"Accurate reconstructions of past climate changes are essential to understand e.g. the sensitivity of Earth’s climate to global increases in atmospheric greenhouse gasses such as CO2. For these reconstructions it is vital to have proxies which are well constrained and are able to provide robust quantitative estimates. However, it has become clear that currently used proxies are sometimes associated with large uncertainties and thus more proxies are needed in order to perform reliable paleoclimate reconstructions.In my group we are developing new proxies based on so-called long chain diols. These compounds are synthesized by several groups of algae and occur abundantly in present day oceans as well as ancient sediments. Initial results have shown that one set of compounds, the 1,14-diols, can be used to reconstruct past primary productivity and upwelling conditions. Excitingly, the distribution of another set of compounds, the long chain 1,13- and 1,15-diols, show a strong relationship with sea surface temperature and can be used to reconstruct past sea surface temperatures in several parts of the oceans. Finally, culture experiments indicate that the stable carbon isotopic composition of diatoms producing 1,14-diols is strongly related to CO2 concentrations, raising the possibility that it may be used to reconstruct ancient pCO2 levels.In this ERC proposal I want to develop, test and apply these exciting new proxies in order to provide robust and accurate reconstructions of past oceans. To this end this ERC project is subdivided in several different subprojects, each designed to investigate long chain diol proxies but from a different perspective, in particular cultivation and molecular biology, organic geochemistry, (paleo)limnology and paleoceanography. The combination of these subprojects will result in a highly multidisciplinary project needed to make progress in the development of these unique proxies."