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Discrete dissolved neodymium isotopes and rare earth element (REE) concentrations from the GEOTRACES process cruise GPpr05 (KM1107)

Responsible investigator

Dr Katharina Pahnke
email: k.pahnke@icbm.de
Max Planck Research Group for Marine Isotope Geochemistry
Institute for Chemistry and Biology of the Marine Environment (ICBM)
University of Oldenburg
Carl-von-Ossietzky-Str. 9-11
26129 Oldenburg
cjd Germany

Data contributor

Dr Katharina Pahnke
email: k.pahnke@icbm.de
Max Planck Research Group for Marine Isotope Geochemistry
Institute for Chemistry and Biology of the Marine Environment (ICBM)
University of Oldenburg
Carl-von-Ossietzky-Str. 9-11
26129 Oldenburg
Germany

Dr Henning Fröllje
email: hfroellj@mpi-bremen.de
Max Planck Research Group for Marine Isotope Geochemistry
Institute for Chemistry and Biology of the Marine Environment (ICBM)
University of Oldenburg
Carl-von-Ossietzky-Str. 9-11
26129 Oldenburg
Germany

Laboratory of analysis

Institute for Chemistry and Biology of the Marine Environment (ICBM)

Dataset brief description

Discrete dissolved neodymium isotopes and rare earth element (REE) concentrations from the GEOTRACES process cruise GPpr05 (KM1107) around Oahu, Hawaii, and Hawaii Ocean Time-series station ALOHA (central North Pacific).

Acquisition description

Sampling methodology

All seawater samples were collected in 12 L Niskin bottles with nylon-coated stainless steel springs attached to a rosette frame equipped with a Sea-Bird CTD. Five litres of seawater per sample were filtered directly from Niskin bottles through AcroPak500 or AcroPak200 cartridges (pore size of 0.8/0.45 µm and 0.8/0.2 µm, respectively) into pre-cleaned LDPE containers.

For dissolved REE concentrations, a volume of 250 mL of filtered seawater was collected into pre-cleaned LDPE bottles. All samples were acidified to a pH of ~2 with ultra-pure 6 N HCl.

Analytical methodology

Nd isotopic composition

For dissolved Nd isotope analyses, REEs were preconcentrated from seawater using C18 SepPak cartridges (Waters Inc.) following a method modified after Shabani et al. (1992) and Jeandel et al. (1998). The C18 cartridges were cleaned using 5-10 mL 0.5 N HCl and rinsed with MilliQ to bring the pH back to neutral. They were filled with 300 mg of a REE complexing agent (HDEHP), followed by another cleaning step with 2 mL 6 N HCl to remove REEs and rinsing with MilliQ prior to further use. After adjusting the samples to a pH of 3.5 using distilled ammonia hydroxide solution, they were pumped through the pre-cleaned C18 cartridges at a pump rate of 20 ml/min. The cartridges were then rinsed with 0.01 N HCl to remove Ba and the REEs were eluted with 35 ml of 6 N HCl. Neodymium was then isolated by two-step column chemistry (Pin and Zaduegui, 1997). The first set of columns was filled with Eichrom TRU-Spec resin (100 µl, particle size 100-150 µm) and used for separation of REEs from any HDEHP that may have leaked out of the C18 cartridges. In the second step, columns filled with Eichrom LN-Spec resin (250 µl, particle size 50-100 µm) were used to isolate Nd with 0.23-0.25 N HCl as eluent. The Nd aliquot was treated with a 1:1 mixture of H2O2 (30%) and concentrated HNO3, dried, and re-dissolved in 2% HNO3 for isotope measurements. All used acids were of ultra-clean quality.

Neodymium isotopes were measured on a ThermoScientific Neptune Plus multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS) at the University of Oldenburg. A Cetac Aridus II desolvation nebulizer system was used for sample introduction. The Nd isotope standard JNdi-1 was measured generally every 2nd-3rd sample at the same concentration as the samples. All samples were corrected for mass bias with ¹⁴⁶ Nd/ ¹⁴⁴ Nd = 0.7219 using an exponential law (O'Nions et al., 1977). We applied a secondary mass bias correction using linear correlation of ¹⁴³ Nd/ ¹⁴⁴ Nd to ¹⁴² Nd/ ¹⁴⁴ Nd (Vance and Thirlwall, 2002). All data were normalized to the accepted JNdi-1 value of ¹⁴³ Nd/ ¹⁴⁴ Nd = 0.512115 (Tanaka et al., 2000). External reproducibility, checked with multiple runs of 5-10 ppb JNdi-1 during each session, was generally better than ± 0.4 ‰ (2σ, n=8-24 per session). An independent secondary in-house standard (5-10 ppb, n=16) was measured one to two times per session and had a reproducibility of ± 0.3 ‰ (2σ) over the entire measurement period. The procedural Nd blank was <10 pg (n=12), representing <1% of the Nd concentration of the samples. Therefore, no blank correction was applied.

REE concentrations

Rare earth element concentrations were determined by isotope dilution ICP-MS using a Thermo Finnigan ELEMENT 2 inductively coupled plasma-mass spectrometer (ICP-MS) at the ICBM, University of Oldenburg. The instrument is coupled to an autosampler (ASX-100, CETAC) and a desolvation introduction system (Aridus 2, CETAC) that is used with a nitrogen-argon gas mixture to enhance sensitivity and to minimise oxide formation to a negligible level (e.g. Rousseau et al., 2013).

The REE concentrations in seawater were determined by isotope dilution (ID) analysis. For this purpose, 10-80 ml aliquots of the samples, depending on REE concentrations, were mixed with a multi-element REE spike and equilibrated for at least 24h. Preconcentration of REE was achieved with the commercially available SeaFAST pico system (Elemental Scientific Inc.) that was operated in offline mode. The pre-concentrated samples were filled with ultra-pure water to volumes of 0.8-1 ml for ICP-MS analysis. Rare earth element concentrations were measured on a Thermo Finnigan Element II sector field inductively coupled plasma mass spectrometer (ICP-MS) at the University of Oldenburg in low resolution mode. The ICP-MS was coupled to a Cetac Aridus II desolvation nebulizer system that ran with argon and nitrogen gas in order to decrease oxide formation rates. Sample introduction was achieved with a 100 µl nebulizer and a Cetac ASX-100 autosampler. Oxide formation rates were monitored for Ba and Ce before each measurement session and were lower than 0.03%. The blank of the ICP-MS measurements was checked by analysis of 2% HNO3 every five samples and the daily-averaged blank counts were subtracted from each sample. Total procedural blanks (n=9) were spiked and prepared analogous to the samples. The reproducibility (2σ) of the measurements between sessions was checked with multiple runs (1-2 per session) of a standard solution that contains REEs at seawater-like relative concentrations ("Coral Sea standard", provided by Gideon Henderson, University of Oxford, UK) and was <7% for all elements except for Gd (7.3%) (n=6). The external reproducibility (2σ) was checked by multiple processing and analysis of the international GEOTRACES reference standards BATS (15 m, n=4; van de Flierdt et al., 2012) and SAFe (3000 m, n=10, including one re-analysis; Pahnke et al., 2012 (published Nd concentration only) and was <8.8% for all elements of BATS, and <8.1% for all elements of SAFe except for Ce (66 %) and Gd (10.8%). The average measured REE concentrations are in good agreement with published values (deviation of <5% for all elements for BATS, van de Flierdt et al., 2012; 5.4% for SAFe (Nd), Pahnke et al., 2012). Analyses of three independently processed duplicate samples agree within analytical uncertainty.

References Cited

van de Flierdt T et al., 2012. GEOTRACES intercalibration of neodymium isotopes and rare earth element concentrations in seawater and suspended particles. Part 1: reproducibility of results for the international intercomparison. Limnol. Oceanogr.: Methods 10, 234-251.

Jeandel, C., Thouron, D., Fieux, M., 1998. Concentrations and isotopic compositions of neodymium in the eastern Indian Ocean and Indonesian straits. Geochimica et Cosmochimica Acta 62, 2597-2607. Concentrations and isotopic compositions of neodymium in the eastern Indian Ocean and Indonesian straits. Geochimica et Cosmochimica Acta 62, 2597-2607.

O'Nions, R.K., Hamilton, P.J., Evensen, N.M., 1977. Variations in ¹⁴³ Nd/ ¹⁴⁴ Nd and ⁸⁷ Sr/ ⁸⁶ Sr ratios in oceanic basalts. Earth and Planetary Science Letters 34, 13-22.

Pahnke K., van de Flierdt T., Jones K.M., Lambelet M., Hemming S.R., Goldstein S.L. 2012., GEOTRACES intercalibration of neodymium isotopes and rare earth element concentrations in seawater and suspended particles. Part 2: Systematic tests and baseline profiles. Limnol. Oceanogr. Methods 10, 252-269.

Pin, C., 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. Analytica Chimica Acta 339, 79-89.

Rousseau T.C.C., Sonke J.E., Chmeleff J., Candaudap F., Lacan F., Boaventura G., Seyler P., Jeandel C., 2013. Rare earth element analysis in natural waters by multiple isotope dilution-sector field ICP-MS. Journal of Analytical Atomic Spectrometry 28, 573-584.

Shabani, M.B., Akagi, T., Masuda, A., 1992. Preconcentration of trace rare-earth elements in seawater by complexation with bis(2-ethylhexyl) hydrogen phosphate and 2-ethylhexyl dihydrogen phosphate adsorbed on a C18 cartridge and determination by inductively coupled plasma mass-spectrometry. Analytical Chemistry 64, 737-743.

Tanaka et al., 2000. JNdi-1: a neodymium isotopic reference in consistency with LaJolla neodymium. Chem. Geol. 168, 279-281.

Vance, D., Thirwall, M., 2002. An assessment of mass discrimination in MC-ICPMS using Nd isotopes Chemical Geology 185, 227-240.

BODC Data Processing Procedures

There was no time information available from site KM1107-02_10 so the time element has been kept to 00:00:00.

The mapping between the originator's channels and BODC parameter codes are as detailed in the table below.

Data Quality Report

Nd isotoptes and REE concentrations that deviated significantly from concentrations above and below that depth in the water column profiles were flagged by the originator. BODC have converted these flags to the appropriate BODC flag 'L'.