Measurement of fossil deep-sea coral Nd isotopic compositions and concentrations by TIMS as NdO+, with evaluation of cleaning protocols

Kirsty C. Crocket, Myriam Lambelet, Tina van de Flierdt, Mark Rehkaemper, Laura F. Robinson

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Abstract

Precise and accurate measurements of Nd concentrations and isotopic compositions of small sample masses (≤ 30 ng Nd) are increasingly necessary in the geosciences. Here, we present a combined chemical separation and TIMS (thermal ionisation mass spectrometry) NdO+ method adapted for fossil deep-sea corals, which represents a significant improvement in precision compared to existing methods, with additional assessment of potential contamination of coral aragonite by external encrustations. After digesting and spiking samples, we purified sample Nd using RE and Ln-spec separation chemistries, and tested the efficiency of these on aliquots of USGS BCR-2. In addition, we prepared a matrix-matched in-house coral reference material to monitor the analytical precision on coral carbonate. Using a micro-loading technique and TaF5 activator on single W filaments, ion beam sizes of up to 0.60 V per ng on mass 160 are achievable, but decline with increasing age of the activator. The long-term average for NdO+ measurements of 5 ng and 15 ng loads of the pure metal oxide JNdi-1 reference material (Geological Survey of Japan) was 0.512106 ± 6 for 143Nd/144Nd (12 ppm 2RSD, n = 44), with an overall deviation from the reference value of 17 ppm (0.512115 ± 7; Tanaka et al., 2000). BCR-2 aliquots of 10 ng and 30 ng generated an average 143Nd/144Nd of 0.512643 ± 8 (16 ppm 2RSD, n = 14), which is identical within uncertainty to the ........
Original languageEnglish
Pages (from-to)128-140
JournalChemical Geololgy
Volume374
DOIs
Publication statusPublished - 26 May 2014

Keywords

  • TIMS
  • NdO+
  • Nd isotopes
  • Deep-sea corals
  • Scleractinian corals
  • Desmophyllum dianthus

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