Centennial-scale oscillations in oxygen and carbon isotopes of endogenic calcite from a 15,500 varve year record of the Piànico interglacial |
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| Institution: | 1. Ecole Pratique des Hautes Etudes (EPHE), UMR CNRS 5805 EPOC, Université de Bordeaux, Allée Geoffroy St Hilaire, 33615 Pessac, France;2. Instituto Geológico y Minero de España, Ríos Rosas 23, 28003 Madrid, Spain;3. Divisão de Geologia e Georecursos Marinhos, Instituto Português do Mar e da Atmosfera (IPMA), Av. de Brasília 6, 1449-006 Lisbon, Portugal;4. CCMAR, Center of Marine Sciences, Algarve, Portugal;5. Université de Bordeaux, UMR CNRS 5805 EPOC, Allée Geoffroy St Hilaire, 33615 Pessac, France;6. Godwin Laboratory for Palaeoclimate Research, Department of earth Sciences, University of Cambridge, UK;7. Department of Earth Sciences, Royal Holloway, University of London, Egham, Surrey TW20 0EX, UK;1. Key Laboratory of Tibetan Environment Changes and Land Surface Processes (TEL), Institute of Tibetan Plateau Research (ITP), Chinese Academy of Sciences, Beijing 100101, China;2. CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China;3. University of Chinese Academy of Sciences, Beijing 100049, China |
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| Abstract: | The palaeolake record from Piànico (Southern Alps) comprises a sequence of 15,500 continuous calcite varves formed during peak interglacial conditions around 400 ka ago. The varved nature of these deposits allows precise sub-sampling of five varve year intervals for stable isotope analyses. All samples consist of calcite precipitated in the epilimnion of the lake, with contents of detrital carbonate below 4%. Four significant negative δ18O oscillations occurred during the upper half of the interglacial. The most prominent of these oscillations has an amplitude of ?1.1‰ and lasted 780 varve years. The three other oscillations are shorter (125–195 varve years) and of lower amplitude (0.4–0.9‰). An additional major drop in δ18O occurs 315 varve years before the end of continuous calcite precipitation in the lake. This shift marks the end of long interglacial conditions and the beginning of harsher climate conditions and glacier advances in the Southern Alps. In contrast, the four δ18O oscillations within the period of continuous formation of calcite varves reflect natural intra–interglacial climate dynamics. |
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