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) and a Kasten corer (KC). The MC were sliced every centimetre, wrapped up in plastic bags, and stored in the fridge. The KC was sub-sampled using a u-channel; and sliced every centimetre once back the home laboratory (IMAS, UTAS, Hobart, Australia). About 200 mg of dried and ground sediment were weighed into a clean Teflon vial and oxidized with a mixture of concentrated HNO3 and 30% H2O2 (1:1). The resulting solutions were gravimetrically spiked with ~ 24 pg of 229Th (NIST 4328C, National Institute of Standards and Technology, USA) and ~ 2 ng of 236U (IRMM-3660a, Institute for Reference Materials and Measurements, European Union) and left to equilibrate overnight. Samples were then digested in open vials using an acid mixture comprising 10 mL HNO3, 4 mL HCl, and 2 mL HF, at 180°C until close to dryness. Digested residues were converted to nitric form before being oxidised with a mixture of 1 mL HNO3 and 1 mL HClO4 at 220°C until fully desiccated. Samples were finally re-dissolved in 4 mL 7.5 M HNO3. Thorium and uranium were isolated from the sediment digest using AG1-X8 anion exchange resin (Bio-Rad, USA), following the procedure described in Negre et al., (2009). Prior to analysis, purified samples were filtered using Pall® Acrodisc® ion chromatography syringes and 0.45 μm filters (Sigma-Alderich®, USA). 229Th, 230Th, 234U and 235U were analysed by Sector Field Inductively Coupled Mass Spectrometry (SF-ICP-MS, Thermo Fisher Scientific, Bremen, Germany) at the Central Science Laboratory (UTAS, Hobart, Australia). Samples were introduced in the ICP using an Aridius® II desolvating nebulizer (DSN, CETAC Technologies, USA) and with the capacitive guard electrode turned on to limit the oxide formation and to enhance sensitivity. Samples were analysed in batches of three and bracketed by a natural uranium standard (Certified Reference Material CRM 145, New Brunswick Laboratory, USA) and two acid blanks (2% HNO3, 0.1% HF). The sample introduction system was rinsed for 5 minutes between each sample with a matching 2% HNO3 and 0.1% HF solution. The raw intensities of 230Th and 234U were corrected for procedural blank, tailing and mass bias (Anderson et al., 2012; Shen et al., 2002). The intensity of 230Th was corrected from the tailing of 232Th using the log mean intensities of the half masses 229.5 and 230.5. The mass bias was determined by the measurements of the 235U/234U ratio of the CRM-145. Concentrations were calculated using isotope dilution equations (Sargent et al., 2002). References - Anderson, R. F., Fleisher, M. Q., Robinson, L. F., Edwards, R. L., Hoff, J. A., Moran, S. B., … Francois, R. (2012). GEOTRACES intercalibration of 230Th, 232Th, 231Pa, and prospects for 10Be. Limnology and Oceanography: Methods, 10(4), 179–213. https://doi.org/10.4319/lom.2012.10.179 - 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 - Negre, C., Thomas, A. L., Mas, J. L., Garcia-orellana, J., Henderson, G. M., Masque, P., and Zahn, R. (2009). Separation and Measurement of Pa , Th , and U Isotopes in Marine Sediments by Microwave-Assisted Digestion and Multiple Collector Inductively Coupled Plasma Mass. Analytical Chemistry, 81(5), 1914–1919. https://doi.org/10.1126/science.276.5313.782.(3) - Sargent, M., Harrington, C., and Harte, R. (2002). Guidelines for Achieving High Accuracy in Isotope Dilution Mass Spectrometry (IDMS). Guidelines for Achieving High Accuracy in Isotope Dilution Mass Spectrometry (IDMS). Royal Society of Chemistry. https://doi.org/10.1039/9781847559302-00001 - Shen, C.-C., Lawrence Edwards, R., Cheng, H., Dorale, J. A., Thomas, R. B., Bradley Moran, S., … Edmonds, H. N. (2002). Uranium and thorium isotopic and concentration measurements by magnetic sector inductively coupled plasma mass spectrometry. Chemical Geology, 185(3–4), 165–178. https://doi.org/10.1016/S0009-2541(01)00404-1

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 Millipore GWSC04510: Ground Water sampling capsule, 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 thorium isotopes (230Th and 232Th), a tracer of particle dynamics. The sample preparation was carried out in the clean lab of the Institute for Marine and Antarctic Studies (UTAS, Hobart). Seawater samples were acidified with HF (final concentration 0.6 mM, Middag et al., 2015), spiked with 10 pg of 229Th (NIST 4328C, National Institute of Standards and Technology, USA) and left to equilibrate for at least 48h. Samples were preconcentrated using Nobias® PA1L (Hitachi Technologies, Japan) cartridges, following the procedure of Pérez-Tribouillier et al., (2019). The separation and purification of thorium isotopes were performed by anion-exchange chemistry (Anderson et al., 2012). Purified Th fractions were analysed using an Element II Sector Field Inductively Coupled Plasma Mass Spectrometer (SF-ICP-MS, Thermo Fischer Scientific, Bremen, Germany) at the Central Science Laboratory (CSL) of the University of Tasmania. Sample introduction was achieved using an Aridius® II desolvating nebulizer (DSN, CETAC Technologies, USA). The capacitive guard electrode was activated to maximise signal sensitivity. Raw intensities of 230Th and 232Th were blank and mass bias corrected. Concentrations were calculated using the isotope dilution equation reported in Sargent et al., (2002). References - Anderson, R. F., Fleisher, M. Q., Robinson, L. F., Edwards, R. L., Hoff, J. A., Moran, S. B., … Francois, R. (2012). GEOTRACES intercalibration of 230Th, 232Th, 231Pa, and prospects for 10Be. Limnology and Oceanography: Methods, 10(4), 179–213. - 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 - Middag, R., Séférian, R., Conway, T. M., John, S. G., Bruland, K. W., and de Baar, H. J. W. (2015). Intercomparison of dissolved trace elements at the Bermuda Atlantic Time Series station. Marine Chemistry, 177, 476–489. - 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. - Sargent, M., Harrington, C., and Harte, R. (2002). Guidelines for Achieving High Accuracy in Isotope Dilution Mass Spectrometry (IDMS). Guidelines for Achieving High Accuracy in Isotope Dilution Mass Spectrometry (IDMS). Royal Society of Chemistry.