DOI: 10.5285/06480f12-4dc7-4c6b-8203-d1df296181a8
title: Neodymium isotopic compositions of glacial, deglacial, and Holocene aged deep-sea corals collected from the Drake Passage of the Southern Ocean

description: This dataset comprises neodymium (Nd) isotopic compositions measured on 145 samples of aragonitic deep-sea corals from the Drake Passage of the Southern Ocean. Most of the samples were previously collected on expeditions NBP0805 and NBP1103 on the RV Nathaniel B. Palmer. The samples include glacial, deglacial and Holocene aged specimens and most are from 0-40 ka BP (thousand years before present) based on uranium-thorium dating. Neodymium isotope analyses were conducted by either thermal ionisation mass spectrometry (TIMS) or multi-collector inductively-coupled plasma mass spectrometry (MC-ICP-MS) in the MAGIC laboratories at Imperial College London by David Wilson, Torben Struve and Tina van de Flierdt. In the modern ocean, dissolved Nd isotopes are a quasi-conservative water mass tracer, while past compositions of seawater are recorded in deep-sea corals. This dataset therefore provides evidence on the proportions of Atlantic versus Pacific waters admixed in the Southern Ocean through time, which places crucial constraints on global deep water chemistry and circulation dynamics during past climate events. Funding was provided by the NERC grant NE/N001141/1. Related datasets are associated with grant NE/N003861/1. Both grants funded the project "Bridging the Timing Gap: Connecting Late Pleistocene Southern Ocean and Antarctic Climate Records".
description: Sample collection: The coral samples were previously collected, mostly during expeditions NBP0805 and NBP1103 on the RV Nathaniel B. Palmer. Cleaning and purification: Coral samples were physically and chemically cleaned, then subjected to iron co-precipitation to concentrate trace metals, followed by uranium (U) and thorium (Th) separation by ion exchange chromatography for U-Th dating (Burke and Robinson, 2012). The Nd fraction was collected during U-Th chemistry, from which Nd was then extracted using a two-step column chemistry. The first step separated the rare earth element fraction using cation exchange resin (200 - 400 um mesh) (Struve et al., 2016). The second step isolated the Nd fraction on volumetrically calibrated columns using Eichrom Ln spec resin (Struve et al., 2016): either 20 - 50 um mesh in preparation for TIMS analysis (after Crocket et al., 2014) or 50 - 100 um mesh in preparation for MC-ICP-MS analysis (after Cook et al., 2013). Thermal ionisation mass spectrometry (TIMS) analysis: For 98 samples, Nd isotopes were analysed as NdO+ on a Thermo Scientific Triton, in the MAGIC laboratories at Imperial College London, as described in Struve et al. (2016). 5 and 15 ng loads of pure JNdi-1 were analysed (143Nd/144Nd = 0.512105 ± 0.000009, 2SD, n = 110) to monitor instrumental offset and normalise mass bias corrected 143Nd/144Nd ratios of samples to the reference ratio of 143Nd/144Nd = 0.512115 ± 0.000007 (Tanaka et al., 2000). Multi-collector inductively-coupled plasma mass spectrometry (MC-ICP-MS) analysis: For 47 samples, Nd isotopes were analysed on a Nu Plasma 2 in static mode, in the MAGIC laboratories at Imperial College London. Interference of 144Sm on 144Nd was corrected for (although this correction was negligible) and mass bias correction was performed using the exponential law (to 146Nd/144Nd = 0.7219). Sample measurements at 10 - 20 ppb (~6 - 12 ng Nd) were bracketed by concentration-matched JNdi-1 Nd isotope standards and sample ratios were corrected for the instrumental offset of session-average JNdi-1 values from the accepted value of 143Nd/144Nd = 0.512115 ± 0.000007 (Tanaka et al., 2000). Neodymium isotope notation: Nd isotopes are reported in standard epsilon notation, as the deviation in parts per 10,000 from the present-day composition of the Chondritic Uniform Reservoir (143Nd/144Nd = 0.512638) (Jacobsen and Wasserburg, 1980). Neodymium concentrations: Where reported, Nd concentration data were generated by doping with a 150Nd spike solution before Nd separation and measurement on TIMS, and are therefore minimum values which do not account for Nd loss during Fe co-precipitation and U-Th separation (Struve et al., 2016, 2017). Sample ages: Ages are reported in thousand years before present (ka BP), where present is 1950. Data are from Burke and Robinson (2012), Chen et al. (2015), or were measured as part of the NERC grant partnering this project (NE/N003861/1). Water Mass Abbreviations: SAMW Subantarctic Mode Water AAIW Antarctic Intermediate Water UCDW Upper Circumpolar Deep Water LCDW Lower Circumpolar Deep Water References: Burke, A., Robinson, L.F., 2012. The Southern Ocean's role in carbon exchange during the last deglaciation. Science 335, 557-561. Chen, T.Y., Robinson, L.F., Burke, A., Southon, J., Spooner, P., Morris, P.J., Ng, H.C., 2015. Synchronous centennial abrupt events in the ocean and atmosphere during the last deglaciation. Science 349, 1537-1541. Cook, C.P., van de Flierdt, T., Williams, T., Hemming, S.R., Iwai, M., Kobayashi, M., Jimenez-Espejo, F.J., Escutia, C., Gonzalez, J.J., Khim, B.K., McKay, R.M., Passchier, S., Bohaty, S.M., Riesselman, C.R., Tauxe, L., Sugisaki, S., Galindo, A.L., Patterson, M.O., Sangiorgi, F., Pierce, E.L., Brinkhuis, H., Scientists, I.E., 2013. Dynamic behaviour of the East Antarctic ice sheet during Pliocene warmth. Nat. Geosci. 6, 765-769. Crocket, K.C., Lambelet, M., van de Flierdt, T., Rehkamper, M., Robinson, L.F., 2014. Measurement of fossil deep-sea coral Nd isotopic compo...(19)
description: Instrumentation used - Thermal ionisation mass spectrometry (TIMS): Thermo Finnigan Triton Multi-collector inductively-coupled plasma mass spectrometry (MC-ICP-MS): NuPlasma 2
description: Thermal ionisation mass spectrometry (TIMS): Rock reference material BCR-2 was processed with every batch of chemistry and yielded JNdi-1 normalized 143Nd/144Nd ratios of 0.512637 ± 0.000011 (2SD, n = 32) on loads of 10 and 30 ng Nd, identical to 143Nd/144Nd = 0.512637 ± 0.000006 published by Weis et al. (2006). A similar precision was obtained from replicate analyses of 10 and 30 ng Nd loads of our in-house coral reference material (143Nd/144Nd = 0.512336 ± 0.000009, 2SD, n = 23; cf. Crocket et al., 2014). We report the higher 2SD uncertainty from repeat BCR-2 analyses as 2SD for coral samples, except where the within-run 2SE was higher than the 2SD of BCR-2 repeat analyses, in which case the propagated error is reported. Full procedural blanks of combined U, Th, and Nd separation from aragonitic matrix ranged from 2 to 27 pg Nd (n = 20), of which the Nd chemistry blank contributed from 1 to 17 pg (n = 10), which are minimal (see also Struve et al., 2017). Multi-collector inductively-coupled plasma mass spectrometry (MC-ICP-MS): The reported external reproducibility on samples was estimated from the within-session 2SD on JNdi-1 Nd isotope standards. Accompanying analyses (also at 10 - 20 ppb) of BCR-2 rock reference material gave 143Nd/144Nd = 0.512641 ± 0.000013 (2SD, n = 11) and our in-house coral reference material yielded 143Nd/144Nd = 0.512337 ± 0.000013 (2SD, n = 5), both indicating long term reproducibility in excellent agreement with the TIMS values. Full procedural blanks of MC-ICP-MS samples including combined U, Th, and Nd separation ranged from 3 to 16 pg Nd (n = 5), while Nd chemistry blanks ranged from 1 to 10 pg (n = 5), which are minimal. References: Crocket, K.C., Lambelet, M., van de Flierdt, T., Rehkamper, M., Robinson, L.F., 2014. Measurement of fossil deep-sea coral Nd isotopic compositions and concentrations by TIMS as NdO+, with evaluation of cleaning protocols. Chemical Geology 374-375, 128-140. Struve, T., van de Flierdt, T., Burke, A., Robinson, L.F., Hammond, S.J., Crocket, K.C., Bradtmiller, L.I., Auro, M.E., Mohamed, K.J., White, N.J., 2017. Neodymium isotopes and concentrations in aragonitic scleractinian cold-water coral skeletons - Modern calibration and evaluation of palaeo-applications. Chemical Geology 453, 146-168. Weis, D., Kieffer, B., Maerschalk, C., Barling, J., de Jong, J., Williams, G.A., Hanano, D., Pretorius, W., Mattielli, N., Scoates, J.S., Goolaerts, A., Friedman, R.M., Mahoney, J.B., 2006. High-precision isotopic characterization of USGS reference materials by TIMS and MC-ICP-MS. Geochem. Geophys. Geosyst. 7, doi: 10.1029/2006gc001283.