Mg/Ca profiles within archaeological mollusc (Patella vulgata) shells: Laser-Induced Breakdown Spectroscopy compared to Inductively Coupled Plasma-Optical Emission Spectrometry

Abstract

Biogenic carbonate mollusc shells have the unique property of being a durable material found in many archaeological and geological sites, recording in their shell chemical composition the ambient environmental conditions during the mollusc's lifespan. In particular, mollusc shell Mg/Ca ratios have been suggested to be related to seawater temperature, although such a relationship is controversial and appears to be species-and even location-specific. This study investigates the use of Laser-Induced Breakdown Spectroscopy (LIBS) for the rapid 2 measurement of Mg/Ca profiles within Patella vulgata shells, via comparison with one established analytical technique that is most often used for this purpose, ICP-OES. LIBS offers some advantages over other spectrometric techniques, including ICP-OES, the latter requiring initial micromilling of sample powders. LIBS offers faster measurement, reduced sample preparation, easier automation and less complex and lower cost instrumentation. A high correlation is evident between LIBS and ICP-OES Mg/Ca profiles within four archaeological P. vulgata shells, as well as strong similarities between LIBS measurements made in two different areas of each P. vulgata shell (i.e. the apex and a more conventional transect along the axis of shell growth). Validation of the LIBS technique for determination of Mg/Ca profiles within P. vulgata shells has implications for archaeological studies, because a greater number of shell specimens sampled from each archaeological site and chronological level can be measured, thereby improving the statistical robustness of data interpretation and conclusions. One example archaeological application that would benefit from application of the LIBS technique is identification of the season-of-capture of marine molluscs as a food resource for prehistoric societies.

Extensive elemental mapping unlocks Mg/Ca ratios as climate proxy in seasonal records of Mediterranean limpets

“…The molluscs experienced the same SST range, but produced different ranges for Mg/Ca intensity ratios (0.25–0.45 and 0.40–0.70, respectively). This difference can be linked partly to the LIBS specific matrix effect, as shown in other experiments 14 . The effect results from the chaotic response of irregular sample matrices (e.g.…”

“…In a recent study, García-Escárzaga et al . 14 showed variable results in linear regression analysis of intensity ratios and absolute ratios of Mg/Ca measurements using LIBS and ICP-OES in the same specimens. The variation of their results is partly due to matrix effects, that skew their LIBS spectra.…”

“…Obviously sufficiently resolved geochemical studies require large sample sizes per shell specimen and with elemental analysis being more cost-effective 10 , this approach is becoming increasingly popular within the last decade 11–14 . Yet, elemental ratios in mollusc shells are more difficult to establish as climate proxies relative to δ 18 Ο values 15–17 .…”

Fast and Simultaneous Determination of Soil Properties Using Laser-Induced Breakdown Spectroscopy (LIBS): A Case Study of Typical Farmland Soils in China

“…The LIBS technique has many merits for sample analysis, including the fact that it is rapid, less destructive, cost-effective, environmentally friendly, little to no sample preparation is required, and simultaneous multi-element detection can be achieved [11][12][13]. Because of these outstanding advantages, the LIBS technique has been widely applied in various fields including space exploration [14][15][16], geological surveying [11,17,18], archaeological investigation [19][20][21], environmental monitoring [22][23][24][25], materials characterization [26][27][28], food detection [29][30][31], agriculture monitoring [32][33][34], and industry monitoring [35,36].…”

Annual Growth Patterns and Interspecimen Variability in Mg/Ca Records of Archaeological Ostrea edulis (European Oyster) from the Late Mesolithic Site of Conors Island

“…Lastly, the impact of organic material occurring within the shell is unavoidable, when measuring in situ (Schöne et al 2013;García-Escárzaga et al 2018). As such, the Mg/Ca ratio measured through LIBS always consists of the carbonate component as well as the insoluble organic matrix (IOM) of the shell.…”