On-going atmospheric and ocean warming is increasingly causing Antarctic ice-sheet volume imbalance and melting. Effective mitigation and adaptation to the consequences of resulting sea-level rise require accurate future projections. However, despite advances in spatial resolution and complex physics, numerical model projections of ice sheet melt are too uncertain, mostly because the ice-ocean interactions are poorly represented. Significant progress in numerical modeling can be obtained by improving their adequacy in reproducing ice volume changes that occurred during past episodes of warming. This requires accurate reconstructions of past ice sheet behaviour for crucial time periods. Oligocene and Miocene (~34-5 Ma ago) atmospheric CO2 concentrations often exceeded that of presentday and the few available paleo-records seem to suggest a dramatic response of the Antarctic ice sheet to past climate changes, providing a prime target for fundamental improvements to future projections. This project aims at reconstructing Oligocene-Miocene oceanographic and coupled ice-sheet variations based on generating key data from circum-Antarctic marine sediments. Our recent key findings allow us to (1) date Southern high latitudes sediments in unprecedented detail using microfossils and (2) reconstruct past sea-ice cover, temperature and ocean structure using biological and geochemical indicators preserved in these sediments. Quantification of such crucial parameters from critical locations around Antarctica will provide the mechanistic understanding required to significantly improve coupled climate-ocean-ice models. In addition, this work will highlight regions where the Antarctic ice-sheet is most sensitive to climate warming, ultimately leading to more accurate sea level projections.

• dr. Francesca Sangiorgi
• dr. ir. Francien Peterse
• dr. Peter Bijl
• dr. F.S. (Frida) Hoem

Unraveling the stability of the Antarctic cryosphere from its inception during the Greenhouse–Icehouse transition (~34 Ma) through the subsequent periods of climate and atmospheric CO2 changes, is a major current scientific theme. Moreover, Southern Ocean dynamics and phytoplankton productivity is important for global biogeochemical cycling, including the sequestration of carbon dioxide (CO2) and the global carbon balance. The recent (2010) drilling of the Wilkes Land (WL) margin (East Antarctica) now provides an unprecedented long-term record of the Cenozoic East Antarctic climate history. Organic remains of dinoflagellates (dinocysts) are abundant throughout the record, and, importantly, are at times the sole microfossil group preserved. Preliminary analyses indicate that the dinocyst assemblages yield a strong paleoenvironmental signal that is likely strongly dependant from cryosphere dynamics, as (heterotrophic) dinoflagellates record sea-ice cover and oceanic polar fronts. Combined with organic geochemical analyses, and within a multidisciplinary context, the stratigraphic and environmental potential of Antarctic dinoflagellate cyst will serve to document trophic state, sea ice coverage and ocean circulation over critical intervals of the last 34 Ma. This information is crucial to quantify ice sheet dynamics and evaluate the vulnerability of Antarctic ecosystems under changing climate forcing.

• dr. Peter Bijl