Evidence from wavelet analysis for a mid-Holocene transition in global climate forcing |
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| Authors: | M Debret D Sebag X Crosta N Massei J-R Petit E Chapron V Bout-Roumazeilles |
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| Institution: | 1. Laboratoire de Glaciologie et de Géophysique de l''Environnement, Université Joseph Fourier, UMR CNRS 5183, BP96, 38402 St Martin d''Hères, France;2. Laboratoire de Morphodynamique Continentale et Côtière, Université de Rouen, UMR CNRS/INSU 6143, Department of Geology, 76821 Mont-Saint-Aignan Cedex, France;3. EPOC, Université Bordeaux I, UMR CNRS 5805, Avenue des Facultés, 33405 Talence, France;4. Institut des Sciences de la Terre d''Orléans, Université d''Orléans, CNRS/INSU, Université François Rabelais-Tours, UMR 6113, 1A rue de la Férollerie, F-45071 Orléans cedex 2, France;5. PBDS Laboratory, Université de Lille 1, UMR 8110 CNRS, 59 655 Villeneuve d''Ascq, France;1. Institute of Geography RAS, Staromonetny-29, 119017, Staromonetny, Moscow, Russia;2. Tomsk State University, Tomsk, Russia;3. Department of Geosciences, University of Massachusetts, Amherst, MA 012003, USA;4. British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK;5. Institute of Particle Physics, ETH Zurich, 8093 Zurich, Switzerland;6. Institute of Geography, University of Zurich, 8057 Zurich, Switzerland;7. Université Paris 1 Panthéon-Sorbonne, CNRS Laboratoire de Géographie Physique, 92195 Meudon, France;8. Antarctic Research Centre, Victoria University Wellington, New Zealand;9. Department of Earth Science, University of Bergen, N-5020 Bergen, Norway;10. Uni Research Klima, Bjerknes Centre for Climate Research, N-5020 Bergen Norway;11. Department of Geology, University of Cincinnati, Cincinnati, OH 45225, USA;12. Institute of Geography and Oeschger Centre for Climate Change Research, University of Bern, Switzerland;13. Department of Geology, The College of Wooster, Wooster, OH 44691, USA;14. Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY, USA;1. School of Geography, University of Nottingham, Nottingham NG7 2RD, UK;2. Volcano Science Center, U.S. Geological Survey, 345 Middlefield Road, MS910 Menlo Park, CA 94025, USA;3. Department of Geography and Earth Sciences, Aberystwyth University, Aberystwyth SY23 3DB, UK;1. Geological Institute, ETH Zurich, Zurich, Switzerland;2. Eawag, Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Switzerland;3. Institute of Geological Sciences and Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland;1. Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;2. National Research Center of Geoanalysis, Beijing 100037, China;1. School of Geography, University of Nottingham, NG7 2RD, UK;2. Department of Geography and Earth Sciences, Aberystwyth University, SY23 3DB, UK;3. Limnological Research Center (LRC), University of Minnesota, Minneapolis MN 55455, USA;1. Department of Earth Sciences, University of Bergen, N-5007 Bergen, Norway;2. Department of Geosciences and Geography, University of Helsinki, FI-00014 Helsinki, Finland;3. School of Earth Sciences & Environmental Sustainability, Northern Arizona University, Flagstaff, AZ, USA;4. Department of Earth Sciences and Institute of Earth Sciences, University of Iceland, IS-101 Reykjavik, Iceland;5. GEOTOP, Université du Québec à Montréal, Montreal, Canada;6. Department of Earth Sciences, VU University Amsterdam, NL-1081HV Amsterdam, The Netherlands;7. Norwegian Polar Institute, Fram Centre, N-9296 Tromsø, Norway;8. Institute of Arctic and Alpine Research, University of Colorado & Department of Geological Sciences, Boulder, USA |
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| Abstract: | A strong mid-Holocene transition has been identified by wavelet analyses in several sea ice cover records from the circum-Antarctic area, ice core records (Taylor dome, Byrd) and tropical marine records. The results are compared with those previously published in a synthesis of North Atlantic records and with 4 new records from the Norwegian and Icelandic seas and from a coastal site in Ireland. These new records confirm the previous pattern for the North Atlantic area, extend this pattern nearly to the Arctic Circle, and include a continental record. We further tested the possibility of extending this scheme using continental records from South America. The Holocene pattern proposed here confirms the importance of external forcing during the Early Holocene (solar activity: 1000 years cyclicity and 2500 years during the entire Holocene), even if the signal is disturbed by meltwater fluxes. The second part of the Holocene is then marked by the gradual appearance of internal forcing (thermohaline circulation around 1500 years), associated with a stabilisation of the signal. Coupling between ocean and atmosphere seems to play a fundamental role in the observed frequencies which vary accordingly in the Atlantic, circum-Antarctic and Pacific areas. The North Atlantic area seems to be the instigator of thermohaline circulation as shown by its sensitivity to meltwater discharges during the Early Holocene, even though each sector is independent with regards to its frequency content (around 1600 years for Atlantic Area; around 1250 years for Antarctica). The Holocene methane pattern, still under debate Ruddiman, W.F., 2003a. Orbital insolation, ice volume and greenhouse gases. Quaternary Science Review 22, 1597–1629; Ruddiman, W.F., 2003b. The anthropogenic greenhouse era began thousands of years ago. Climatic Change 61, 261–293], could be explained by a more efficient thermohaline circulation around the mid-Holocene with an anthropogenic effect initiated at  2500 BP as shown by the inter-hemispheric gradient. |
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