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Abstract

Morphological changes in coccoliths, tiny calciteplatelets covering the outer surface of coccolithophores, can be induced byphysiological responses to environmental changes. Coccoliths recovered fromsedimentary successions may therefore provide information onpaleo-environmental conditions prevailing at the time when thecoccolithophores were alive. To calibrate the biomineralization responses ofancient coccolithophore to environmental changes, studies often compared thebiological responses of living coccolithophore species with paleo-data fromcalcareous nannofossils. However, there is uncertainty whether themorphological responses of living coccolithophores are representative ofthose of the fossilized ancestors. To investigate this, we exposed fourliving coccolithophore species (Emiliania huxleyi, Gephyrocapsa oceanica, Coccolithus pelagicus subsp. braarudii, and Pleurochrysis carterae) that have been evolutionarilydistinct for hundreds of thousands to millions of years, to a range ofenvironmental conditions (i.e., changing light intensity, Mg∕Ca ratio,nutrient availability, temperature, and carbonate chemistry) and evaluatedtheir responses in coccolith morphology (i.e., size, length, width,malformation). The motivation for this study was to test if there is aconsistent morphological response of the four species to changes in any ofthe tested abiotic environmental factors. If this was the case, then thiscould suggest that coccolith morphology can serve as a paleo-proxy for thatspecific factor because this response is conserved across species that havebeen evolutionary distinct over geological timescales. However, we foundthat the four species responded differently to changing light intensity,Mg∕Ca ratio, nutrient availability, and temperature in terms of coccolithmorphology. The lack of a common response reveals the difficulties in usingcoccolith morphology as a paleo-proxy for these environmental drivers.However, a common response was observed under changing seawater carbonatechemistry (i.e., rising CO2), which consistently induced malformations.This commonality provides some confidence that malformations found in thesedimentary record could be indicative of adverse carbonate chemistryconditions.

Item Type:	Article
Authors/Creators:	Faucher, G and Riebesell, U and Bach, LT
Keywords:	coccolithophores, paleo proxy, morphology
Journal or Publication Title:	Climate of the Past
Publisher:	Copernicus GmbH
ISSN:	1814-9324
DOI / ID Number:	10.5194/cp-16-1007-2020
Copyright Information:	Copyright 2020 The Authors. Licensed under Creative Commons Attribution 4.0 International (CC BY 4.0) https://creativecommons.org/licenses/by/4.0/
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