Optical measurements to determine the thickness of calcite crystals and the mass of thin carbonate particles such as coccoliths

• Published in: Nature Protocols
• Main Authors: Beaufort, Luc, L, Barbarin, Nicolas, Gally, Yves
• Other Authors: Centre européen de recherche et d'enseignement des géosciences de l'environnement (CEREGE), Institut de Recherche pour le Développement (IRD)-Institut National de la Recherche Agronomique (INRA)-Aix Marseille Université (AMU)-Collège de France (CdF (institution))-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2014
• Subjects: [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Ocean acidification
• Online Access: https://hal.science/hal-01458300; https://doi.org/10.1038/nprot.2014.028

International audience We describe a procedure for measuring the thickness and mass of calcite particles that works for most calcite particles <4.5-mu m thick. The calcite particles are observed in cross-polarized light, which enables the light transmitted through the calcite particles to be correlated with their thickness. Three polarizing planes are used to minimize the darkening of crystals at some orientations (black cross). This allows direct measurement of the thickness without recourse to a transfer function. This procedure has been used recently to determine the degree of calcification of coccoliths, which provides an indicator of ocean acidification. It takes only a few minutes per sample, and it is an improvement over the former protocol, which did not allow measurement of the thickness and mass of particles thicker than 1.5 mu m.