Antarctic ice sheets are destabilizing because Southern Ocean warming causes basal melt. It is unknown how these processes will develop during future climate warming, which creates an inability to project ice sheet

melt and thus global sea level rise scenarios into the future. Studying past geologic episodes, during which atmospheric carbon dioxide levels (CO2) were similar to those projected for this century and beyond, is the only way to achieve mechanistic understanding of long-term ice sheet- and ocean dynamics in warm climates.

Past ocean-induced ice sheet melt is not resolved because of a paucity of quantitative proxies for past ice-proximal oceanographic conditions: sea ice, upwelling of warm water and latitudinal temperature gradients. This hampers accurate projections of future ice sheet melt and sea level rise. OceaNice will provide an integral understanding of the role of oceanography in ice sheet behavior during past warm climates, as analogy to the future. I will quantify past sea ice, upwelling of warm water and latitudinal temperature gradients in three steps:

1. Calibrate newly developed dinoflagellate cyst and biomarker proxies for past oceanographic conditions to glacial-interglacial oceanographic changes. This yields quantitative tools for application further back in time.

2. Apply these to two past warm climate states, during which CO2 was comparable to that of the future under strong and moderate fossil fuel emission mitigation scenarios.

3. Interpolate between new reconstructions using high-resolution ocean circulation modelling for circum- Antarctic quantification of past oceanographic conditions, which will be implemented into new ice sheet model simulations.

The groundbreaking new insights will deliver mechanistic understanding and quantitative estimates of iceproximal oceanographic changes and consequent ice sheet melt during past warm climates, which will finally allow accurate future sea level rise projections given anticipated warming.

• Mariska Hoorweg
• dr. F.S. (Frida) Hoem
• Suning Hou MSc

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.

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
• prof. dr. Henk Brinkhuis
• dr. ir. Francien Peterse
• dr. F.S. (Frida) Hoem

Uncertainties in the climatic responses to the current increase in atmospheric carbon dioxide (CO2) concentrations threat economic stability and societal welfare. One way to improve projections of the Earth’s response to increased CO2 is the study of past episodes with high CO2 concentrations. While reconstructions of the very warm and high- CO2 climates of the Eocene ‘hothouse’ (56-34 million years ago) have provided valuable insights in a potential ‘end-member climate state’, we lack insight in the transition towards such a ‘hothouse’ climate. The transition from the cold (and possibly glaciated) mid-Paleocene (~60 Ma) to the ‘hothouse’ of the Eocene (~50 Ma), albeit on longer time scales, bears similarities to the climatic transition of our future; mid-Paleocene CO2 concentrations were similar to today, while those of the Eocene approach the predicted levels when all fossil fuels are combusted.

In this project I will reconstruct the paleo-climates of the sparsely studied and cold mid- Paleocene and the subsequent late Paleocene to Eocene warming. I will estimate surface paleotemperature (1) sea level changes (2) and global carbon cycle dynamics (3), by integrating results from organic biomarker proxies (e.g., TEX86) dinoflagellate cyst assemblages and carbon cycle box modelling. The results of my work will be evaluated using ice-sheet- and fully coupled climate models, for an integrated perspective of the climatic reversal that took place in the Paleocene. A better understanding of the mechanisms causing the climatic transition during the Paleocene will help better constrain the sensitivity of global climates to future CO2 forcing.

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.

• prof. dr. Henk Brinkhuis