The forgotten variable: Impact of cleaning on the skeletal composition of a marine invertebrate

Abstract

For centuries, invertebrate collections have been subjected to various postcollection and curatorial cleaning techniques. Cleaning, however, may damage or even dissolve skeletal calcium carbonate and consequently influence any subsequent geochemical analysis. We investigated the combined effects of three cleaning variables: water (deionized and tap water), bleach (10% and 78%) and ultrasound (all for a range of durations), on the skeleton of Flustra foliacea (Linnaeus, 1758), a marine bryozoan. Treated and control carbonates were analysed both before and after cleaning, measuring: MgCO 3 in calcite (X-ray diffractometry and staining); organic:inorganic carbon ratio, using elemental analysis for total carbon by combustion and for organic carbon by acid dissolution and combustion. Treatment solutions were analysed using inductively coupled plasma atomic emission spectroscopy (ICP-AES) to detect any Ca 2+ and Mg 2+ that may have leached out.

Effects of organic removal techniques prior to carbonate stable isotope analysis of lacustrine marls: A case study from palaeo‐lake Fucino (central Italy)

“…15 Compared with the H pre-treatment, the N pre-treatment produced a more pronounced increase in the TOC/TN ratio which could be explained by a different extent of removal of readily movable inter-crystalline and strongly bound intra-crystalline OM. 17,18 Previous studies have shown that the H and N pre-treatments both bias measurements towards lower isotopic ratios. 4,16 However, our data do not fully support this general rule.…”

“…Moreover, carbonate loss during pre‐treatment could be induced by the large volumes of deionised water used to rinse the samples in our experiment (at least 1500 mL of deionised water per 500 mg of sample was used). Even if weakly acidic, deionised water has the potential to dissolve carbonates …”

“…Stable carbon and oxygen isotope ratios (δ 13 C and δ 18 O values) of biogenic and endogenic carbonates are commonly used in palaeoenvironmental studies as proxies for hydrological and environmental processes. 1,2 The most common analytical procedure involves digestion of bulk sample material in orthophosphoric acid (H 3 PO 4 ) followed by isotope ratio mass spectrometry of the evolved carbon dioxide (CO 2 ).…”

“…1,2 The most common analytical procedure involves digestion of bulk sample material in orthophosphoric acid (H 3 PO 4 ) followed by isotope ratio mass spectrometry of the evolved carbon dioxide (CO 2 ). Although this method is highly precise, the accuracy of the δ 13 C and δ 18 O values can be biased by organic matter (OM) naturally occurring in lake sediments. During acid reaction, OM can evolve volatile organic impurities (e.g.…”

“…shells, synthetic calcite, ground marble or limestone) with variable amounts of the organic compounds which are typically found in lacustrine sediments, 4,5 or with decarbonated lacustrine sediments. 8 By analysing artificial calcite-OM mixtures with variable total inorganic carbon/total organic carbon (TIC/TOC) ratios, Oehlerich and coauthors observed that δ 13 C and δ 18 O values are biased only up to TIC/TOC = 0.3, and they advised only pre-treating samples lying below this threshold. 5 However, chemical pre-treatment with sodium hypochlorite (NaOCl) or hydrogen peroxide (H 2 O 2 ) is still routinely applied in palaeolimnological studies as its effect on geologic materials is poorly understood.…”