HR: 1330h
AN: B12C-0797 [PDF]
TI: Temperature Dependent Sr-Isotope ($\delta$$^{88}$Sr) and Ca-Isotope ($\delta$$^{44}$Ca) Fractionation
in Carbonate Precipitates and Corals
AU: * Eisenhauer, A
EM: aeisenhauer@geomar.de
AF: GEOMAR, Wischhofstr. 1-3, Kiel, 24148
Germany
AU: Fietzke, J
EM: jf@gpi.uni-kiel.de
AF: GEOMAR, Wischhofstr. 1-3, Kiel, 24148
Germany
AU: Gussone, N
EM: ngussone@geomar.de
AF: GEOMAR, Wischhofstr. 1-3, Kiel, 24148
Germany
AU: B\"{o}hm, F
EM: fboehm@geomar.de
AF: GEOMAR, Wischhofstr. 1-3, Kiel, 24148
Germany
AU: Bock, B
EM: bbock@geomar.de
AF: GEOMAR, Wischhofstr. 1-3, Kiel, 24148
Germany
AU: N\"{a}gler, T
AF: Isotopengeologie, Universit\"{a}t Bern, Erlachstr. 9a, Bern, 3012
Switzerland
AB:
The knowledge of the influence of temperature and other environmental factors on isotope fractionation of divalent cations
like Ca$^{2+}$ and Sr$^{2+}$ during inorganic and biogenic controlled precipitation of calcium carbonate is crucial for their
interpretation as paleo proxies. In order to extend our earlier studies on Ca-isotope fractionation (e.g. Gussone et al.,
2003), we determined $\delta$$^{88}$Sr isotope ratios on seawater and on corals. We define the stable Sr isotope ratio as
$\delta$$^{88}$Sr=(($^{88}$Sr/$^{86}$Sr)$_{Sample}$/($^{88}$Sr/$^{86}$Sr)$_{Standard}$ -1)*1000; Sr Standard is NBS 987.
First measurements of the IAPSO seawater standard result in $\delta$$^{88}$Sr of 0.38$\pm$0.02 $\permil$. Coral CaCO$_{3}$
precipitated from seawater in a temperature range from about 22$\deg$C to about 27$\deg$C correspond to
$\delta$$^{88}$Sr-values ranging from 0.17 $\permil$ to about 0.32 $\permil$ indicating that carbonate precipitated from
seawater is isotopically lighter than seawater itself. The slope of 0.027 $\permil$/$\deg$C for the
temperature-$\delta$$^{88}$Sr relationship in corals is about a factor of 1.7 larger than the slope of $\delta$$^{44}$Ca
ratios in inorganically precipitated aragonite. However, the fractionation
$\alpha$(T)=(($^{88}$Sr/$^{86}$Sr)$_{CaCO3}$)/($^{88}$Sr/$^{86}$Sr)$_{Seawater}$) at a given temperature is about one order
of magnitude less for Sr-isotopes relative to Ca-isotopes. The larger temperature-$\delta$$^{88}$Sr gradient in comparison to
the Ca-isotopes is interpreted to reflect the smaller ion potential and the correspondingly smaller mass of the associated
Sr$^{2+}$-aquocomplex. The observation that $\delta$$^{88}$Sr and $\delta$$^{44}$Ca are positively correlated with
temperature points to the likelihood that kinetic or equilibrium fractionation effects and the mass of the associated
acquocomplex control the degree of divalent cation isotope fractionation during CaCO$_{3}$-precipitation.
Reference:
Gussone N., Eisenhauer A., Heuser A., Dietzel M., Bock B., B\"{o}hm F., Spero H., Lea D. W., Bijma J., and N\"{a}gler T. F.
(2003) Model for Kinetic Effects on Calcium Isotope Fractionation ($\delta$$^{44}$Ca) in Inorganic Aragonite and Cultured
Planktonic Foraminifera. Geochim Cosmochim Acta 67(7), 1375-1382.
DE: 1000 GEOCHEMISTRY (New field, replaces Rock Chemistry)
DE: 1040 Isotopic composition/chemistry
DE: 1050 Marine geochemistry (4835, 4850)
DE: 4267 Paleoceanography
SC: Biogeosciences [B]
MN: 2003 Fall Meeting