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| Titel |
Fractionation of stable isotopes of strontium in continental carbonate environments as a potential contributor to the δ⁸⁸/⁸⁶Sr in the oceans |
| VerfasserIn |
Netta Shalev, Ludwik Halicz, Mordechai Stein, Ittai Gavrieli, Amir Sandler, Irena Segal, Boaz Lazar |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250098154
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| Publikation (Nr.) |
 EGU/EGU2014-13801.pdf |
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| Zusammenfassung |
| Several fluxes dictate the concentration and isotope composition of strontium in the oceans
including: continental crust weathering, the hydrothermal flux and the precipitation of marine
carbonates. These fluxes were traditionally evaluated by the radiogenic ratio of 87Sr/86Sr and
recently by the stable isotope ratio of 88Sr/86Sr. In this study the Sr fractionation in carbonate
continental environments were investigated in order to evaluate the continental weathering
88Sr/86Sr component.
The δ88-86Sr values of mountain soils along a precipitation gradient and their parent
desert dust were analyzed, as well as the δ88-86Sr values of continental waters that
precipitated carbonate minerals. Isotopic measurements were conducted by MC-ICP-MS
using double-spike method to correct for the instrumental mass bias.
The results show that the desert dust and all mountain soils have a similar δ88-86Sr values.
These results suggest that there is no significant Sr isotope fractionation during weathering
(including leaching and dissolution). In contrast, we found significant Sr isotope fractionation
during precipitation of continental solid carbonates. Speleothems and tufa were isotopically
depleted with respect to the dripping and stream waters from which they precipitated. The
Δ88-86Srcarb-water, the average isotope fractionation factor between the solid carbonate and
the conjugate water was found to be -0.20±0.08o(2SD, n=5). This fractionation
factor is similar within 2SD to the previously published Δ88-86Srcarb-water for
precipitation of marine carbonates (Δ88-86Srcarb-sw=-0.24). The continental carbonate
precipitation is substantially smaller than the marine carbonate deposition and hence has
a little impact on the Sr isotopic composition of the continental runoff into the
oceans.
Our results indicate that δ88-86Sr value of the continental flux to the ocean is
predominantly dictated by the relative contribution of Sr derived by weathering of two end
members: silicates with δ88-86Sr of -0.27oand isotopically depleted carbonates. Hence,
the variations in the weathering terrains during geological time play a major role
in controlling the secular variations of the Sr isotopic composition of the oceans. |
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