BG Biogeosciences BG Biogeosciences 1726-4189 Copernicus Publications Göttingen, Germany 10.5194/bg-5-1651-2008 Evidence for a multi-species coccolith volume change over the past two centuries: understanding a potential ocean acidification response Halloran P. R. 1 4 Hall I. R. 2 Colmenero-Hidalgo E. 3 Rickaby R. E. M. 1 Department of Earth Sciences, University of Oxford, Oxford, UK Department of Earth and Ocean Sciences, Cardiff University, Cardiff, UK Departamento de Geología, Facultad de Ciencias, Universidad de Salamanca, Salamanca, Spain now at: Met Office Hadley Centre, FitzRoy Road, Exeter, EX1 3PB, UK 10 12 2008 5 6 1651 1655 Copyright: © 2008 P. R. Halloran et al. 2008 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://bg.copernicus.org/articles/5/1651/2008/bg-5-1651-2008.html The full text article is available as a PDF file from https://bg.copernicus.org/articles/5/1651/2008/bg-5-1651-2008.pdf

Major questions surround the species-specific nature of coccolithophore calcification in response to rising atmospheric CO<sub>2</sub> levels. Here we present CaCO<sub>3</sub> particle volume distribution data from the coccolith size-fraction of a rapidly accumulating North Atlantic sediment core. Without direct volume measurements on coccoliths produced by individual coccolithophore species, and knowledge of organic, as well as inorganic carbon production, it is not possible to state conclusively the coccolithophore calcification change at this site. However, by analysing the size distribution of CaCO<sub>3</sub> particles in the less than 10 μm sediment fraction, we demonstrate a changing particle volume since the late 20th Century consistent with an increase in the mass of coccoliths produced by the larger coccolithophore species, and potentially a decrease in mass of coccoliths produced by the smaller species, present at this location. This finding has significant implications for the realistic representation of an assemblage-wide coccolithophore CO<sub>2</sub>-calcification response in numerical models.

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