The Paleocene and particularly the early Eocene are characterized by high global mean temperatures and carbon dioxide levels. Therefore, this period is considered  as a deep-time analog for future global warming, induced by anthropogenic greenhouse gas emissions. Thorough and critical paleotemperature proxy development is crucial in order to establish reliable paleoclimate reconstructions.

The purpose of this PhD study is to critically assess the application of fish otolith (ear stones with seasonal growth rings) O and C stable isotopes as reliable paleotemperature and seasonality proxies for the early Paleogene. Fish otolith ¹⁸O/¹⁶O-ratios are known to precipitate in equilibrium with those of ambient water, and fractionation is directly related to temperature (e.g. Thorrold et al., 1997).

The main objective is to erect a latitudinal and seasonal record of fish otolith paleotemperature data throughout the early Paleogene greenhouse climate, in the shallow marine North Sea Basin. A selection of about thousand otoliths from the otolith collection of the Royal Belgian Institute of Natural Sciences will be sampled and their O and C stable isotope signature measured. The sampling comprises mainly otoliths of bottom-dwelling fish, representing sea floor temperatures.

The research includes the following additional subthemes: the quantification of ambient water isotope compositions through the combination of our proxy with the new method of ‘clumped isotope’ paleothermometry, and the quantification of migration effects on the isotope signatures by comparison of analyses measured on recent and fossil otoliths of migrating and non-migrating commercial fishes (e.g. Gadiids, Congrids).

Related publications

• Vanhove, D., Stassen, P., Speijer, R. P., Claeys, P. & Steurbaut, E. Intra- and Intertaxon stable O and C isotope variability of fossil fish otoliths: an early Eocene test case. Austrian Journal of Earth Sciences 105, 200-207 (2012).
• Vanhove, D., Stassen, P., Speijer, R. P. & Steurbaut, E. Assessing paleotemperature and seasonality during the early Eocene climatic optimum (EECO) in the Belgian Basin by means of fish otolith stable O and C isotopes. Geologica Belgica 14, 143-158 (2011).