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Technical note: An empirical method for absolute calibration of coccolith thickness

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Author González-Lemos Saúl, Guitián José, Fuertes Miguel-Ángel, Flores José-Abel, Stoll Heather M.,
Project Swiss participation in the International Ocean Discovery Program (IODP) through membership in the European Consortium for Ocean Research Drilling (ECORD)
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Original article (peer-reviewed)

Journal Biogeosciences
Volume (Issue) 15(4)
Page(s) 1079 - 1091
Title of proceedings Biogeosciences
DOI 10.5194/bg-15-1079-2018

Open Access

URL http://doi.org/10.5194/bg-15-1079-2018
Type of Open Access Publisher (Gold Open Access)

Abstract

Abstract. As major calcifiers in the open ocean, coccolithophores play a key role in the marine carbon cycle. Because they may be sensitive to changing CO 2 and ocean acidification, there is significant interest in quantifying past and present variations in their cellular calcification by quantifying the thickness of the coccoliths or calcite plates that cover their cells. Polarized light microscopy has emerged as a key tool for quantifying the thickness of these calcite plates, but the reproducibility and accuracy of such determinations has been limited by the absence of suitable calibration materials in the thickness range of coccoliths (0–4 µm). Here, we describe the fabrication of a calcite wedge with a constant slope over this thickness range, and the independent determination of calcite thickness along the wedge profile. We show how the calcite wedge provides more robust calibrations in the 0 to 1.55 µm range than previous approaches using rhabdoliths. We show the particular advantages of the calcite wedge approach for developing equations to relate thickness to the interference colors that arise in calcite in the thickness range between 1.55 and 4 µm. The calcite wedge approach can be applied to develop equations relevant to the particular light spectra and intensity of any polarized light microscope system and could significantly improve inter-laboratory data comparability.
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