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U-Th dating of deep-sea corals

Cheng, Hai and Adkins, Jess and Edwards, R. Lawrence and Boyle, Edward A. (2000) U-Th dating of deep-sea corals. Geochimica et Cosmochimica Acta, 64 (14). pp. 2401-2416. ISSN 0016-7037. doi:10.1016/S0016-7037(99)00422-6.

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^(230)Th, ^(232)Th, ^(234)U and ^(238)U compositions of several deep-sea solitary corals, mainly the species Desmophyllum cristagalli, were determined by thermal ionization mass spectrometry (TIMS). It is possible to obtain high precision ages on modern pristine corals that have low [^(232)Th] (5 to a few hundred ppt). However, because older deep-sea corals tend to have higher [^(232)Th] compared to surface corals, and the initial ^(230)Th/^(232)Th ratio is uncertain, older deep-sea corals have larger age uncertainties (± several hundred years for samples with a few thousand ppt ^(232)Th). Therefore, the key hurdle for precise U-Th dating is to remove or account for contaminants which contain elevated ^(232)Th and associated ^(230)Th not due to closed system decay within the coral lattice. A modification of the trace metal cleaning methods used for foraminifera and surface corals can significantly reduce this contamination. By counting the visible growth bands and measuring the mean age of a single septum, the extension rate of D. cristagalli was estimated to be between 0.1 and 3.1 mm/year. In a mean sense, bands appear to be precipitated annually, but this estimate has a large uncertainty. If appropriate tracer calibrations can be established, these corals are therefore suitable to record decadal or sub-decadal oceanographic changes over the course of their lifetime. The δ^(234)U values of all modern samples from different localities and different depths are similar (mean 145.5 ± 2.3‰) and indistinguishable from the data obtained from surface corals. At a precision of about ±2‰, we find no structure in the oceanic profile of δ^(234)U ratios over the top 2000 m of the water column.

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Adkins, Jess0000-0002-3174-5190
Additional Information:© 2000 Elsevier Science Ltd. Received 24 February 1999; Revised 16 November 1999; Accepted 16 November 1999; Available online 6 July 2000. D. Richards and J. Doral provided stimulating discussions about many of the issues raised in this work. S. Cairns helped identify the coral samples. T. Kleindinst of WHOI produced the photograph in Figure 4. We would like to thank G. Henderson and D. Muhs for helpful reviews of the manuscript. JFA thanks the UCAR Post-Doctoral Fellowship Program and LDEO for support during the writing of this paper.
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University Corporation for Atmospheric Research (UCAR)UNSPECIFIED
Lamont–Doherty Earth Observatory (LDEO)UNSPECIFIED
Issue or Number:14
Record Number:CaltechAUTHORS:20120828-093103827
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Official Citation:Hai Cheng, Jess Adkins, R.Lawrence Edwards, Edward A. Boyle, U-Th dating of deep-sea corals, Geochimica et Cosmochimica Acta, Volume 64, Issue 14, July 2000, Pages 2401-2416, ISSN 0016-7037, 10.1016/S0016-7037(99)00422-6. (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:33596
Deposited On:28 Aug 2012 17:03
Last Modified:09 Nov 2021 21:35

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