HR: 1330h
AN: B12B-0785    [PDF]
TI: Sr/Ca and Mg/Ca in Aragonitic Bivalves: Do They Record Temperature?
AU: * Gillikin, D P
EM: david.gillikin@vub.ac.be
AF: Vrije Universiteit Brussel, Department of Analytical and Environmental Chemistry, Pleinlaan 2, Brussels, 1050 Belgium
AU: Ulens, H
EM: hans.ulens@pandora.be
AF: University of Gent, Marelac, Gent, 9000 Belgium
AU: Dehairs, F
EM: fdehairs@vub.ac.be
AF: Vrije Universiteit Brussel, Department of Analytical and Environmental Chemistry, Pleinlaan 2, Brussels, 1050 Belgium
AU: Baeyens, W
EM: wbaeyens@vub.ac.be
AF: Vrije Universiteit Brussel, Department of Analytical and Environmental Chemistry, Pleinlaan 2, Brussels, 1050 Belgium
AU: Navez, J
EM: jnavez@africamuseum.be
AF: Vrije Universiteit Brussel, Department of Analytical and Environmental Chemistry, Pleinlaan 2, Brussels, 1050 Belgium
AU: Navez, J
EM: jnavez@africamuseum.be
AF: Royal Museum for Central Africa, Section of Mineralogy, Petrography and Geochemistry, Leuvensesteenweg 13, Tervuren, 8080 Belgium
AU: Andre, L
EM: lucandre@africamuseum.be
AF: Royal Museum for Central Africa, Section of Mineralogy, Petrography and Geochemistry, Leuvensesteenweg 13, Tervuren, 8080 Belgium
AU: Keppens, E
EM: ekeppens@vub.ac.be
AF: Vrije Universiteit Brussel, Department of Geology, Pleinlaan 2, Brussels, 1050 Belgium
AU: CALMARs group, .
EM: calmar@vub.ac.be
AF: An OSTC funded project, http://www.vub.ac.be/calmar, Brussels, 1050 Belgium
AB: The chemical or isotopic composition of calcareous skeletons have long been recognized as archives of past and present environmental conditions. Oxygen isotopes (d18O) of biogenic carbonates are a powerful proxy of SST, however, although usually dominated by SST, salinity (SSS) also significantly effects the oxygen isotopic signal recorded in the carbonate. This has led researchers to explore new proxies, which are independent of SSS. Generally, Sr/Ca and Mg/Ca of seawater remains unchanged above salinities of 10 and marine animals will commonly live in habitats that do not fluctuate below this salinity. To solve the issue of SSS complicating paleotemperature records, these "new" proxies must be at least as reliable as d18O. If an environmental control is dominant, the proxies should be reproducible between specimens growing under the same field conditions. Both Sr and Mg have been used as paleotemperature proxies in corals and foraminifera, whereas a fewer attempts have been made to use these proxies in bivalves. Some report a clear seasonal periodicity in Sr/Ca profiles of bivalves, which covaries with d18O (i.e., temperature), whereas others have found no clear periodicity. We test the robustness of these proxies by analyzing the shell material from three species of aragonitic clams from around the world using a LA-ICP-MS. Three individuals of M. mercenaria from North Carolina, USA, three individuals of Saxidomus giganteus from Washington, USA and one Arctica islandica from Norway have been analyzed. As expected, there is excellent reproducibility of d18O between specimens (both M. mercenaria and S. giganteus) indicating external environmental conditions control this proxy (i.e. SST and SSS). Preliminary data analysis show that Sr and Mg are not reproducible between specimens from the same site nor do they exhibit a clear seasonal cyclicity, indicating individual metabolic effects (i.e., vital effects) dominate the incorporation of these elements. A. islandica on the other hand, also does not have an easily discernable periodicity in the Sr signal, but Mg does seem to be more in sync with d18O. Also, both Sr and Mg are higher in the more recently formed shell section (when the clam is older) indicating that this may be due to the ontogenic change in physiology and hence, again, suggests a physiological control on the incorporation of both these elements. If there is an effect of temperature on the incorporation of these elements in these three species, the signal is masked by the larger signal produced by vital effects.
DE: 1035 Geochronology
DE: 1045 Low-temperature geochemistry
DE: 1050 Marine geochemistry (4835, 4850)
DE: 1065 Trace elements (3670)
DE: 1600 GLOBAL CHANGE (New category)
SC: Biogeosciences [B]
MN: 2003 Fall Meeting