat is rare and severely understudied in the tropics. The montane peat bogs of the Nilgiris, southern India have been found to preserve global climatic signals including the Holocene Optimum and the Last Glacial Maximum (LGM). At Sandynallah, one of the oldest peat accumulations in the world at >40 kyr BP, we had undertaken a high resolution paleoenvironmental reconstruction using multiple proxies which are yet to be evaluated in the tropical context. The study consists of 3 main objectives, i. Establishing an accurate high resolution chronology for the peat profile using radiocarbon dating, ii. Extracting vegetation and climate information from C/N ratio and Rock-Eval indices and iii. Using elemental profiles to establish the utility of inorganic geochemical proxies for processes such as weathering and dust transport. High resolution chronology for the site was built using Accelerator Mass Spectrometry (AMS) radiocarbon dates. To improve accuracy of the age-depth model, we also tested 4 samples for the effects of the AAA (Acid-Alkali-Acid) extraction method, the most common pre-treatment method for peat in the world. We compared ages on bulk samples (acid washed) and AAA treated samples from 4 different depths. We find that for all depths, the ages of the untreated samples do not lie within the internal uncertainty window and differ from the AAA treated sample age by at least an order of magnitude of the internal error, if not more. Based on these results we argue that the internal error should be used in conjunction with a reliable estimate of external error in an age-depth model for more realistic dating of paleoclimatic events. C/N ratios were explored for their paleoclimatic potential in conjunction with Rock-Eval indices and it was found that decomposition in tropical peat, as opposed to temperate peat, may not be sensitive to climatic perturbations. Inorganic geochemical proxies were also evaluated through this study. We see that the major and trace elements, except the lanthanide series do not show many significant trends for paleoenvironmental interpretation. But the lanthanides show some promise for identifying potential sources of dust and weathered material. Our study has addressed the gap in knowledge about the utility of recent geochemical proxies in tropical peat and has attempted to provide a solution to improve reliability in constructing age-depth models.
 
Contributor Krishnan, Sanjeev
 
Date 2018-05-14T07:27:57Z
2018-05-14T07:27:57Z
2018-05-14
2015
 
Type Thesis
 
Identifier http://etd.iisc.ernet.in/2005/3537
http://etd.iisc.ernet.in/abstracts/4405/G27615-Abs.pdf
 
Language en_US
 
Relation G27615