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

Waltham, D.A.; Gröcke, D.R.

Authors

D.A. Waltham



Abstract

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.

Citation

Waltham, D., & Gröcke, D. (2006). Non-uniqueness and interpretation of the seawater 87Sr/86Sr curve. Geochimica et Cosmochimica Acta, 70(2), 384-394. https://doi.org/10.1016/j.gca.2005.09.014

Journal Article Type Article
Acceptance Date Sep 14, 2005
Online Publication Date Nov 7, 2005
Publication Date Jan 15, 2006
Deposit Date Jun 4, 2010
Journal Geochimica et Cosmochimica Acta
Print ISSN 0016-7037
Publisher Meteoritical Society
Peer Reviewed Peer Reviewed
Volume 70
Issue 2
Pages 384-394
DOI https://doi.org/10.1016/j.gca.2005.09.014