April 29, 2021
16h30
The Antarctic Ice Sheet is the biggest reservoir of fresh water on Earth, that represents a potential 57 meters sea-level rise if the entire Ice Sheet melted. Therefore, any changes in its mass has a large impact on the global sea-level. During the 20th century, the Antarctic Ice Sheet has gained mass at its surface through an enhanced snow accumulation. This increase has mitigated the global sea-level rise by about 1 centimeter during the past century. However, our understanding of the Antarctic snow accumulation variability is still limited due to a sparse observational instrumental network that only covers a short period of time. This directly impacts on our confidence in the origin of the 20th century increase and the future contribution of the Antarctic Ice Sheet to the sea-level rise. The main objective of this thesis is to highlight the physical mechanisms behind snow accumulation variability by investigating the links between snow accumulation and other variables characterizing the surface climate at high southern latitudes. As the observational network is particularly limited in the Antarctic, the present work is based on various types of data – instrumental observations, paleoclimate records and climate model simulations –, focused on different time periods – from the last millennium to the 21st century – and uses diverse methodologies, such as a data assimilation procedure.
Our results show that the variability in snowfall and temperature are strongly related over Antarctica, and therefore that the classical Clausius-Clapeyron relationship explains relatively well the multi-decadal, regional to continental-scale snow accumulation changes. In contrast, modifications in the atmospheric circulation plays an important role in the year-to-year variations, in particular at smaller scales. Additionally, the local link between the temperature and snow accumulation can changes with time and depend on small modifications of the mean state, in particular of the atmospheric circulation. Our work also highlights that data assimilation is particularly appropriate for reconstructing the surface climate changes in the Antarctic over the past centuries as the observational network is sparse and includes various types of records and because of the non-stationarity of the link between the proxy records and reconstructed variables. With this technique, we have been able to provide robust past estimates for temperature and snow accumulation but also of variables that cannot be directly obtained from the record themselves such as the atmospheric circulation and even the sea-ice coverage.
en téléconférence et publiquement accessible via le lien
Meeting ID: 872 7870 8561
Passcode: 451010