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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2018-469
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2018-469
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 09 Nov 2018

Research article | 09 Nov 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Architecture, Growth Dynamics and Biomineralization of Pulsed Sr-Labelled Katelysia rhytiphora (Mollusca, Bivalvia)

Laura M. Otter1, Oluwatoosin B. A. Agbaje1, Matt R. Kilburn2, Christoph Lenz3,4, Hadrien Henry1,3, Patrick Trimby5, Peter Hoppe6, and Dorrit E. Jacob1,3 Laura M. Otter et al.
  • 1Department of Earth & Planetary Science, Macquarie University, Sydney, NSW 2109, Australia
  • 2Centre for Microscopy Characterisation and Analysis, University of Western Australia, Perth, WA 6009, Australia
  • 3Australian Research Council Centre of Excellence for Core to Crust Fluid System (CCFS) / GEMOC
  • 4Institute of Mineralogy and Crystallography, University of Vienna, Althanstr. 14, 1090 Vienna, Austria
  • 5Oxford Instruments NanoAnalysis, High Wycombe, HP12 3SE, UK
  • 6Particle Chemistry Department, Max Planck Institute for Chemistry, Hahn-Meitner-Weg 1, 55128 Mainz, Germany

Abstract. We use pulsed Sr-labelling experiments to visualize growth of aragonitic Katelysia rhytiphora (Mollusca, Bivalvia) shells. The outer compound composite prismatic structure is organized into three orders of prisms, and the inner crossed acicular structure consists of intersecting lamellae. Electron Backscatter Diffraction (EBSD) reveals substantial twinning of the aragonite crystals (>46%) and an overall reduced and strategically oriented anisotropy of the Young’s modulus in the whole shell compared to that of monolithic aragonite. All structural orders in both layers are enveloped by an organic sheath and the smallest mineralized units are nanogranules. Total organic contents are 2.2 (outer) and 1.4wt.% (inner layer) and are, thus, intermediate between those of nacreous and crossed-lamellar shells. Prisms in the outer structure can be correlated to yearly, daily and sub-daily growth rates. Average daily growth rates at the ventral margin for the outer structure are 17% higher than for the inner crossed acicular structure. The calcification front runs evenly across all structures and architectural orders independently of the current growth rate. Sharply defined transitions from labelled to unlabelled areas in the shell indicate that physiological processes driving calcification have no lag. This suggests that the extrapallial fluid cannot be very voluminous. Narrow increments of varying Sr content within labelled shell, despite constant Sr concentrations in seawater, suggest cyclic metabolic activity during calcification. Micro-Raman spectroscopy maps validate a low impact of high Sr-conditions on the aragonite crystal structure. Identical Sr-enrichment factors for labelled and ambient conditions support models of ion transport via a passive selective pathway to the mantle epithelium followed by calcification via amorphous calcium carbonate.

Laura M. Otter et al.
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Laura M. Otter et al.
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Short summary
This study uses a trace elemental marker and high resolution nano-analytical techniques to label the growth fronts of bivalves in controlled aquaculture conditions. The growing shells incorporate the labels and are used as snapshots visualizing the growth processes across different shell microstructures and architectures.
This study uses a trace elemental marker and high resolution nano-analytical techniques to label...
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