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abstracts
δ15N measurements of nitrogen gas trapped in ice cores during Marine Isotopic Stage 3 at Berkner Island, Antarctica
Francis Mani, Robert Mulvaney, William Sturges, Paul Dennis, Jérôme Chappellaz, Jean-Marc Barnola, Daphné Buiron, Amaelle Landais, Emilie Capron
An ice core from Berkner Island, a coastal site on the Weddell Sea facing the Southern Atlantic Ocean, provides a new climate record and further insights into the phasing relationship of Northern/Southern Hemisphere climate changes. Isotopic measurements (δD and δ18O) show two distinct peaks during MIS 3 corresponding to the AIM 8 and AIM 12 climate events. High resolution δ15N measurements of air occluded in bubbles were carried out across these two events and changes of ~ +0.07‰ in δ15N were observed. Attempts to extract the thermal isotopic anomaly for the two climatic events were unsuccessful due to the inability of the firn diffusion model to reproduce the magnitude of this fractionation, while δ15N excess calculations were hindered by the scatter in the δ40Ar measurements. The ∆depth of 2 m obtained by matching variations in δD and δ15N is consistent with the model predictions, hence constraining the chronology of the ice core. Based on the classical δD/temperature spatial relationship a warming of approximately 3˚C for the AIM 8 event and 5˚C for AIM 12 was obtained. Another δ15N change of +0.18 ‰ was observed around 33,000 Yrs BP, which does not correlate to any events in the δD profile but correlates with the period where large altitudinal changes occurred in the ice sheet at Berkner Island. An important aspect of this study is the opportunity it provides to phase δ15N with methane, the latter being considered as a proxy for climate change in the northern hemisphere. Preliminary methane data show that the time lag for climate events between the northern hemisphere and southern hemisphere is on the order of a few hundred years.
Francis Mani, School of Environmental Sciences, University of East Anglia,Earlham Road, Norwich, NR4 7TJ, United Kingdom, f.mani@uea.ac.uk
Robert Mulvaney, British Antarctic Survey, Physical Sciences Division, Cambridge, CB3 0ET, United Kingdom
William Sturges, University of East Anglia, School of Environmental Sciences, Norwich, NR4 7TJ, United Kingdom
Paul Dennis, University of East Anglia, School of Environmental Sciences, Norwich, NR4 7TJ, United Kingdom
Jérôme Chappellaz, CNRS, Laboratoire de Glaciologie et Géophysique de l'Environnement, 54 rue Molière, BP 96, 38402 Saint-Martin-d'Hères Cedex, France
Jean-Marc Barnola, CNRS, aboratoire de Glaciologie et Géophysique de l'Environnement, 54 rue Molière, BP 96, 38402 Saint-Martin d'Hères Cedex, France
Daphné Buiron, CNRS, aboratoire de Glaciologie et Géophysique de l'Environnement, 54 rue Molière, BP 96, 38402 Saint-Martin d'Hères Cedex, France
Amaelle Landais, CNRS, Laboratoire des Sciences du Climat et de l'Environnement , Gif-sue-Yvette, France
Emilie Capron, CNRS, Laboratoire des Sciences du Climat et de l'Environnement, Gif-sur-Yvette, France
Session: F1: Climate Forcings
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