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Published September 26, 2013 | public
Journal Article

Distribution of sulphur and magnesium in the red coral

Abstract

The concentrations of major and trace elements were measured in red coral skeletons (Corallium rubrum) by electron microprobe (EMP), isotope dilution inductively coupled mass spectrometry (ID-ICPMS) and laser ablation-ICPMS (LA-ICPMS). The average composition (in mg/kg or ppm) is as follows: Ca: 356300 ± 3200, Mg: 29500 ± 2400, Sr: 2600 ± 250, S: 3100 ± 400, Na: 4200 ± 500, K: 140 ± 20, P: 140 ± 40, B: 28 ± 4, Ba: 9 ± 1, Fe: 8 ± 3, Li: 4 ± 1, Mn: 1 ± 0.5, Pb: 0.5 ± 0.3, U: 0.08 ± 0.05. In terms of Mg, the compositions of the red coral skeletons range from 9 to 15 mol% MgCO_3 with a mean value of 12 ± 1%. Concentrations of sulphur are high (approx. 3000 ppm) and among the highest reported in biogenic calcites. EMP maps (Mg and S) and organic matter (OM) staining show a regular alternation of 100–200 μm wide annual growth rings. Combination of these results with a previous study (Marschal et al., 2004) suggests that Mg-rich rings form during the period spring to early fall, while S-rich rings form immediately after (late autumn and winter). Elemental mapping by EMP shows an unexpected anticorrelation between S and Mg confirmed by LA-ICPMS. This anticorrelation is ascribed to the concomitant presence of S in the organic matter and the anticorrelation between Mg and OM in the skeleton. However, mass balance constraints indicate that in the skeleton sulphur is probably present both as organo-sulphur and structurally substituted sulphur. The studied samples of red coral were collected at various locations and different depths (8–73 m) where the temperature of the sea water was monitored for long periods of time. Although overall decreases of the Mg/Ca and Sr/Ca are observed as a function of depth (and temperature), the use of these ratios as an indication of the sea water temperature (SWT) seems difficult. In addition, a single colony that grew in an area where the temperature was monitored for 30 years did not register the measured increase of SWT of about 1 °C. However, Mg and OM distributions inside skeletons could be good indicators of variations of growth rates on decadal time scales and anomalous 'summer suffering' events that could be associated with periods of unusually high SWT conditions. The red coral is thus an example of how growth dynamics (and not temperature alone) affects the chemistry of biominerals.

Additional Information

© 2013 Elsevier B.V. All rights reserved. Received 31 October 2012. Received in revised form 8 July 2013. Accepted 9 July 2013. Available online 15 July 2013. This work has been supported by the Centre National de la Recherche Scientifique (CNRS) – Institut National des Sciences de l'Univers (INSU) through grant ECLIPSE 2005, INTERRVIE 2009, by the Agence Nationale pour la Recherche through ANR CoRo 2011–2015, and by the Centre Interdisciplinaire de Nanoscience de Marseille (CINaM) through internal grants. This work is also part of the European Union COST action TD0903. D.V. also benefited from a financial support by E.M. Stolper for a three month stay at Caltech in 2010. We thank H. Zibrowius for providing generously the samples of fossil red coral, C. Marschal and P. Raffin for supplying some of the present-day red coral colonies, J. Pascual and J. Salat for allowing access to the long-term temperature data series from the Medes Islands (Spain), and N. Bensoussan for his help in the processing of the temperature series from the Riou Island (Marseille, France). Reviews by Andres Rüggeberg and an anonymous reviewer as well as editorial handling by Uwe Brand are gratefully acknowledged. This is contribution ANR CoRo n° 03.

Additional details

Created:
August 22, 2023
Modified:
October 25, 2023