Agnes Heinemann

Modification of Ca isotope and trace metal composition of the major matrices involved in shell formation of Mytilus edulis

[1] In this study we present the first combined investigation into the composition of the major matrices involved in calcification processes (surrounding water, extrapallial fluid, aragonite, and calcite) of Mytilus edulis with respect to their calcium isotope (d44/40Ca) and elemental compositions (Sr/Ca and Mg/Ca). Our aim was to examine the suitability of Mytilus edulis as a proxy archive and to contribute to the understanding of the process of biomineralization. Mytilus edulis specimens were live collected from the Schwentine Estuary, Kiel Fjord, and North Sea (Sylt). d44/40Ca was determined by thermal ionization mass spectrometry (TIMS) accompanied by measurements of Mg/Ca and Sr/Ca using inductively coupled plasma–optical emission spectroscopy (ICP-OES). The elemental and isotopic compositions of the investigated matrices showed systematic offsets. The carbonates are strongly depleted in their magnesium and strontium concentrations and fractionated toward lighter calcium isotope compositions relative to the surrounding Schwentine Estuary water. The opposite is observed for the extrapallial fluid (EPF). Our findings extend the results of previous studies reporting a strong biological control and the interaction of different environmental conditions influencing biomineralization. Future studies should focus on the temporal development of the interrelation between the different matrices.

Disentangling the biological and environmental control of M. edulis shell chemistry

Blue mussel individuals (Mytilus edulis) were cultured at four different salinities (17, 20, 29, and 34). During the course of the experiment, temperature was gradually increased from 6°C to 14°C. Mg/Ca and Sr/Ca ratios of the shell calcite portions produced during the 9 weeks of experimental treatment as well parts that were precipitated before the treatment phase were measured by laser ablation–multicollector–inductively coupled plasma–mass spectrometry. Mg/Ca ratios show a positive correlation with temperature for individuals cultured at salinity 29 and 34 (Mg/Ca (mmol/mol) ∼ (0.2–0.3)*T (°C)), while for individuals cultured at low salinities (17, 20) no trend was observed. Sr/Ca ratios were not affected by temperature but strongly by salinity. The data show very strong biological influence (“individual differences” and “physiological variability”) on elemental ratios (79% on Mg/Ca and 41% on Sr/Ca) in M. edulis calcite. The results challenge the use of blue mussel shell data as environmental proxies.

Correction to “Disentangling the biological and environmental control of M. edulis shell chemistry”

[1] Blue mussel individuals (Mytilus edulis) were cultured at four different salinities (17, 20, 29, and 34). During the course of the experiment, temperature was gradually increased from 6°C to 14°C. Mg/Ca and Sr/Ca ratios of the shell calcite portions produced during the 9 weeks of experimental treatment as well parts that were precipitated before the treatment phase were measured by laser ablation–multicollector– inductively coupled plasma–mass spectrometry. Mg/Ca ratios show a positive correlation with temperature for individuals cultured at salinity 29 and 34 (Mg/Ca (mmol/mol) ∼ (0.2–0.3)*T (°C)), while for individuals cultured at low salinities (17, 20) no trend was observed. Sr/Ca ratios were not affected by temperature but strongly by salinity. The data show very strong biological influence (“individual differences” and “physiological variability”) on elemental ratios (79% on Mg/Ca and 41% on Sr/Ca) in M. edulis calcite. The results challenge the use of blue mussel shell data as environmental proxies.

Acidification-sensitivity of M. edulis

HCl molecules emitted from volcanoes breakdown to form chlorine free radicals via heterogeneous chemical reactions and photolysis, which act as catalysts to the breakdown of ozone in the stratosphere. Ozone depletion of up to 2-7% was estimated following the Pinatubo 1991 eruption [1]. However, only stratospheric HCl is dangerous to ozone, and the amount of HCl that reaches these levels is often lower than expected [2]. This suggests that HCl is removed from the eruption column at tropospheric levels. Previously suggested mechanisms include inclusion of HCl into supercooled droplets or ice crystals [3]. In order to investigate the removal of HCl from the atmosphere by adsorption onto ash in volcanic plumes, glass with the composition of the Pinatubo 1991 dacite [4] was synthesised and ground to ash-sized particles using a planetary mill. The ash was then placed in a simple volumetric vacuum device, which was purged with HCl gas to a desired pressure. The ash was connected to the system and the adsorption of HCl onto the ash surface recorded by the resulting pressure drop until an equilibrium pressure was reached. Preliminary results from experimental runs beginning with an HCl gas pressure of 31 mbar, 100 mbar, 250 mbar, 504 mbar and 975 mbar indicate that adsorption on the order of 0.5 mgm-2 occurs even at low partial pressures of HCl. [1] Robock (2000) Rev. Geophys. 38, 191-219. [2] Oppenheimer (2003) In Treatise on Geochemistry. [3] Textor et al. (2003) Geol Soc Lon Spec Pub 213, 307-328. [4] Scaillet & Evans (1999) J. Petr. 40, 381-411