Antarctic Science

Biological Sciences

Silicon isotopes in Antarctic sponges: an interlaboratory comparison

Katharine R. Hendrya1a3 c1, Melanie J. Lenga2, Laura F. Robinsona1, Hilary J. Sloanea2, Jerzy Blusztjana1, Rosalind E.M. Rickabya3, R. Bastian Georga3a4 and Alex N. Hallidaya3

a1 Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA

a2 NERC Isotope Geosciences Laboratory, British Geological Survey, Keyworth, Nottingham NG12 5GG, UK

a3 Department of Earth Sciences, University of Oxford, Parks Road, Oxford OX1 3PR, UK

a4 Trent University, Worsfold Water Quality Centre, Peterborough, Ontario, Canada

Abstract

Cycling of deepwater silicon (Si) within the Southern Ocean, and its transport into other ocean basins, may be an important player in the uptake of atmospheric carbon, and global climate. Recent work has shown that the Si isotope (denoted by δ29Si or δ30Si) composition of deep sea sponges reflects the availability of dissolved Si during growth, and is a potential proxy for past deep and intermediate water silicic acid concentrations. As with any geochemical tool, it is essential to ensure analytical precision and accuracy, and consistency between methodologies and laboratories. Analytical bias may exist between laboratories, and sponge material may have matrix effects leading to offsets between samples and standards. Here, we report an interlaboratory evaluation of Si isotopes in Antarctic and sub-Antarctic sponges. We review independent methods for measuring Si isotopes in sponge spicules. Our results show that separate subsamples of non-homogenized sponges measured by three methods yield isotopic values within analytical error for over 80% of specimens. The relationship between δ29Si and δ30Si in sponges is consistent with kinetic fractionation during biomineralization. Sponge Si isotope analyses show potential as palaeoceaongraphic archives, and we suggest Southern Ocean sponge material would form a useful additional reference standard for future spicule analyses.

(Received March 26 2010)

(Accepted May 28 2010)

(Online publication August 20 2010)

Correspondence:

c1 khendry@whoi.edu

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