ENRICH 2019 Trace element data (RV Investigator IN2019_V01 Southern Ocean voyage)

Full description

Trace element data collected from 18 stations near the Mertz Glacier on the 2019 ENRICH voyage. Sea water was collected using a 12-bottle trace metal rosette (TMR) and acidified for analysis back in Hobart. Samples were measured using an offline seaFAST pre-concentration system and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) at the University of Tasmania. This data contributed to Smith et al., Circumpolar Deep Water and shelf sediments support late summer microbial iron remineralisation in Global Biogeochemical Cycles (2021).

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Maintenance and Update Frequency: notPlanned

Statement: Cleaning: All trace metal sampling and analyses techniques were based on the international GEOTRACES program’s cookbook (Cutter et al., 2017). Briefly, new 60 mL LDPE sample bottles were cleaned in 2% v:v Decon-90 for one week to remove any residue from manufacturing, after which bottles were rinsed four times with deionised water and thrice in ultra-high purity (UHP) water. The bottles were filled with 6M hydrochloric acid (HCl) and placed in a 1.2M HCl bath for one month. Bottles were rinsed again with UHP water, filled with trace metal grade 1.2M HCl and triple-bagged for transportation. Bottles were rinsed thrice with freshly collected seawater prior to sampling. Dissolved trace elements: Water profiles were sampled using a purpose-built Trace Metal Rosette (TMR; General Oceanics Inc.), comprising twelve 10L Teflon-lined Niskin bottles, each equipped with an external spring and automatic firing mechanism. The TMR was deployed from the ship with a Dyneema™ line to a maximum depth of 1,200 m. Bottles were programmed to fire at predetermined depths to sample the water column during the ascent. Once onboard, Niskin bottles were carefully transported to a trace-metal-clean laboratory equipped with an ISO 5 HEPA filtered air system. Sixty mL of seawater from each depth was sampled using acid-washed AcroPak 0.2 µm filters and acidified to pH 1.8 with ultrapure HCl (Seastar Baseline) for trace element analysis in Australia. Seawater samples were analysed for a suite of dissolved trace elements (including Fe, Mn, and Ti, among others) using a commercially available, offline seaFAST preconcentration system (SC-4 DX seaFAST S2/pico, ESI, USA) with sector-field inductively coupled plasma mass spectrometry (SF-ICP-MS) detection. Briefly, samples were loaded onto a Nobias PA1 resin column (200 µL) to retain metals of interest. Trace metals were then eluted with 0.75 mL of 1.6 M ultrapure nitric acid (HNO3; Seastar Baseline). This method allowed the seawater matrix to be removed and trace metals of interest to be concentrated to levels more reliably measurable by ICP-MS. Samples were typically pre-concentrated 40 times, and 10 times where sample volume was low. An internal standard of 10 µg L-1 rhodium (Rh) was added to the eluent to monitor instrument drift. Samples were quantified using commercially-prepared multi-element mixes for internal (on-column) and external (off-column, ICP-MS) calibrations. Further details of the seaFAST method are outlined in Wuttig et al. (2019). Following preconcentration, trace element concentrations were determined typically within 24 h using a Thermo Fisher Scientific ELEMENT 2 SF-ICP-MS (Central Science Laboratory, Tasmania), employing medium resolution mode. Precise dTi concentrations used in this work require some caution as extraction conditions (pH) used to preconcentrate dFe may be sub-optimum for dTi extraction (Wuttig et al., 2019); however trends and ratios between elements may still be used to identify potential sources of dFe across a broad scale. Analytical precision and accuracy were monitored throughout the seaFAST and SF-ICP-MS processing sequences using globally inter-calibrated seawater consensus materials including GSP (2009 GEOTRACES Pacific surface seawater), GSC (2009 GEOTRACES coastal surface seawater), NASS-6 and NASS-7 (National Research Council of Canada), in addition to regularly measured in-house seawater reserves. A full outline of CRM analyses, blanks and detection limits are provided in the supplementary information (Tables S1 & S2). Full intercalibration of this data is provided with the GEOTRACES Intermediate Data Product (IDP) 2021.

Notes

Credit
The Authors are indebted to the Australian Antarctic Division (AAD) for their support in funding, organisation, and development of this research and to the CSIRO Marine National Facility (MNF) for its support in the form of sea time on RV Investigator, support personnel, scientific equipment and data management. We are grateful to ENRICH voyage Chief Scientist and project leader Mike Double, as well as participants of the voyage. All data and samples acquired on the voyage are made publicly available in accordance with MNF Policy. Antarctic research on the ENRICH voyage was permitted under the Notice of Determination and Authorisation for the Antarctic Treaty (Environment Protection) Act 1980 issued by the AAD on 27 September 2018. The Authors declare no conflicts of interest. This work was conducted as part of the Australian Antarctic Program under Australian Antarctic Science Project 4101 - Antarctic baleen whale habitat utilisation and linkages to environmental characteristics and/or Australian Antarctic Science Project 4102 - Population abundance, trend, structure and distribution of the endangered Antarctic blue whale, and/or Australian Antarctic Science Project 4600 - Conservation and management of Australian and Antarctic whales – post-exploitation status, distribution, foraging ecology and their role in the Southern Ocean ecosystem and/or Australian Antarctic Science Project 4512 - Ensuring sustainable management of the krill fishery in waters off the Australian Antarctic Territory. LR received support from BYONIC (ERC award number 724289). DL is funded by the Australian Research Council (ARC Future Fellowship L0026677). Access to SF-ICP-MS instrumentation was made possible by an Australian Research Council grant (LE0989539). All data and samples acquired on the voyage are made publicly available in accordance with MNF Policy and the raw data supporting the conclusions of this manuscript will be made available with the GEOTRACES Intermediate Data Product 2021.

Credit
We acknowledge the use of the CSIRO Marine National Facility - grid.473585.8 - in undertaking this research.