Abstract
Abstract. Mussel shells are potential bioarchives of proxies for changes in the physicochemical conditions in the bivalve's habitat. One such proxy is the distribution of rare earths and yttrium (REY) in seawater, as REY speciation in seawater is sensitive to pH and temperature variations, due to the impact of these parameters on the activity of CO32− in seawater. We present a new protocol for sample preparation and determination of ultratrace concentrations of REY in bulk bivalve shells (comprised of calcite and aragonite) that includes sample treatment with NaOCl followed by REY separation and preconcentration. The data obtained were used to calculate REY partition coefficients between bulk bimineralic shells of Mytilus edulis (calcite aragonite mix) and ambient seawater, and the results acquired were then used to investigate the potential effects of pH and temperature on REY partitioning.Shells of Mytilus edulis mussels from the North Sea show consistent shale-normalized (SN) REY patterns that increase from the light REY to the middle REY and decrease from the middle REY to the heavy REY. Despite being different from the general seawater REYSN pattern, the shells still display distinct REY features of seawater, such as a negative CeSN anomaly and small positive YSN and GdSN anomalies. Apparent REY partition coefficients between shells and seawater (appDTot.REYshell/seawater) are low and decrease strongly from the light REY (4.04 for La) to the heavy REY (0.34 for Lu). However, assuming that only the free REY3+ are incorporated into the shell, modDFreeREY3+shell/seawater values are higher and comparatively similar for all REY (102.46 for La; 113.44 for Lu) but show a slight maximum at Tb (199.18). Although the impact of vital effects, such as REY speciation in a mussel's extrapallial fluid from which the carbonate minerals precipitate, cannot be quantified yet, it appears that M. edulis shells are bioarchives of some REY features of seawater.We modeled the REYSN patterns of a hypothetical mussel shell at pH 8.2 and 7.6 and at temperatures of 25 and 5 °C, assuming that only free REY3+ are incorporated into the carbonate's crystal lattice and that vital effects do not obliterate the REY signal of the shells. The results suggest that with lower pH, REY concentrations in shells increase, but with little effect on the shape of the REYSN patterns, while a temperature change has an impact on the REYSN pattern but only minor effects on REY concentrations. Hence, after additional calibration studies, the REY systematics in mussel shells may become a valuable proxy for paleo-pH and ocean acidification.
Highlights
Mussels and mussel shells have increasingly gained importance as bioarchives of proxies that record physicochemical changes in their marine or freshwater habitat (Bau et al, 2010; Gillikin et al, 2006a; Merschel and Bau, 2015; Puente et al, 1996; Vander Putten et al, 2000; Scourse et al, 2006; Sturesson, 1976; Wanamaker et al, 2008)
The shells of Mytilus edulis used in our study demonstrate the potential of using bivalve shells as bioarchives of proxies for changes in the physicochemical conditions in the bivalve’s habitat
All shells from three different sites in the southern North Sea show distinct REYSN distribution patterns that increase from the light REY (LREY) to the middle REY (MREY) and decrease from the MREY to the heavy REY (HREY)
Summary
Mussels and mussel shells have increasingly gained importance as bioarchives of proxies that record physicochemical changes in their marine or freshwater habitat (Bau et al, 2010; Gillikin et al, 2006a; Merschel and Bau, 2015; Puente et al, 1996; Vander Putten et al, 2000; Scourse et al, 2006; Sturesson, 1976; Wanamaker et al, 2008). Mussel shells may be valuable high-resolution bioarchives of past marine, estuarine, fluviatile and limnic conditions Trace elements such as the rare earths and yttrium (REY) have been shown to be useful indicators of environmental change (Bau and Dulski, 1996; Bau et al, 2010; Bolhar et al, 2004; Kulaksız and Bau, 2013; Lee et al, 2003; Möller et al, 2000; Murray et al, 1990; Nothdurft et al, 2004; Tepe et al, 2014; Viehmann et al, 2014; Webb and Kamber, 2000; Wyndham et al, 2004). Their speciation in seawater and the distinct REY patterns exhibited by different geological materials make them very useful as geochemical proxies of oceanic change (Byrne, 2002; Byrne and Miller, 1985)
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