Understanding C and Ca acquisition by coccolithophores

One focus is on the mechanisms for carbon acquisition and allocation in coccolithophorids. Carbon acquisition and allocation are proposed to vary with ocean pH and CO₂ aq. Contrasting models have been suggested, including our “reallocation hypothesis” (Bolton and Stoll, Nature, 2013) which proposed that under C limitation, coccolithophores reallocate intracellular HCO₃- transport from calcification to photosynthesis. We are working to produce new experimental constraints on carbon fluxes in coccolithophorids using isotope labeling techniques, in collaboration with Brian Hopkinson at the University of Georgia. With these new perspectives, our goal is to propose to produce a new, experimentally-supported model of the carbon concentrating mechanism in coccolithophorid algae. 

At the same time, we are exploring how stable Ca and Sr isotopes may constrain the regulation of Ca uptake and use in coccolithophorids. We have developed a first model of coccolithophorid Ca isotope budget, and this model and new experimental data suggest that in addition to cellular processes, Ca isotopic fractionation is sensitive also to the water solvation structure in the seawater media in which the cells grow. Comparable modeling with stable Sr isotopes should provide further constraints on cellular cation uptake and the mechanisms for an apparent growth rate dependence of coccolith Sr/Ca observed in the modern and recent ocean environment. 

This work is supported in part by Swiss National Science Foundation for postdoctoral researcher Sonia Blanco, and Marie Curie Fellowship to Luz Maria Mejia.  

Publications

Mejía, L. M.*, Paytan, A., Eisenhauer, A., Böhm, F., Kolevica, A., Bolton, C., Méndez-Vicente, A., , Abrevaya, L., Isensee, K., & Stoll, H. (2018). Controls over δ 44/40 Ca and Sr/Ca variations in coccoliths: New perspectives from laboratory cultures and cellular models. Earth and Planetary Science Letters, 481, 48-60.