High precision U-series dating of scleractinian cold-water corals using an automated chromatographic U and Th extraction

Type Article
Date 2017-12
Language English
Author(s) Wefing Anne-Marie1, Arps Jennifer1, Blaser Patrick1, Wienberg Claudia2, Hebbeln Dierk2, Frank Norbert1, 3
Affiliation(s) 1 : Heidelberg Univ, Inst Environm Phys, Neuenheimer Feld 229, D-69120 Heidelberg, Germany.
2 : Univ Bremen, MARUM Ctr Marine Environm Sci, Leobener Str 8, D-28359 Bremen, Germany.
3 : Heidelberg Univ, Inst Geosci, Neuenheimer Feld 234, D-69120 Heidelberg, Germany.
Source Chemical Geology (0009-2541) (Elsevier Science Bv), 2017-12 , Vol. 475 , P. 140-148
DOI 10.1016/j.chemgeo.2017.10.036
WOS© Times Cited 24
Keyword(s) U-series dating, prepFAST-MC, Cold-water corals, South Atlantic, Angola, Past climate
Abstract

High-precision U-series dating of scleractinian cold-water corals is a key chronological tool for studies of past environmental and climate conditions. Here, we tested and optimized an automated chemical extraction system (ESI prepFAST-MC equipped with an Eichrom TRU-resin chromatographic column) for its ability to purify U and Th isotopes for mass spectrometric U-series dating at the sub-‰ precision level. Chemical yields are constantly high, on average around 90% for both U and Th. Analytical blanks are comparable to manual purification (< 0.15 pg U, 0.15 pg Th for a typical sample of 50 mg) and memory effects due to the recycling of the column are mostly insignificant as the carry-over fraction is about 10− 5 for Th and 10− 3 for U isotopes. However, it was found that the built-in UTh (TRU-resin) column must be pre-conditioned for analysis using > 1 μg g− 1 Th and U in order to achieve the above mentioned chemical yields. This conditioning has no impact on the Th/U data. The automated chemical preparation protocol described here is compared to conventional ultra-high precision U-series dating with manual sample purification. For the 34 cold-water corals extracted from a sediment core collected from a coral mound off Angola, the differences between 230Th/238U- and 234U/238U-ratios and U-series ages measured with the two analytical methods are smaller than the respective analytical uncertainty of < 3.0‰, 0.8‰ and 3.0‰, respectively. Overall, ages of the studied corals span 34,000 years and perfectly meet quality control constrains, such as initial seawater δ234U0. Finally, our record of coral ages indicates vigorous coral growth under warm and cold climate conditions in the temperate south-eastern Atlantic, contrasting climate influenced coral occurrences in the north-eastern Atlantic.

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