Determination of temperature-dependent stable strontium isotope (88Sr/86Sr) fractionation via bracketing standard MC-ICP-MS

[1] Stable strontium isotopes ( here Sr-88/Sr-86) are introduced as a new member of the nontraditional stable isotopes. We have developed a bracketing standard method for the determination of delta Sr-88/86 using an AXIOM MC-ICP-MS and normalizing to strontium SRM NBS987. For individual measurements the external reproducibility is better than about 25 ppm (1 sigma RSD). For the IAPSO seawater standard a delta Sr-88/86 value of 0.381 +/- 0.010 parts per thousand (2SEM) was determined. For the first time a temperature-dependent strontium isotope fractionation during calcium carbonate precipitation could be shown. Aragonite samples inorganically precipitated under temperature control between 10 and 50 degrees C revealed a delta(88/86) Sr/ temperature dependency of 0.0054(5)parts per thousand/ degrees C (R-2 = 0.987). In contrast, for natural coral samples (Pavona clavus) from a proxy calibration study (23 to 27 degrees C) we did determine 0.033( 5)parts per thousand/ degrees C (R-2 = 0.955). The processes causing this sixfold stronger temperature dependency for the natural coral samples have to be studied in more detail in future studies. In a first approach the different slopes can be interpreted as effects of kinetic fractionation of strontium ions with or without a hydrate shell of 22 to 29 water molecules.