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Non-uniqueness and interpretation of the seawater 87Sr/86Sr curve.

Waltham, D. A. and Gröcke, D. R. (2006) 'Non-uniqueness and interpretation of the seawater 87Sr/86Sr curve.', Geochimica et cosmochimica acta., 70 (2). pp. 384-394.


Variations in the seawater 87Sr/86Sr curve through time can be caused by fluctuations in the strontium flux or variations in the isotopic ratio from at least six different sources and sinks. Thus, 12 or more parameters control each single measurement although widely accepted assumptions allow this to be reduced to typically six unknowns. Interpreting the causes of time-variation in the seawater 87Sr/86Sr curve is therefore hampered by inherent non-uniqueness. However, this problem is under-constrained rather than unconstrained. As a result, whilst there are an infinite number of possible interpretations, these all come from a few families of very similar solutions. Using this insight, it is possible to find solutions having the smallest possible variations in source flux or source 87Sr/86Sr ratio. Thus, lower-bounds can be placed upon the source variations responsible for the observed fluctuations in the seawater 87Sr/86Sr curve. When applied to the evolution of the Early Jurassic 87Sr/86Sr seawater curve, this approach demonstrates that a short-lived Toarcian event is genuine since it is present in all models, regardless of the values chosen for the unknown source fluxes and unknown source isotope ratios. However, the variations in strontium flux or isotopic ratio necessary to explain the Toarcian event may be significantly smaller than would be predicted assuming modern values for the unknown parameters.

Item Type:Article
Full text:Full text not available from this repository.
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Date accepted:14 September 2005
Date deposited:No date available
Date of first online publication:07 November 2005
Date first made open access:No date available

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