title: The origin of carbon isotope vital effects in coccolith calcite.
abstract: Calcite microfossils are widely used to study climate and oceanography in Earth's geological past. Coccoliths, readily preserved calcite plates produced by a group of single-celled surface-ocean dwelling algae called coccolithophores, have formed a significant fraction of marine sediments since the Late Triassic. However, unlike the shells of foraminifera, their zooplankton counterparts, coccoliths remain underused in palaeo-reconstructions. Precipitated in an intracellular chemical and isotopic microenvironment, coccolith calcite exhibits large and enigmatic departures from the isotopic composition of abiogenic calcite, known as vital effects. Here we show that the calcification to carbon fixation ratio determines whether coccolith calcite is isotopically heavier or lighter than abiogenic calcite, and that the size of the deviation is determined by the degree of carbon utilization. We discuss the theoretical potential for, and current limitations of, coccolith-based CO2paleobarometry, that may eventually facilitate use of the ubiquitous and geologically extensive sedimentary archive.
authors.affiliation: Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, UK.|Department of Earth and Planetary Science, Washington University in St Louis, Campus box 1169, 1 Brookings Dr, St Louis, Missouri 63130, USA.
authors.forename: H L O
authors.initials: HL
authors.lastname: McClelland
authors.affiliation: Plymouth Marine Laboratory, Prospect Place, The Hoe, Plymouth PL1 3DH, UK.
authors.forename: J
authors.initials: J
authors.lastname: Bruggeman
authors.affiliation: Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, UK.|Équipe de Géochimie des Isotopes Stables, Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Univ Paris Diderot, UMR 7154 CNRS, F-75005 Paris, France.
authors.forename: M
authors.identifier: 0000-0003-1427-1891
authors.initials: M
authors.lastname: Hermoso
authors.affiliation: Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, UK.
authors.forename: R E M
authors.initials: RE
authors.lastname: Rickaby