Biogenic and diagenetic indicators in archaeological and modern otoliths: Potential and limits of high definition synchrotron micro-XRF elemental mapping Phil K. Cook a,b, ⁎, Marie-Angélique Languille a,1 , Elise Dufour c , Cristian Mocuta b , Olivier Tombret c , Franck Fortuna d , Loïc Bertrand a,b, ⁎ a IPANEMA (USR 3461), CNRS, Ministère de la Culture et de la Communication; Site du Synchrotron SOLEIL, BP48 Saint Aubin, F‐91192 Gif‐sur‐Yvette, France b Synchrotron SOLEIL, BP48 Saint-Aubin, F-91192 Gif-sur-Yvette, France c Archéozoologie, archéobotanique: Sociétés, pratiques et environnements (UMR 7209), Sorbonne Universités, Muséum national d’histoire naturelle, CNRS, CP55, 55 rue Buffon, 75005 Paris, France d Centre de Sciences Nucléaires et de Sciences de la Matière (CSNSM), Université Paris‐Sud and CNRS/IN2P3; Bâtiments 104 et 108, F‐91405 Orsay cedex, France abstract article info Article history: Received 2 October 2014 Received in revised form 21 July 2015 Accepted 14 August 2015 Available online 29 August 2015 Keywords: Otoliths Paleoenvironment Synchrotron micro X-ray fluorescence spectroscopy Elemental mapping Strontium Fish otoliths are biogeochemical archives of environmental conditions and are a valuable tool for examining life traits. These sclerochronological life history records, accessed through geochemical analyses, are widely used in fisheries sciences, and are seeing growing use as palaeoenvironmental archives or for reconstruction of past human activities. The fidelity of such reconstructions relies on the preservation of the biogenic geochemistry, which may be altered through diagenetic processes. In this work, a methodology is provided that enables measurement of elemental concentrations with a high precision with simultaneous quality control of the data to ensure high reliability and a multi-technique sample marking strategy to ensure precise alignment. Thin sec- tions of four archaeological and two modern otoliths from the Pacific coast of South America were examined by synchrotron μXRF. High-definition elemental maps of sample sections up to 3.2 × 1.0 mm 2 (V × H) were pro- duced with an on-sample spot size of 6.0 × 16 μm 2 . Thirteen elements were detected, some of which may be use- ful indicators of diagenetic alteration. Strontium was accurately quantified and one sample presented local concentrations above the previously described range in literature. The quantity of collected data allows the use of statistical approaches to examine the intra- and inter-sample Sr distribution. A highly reliable profile, produced by integrating multiple points, additionally permits identification of defects and potential alteration along its length through changes in median absolute deviation. Contamination at the edge of some of the specimens was evidenced from preparation and other post-mortem alterations, even in modern samples, however diagenet- ic alteration in the elemental signals was not evidenced significantly further than a few hundred micrometres deep in the samples. Medium-energy SR-μXRF therefore provides a fast and sensitive elemental probe without a visible effect on the sample, and the integration volume which limits the attainable lateral resolution in this energy range is discussed. This paper discusses the methodological limitations and opens new perspectives in the analysis of biomineral carbonate palaeoproxies. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Otoliths (oto, “ear” + lithos, “stone”) are accretionary structures that form a part of the auditory, orientation, and motion sensing system of teleost fish (Nolf, 1985; Panfili et al., 2002). The term ‘otolith’ can refer to any one of three pairs of accretions, occurring in otosacs filled with endolymph on the left and right sides of the individual (Panfili et al., 2002). The largest otoliths usually have a species-specific shape which is used for taxonomic determination. Growth occurs from before hatch- ing until death via the deposition of mineral calcium carbonate (CaCO 3 ) (Campana and Neilson, 1985), templated by an organic mixture of Chemical Geology 414 (2015) 1–15 Abbreviations: EDX, energy dispersive X-ray spectroscopy; EPMA, Electron Probe Microanalysis; FIB, Focused Ion Beam; FT, Fourier transform; FWHM, full-width at half maximum; LA-ICP-MS, Laser Ablation Inductively Coupled Plasma Mass Spectrometry; LM, light microscopy; MAD, median absolute deviation; MCA, multi-channel analyser; PIXE, Proton Induced X-ray Emission; RISE, radiation-induced side effects; ROI, region of interest; SEM, scanning electron microscopy; SNR, signal-to-noise ratio; SR, synchrotron radiation; XRF, X-ray fluorescence; μXRF, micro-X-ray fluorescence. ⁎ Corresponding authors at: IPANEMA, CNRS, Ministère de la Culture et de la Communication, Site du synchrotron SOLEIL, BP48 Saint-Aubin, F-91192 Gif-sur-Yvette, France. E-mail address: loic.bertrand@synchrotron-soleil.fr (L. Bertrand). URL: http://ipanema.cnrs.fr (L. Bertrand). 1 Current address: Centre de recherche sur la conservation (CRC, USR 3224), Sorbonne Universités, Muséum national d'Histoire naturelle, Ministère de la Culture et de la Communication, CNRS, CP21, 36 rue Geoffroy-Saint-Hilaire, 75005 Paris, France. http://dx.doi.org/10.1016/j.chemgeo.2015.08.017 0009-2541/© 2015 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Chemical Geology journal homepage: www.elsevier.com/locate/chemgeo