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Deep-sea coral aragonite as a recorder for the neodymium isotopic composition of seawater

van de Flierdt, Tina and Robinson, Laura F. and Adkins, Jess F. (2010) Deep-sea coral aragonite as a recorder for the neodymium isotopic composition of seawater. Geochimica et Cosmochimica Acta, 74 (21). pp. 6014-6032. ISSN 0016-7037.

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Deep-sea corals have been shown to be useful archives of rapid changes in ocean chemistry during the last glacial cycle. Their aragonitic skeleton can be absolutely dated by U–Th data, freeing radiocarbon to be used as a water-mass proxy. For certain species of deep-sea corals, the growth rate allows time resolution that is comparable to ice cores. An additional proxy is needed to exploit this opportunity and turn radiocarbon data into rates of ocean overturning in the past. Neodymium isotopes in seawater can serve as a quasi-conservative water-mass tracer and initial results indicate that deep-sea corals may be reliable archives of seawater Nd isotopes. Here we present a systematic study exploring Nd isotopes as a water-mass proxy in deep-sea coral aragonite. We investigated five different genera of modern deep-sea corals (Caryophyllia, Desmophyllum, Enallopsamia, Flabellum, Lophelia), from global locations covering a large potential range of Nd isotopic compositions. Comparison with ambient seawater measurements yields excellent agreement and suggests that deep-sea corals are reliable archives for seawater Nd isotopes. A parallel study of Nd concentrations in these corals yields distribution coefficients for Nd between seawater and coral aragonite of 1–10, omitting one particular genus (Enallopsamia). The corals and seawater did however not come from exactly the same location, and further investigations are needed to reach robust conclusions on the incorporation of Nd into deep-sea coral aragonite. Lastly, we studied the viability of extracting the Nd isotope signal from fossil deep-sea corals by carrying out stepwise cleaning experiments. Our results show that physical removal of the ferromanganese coating and chemical pre-cleaning have the highest impact on Nd concentrations, but that oxidative/reductive cleaning is also needed to acquire a seawater Nd isotope signal.

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Adkins, Jess F.0000-0002-3174-5190
Additional Information:© 2010 Elsevier Ltd. Received 15 March 2010; accepted 27 July 2010. Associate editor: Miryam Bar-Matthews. Available online 6 August 2010. This study was supported by NSF Grant OCE-0623107 to T.v.d.F. and L.F.R., NSF Grant ANT-063678 to L.F.R., a Marie Curie International Reintegration grant (IRG 230828) and NERC Grant NE/F016751/1 to T.v.d.F., and NSF Grant OCE-0929272 to J.F.A. We thank the Lamont geochemistry group for their help in keeping the labs and the mass specs running smoothly, particularly Jenna Cole for initial help in getting familiar with the TIMS, and Sidney Hemming for invaluable discussions while developing the coral measurements on the TIMS. Alex Gagnon is thanked for help with coral sampling. We are very grateful to Stephen Cairns from the Smithsonian Museum in Washington (DC) for lending us the majority of the coral specimen used for this study and for fruitful discussion. Constructive reviews by M. Gutjahr and two anonymous referees, as well as the editorial handling of M. Bar-Matthews are gratefully acknowledged.
Funding AgencyGrant Number
Marie Curie International Reintegration grantIRG 230828
Natural Environment Research Council (NERC)NE/F016751/1
Issue or Number:21
Record Number:CaltechAUTHORS:20101028-094932327
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:20582
Deposited By: Jason Perez
Deposited On:28 Oct 2010 20:22
Last Modified:24 Feb 2020 10:30

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