The statistical analysis of compositional data

Statistics for spatial data: by Noel Cressie, 1991, John Wiley & Sons, New York, 900 p., ISBN 0-471-84336-9, US $89.95

The most direct method of investigating past variations of the atmospheric CO2 concentration before 1958, when continuous direct atmospheric CO2 measurements started, is the analysis of air extracted from suitable ice cores. Here we present a new detailed CO2 record from the Dronning Maud Land (DML) ice core, drilled in the framework of the European Project for Ice Coring in Antarctica (EPICA) and some new measurements on a previously drilled ice core from the South Pole. The DML CO2 record shows an increase from about 278 to 282 parts per million by volume (ppmv) between ad 1000 and ad 1200 and a fairly continuous decrease to a mean value of about 277 ppmv around ad 1700. While the new South Pole measurements agree well with DML at the minimum at ad 1700 they are on average about 2 ppmv lower during the period ad 1000–1500. Published measurements from the coastal high-accumulation site Law Dome are considered as very reliable because of the reproducibility of the measurements, high temporal resolution and an accurate time scale. Other Antarctic ice cores could not, or only partly, reproduce the pre-industrial measurements from Law Dome. A comparison of the trends of DML and Law Dome shows a general agreement. However we should be able to rule out co-variations caused by the same artefact. Two possible effects are discussed, first production of CO2 by chemical reactions and second diffusion of dissolved air through the ice matrix into the bubbles. While the first effect cannot be totally excluded, comparison of the Law Dome and DML record shows that dissolved air diffusing to bubbles cannot be responsible for the pre-industrial variation. Therefore, the new record is not a proof of the Law Dome results but the first very strong support from an ice core of the Antarctic plateau.

Supporting evidence from the EPICA Dronning Maud Land ice core for atmospheric CO2 changes during the past millenium

Le pollen conserve dans les sediments lacustres constitue un indicateur essentiel pour reconstruire l' evolution de la vegetation et du climat passes sur les continents. Actuellement, les reconstructions climatiques se basent sur des modeles statistiques decrivant le lien climat-pollen. Ces modeles posent des problemes methodologiques car ils sont tous bases sur l'hypothese que la relation pollen-climat est constante au cours du temps, impliquant que les parametres non climatiques determinant cette relation aient une influence faible. Cela est contredit par les developpements recents en ecologie et en ecophysiologie. C'est pourquoi, dans ce travail, nous developpons une approche integrant un modele dynamique de vegetation et les processus majeurs liant la vegetation au pollen capte par les lacs. Le cadre bayesien fournit une base theorique ainsi que les outils pour inferer les parametres des modeles et le climat passe. Nous utilisons ces nouveaux modeles pour reconstruire le climat de l'Holocene en differents sites europeens. Cette approche qui permettra des reconstructions spatio-temporelles requiert encore des developpements autour de l'inference de modeles semi-mecanistes.

Approche bayésienne de la reconstruction des paléoclimats à partir du pollen : vers la modélisation des mécanismes écologiques

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Approche bayésienne de la reconstruction des paléoclimats à partir du pollen : vers la modélisation des mécanismes écologiques