To understand the phasing of external forcing (amount of solar energy received at the Earth’s surface), climate response and internal feedbacks (greenhouse gases concentration, ice sheet dynamics, oceanic and atmospheric circulations, …) dating climate archives is crucial. Ice cores are unique archives because they provide a direct record of greenhouse gas concentration. However, dating ice cores is particular since they require two chronologies: one for the ice and one for the younger air trapped in bubbles.

The temperature of the Earth is one of the most important climate parameters. Proxy records of past climate changes, in particular temperature, represent a fundamental tool for exploring internal climate processes and natural climate forcings. Despite the excellent information provided by ice core records in Antarctica, the temperature variability of the past 2000 years is difficult to evaluate from the low-accumulation sites in the Antarctic continent interior. Here we present the results from the Aurora Basin North (ABN) ice core (71∘ S, 111∘ E, 2690 m a.s.l.) in the lower part of the East Antarctic plateau, where accumulation is substantially higher than other ice core drilling sites on the plateau, and provide unprecedented insight into East Antarctic past temperature variability.

We present an age model for the 651 m deep ice core from Skytrain Ice Rise, situated inland of the Ronne Ice Shelf, Antarctica. The top 2000 years have previously been dated using age markers interpolated through annual layer counting. Below this, we align the Skytrain core to the AICC2012 age model using tie points in the ice and air phase, and we apply the Paleochrono program to obtain the best fit to the tie points and glaciological constraints.

The isotopic composition of dioxygen in the atmosphere is a global tracer which depends on the biosphere flux of dioxygen toward and from the atmosphere (photosynthesis and respiration) as well as exchanges with the stratosphere. When measured in fossil air trapped in ice cores, the relative concentration of ¹⁶O, ¹⁷O, and ¹⁸O of O₂ can be used for several applications such as ice core dating and past global productivity reconstruction. However, there are still uncertainties about the accuracy of these tracers as they depend on the integrated isotopic discrimination of different biological processes of dioxygen production and uptake, for which we currently have very few independent estimates. Here we determined the respiration and photosynthesis fractionation factors for atmospheric dioxygen from experiments carried out in a replicated vegetation–soil–atmosphere analogue of the terrestrial biosphere in closed chambers with growing Festuca arundinacea (Fig. 1).

The EPICA Dome C (EDC) ice core provides the longest continuous climatic record covering the last 800,000 years (800 kyrs). The high resolution (11 cm) water isotopic record (δ¹⁸O and δD) is available for the EDC ice core and accounting for water isotopic diffusion provides a unique opportunity to investigate decadal to millennial variability during past glacial and interglacial periods.

La productivité primaire de la biosphère globale via la photosynthèse est le plus fort flux d’absorption de dioxyde de carbone atmosphérique. Il est donc essentiel de comprendre sa variabilité naturelle pour une meilleure projection du futur cycle du carbone. Les observations modernes indiquent une relation étroite entre la productivité globale et la concentration de dioxyde de carbone atmosphérique, par l’effet de fertilisation du carbone. Cependant, aucune donnée ne permet de documenter la persistance de ce mécanisme de rétroaction pour différentes configurations climatiques et différentes concentrations en dioxyde de carbone.

Dans le cadre d’une étude internationale menée par une équipe française, nous avons effectué les premières mesures du rapport isotopique triple du dioxygène atmosphérique couvrant les 800 000 dernières années à partir de l’analyse des bulles d’air extraites de la carotte de glace EPICA Dome C. Le rapport isotopique triple du dioxygène de l’air est un traceur unique de la productivité de la biosphère globale, incluant la productivité terrestre et océanique, contrairement à d’autres enregistrements paléoclimatiques de la productivité qui sont locaux ou régionaux. En combinant notre série de mesures et des modèles simples représentant les processus importants d’échange de dioxygène dans la biosphère et la stratosphère, nous avons pu quantifier les changements de productivité de la biosphère globale lors des changements glaciaires – interglaciaires et pendant les périodes glaciaires des 800 000 dernières années.

Pouvant contribuer de manière significative aux variations du niveau marin, la question de la stabilité de la calotte polaire de l’Antarctique de l’Est face aux réchauffements atmosphériques et océaniques est encore largement ouverte. Alors que l’on a pu observer ces dernières décennies une diminution de l’épaisseur de glace et des pertes de masse accrues dans la région du bassin sous-glaciaire de Wilkes, cette question revêt une importance capitale.