Mg/Ca, Sr/Ca, and stable‐isotope (δ¹⁸O and δ¹³C) ratio profiles from the fan mussel Pinna nobilis: Seasonal records and temperature relationships

Abstract

[1] We present new annually resolved d18 O, d13 C, Mg/Ca, and Sr/Ca ratio records for two shells of the fast growing Mediterranean fan mussel Pinna nobilis, collected from proximal Spanish coast sea grass meadows. The relationship between the potential geochemical proxies and ontogenetic and environmental controlling factors is investigated. Specifically, the use of shell Mg/Ca and Sr/Ca ratios as potential calcification temperature proxies, the latter calculated from measured shell d 18O values, has been assessed. The d 18O cycles along the growth axis indicate that our P. nobilis specimens are $10.5 and $4.5 years old Shell Sr/Ca ratios do not exhibit any consistent interannual cyclicity and are not correlated to temperature. A subtle ontogenetic effect on shell Mg/Ca ratios was observed during the first 4.5 years of recorded growth but was highly evident during the organism's later growth years. In P. nobilis shells, different mechanisms influence ontogenetic variation in shell Mg/Ca and d 18 O records. Shell Mg/Ca ratios from the first 4.5 years of growth correlate significantly to temperature, in a best fit relationship described by the equation Mg/Ca = 17.16 ± 1.95 * exp(0.022 ± 0.004 * T). P. nobilis shell Mg/Ca records therefore are a valid temperature proxy only during an early growth phase. For the same range of temperatures, shell Mg/Ca ratios in P. nobilis are approximately 1/3 lower than those reported for inorganic calcite but 3 to 4 times higher than in another bivalve species, Mytilus trossulus, and 4 to 16 times higher than in foraminifera. We suggest these offsets are due to a higher degree of similarity between seawater and calcification-fluid composition in P. nobilis than in other bivalves and foraminifera. The observed shell Mg/Ca ratio change per°C of 2.2% also is lower than that observed for inorganic and other biogenic calcites. Our findings strongly support taxon-and species-specific Mg/Ca-temperature relationships for bivalves and other calcifying organisms. An appreciation of the physiology and calcification mechanisms of any biogenic carbonate archive therefore is paramount prior to the application of stable-isotope and element/Ca ratio proxies for paleotemperature reconstructions.

Effect of organic matrices on the determination of the trace element chemistry (Mg, Sr, Mg/Ca, Sr/Ca) of aragonitic bivalve shells (<i>Arctica islandica</i>)&mdash;Comparison of ICP-OES and LA-ICP-MS data

“…Mg/Ca ratios of some calcitic (Dodd, 1965;Lorens and Bender, 1977;Freitas et al, 2005;Lorrain et al, 2005;Lazareth et al, 2007) and aragonitic bivalve shells (Takesue and van Geen, 2004) are lower than predicted by thermodynamics. Shell Mg/Ca and Sr/Ca ratios can also vary contradictorily among different species and even among conspecific and contemporaneous specimens from one locality (corals: Cardinal et al, 2001;brachiopods: England et al, 2007;bivalves: Dodd, 1965;Gillikin et al, 2005a;Lorrain et al, 2005;Freitas et al, 2008).…”

“…The ratios of trace elements to calcium show little consistency in the long-lived bivalve mollusk, Arctica islandica (Toland et al, 2000). Skeletal Mg and Sr contents sometimes correlate with skeletal growth (corals: de Villiers et al, 1995;bivalves: Swan, 1956;Takesue and van Geen, 2004;Gillikin et al, 2005aLorrain et al, 2005, and also with ontogenetic age (Palacios et al, 1994;Freitas et al, 2005). Such findings suggest that non-thermodynamic factors (e.g., an active, protein-mediated removal of Mg from the inorganic carbonate phase during biomineralization) influence the incorporation of trace elements into biogenic carbonates.…”

Increased seasonality in the Western Mediterranean during the last glacial from limpet shell geochemistry

“…Beck et al, 1997;Gagan et al, 2000). However there has been little success in identifying independent trace element palaeothermometers in the mollusc species so far examined (Carré et al, 2006;Freitas et al, 2005Freitas et al, , 2008Gentry et al, 2008;Takesue and Van Geen, 2004).…”

Barium uptake into the shells of the common mussel (Mytilus edulis) and the potential for estuarine paleo-chemistry reconstruction

“…Unlike corals and foraminifera, much of the bivalve data presented suggests that many of these elemental profiles (e.g., Sr, Mn, Pb, U), which often largely differ from expected concentrations based on inorganic and other biogenic carbonates, cannot be used as proxies of environmental conditions (e.g., Stecher et al, 1996;Purton et al, 1999;Vander Putten et al, 2000; 70 Takesue and van Geen, 2004;Freitas et al, 2005;Gillikin et al, 2005a;Gillikin, 2005). There have been some promising reports of bivalve shell Mg/Ca ratios as a proxy of sea surface temperature (SST) (Klein et al, 1996), but other reports illustrate that this is not always the case, and is apparently strongly species specific (Vander Putten et al, 2000;Takesue and van Geen, 2004;Freitas et al, 2005;Gillikin, 2005;75 Lorrain et al, in press). Bivalve shell Ba/Ca ratios on the other hand have been shown to be highly reproducible between specimens and have been hypothesized to be a proxy of both particulate Ba (Stecher et al, 1996;Vander Putten et al, 2000;Lazareth et al, 2003) and dissolved Ba (Torres et al, 2001), and therefore could be particularly…”