Automated Measurement of Magnesium/Calcium Ratios in Gastropod Shells Using Laser-Induced Breakdown Spectroscopy for Paleoclimatic Applications

Abstract

The chemical composition of mollusk shells offers information about environmental conditions present during the lifespan of the organism. Shells found in geological deposits and in many archeological sites can help to reconstruct past climatic conditions. For example, a correlation has been found between seawater temperature and the amount of some substituent elements (e.g., magnesium, strontium) in the biogenerated calcium carbonate matrix of the shell, although it is very species-specific. Here we propose the use laser-induced breakdown spectroscopy (LIBS) to estimate Mg/Ca ratios in modern specimens of the common limpet Patella vulgata. An automated setup was used to obtain a sequence of Mg/Ca ratios across a sampling path that could be compared with the seawater temperatures recorded during the organism's lifespan. Results using four shells collected in different months of the year showed a direct relationship between the Mg/Ca ratios and the seawater temperature, although the sequences also revealed small-scale (short-term) variability and an irregular growth rate. Nevertheless, it was possible to infer the season of capture and the minimum and maximum seawater temperatures from the LIBS sequences. This fact, along with the reduction in sampling and measurement time compared with other spectrometric techniques (such as inductively coupled plasma mass spectrometry [ICP-MS]), makes LIBS useful in paleoclimatic studies.

The Giant Marine Gastropod Campanile Giganteum (Lamarck, 1804) as a High‐Resolution Archive of Seasonality in the Eocene Greenhouse World

“…Aragonite in the columella and shell walls of C. giganteum shells has trace element (Mg, Mn, Fe, and Sr) concentrations characteristic of unaltered biogenic aragonite (Brand & Veizer, 1980; see section 3.1). Mg concentrations in Campanile gastropods are comparable to those measured in modern littoral gastropods (200–700 μg/g; Krinsley, 1960; Cobo et al, 2017). XRF mapping shows that both species of Campanile precipitated aragonite with a different composition on the inside of their whorls (e.g., elevated Sr concentrations compared to the rest of the shell; see Figure 3 and S5).…”

Elemental mapping of Mg/Ca intensity ratios in marine mollusc shells using laser-induced breakdown spectroscopy

“…2A). To verify the correlation between the Mg/Ca intensity ratio values measured and the Mg/Ca concentration ratio (mmol/mol) we followed the approach by Cobo et al 12 using the same set of reference samples. These were composed of mixtures of magnesium and calcium carbonate powders, in different proportions (2-100 mmol/mol), incorporated into a silicone"rubber medium (Wacker Chemie AG, Elastosil M4601) having similar physical properties as the carbonate, found in marine shells, to account for matrix effects 24 .…”

“…It features several distinct advantages such as high speed operation, minimal sample preparation, and " measurements. The successful analysis of shell carbonate through LIBS has recently been reported [12][13][14] and the mapping in a pixel"by"pixel manner has been shown on various scales and materials including "# organic samples and geological settings 15"18 . However, the use of a time"efficient multi" elemental mapping feature to address elemental spatial variation in shell carbonate has not been explored as of yet.…”

Red Sea Palaeoclimate: Stable Isotope and Element-Ratio Analysis of Marine Mollusc Shells

“…Graniero et al 2017). Nevertheless, elemental ratios have the advantage that they can be assessed very quickly (Cobo et al, 2017;Durham et al 2017;Giakoumaki et al, 2007) and can easily be analysed in the form of spatially detailed maps (Cáceres et al, 2017;Hausmann et al, 2017). Additionally, fast analyses have the benefit of lower costs for individual samples, which can result in larger archaeological datasets of seasonal coastal exploitation.…”