Growth Kinetics and Distribution of Trace Elements in Precious Corals

Abstract

The concentration and spatial distribution of major (Ca, Mg) and trace elements (Na, Sr, S, Li, Ba, Pb, and U) in different Corallium skeletons (C. rubrum, C. japonicum, C. elatius, C. konojoi) have been studied by electron microprobe (EMP) and laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). EMP data show positive Na-Mg and negative Na-S and Mg-S correlations in all skeletons. LA-ICPMS data display additional Sr-Mg, Li-Mg, and U-Mg positive correlations. Medullar zones in the skeletons, corresponding to fast growing zones, are systematically richer in Mg, Na, Sr, Li, and U and poorer in S than the surrounding slow growing zones. These spatial distributions are mostly interpreted in terms of growth kinetics combined with steric effects influencing the incorporation of impurities in biogenic calcites. This interpretation is in agreement with available experimental data on kinetic effects on the incorporation of elements in calcite. At a different scale, annual growth rings in annular slow growing zones show oscillations in Mg, Na, Sr, and S. These chemical oscillations probably result from growth rate variations: fast growth would produce rings enriched in Mg, Sr, and Na, while slow growth would produce rings enriched in Ca, S and organic matter. From previous studies in C. rubrum, the Mg-rich rings would develop during the spring to fall period while the S-rich rings would form immediately after (late fall and winter). Analytical traverses performed in annular zones of different Corallium skeletons indicate that Mg, Na, Sr, Li, and U decrease from core to rim. This observation indicates that radial growth rate decreases as the colony gets older. Contrary to Mg, Na, Sr, Li, S, and U, barium and lead concentrations are identical in medullar and annular zones and appear independent of growth kinetics. Thus, concentrations in Corallium skeletons could provide indications on Ba and Pb contents in the oceans. Barium and lead concentrations are higher in Mediterranean than in Pacific precious corals, these two elements can be used to discriminate C. rubrum from C. japonicum, and contribute enforcing regulations on the trade of precious corals.

Lead (Pb) profiles in red coral skeletons as high resolution records of pollution in the Mediterranean Sea

“…The Sciacca samples dated ~2100-2400 BP and ~4050-4400 BP represent times before the widespread introduction of Pb into the environment through human activities. Interestingly, the mean concentrations measured on present-day corals in this dataset are remarkably consistent with those determined by Vielzeuf et al (2018), except for K and Zn that show slight differences. In the VT dataset, compared to present-day corals, the sub-fossil samples are enriched in Mn (48 ± 17 vs 0.9 ± 0.5 µg/g), Fe (172 ± 107 vs 0.69 ± 0.04 µg/g), Cu (1.6 ± 1.6 vs 0.15 ± 0.02 µg/g), and U (0.26 ± 0.15 vs 0.08 ± 0.04 µg/g).…”

“…Conversely, it was shown that growth kinetics does not influence the incorporation of Ba and Pb. Concerning lead, large variations of concentrations in corals were observed (Vielzeuf et al, 2018). These data raised the question of the origin and significance of the variations of lead in Corallium skeletons.…”

“…Among biominerals, biogenic calcium carbonates are able to incorporate different elements in significant amounts. In the case of Corallium species, these include magnesium, strontium, sodium, sulfur, lithium, barium, lead and uranium [see Vielzeuf et al (2018); Vielzeuf et al (2013) for summaries]. However the ability to incorporate an element is not a guarantee of a faithful environmental proxy as concentration variations can also be due to biological or physico-chemical effects, or combinations of factors.…”

“…Its skeleton has a slow radial growth of about 100 to 200 µm per year (Marschal et al, 2004) and can live several decades (Garrabou and Harmelin, 2002). In a companion paper, it has been determined that growth kinetics plays a role in the incorporation of Mg, Na, Sr, Li, S and U in the skeletons of Corallium species (Vielzeuf et al, 2018). Conversely, it was shown that growth kinetics does not influence the incorporation of Ba and Pb.…”

Intrashell Variability of Trace Elements in Benthic Foraminifera Grown Under High CO2 Levels

“…We cannot resolve with our data set the causes for these multi elemental cycles, but it should be mentioned that such cycles are also observed in other biomineralizing systems: clams (e.g,. Warter et al, 2018), corals (e.g., Vielzeuf et al, 2018) and others. Our observation that DIC did not affect the pattern of elemental cycles within the shells suggest that these variations are indeed an essential part of the calcification process that may be strongly biologically controlled and therefore are not influenced by the DIC.…”