Neodymium isotopic compositions measured in sediment leachates from samples collected during the IN2017-V01 voyage of the RV Investigator

Sediment cores were collected from the East Antarctic margin, aboard the Australian Marine National Facility R/V Investigator, during the IN2017_V01 voyage from January 14th to March 5th 2017 (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. The cores were collected using a multi-corer (MC), were sliced every centimetre, wrapped up in plastic bags, and stored in the fridge. Back at the home laboratory (IMAS, UTAS, Hobart, Australia), sediment samples were dried in an oven at 40°C. Three hundred mg of dry sediment was then homogenised and vortexed for 10-sec with 12 mL of a reductive solution of 0.005M hydroxylamine hydrochloride (HH) / 1.5% Acetic Acid (AA) / 0.001M Na-EDTA / 0.033M NaOH, at pH 4 (Huang et al., 2021). This reductive leaching solution was designed to target Fe-Mn oxides phases, with chelating ligand to avoid re-adsorption of leached REE onto the sediment. The leach mixture was then centrifuged, and 6 mL of the supernatant solution was collected into a Teflon vial. This solution was taken to dryness, oxidized with 1 mL HNO3 + 100 µL H2O2, and redissolved in 4 mL of 7.5M HNO3. The solution was then taken to dryness before being taken up with 0.5 mL 3M HNO3 – 2.5M HCl (3:1) for cation exchange chromatography (Struve et al., 2016) and Nd purification via LN-Spec column chemistry (Pin and Zalduegui, 1997).Purified 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 10^13Ω amplifiers, vs. 143Nd/144Nd = 0.512112 ± 3 2sd (6 ppm 2rsd, n = 6) for 100 ng loads using 10^11Ω 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 Nd = [(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- Armand, L. K., O’Brien, P. E., Armbrecht, L., Baker, H., Caburlotto, A., Connell, T., … Young, A. (2018). Interactions of the Totten Glacier with the Southern Ocean through multiple glacial cycles (IN2017-V01): Post-survey report. ANU Research Publications, (March). https://doi.org/http://dx.doi.org/10.4225/13/5acea64c48693- Huang, H., Gutjahr, M., Kuhn, G., Hathorne, E. C., and Eisenhauer, A. (2021). Efficient Extraction of Past Seawater Pb and Nd Isotope Signatures From Southern Ocean Sediments. Geochemistry, Geophysics, Geosystems, 22(3), 1–22. https://doi.org/10.1029/2020GC009287- Jacobsen, S. B., and Wasserburg, G. J. (1980). Sm-Nd isotopic evolution of chondrites. Earth and Planetary Science Letters, 50(1), 139–155. https://doi.org/10.1016/0012-821X(80)90125-9- 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. Analytica Chimica Acta, 339, 79–89.- Struve, T., Van De Flierdt, T., Robinson, L. F., Bradtmiller, L. I., Hines, S. K., Adkins, J. F., … Auro, M. E. (2016). Neodymium isotope analyses after combined extraction of actinide and lanthanide elements from seawater and deep-sea coral aragonite. Geochemistry, Geophysics, Geosystems, 17(1), 232–240. https://doi.org/10.1002/2015GC006130- Tanaka, T., Togashi, S., Kamioka, H., Amakawa, H., Kagami, H., Hamamoto, T., … Dragusanu, C. (2000). JNdi-1: A neodymium isotopic reference in consistency with LaJolla neodymium. Chemical Geology, 168(3–4), 279–281. https://doi.org/10.1016/S0009-2541(00)00198-4

2017年1月14日至3月5日，研究团队搭乘澳大利亚国家海洋研究设施“调查者号”（R/V Investigator）科考船，在IN2017_V01航次（命名为“萨布里纳海底调查”）期间，于南极东部陆缘采集了沉积物岩芯（Armand等，2018）。本次海洋地球科学考察的核心研究目标为：通过多个冰期旋回解析托滕冰川（Totten Glacier）与南大洋的相互作用。

本次获取的沉积物岩芯采用多管取样器（multi-corer, MC）采集，随后以1cm间隔进行切片，封装入塑料袋后冷藏保存。返回位于澳大利亚霍巴特塔斯马尼亚大学（UTAS）海洋与南极研究所（IMAS）的实验室后，沉积物样品置于40℃烘箱中烘干。

称取300mg干燥沉积物样品，与12mL pH为4的还原浸提液（含0.005M盐酸羟胺、1.5%乙酸、0.001M乙二胺四乙酸钠、0.033M氢氧化钠）混合，经10秒涡旋振荡完成均质化处理（Huang等，2021）。该还原浸提液靶向萃取铁锰氧化物相，通过添加螯合配体避免浸出的稀土元素（Rare Earth Element, REE）重新吸附于沉积物基质中。

浸提混合液经离心分离后，取6mL上清液转移至聚四氟乙烯（Teflon）瓶中。将该溶液蒸干后，加入1mL硝酸与100μL过氧化氢进行氧化消解，随后用4mL 7.5mol/L硝酸重新溶解残渣。再次蒸干溶液后，用0.5mL 3mol/L硝酸-2.5mol/L盐酸（体积比3:1）复溶，随后通过阳离子交换色谱（Struve等，2016）与LN-Spec柱层析法（Pin与Zalduegui，1997）完成钕（Nd）的分离纯化。

纯化后的钕样品浓度先通过澳大利亚霍巴特塔斯马尼亚大学中央科学实验室的扇形场电感耦合等离子体质谱仪（Sector Field Inductively Coupled Mass Spectrometry, ICP-MS）进行定量测定。随后，钕同位素比值分析在新西兰惠灵顿维多利亚大学地理、环境与地球科学学院地球化学实验室完成，采用赛默飞世尔Triton热电离质谱仪（Thermo Finnigan Triton thermal ionization mass spectrometer, TIMS）进行检测。

数据采用离线处理流程：首先剔除异常值，随后通过指数定律进行质量分馏校正（以146Nd/144Nd=0.7219为校正基准），并以144Sm/147Sm=0.20667校正质量数144处的钐（Sm）干扰。针对两种进样量与两种放大器配置的JNdi标准物质测试结果完全一致：采用10^13Ω放大器、进样量为1ng时，143Nd/144Nd=0.512110±24（2倍标准偏差，2sd；相对标准偏差2rsd=46ppm，n=16）；采用10^11Ω放大器、进样量为100ng时，143Nd/144Nd=0.512112±3（2sd，2rsd=6ppm，n=6）。将校正后的143Nd/144Nd比值以已发表值为0.512115的JNdi标准物质进行归一化处理（Tanaka等，2000）。

钕同位素组成以εNd值报告，计算公式为：εNd = [(143Nd/144Nd)样品 / (143Nd/144Nd)CHUR - 1]×10000，其中CHUR为球粒陨石均一储库（Chondritic Uniform Reservoir, CHUR），其143Nd/144Nd参考值为0.512638（Jacobsen与Wasserburg，1980）。

参考文献：
- Armand, L. K., O’Brien, P. E., Armbrecht, L., Baker, H., Caburlotto, A., Connell, T., … Young, A. (2018). 多冰期旋回下托滕冰川与南大洋的相互作用（IN2017-V01）：航后调查报告. ANU研究出版物, (3月). https://doi.org/http://dx.doi.org/10.4225/13/5acea64c48693
- Huang, H., Gutjahr, M., Kuhn, G., Hathorne, E. C., and Eisenhauer, A. (2021). 从南大洋沉积物中高效提取古海水铅与钕同位素信号. 《地球化学、地球物理学、地球系统学》, 22(3), 1–22. https://doi.org/10.1029/2020GC009287
- Jacobsen, S. B., and Wasserburg, G. J. (1980). 球粒陨石的Sm-Nd同位素演化. 《地球与行星科学通讯》, 50(1), 139–155. https://doi.org/10.1016/0012-821X(80)90125-9
- Pin, C., and Zalduegui, J. F. S. (1997). 微型萃取色谱法依次分离轻稀土元素、钍与铀：在硅酸盐岩石同位素分析中的应用. 《分析化学学报》, 339, 79–89.
- Struve, T., Van De Flierdt, T., Robinson, L. F., Bradtmiller, L. I., Hines, S. K., Adkins, J. F., … Auro, M. E. (2016). 从海水与深海珊瑚文石中联合萃取锕系与镧系元素后的钕同位素分析. 《地球化学、地球物理学、地球系统学》, 17(1), 232–240. https://doi.org/10.1002/2015GC006130
- Tanaka, T., Togashi, S., Kamioka, H., Amakawa, H., Kagami, H., Hamamoto, T., … Dragusanu, C. (2000). JNdi-1：与LaJolla钕一致的钕同位素标准物质. 《化学地质学》, 168(3–4), 279–281. https://doi.org/10.1016/S0009-2541(00)00198-4