Interlaboratory study for coral Sr/Ca and other element/Ca ratio measurements

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Hathorne, Ed C.
Gagnon, Alexander C.
Felis, Thomas
Adkins, Jess F.
Asami, Ryuji
Boer, Wim
Caillon, Nicolas
Case, David H.
Cobb, Kim M.
Douville, Eric
deMenocal, Peter B.
Eisenhauer, Anton
Garbe-Schonberg, Dieter
Geibert, Walter
Goldstein, Steven L.
Hughen, Konrad A.
Inoue, Mayuri
Kawahata, Hodaka
Kolling, Martin
Cornec, Florence L.
Linsley, Braddock K.
McGregor, Helen V.
Montagna, Paolo
Nurhati, Intan S.
Quinn, Terrence M.
Raddatz, Jacek
Rebaubier, Helene
Robinson, Laura F.
Sadekov, Aleksey
Sherrell, Robert M.
Sinclair, Dan
Tudhope, Alexander W.
Wei, Gangjian
Wong, Henri
Wu, Henry C.
You, Chen-Feng
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Coral Sr/Ca ratios
The Sr/Ca ratio of coral aragonite is used to reconstruct past sea surface temperature (SST). Twenty-one laboratories took part in an interlaboratory study of coral Sr/Ca measurements. Results show interlaboratory bias can be significant, and in the extreme case could result in a range in SST estimates of 7°C. However, most of the data fall within a narrower range and the Porites coral reference material JCp-1 is now characterized well enough to have a certified Sr/Ca value of 8.838 mmol/mol with an expanded uncertainty of 0.089 mmol/mol following International Association of Geoanalysts (IAG) guidelines. This uncertainty, at the 95% confidence level, equates to 1.5°C for SST estimates using Porites, so is approaching fitness for purpose. The comparable median within laboratory error is <0.5°C. This difference in uncertainties illustrates the interlaboratory bias component that should be reduced through the use of reference materials like the JCp-1. There are many potential sources contributing to biases in comparative methods but traces of Sr in Ca standards and uncertainties in reference solution composition can account for half of the combined uncertainty. Consensus values that fulfil the requirements to be certified values were also obtained for Mg/Ca in JCp-1 and for Sr/Ca and Mg/Ca ratios in the JCt-1 giant clam reference material. Reference values with variable fitness for purpose have also been obtained for Li/Ca, B/Ca, Ba/Ca, and U/Ca in both reference materials. In future, studies reporting coral element/Ca data should also report the average value obtained for a reference material such as the JCp-1.
Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 14 (2013): 3730–3750, doi:10.1002/ggge.20230.
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Geochemistry, Geophysics, Geosystems 14 (2013): 3730–3750
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