Journal
GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS
Volume 12, Issue -, Pages -Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1029/2010GC003322
Keywords
lithium; isotope; aragonite; rate; SIMS; magnesium
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Funding
- U.S. NSF
- EAR
- NSF [EAR/IF-0318137, OCE-0402728, OCE-0527350, OCE-0823527, EAR-0337481]
- Division Of Ocean Sciences
- Directorate For Geosciences [0823527] Funding Source: National Science Foundation
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In situ secondary ion mass spectrometry (SIMS) analyses of delta Li-7, Li/Ca, and Mg/Ca were performed on five synthetic aragonite samples precipitated from seawater at 25 degrees C at different rates. The compositions of delta Li-7 in bulk aragonites and experimental fluids were measured by multicollector inductively coupled plasma-mass spectrometry (MC-ICP-MS). Both techniques yielded similar delta Li-7 in aragonite when SIMS analyses were corrected to calcium carbonate reference materials. Fractionation factors alpha Li-7/Li-6 range from 0.9895 to 0.9923, which translates to a fractionation between aragonite and fluid from -10.5% to -7.7%. The within-sample delta Li-7 range determined by SIMS is up to 27%, exceeding the difference between bulk delta Li-7 analyses of different aragonite precipitates. Moreover, the centers of aragonite hemispherical bundles (spherulites) are enriched in Li/Ca and Mg/Ca relative to spherulite fibers by up to factors of 2 and 8, respectively. The Li/Ca and Mg/Ca ratios of spherulite fibers increase with aragonite precipitation rate. These results suggest that precipitation rate is a potentially important consideration when using Li isotopes and elemental ratios in natural carbonates as a proxy for seawater composition and temperature.
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