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Dissolved Neodymium concentration and isotopic composition collected on the U.S GEOTRACES GA04 cruises KN199 (GT10) and KN204-01 (GT11)

Responsible investigator

Howie Scher ¹ , Torben Stichel ²

¹ School of the Earth, Ocean and Environment, University of South Carolina
² University of Southampton School of Ocean and Earth Science

Sampling methodology

A detailed description can be found in Stichel et al. (2015). The text below summarizes the described methodology from the paper.

Onboard procedure
The samples were collected along the cruise transects of KN199-4 (October to December 2010) and KN204-01 (November to December 2011) at 9 stations. Samples were collected from 10-L standard General Oceanics Niskin bottles with 0.25 mm thick nylon-coated stainless steel springs, Viton O-rings at the end caps and spigots, and mounted on a 24-position powder-coated stainless-steel rosette frame. Seawater was filtered directly from the Niskin bottles through AcroPak500 0.8/0.45 µm filter cartridges, which were re-used at each station for the same depth and flushed with seawater prior to sample collection into acid-cleaned LDPE containers. From each bottle, a ~4-L aliquot was collected for Nd isotopes and concentrations. After collection, the samples were acidified to pH < 2 using ultra-clean 6N hydrochloric acid and stored for further processing in the home laboratory. At each station, one 4-L container previously filled with 18.2 MΩ cm water (Millipore) at Lamont-Doherty Earth Observatory (LDEO) was acidified and stored to estimate a conservative procedural blank. The resulting blanks ranged between 30 and 100 pg Nd, which is less than 1.5% of the smallest sample size of 8 ng Nd. No blank correction was applied.

Analytical methodology

An aliquot of ~500 ml was kept separately for later concentration analysis. From the remaining unspiked sample, Nd was extracted using C-18 cartridges (Waters Inc.) loaded with ~300mg bis(2-ethylexyl) hydrogen phosphate (HDEHP) as a REE complexant following a procedure modified after Shabani et al. (1992). Seawater was pumped through the cartridge at 20ml/min, removing major ions. The cartridges were subsequently washed with 5ml 0.01N HCl to remove barium, and 35ml 6N HCl to elute Nd.

2 ml Eichrom LN-Spec resin bed (50-100µm) was used to isolate Nd from other mass interfering REEs (Pin and Zalduegui, 1997).

Mass Spectrometry:
Nd IC was measured on a Thermo Neptune Multi-collector ICPMS. A JNdi-1 standard was analysed periodically during analytical sessions. Samples and standards were run at 20 ppb. Overall replicate analyses of JNdi yielded 0.512119 ± 0.000030 (2σ, n = 59). A correction was made at each lab for internal mass fractionation with ¹⁴⁶ Nd/ ¹⁴⁴ Nd = 0.7219 in an exponential mass fractionation law and the ¹⁴³ Nd/ ¹⁴⁴ Nd ratio was normalized to JNdi - 1 = 0.512115 (Tanaka et al., 2000).

Nd concentration measurements were done using a novel technique developed as a method to extract REE from marsh water (Antle, 2013). A precisely known amount ¹⁴⁵ Nd spike was added to the previously separated 500ml aliquot. Neodymium was pre-concentrated with 100µl of cleaned Toyopearl AF Chelate 650 resin. After 24h the resin was washed with 1-2ml of Millipore water, followed by 1ml of single distilled 1M HNO ₃ to elute and collect Nd. Once re-moved from the resin, this aliquot was directly analysed using the Element-2 ICP-MS. These samples were corrected for instrumental blanks, which accounted for up 0.8% of the overall intensities. Accuracy of the analysis was checked with a seawater sample from the North Pacific (SAFe, 3000 m), which yielded an average [Nd] of 47.55 pmol/kg ±3% (n =6). This is within error equal to the published average value of two laboratories of 44.37 pmol/kg (Pahnke et al., 2012).

References cited

Antle, R., (2013) Tidal Flux of Transition Metals and Rare Earth Elements from a Barrier Island Salt Marsh. University of South Carolina.

Basak, C., Pahnke, K., Frank, M., Lamy, F., Gersonde, R., (2015) Neodymium isotopic characterization of Ross Sea Bottom Water and its advection through the southern South Pacific. Earth Planet. Sci. Lett. 1, 211-221. doi:10.1016/j.epsl.2015.03.011

Jacobsen, S.B., Wasserburg, G.J., (1980) Sm-Nd Isotopic Evolution of Chondrites. Earth Planet. Sci. Lett. 50, 139-155.

Lambelet, M., van de Flierdt, T., Crocket, K., Rehkämper, M., Kreissig, K., Coles, B., Rijkenberg, M.J.A., Gerringa, L.J.A., de Baar, H.J.W., Steinfeldt, R., (2016) Neodymium isotopic composition and concentration in the western North Atlantic Ocean: Results from the GEOTRACES GA02 section. Geochim. Cosmochim. Acta 177, 1-29. doi:10.1016/j.gca.2015.12.019

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. doi:10.4319/lom.2012.10.252

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. Anal. Chim. Acta 339, 79-89. doi:10.1016/S0003-2670(96)00499-0

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. Anal. Chem. 64, 737-743. doi:10.1021/ac00031a008

Stichel, T., Hartman, A.E., Duggan, B., Goldstein, S.L., Scher, H., Pahnke, K., (2015) Separating biogeochemical cycling of neodymium from water mass mixing in the Eastern North Atlantic. Earth Planet. Sci. Lett. 412, 245-260. doi:10.1016/j.epsl.2014.12.008

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., Dragusanu, C., (2000) JNdi-1: a neodymium isotopic reference in consistency with LaJolla neodymium. Chem. Geol. 168, 279-281.

van de Flierdt, T., Pahnke, K., Hiroshi Amakawa, Per Andersson, Chandranath Basak, Barry Coles, Christophe Colin, Kirsty Crocket, Martin Frank, Norbert Frank, Steven L. Goldstein, Vineet Goswami, Brian A. Haley, Ed C. Hathorne, Sidney R. Hemming, Gideon M. Henderson, Catherine Jeandel, J.Y., (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. doi:10.4319/lom.2012.10.234

BODC Data Processing Procedures

Data were received and were loaded using established BODC data banking procedures.

This document covers data submitted using the following GEOTRACES parameters: