ALBERT

Description: The drill of the EPICA Dome C ice core has been completed almost 20 years ago. This ice core already provided many reference records for climate and atmospheric greenhouse gase concentrations over the last 800,000 years, hence covering 9 glacial interglacial transitions or glacial terminations. These records combined to records from other archives have already shown the diversity in term of amplitudes and durations of the last 9 glacial terminations occurring in different orbital contexts. Still, the relatively low resolution of the current records hampered a good chronology of the oldest deglaciations as well as the study of the rapid climatic variability at centennial to multi-millennial scale superimposed to the longer term orbital climatic variability. Here, we will present high resolution measurements of water and air isotopes on the EPICA Dome C ice core over the last 800,000 years with a particular focus on glacial terminations. These new data enable to improve the chronology of the EPICA Dome C ice core hence improving the link between orbital forcing and climatic variability, especially for the period between 800,000 years and 200,000 years before present. In addition, our relatively high resolution records (50-300 years) of water and air isotopes enable us to describe on the same chronology the occurrence of millennial scale variability in the low to mid latitudes over the terminations 2, 3, 4 and 5 (occurring between 440,000 and 120,000 years before present) while local climate at the drilling site of EPICA Dome C has a much smoother evolution.

Description: Water isotopes measurements in polar ice cores are key to reconstruct past climatic variations. However, the relationship between surface temperature and water isotopic composition is not straightforward because snow isotopic composition is influenced by many factors in addition to local temperature of condensation (evaporation origin, trajectory of moist air, post deposition effects). In order to refine this interpretation, parallel observation of water vapor and surface snow isotopic composition in polar regions is essential. Measuring atmospheric water isotopic composition is however an important challenge, especially in dry places like the East Antarctic plateau, where water mixing ratio can be as low as 10 ppmv. Laser spectrometers based on the cavity ring-down spectroscopy (CRDS), commonly used for field measurement, fail to precisely measure water vapor isotopic composition for the lower range of water mixing ratios recorded in East Antarctica.The optical feedback cavity enhanced absorption spectroscopy (OF-CEAS) technique offers an interesting alternative for low humidity detection. During the austral summer 2022 – 2023, two OF-CEAS spectrometers were respectively installed at Dumont-d’Urville, situated along the coast, and Dome C, situated on the plateau, at 3230 m above sea level. We present here results obtained with this OF-CEAS technique, which shows an improved limit of detection, while keeping a low humidity dependence.This work is part of the AWACA ERC project, in which we intend to install several OF-CEAS instruments, in three remote sites situated along the Dumont-d’Urville – Dome C transect, in addition to the two permanent polar stations.

Description: Dome C is located on the high Antarctic plateau, at 3233m above sea level, and 1200km away from the coastline. At this location, the EPICA ice core was retrieved from the ice sheet and allowed the reconstruction of past climatic information 800,000 years back in time. Amongst several atmospheric parameters, the past local temperature was inferred from the stable water isotope record measured in the ice.To interpret this record, it is necessary to understand how it was formed in such a dry and cold environment. This includes understanding the water cycle dynamics in Antarctica, from evaporation to precipitation and moisture pathways, as well as the processes affecting the record after deposition of the precipitation, such as snow-atmosphere exchanges.During the austral summer 2018-2019, a Picarro laser spectrometer was installed on site to monitor continuously the isotopic composition of the atmosphere. It provided measurements for all austral summers since then and allowed the detection of two major atmospheric river events, including a rare event during the onset of the cold Antarctic winter. To go beyond the limitations of the Picarro instrument when measuring at very low humidity levels, as encountered during the wintertime at Dome C, a new laser spectrometer dedicated to low humidity measurements has been developed and installed it in parallel to the Picarro instrument during the summer season 2022-2023. Here we present the results of the atmospheric isotopic composition during four consecutive austral summers and the comparison of the two laser instruments during the most recent period.