Preprints
https://doi.org/10.5194/bg-2022-66
https://doi.org/10.5194/bg-2022-66
 
19 May 2022
19 May 2022
Status: this preprint is currently under review for the journal BG.

Variation in calcification of Reticulofenestra coccoliths over the Oligocene-Early Miocene

José Guitián1,a,, Miguel Ángel Fuertes2,, José-Abel Flores3, Iván Hernández-Almeida1, and Heather Stoll1 José Guitián et al.
  • 1Dept. of Earth Science, ETH Zürich, 8092 Zurich, Switzerland
  • 2Dept. of Didactics of Mathematics and Experimental Sciences, University of Salamanca, Salamanca 37008 Spain
  • 3Dept. of Geology, University of Salamanca, Salamanca, 37008, Spain
  • anow at: Centro de Investigación Mariña, Universidade de Vigo, GEOMA, Vigo, 36310, Spain
  • These authors contributed equally.

Abstract. Coccolithophores are calcifying marine phytoplankton whose intracellularly produced calcite plates, or coccoliths, have been the dominant source of calcium carbonate in open ocean settings since the Cretaceous. An open question is whether their calcification has been affected by variation in environmental parameters such as the ocean carbon system over geological timescales. Previous methods using circular polarized light microscopy allowed only the thickness of small coccoliths thinner than 1.5 microns to be quantified but prior to the Pliocene, a significant fraction of the coccoliths exceed this thickness and have not been quantifiable. Here, we implement a new approach for calibration of circular polarized light microscopy enabling us to quantify coccoliths which feature calcite up to 3 microns thick. We apply this technique to evaluate the evolution of calcification in the Reticulofenestra from the Early Oligocene to Early Miocene in exceptionally well-preserved sediments from the Newfoundland margin. Through this time interval, coccolith thickness and the scale-invariant shape factor kse vary by about 20 % around the mean thickness of 0.37 µm and mean kse of 0.16. Lower shape factors characterize samples with higher relative abundance of dissolution-resistant nannoliths, suggesting that dissolution may contribute to thinning of placoliths. We therefore define temporal trends in calcification only in samples in which the assemblage suggests minimal dissolution. Lowest kse characterizes the Middle Oligocene, and highest kse around 18 Ma in the Early Miocene. High ocean DIC concentrations have been proposed for this period of the Miocene, and may be one factor contributing to high coccolith kse.

José Guitián et al.

Status: open (until 27 Jul 2022)

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José Guitián et al.

José Guitián et al.

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Short summary
The effect of environmental conditions on the degree of calcification of marine phytoplankton remains unclear. This study implements a new microscopic approach to quantify the calcification of ancient coccolithophores, using North Atlantic sediments. Results show significant differences in thickness and shape factor of coccoliths for samples with minimum dissolution, providing the first evaluation of phytoplankton physiology adaptation to million-year scale variable environmental conditions.
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