Ion microprobe assessment of the heterogeneity of Mg/Ca, Sr/Ca and Mn/Ca ratios in Pecten maximus and Mytilus edulis (bivalvia) shell calcite precipitated at constant temperature
Other literature type
Freitas, P. S.
Clarke, L. J.
Richardson, C. A.
Small-scale heterogeneity of biogenic carbonate elemental composition can be
a significant source of error in the accurate use of element/Ca ratios as
geochemical proxies. In this study ion microprobe (SIMS) profiles showed
significant small-scale variability of Mg/Ca, Sr/Ca and Mn/Ca ratios in new
shell calcite of the marine bivalves <i>Pecten maximus</i> and <i>Mytilus edulis</i> that was precipitated during a
constant-temperature culturing experiment. Elevated Mg/Ca, Sr/Ca and Mn/Ca
ratios were found to be associated with the deposition of elaborate shell
features, i.e. a shell surface stria in <i>P. maximus</i> and surface shell disturbance marks
in both species, the latter a common occurrence in bivalve shells. In both
species the observed small-scale elemental heterogeneity most likely was not
controlled by variable transport of ions to the extra-pallial fluid, but by
factors such as the influence of shell organic content and/or crystal size
and orientation, the latter reflecting conditions at the shell
crystal-solution interface. In the mid and innermost regions of the <i>P. maximus</i> shell
the lack of significant small-scale variation of Mg/Ca ratios, which is
consistent with growth at constant temperature, suggest a potential
application as a palaeotemperature proxy. Cross-growth band element/Ca ratio
profiles in the interior of bivalve shells may provide more promising
palaeo-environmental tools than sampling from the outer region of bivalve