SIZE MATTERS : THE INFLUENCE OF COCCOLITH SIZE AND GROWTH RATE ON PALEOBAROMETRY
Hanno Kinkel(1), Jeremy Young(2), Heather Stoll(3), Patrizia Ziveri(4), Markus Geisen(2), Ian Probert(5) & Karl-Heinz Baumann(6)
1 Netherlands Institute for Sea Research, Den Burg, Texel, The Netherlands
2 Geological Institute, Swiss Federal Institute of Technology, Switzerland
3 Geology Dept., Univ. of Oviedo, Spain
4 Facult. Aardwetenschappen, Vrije Univ. Amsterdam
5 Natural History Museum Londoner Laboratoire de Biologie et Biotechnologie Marines, Universitae de Caen, France
The use of compound specific carbon isotopes has provided paleoceanographers with the fascinating tool of a paleobarometer that could enable them to solve the unanswered question of the interaction between greenhouse gas concentrations and global climate change. Results from laboratory cultures and field studies suggested that the coccolithophore derived biomarkers, soa called long chain alkenones, and their carbon isotopic composition should provide the most promising proxy for a palobarometer. Besides the carbon isotope mass ratio, there are two other factors that influence the accuracy of such a paleobarometer, i.e. growth rate, and cell surface to volume ratio. Both factors varied considerably over the geological history, and introduce large errors in the paleo pCO2 reconstructions. We show a simple model, that allows to estimate cell size from the length of single coccoliths. A new paleo growth rate proxy, based on the Sr/Ca ratio in coccolith carbonate is presented. The influence of the size and growth rate variation of coccolithophores is demonstrated for a number of different geological settings and different time scales.
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