Yes / The Mg/Ca ratios of biogenic calcite is commonly
seen as a valuable palaeo-proxy for reconstructing
past ocean temperatures. The temperature dependence of
Mg/Ca ratios in bivalve calcite has been the subject of contradictory
observations. The palaeoceanographic use of a
geochemical proxy is dependent on initial, rigorous calibration
and validation of relationships between the proxy
and the ambient environmental variable to be reconstructed.
Shell Mg/Ca ratio data are reported for the calcite of two bivalve
species, Mytilus edulis (common mussel) and Pecten
maximus (king scallop), which were grown in laboratory
culturing experiments at controlled and constant aquarium
seawater temperatures over a range from 10 to 20 C.
Furthermore, Mg/Ca ratio data of laboratory- and fieldgrown
M. edulis specimens were compared. Only a weak,
albeit significant, shell Mg/Ca ratio¿temperature relationship
was observed in the two bivalve species: M. edulis
(r2=0.37, p<0.001 for laboratory-cultured specimens and
r2=0.50, p<0.001 for field-cultured specimens) and P. maximus
(r2=0.21, p<0.001 for laboratory-cultured specimens
only). In the two species, shell Mg/Ca ratios were not found
to be controlled by shell growth rate or salinity. The Mg/Ca
ratios in the shells exhibited a large degree of variability
among and within species and individuals. The results suggest
that the use of bivalve calcite Mg/Ca ratios as a temperature
proxy is limited, at least in the species studied to
date. Such limitations are most likely due to the presence
of physiological effects on Mg incorporation in bivalve calcite.
The utilization is further limited by the great variability
both within and among shells of the same species that were
precipitated under the same ambient conditions
| Identifer | oai:union.ndltd.org:BRADFORD/oai:bradscholars.brad.ac.uk:10454/4760 |
| Date | January 2008 |
| Creators | Freitas, P.S., Clarke, Leon J., Kennedy, H.A., Richardson, C.A. |
| Source Sets | Bradford Scholars |
| Language | English |
| Detected Language | English |
| Type | Article, Published version |
| Rights | © Author(s) 2008. This work is distributed under the Creative Commons Attribution 3.0 License., CC-BY |
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