An important part of climate variability takes place at the sub-annual to decadal scale. However, climate reconstructions mostly focus on long-term trends (thousands to millions of years), while data of past, fast and short-term changes is limited. To calibrate climate models and extend our knowledge of the causes and effects of rapid climate change, archives recording higher resolution climate change are needed. Contrary to sedimentary records, bivalve shells record environmental conditions at a resolution of days to months. Conventional climate proxies in bivalve shells (stable isotopes and trace elements) depend on multiple physiological and environmental parameters, complicating the reconstruction of individual climate parameters. UNBIAS aims to develop new, more accurate tools for absolute reconstructions of climate parameters on a sub-annual scale from bivalve shells. Parameters influencing climate proxies will be disentangled by combining state-of the art trace element and microstructure analyses with the new powerful carbonate clumped isotope method, which reconstructs absolute temperature. These techniques are applied directly on cross sections through shells of Arctica islandica, Ostrea edulis and Cerastoderma edule. 

• dr. Niels de Winter

Projections of future sea-level rise due to polar ice-sheet loss are vital but difficult to make on the basis of modern observations. Determining how ice sheets have varied in volume during key periods in the past - Eemian, Pliocene Warm Period - can help us to better constrain ice-sheet sensitivity to elevated global temperatures. At present foraminiferal oxygen isotope records are key to this approach and reveal vast ice-volume changes during Earth’s history. A major limitation of this method lies in the fact that the isotope signal combines both, deep-sea temperature and ice-volume. Until now, no reliable proxy data exists that is capable of isolating the two components. The carbonate clumped isotope thermometer has great potential to solve this problem. In this project, this innovative technique on benthic foraminiferal carbonate to determine deep-sea temperatures over the last 65 million years. 

• dr. Ilja Kocken

This project established the carbonate clumped isotope lab at Utrecht University, in order to produce more accurate temperature reconstructions of past hot-house climates such as the Early Eocene.