The Antarctic temperature changes over the past millennia remain more uncertain than in many other continental regions. This has several origins: (1) the number of high-resolution ice cores is small, in particular on the East Antarctic plateau and in some coastal areas in East Antarctica; (2) the short and spatially sparse instrumental records limit the calibration period for reconstructions and the assessment of the methodologies; (3) the link between isotope records from ice cores and local climate is usually complex and dependent on the spatial scales and timescales investigated. Here, we use climate model results, pseudoproxy experiments and data assimilation experiments to assess the potential for reconstructing the Antarctic temperature over the last 2 millennia based on a new database of stable oxygen isotopes in ice cores compiled in the framework of Antarctica2k (Stenni et al., 2017).

Tropospheric ozone (O3) is key component of air pollution and an important anthropogenic greenhouse gas. During the 20th century, proliferation of the internal combustion engine, rapid industrialization, and land-use change led to a global-scale increase in its concentrations, but the magnitude of this increase is not known. Atmospheric chemistry models typically predict an increase in the tropospheric O3 burden of less than 50% since 1900,1,2 while direct measurements made in the late 19th century imply that surface O3 mixing ratios increased by much more, up to 300%3-5.

The Antarctic ice sheet mass balance is a major component of the sea level budget and results from the difference of two fluxes of a similar magnitude: ice flow discharging in the ocean and net snow accumulation on the ice sheet surface, i.e. the surface mass balance (SMB). Separately modelling ice dynamics and SMB is the only way to project future trends. In addition, mass balance studies frequently use regional climate models (RCMs) outputs as an alternative to observed fields because SMB observations are particularly scarce on the ice sheet.

Each glacial – interglacial transition of the Quaternary occurs in a different orbital context leading to various timing for the deglaciation and sequence of high vs low latitudes events. Termination 3, 250 kiloyears before present (ka), is an unusual deglaciation in the context of the last 9 deglaciations recorded in the old EPICA Dome C (EDC) Antarctic ice core: it exhibits a three–phase sequence, two warming phases separated by a small cooling, the last phase suggesting a particularly rapid temperature increase. We present here new high resolution d¹⁵N and deuterium excess (d–excess) data from the EDC ice core to provide a detailed temperature change estimate during this termination. Then, we combined the dD and d¹⁸O to discuss the relationship between high and low latitude changes through the d-excess. We also provide the high vs low latitude sequence of events over this deglaciation without chronological uncertainty using low latitude ice core proxies. In agreement with previous studies based on speleothem analyses, we show that the first phase of Termination 3 (256 to 249 ka) is associated with small Heinrich like events linked to changes in ITCZ position, monsoon activity and teleconnections with Antarctica. In a context of minimum Northern Hemisphere insolation, this leads to a rather strong Antarctic warming, as observed in the d¹⁵N record in contrast to the relatively small dD increase. The second warming phase occurs during the rise of the Northern hemisphere insolation, with a large Heinrich like event leading to the characteristic Antarctic warming observed in the d¹⁵N and dD increase as for the more recent terminations.

Auteurs : C. Bréant, A. Landais, A. Orsi, P. Martinerie, T. Extier, F. Prié, V. Masson-Delmotte, J. Jouzel, M. Leuenberger

Ref. : Quaternary Science Reviews, 211, 156-165, 2019

Projet/financement: ERC Combiniso, LEFE NEVE/CLIMAT

Dumont d’Urville station, located on the East coast of Antarctica in Adélie Land, is in one of the windiest coastal region on Earth, due to katabatic winds downslope from the East Antarctic ice sheet. In summer, the season of interest in this study, coastal weather is characterized by well-marked diel cycles in temperature and wind patterns.

Continuer la lecture de Coastal water vapor isotopic composition driven by katabatic wind variability in summer at Dumont d’Urville, coastal East Antarctica →

The Antarctic ice sheet mass balance is a major component of the sea level budget and results from the difference of two fluxes of a similar magnitude: ice flow discharging in the ocean and net snow accumulation on the ice sheet surface, i.e. the surface mass balance (SMB). Separately modelling ice dynamics and SMB is the only way to project future trends.

Continuer la lecture de Estimation of the Antarctic surface mass balance using the regional climate model MAR (1979–2015) and identification of dominant processes →