Neodymium isotopes in seawater samples collected during the IN2017-V01 voyage of the RV Investigator

Brief description

Samples were collected from the East Antarctic margin, aboard the Australian Marine National Facility R/V Investigator from January 14th to March 5th 2017 (IN2017_V01; Armand et al., 2018). This marine geoscience expedition, named the “Sabrina Sea Floor Survey”, focused notably on studying the interactions of the Totten Glacier with the Southern Ocean through multiple glacial cycles.
Ten litres seawater samples were collected using a CTD rosette equipped with Niskin® bottle and filtered through a 0.45µm Acropak® capsule filter directly into acid-cleaned 10 L polyethylene jerrycans. Samples were then acidified to pH 2 with 2 mL/L of distilled 6M HCl in a laminar flow hood. These samples were analysed for neodymium (Nd) isotopes, a tracer of ocean circulation.

In the home laboratory (IMAS Trace-Metal Lab, UTAS, Hobart, Australia), seawater samples were pre-concentrated using pre-packed Nobias® PA1L (Hitachi Technologies, Japan) chelating resin cartridges following the method of Pérez-Tribouillier et al., (2019). Rare Earth Elements were separated using anion-exchange chromatography (Anderson et al., 2012) and cation-exchange chromatography (Struve et al., 2016). Finally, Nd isotopes were isolated using LN-Spec column chemistry (Pin and Zalduegui, 1997).
Purified seawater sample Nd concentrations were checked prior to isotopic analysis using Sector Field Inductively Coupled Mass Spectrometry (ICP-MS) at the Central Science Laboratory (UTAS, Hobart, Australia). Nd isotope ratio measurements were then carried out at the Geochemistry Laboratory of the School of Geography, Environment and Earth Sciences of Victoria University of Wellington, New Zealand, using a Thermo Finnigan Triton thermal ionization mass spectrometer (TIMS). Data were reduced offline for outlier rejection and corrected using 146Nd/144Nd = 0.7219 for mass fractionation using the exponential law, and 144Sm/147Sm = 0.20667 for the Sm interference correction on mass 144. JNdi standard data produced for two load sizes using two amplifier configurations were identical: 143Nd/144Nd = 0.512110 ± 24 2sd (46 ppm 2rsd, n = 16) for 1 ng loads using 1013Ω amplifiers, vs. 143Nd/144Nd = 0.512112 ± 3 2sd (6 ppm 2rsd, n = 6) for 100 ng loads using 1011Ω amplifiers. The corrected 143Nd/144Nd were normalised to the JNdi standard with the published value of 0.512115 (Tanaka et al., 2000). Nd isotopic compositions are reported as eNd = [(143Nd/144Nd)sample / (143Nd/144Nd)CHUR - 1]x10,000 , where CHUR is the Chondritic Uniform Reservoir with 143Nd/144Nd)CHUR = 0.512638 (Jacobsen and Wasserburg, 1980).


References
- Anderson R. F., Fleisher M. Q., Robinson L. F., Edwards R. L., Hoff J. A., Moran S. B., van der Loeff M. R., Thomas A. L., Roy-Barman M. and Francois R. (2012) GEOTRACES intercalibration of 230Th, 232Th, 231Pa, and prospects for 10Be. Limnol. Oceanogr. Methods 10, 179–213. A
- Armand L. K., O’Brien P. E., Armbrecht L., Baker H., Caburlotto A., Connell T., Cotterle D., Duffy M., Edwards S., Evangelinos D., Fazey J., Flint A., Forcardi A., Gifford S., Holder L., Hughes P., Lawler K.-A., Lieser J., Leventer A., Lewis M., Martin T., Morgan N., López-Quirós A., Malakoff K., Noble T., Opdyke B., Palmer R., Perera R., Pirotta V., Post A., Romeo R., Simmons J., Thost D., Tynan S. and Young A. (2018) Interactions of the Totten Glacier with the Southern Ocean through multiple glacial cycles (IN2017-V01): Post-survey report. ANU Res. Publ.
- Jacobsen S. B. and Wasserburg G. J. (1980) Sm-Nd isotopic evolution of chondrites. Earth Planet. Sci. Lett. 50, 139–155.
- Pérez-Tribouillier H., Noble T. L., Townsend A. T., Bowie A. R. and Chase Z. (2019) Pre-concentration of thorium and neodymium isotopes using Nobias chelating resin: Method development and application to chromatographic separation. Talanta, 1–10.
- Pin C. and Zalduegui J. F. S. (1997) Sequential separation of light rare-earth elements , thorium and uranium by miniaturized extraction chromatography: Application to isotopic analyses of silicate rocks. Anal. Chim. Acta 339, 79–89.
- Struve T., Van De Flierdt T., Robinson L. F., Bradtmiller L. I., Hines S. K., Adkins J. F., Lambelet M., Crocket K. C., Kreissig K., Coles B. and Auro M. E. (2016) Neodymium isotope analyses after combined extraction of actinide and lanthanide elements from seawater and deep-sea coral aragonite. Geochemistry, Geophys. Geosystems 17, 232–240.
- Tanaka T., Togashi S., Kamioka H., Amakawa H., Kagami H., Hamamoto T., Yuhara M., Orihashi Y., Yoneda S., Shimizu H., Kunimaru T., Takahashi K., Yanagi T., Nakano T., Fujimaki H., Shinjo R., Asahara Y., Tanimizu M. and Dragusanu C. (2000) JNdi-1: A neodymium isotopic reference in consistency with LaJolla neodymium. Chem. Geol. 168, 279–281.

Lineage

Progress Code: completed

Statement: Multiple procedural blanks and certified standards were processed and analysed in the same manner as samples. Accuracy and precision of the seawater - Nd analysis were assessed using JNdi-1 isotopic reference material (Geological Survey of Japan, Tanaka et al., 2000).

We suspect issues with sample filtration at the CTD stations 9, 16 and 19 of the voyage, with the measurements representing a ‘total’ (and less radiogenic eNd) rather than dissolved fraction.

Notes

Purpose
These data were collected in order to determine the Nd isotopic composition of water masses and for paleo-proxies calibration.