A diverse group of NESSC-researchers is presenting a poster of their work at the 12th International Conference on Paleoceanography (ICP12) this week. Among them are Caitlyn Witkowski, Anne Roepert, Carolien van der Weijst and Robin van der Ploeg:

Caitlyn Witkowski

“For my PhD-research, I’m developing a proxy for the atmospheric CO2-concentrations during the earth’s geological history. There are already many proxies available for this, but unfortunately, they have great uncertainties, especially beyond fifty million years ago. This is a huge problem for our understanding on carbon dioxide, a keystone of the carbon cycle, biosphere, and climate change.

On my poster, I present a general phytoplankton biomarker as a proxy for atmospheric CO2 using the stable carbon isotopic fractionation due to carbon fixation. We use this general biomarker, phytane, because it is ubiquitous in the sediment record for over 600 Ma, possibly averages species-specific concerns, maintains a stable isotopic composition, and is readily analyzable. Our compilation indicates much less uncertainty than other long-scale proxies in reconstructing CO2-concentrations back to 600 million years ago. To validate this proxy, we study marine algae in different CO2 conditions in both fieldwork at CO2 seeps and in lab cultures.”


ICP12_Anne Roepert
Anne Roepert

“On my poster I present the first data of my research which focusses on developing a proxy for reconstructing seawater salinity. Several proxies are already available to reconstruct seawater temperatures of the geological past, but proxies for salinity are only in development – which is a problem for the modelling of ocean currents.

Specifically, I’m investigating whether chlorine ions which are incorporated as trace element in coccoliths, the microscopic skeletons of single-celled calcifying algae, could serve as a salinity proxy. To test whether the chlorine content of cocooliths show a relation with salinity, we’ve taken samples from the Mediterranean and the Black Sea. Although the chlorine content does appear to vary between the investigated sites, our first results show no indication yet of a corresponding link to salinity. Whether other factors, such as the growth rate of the coccoliths or water temperature, are of influence to the chlorine concentration, still needs to be investigated further.”


Carolien van der Weijst

“I present on my poster the preliminary results of my reconstruction of ocean surface temperature in the Eastern Equatorial Atlantic Ocean during the Late Pliocene, approximately 3 million years ago.

At that time, Earth’s climate was 2 to 3 degrees warmer compared to today. Climate change scenarios suggest a similar global temperature increase for the next century. The climate system of the Late Pliocene thus forms an analogue climate system for studying projected future climate change, which makes it an important study target.

To reconstruct past ocean temperature, I study fossil molecules of marine microbes. The first results suggest that the Eastern Equatorial Atlantic was not much warmer, or possibly cooler than it is today – even while the Earth as a whole was significantly warmer. Only by combining the results obtained with different techniques, can we ensure that our reconstructions are accurate. I will therefore continue to study dinoflagellates – microfossil communities which are very sensitive to environmental change, and thus are a perfect addition to our chemical techniques.”


Robin van der Ploeg

“I study the cause of the high atmospheric CO2 concentrations during the middle Eocene, a time period about 40 million years ago. Using osmium-isotopes, preserved in marine sediments, we’ve made an estimate of the rate of erosion and chemical weathering on land during that time.

One would expect a high rate of weathering and erosion during a period with high temperatures. Interestingly, we have found that the rate was relatively low during this time period, even while temperatures were high.

We now have proposed the idea that this low rate of weathering and erosion has contributed to causing the high temperatures during the middle Eocene. This is a rather controversial idea and there still are many questions that need further investigation. The hypothesis has already sparked many discussions and questions at my poster!”