Past changes in coccolithophorid calcification

Because measurements of the thickness of fossil coccoliths can be used to estimate the degree of cellular calcification, we are also reconstructing long term changes in the calcification of coccolithophores. Such datasets allow us to examine if there is evidence for short or long term selective pressures on calcification related to changes in CO₂, temperature, or the structure of the upper ocean. Such study requires careful evaluation of the influence of dissolution/preservation on the estimates of thickness and calcification. It also requires development of new techniques for calibration of coccolith thickness, in collaboration with Miguel Angel Fuertes and Jose Abel Flores of the University of Salamanca. These techniques will enable, for the first time, data on the cellular calcification of the full population of coccolithophorid algae from the fossil record, rather than limited to the small coccoliths of thickness less than 1.5 microns.  

Current applications of this approach include evaluation of calcification changes over the last million years and their relationship with changes in ocean carbon chemistry and nutrients. We are also studying exceptionally well preserved coccoliths from the Oligocene and Miocene periods which coincide with a period of major inferred CO₂ decline.  

This project is supported by Swiss National Science Foundation for PhD student Jose Guitian, and a scholarship from the China Scholarship Council for visiting PhD student Hongrui Zhang.  

Publications

González-Lemos, S., Guitián, J., Fuertes, M.-Á., Flores, J.-A., & Stoll, H. M. An empirical method for absolute calibration of coccolith thickness. Biogeosciences, 2018.

Bolton, C.T., Hernandez-Sanchez, M T. , Fuertes, M-Á. , Gonzalez-Lemos, S., Abrevaya, L., Mendez-Vicente, A., Flores, J.A., Probert, I., Giosane, L. , Johnson, J., and Stoll, H.M., 2016. Decrease in coccolithophore calcification and CO₂ since the middle Miocene. Nature Communications 7.