Total sediment metabolism, bulk carbonate, mineral specific surface area, major and trace elements and carbon and nitrogen concentrations and isotopes of seabed sediments - Caswell Sub-basin, Browse Basin Marine Survey (GA0345/GA0346/TAN1411)

Brief description

Geoscience Australia (GA) conducted a marine survey (GA0345/GA0346/TAN1411) of the north-eastern Browse Basin (Caswell Sub-basin) between 9 October and 9 November 2014 to acquire seabed and shallow geological information to support an assessment of the CO2 storage potential of the basin. The survey, undertaken as part of the Department of Industry and Science's National CO2 Infrastructure Plan (NCIP), aimed to identify and characterise indicators of natural hydrocarbon or fluid seepage that may indicate compromised seal integrity in the region. The survey was conducted in three legs aboard the New Zealand research vessel RV Tangaroa, and included scientists and technical staff from GA, the NZ National Institute of Water and Atmospheric Research Ltd. (NIWA) and Fugro Survey Pty Ltd. Shipboard data (survey ID GA0345) collected included multibeam sonar bathymetry and backscatter over 12 areas (A1, A2, A3, A4, A6b, A7, A8, B1, C1, C2b, F1, M1) totalling 455 km2 in water depths ranging from 90 - 430 m, and 611 km of sub-bottom profile lines. Seabed samples were collected from 48 stations and included 99 Smith-McIntyre grabs and 41 piston cores. An Autonomous Underwater Vehicle (AUV) (survey ID GA0346) collected higher-resolution multibeam sonar bathymetry and backscatter data, totalling 7.7 km2, along with 71 line km of side scan sonar, underwater camera and sub-bottom profile data. Twenty two Remotely Operated Vehicle (ROV) missions collected 31 hours of underwater video, 657 still images, eight grabs and one core. This catalogue entry refers to total sediment metabolism, bulk carbonate and mineral specific surface area measurements, and major and minor trace elements and carbon and nitrogen concentrations and isotopes in the upper 2 cm of seabed sediments.

Lineage

Maintenance and Update Frequency: asNeeded

Statement: Surface sediments (0-2 cm) from a Smith McIntyre grab were spooned into falcon vials and the pore waters were removed by centrifugation. Pore waters were removed within 20 minutes of collection, and salinity, temperature and pH measurements were taken. The pore waters were then filtered (0.45 µm) into 3 ml gas-tight vials (that were pre-charged with 0.025 HgCl2). The procedure was repeated on pore waters from a second bulk sample that was incubated for ~24 hrs at sea surface temperatures. The samples were then frozen for transport to the laboratories at Geoscience Australia (GA) where they were: (1) subsampled for specific surface area analysis; and (2) freeze-dried and ground in a tungsten carbide mill. The dried residue was divided into fractions for: (i) major and trace element analysis; (ii) bulk carbonate analyses; and (ii) total organic carbon and total nitrogen concentrations and isotopic ratios (after de-carbonation). Dissolved inorganic carbon (DIC) concentrations were determined on pore waters using a DIC analyser and infrared-based CO2 detector (Geoscience Australia). CO2 production rates were calculated by concentration differences over the incubation period, after correction for CaCO3 fluxes. The average %RSD of the precisions and accuracies of the dissolved inorganic carbon measurements were 0.22 and 0.4 respectively. The accuracy of the wet/dry weight used in the calculations were better than 1%. Bulk carbonate was determined on dried sediment using the carbonate bomb method. Specific surface areas were determined using a 5-point Brunauer-Emmett-Teller (BET) adsorption isotherm on a Quantachrome NOVA 2200e analyser, with nitrogen used as the adsorbate. The samples were first cleaned of organic matter by slow heating for 12 hours to 350oC. The average %RSD of the carbonate and specific surface area replicates were 2.1 +/- 1.1% and 17.5 +/- 10.9 % respectively. Major and trace elements were determined by X-Ray fluorescence at GA using a Phillips PW204 4kW sequential spectrometer. A more comprehensive suite of trace elements was determined using an AGILENT 7500ce ICP-MS, also at GA. For the XRF, a single Standard Reference Material (SRM) called CH-1 (Marine Sediment; Institute of Rock and Mineral Analysis, Beijing) was used to calculate accuracy. The average deviation of measured values from expected values (across the elements) was -1.08 +/- 7.0 (CH-1). Four samples were run in duplicate to measure precision, and the average % RSD across the elements and duplicates was 0.98 +/- 1.2. The accuracy and precision information is presented on an element by element basis in accompanying spreadsheet. For the ICP-MS analyses, three different SRM's were used to calculate accuracy: OU-8-1 (a calcareous sandstone), SARM 41 (A carbonaceous shale; South African Bureau of Standards) and CH-1 (Marine Sediment; Institute of Rock and Mineral Analysis, Beijing). The average deviation of measured values from expected values (across the elements) were -9.2 +/- 15.9 and -6.3 +/- 21.4 (CH-1), 9.2 +/- 31.7 and 1.1 +/- 19.7 (OU-8) and 12.9 +/- 27.3 and 14.1 +/- 25.1 (SARM 41) for each SRM run in duplicate. Four of the marine sediment samples were run in duplicate to measure precision. The %RSD varied considerably across the elements. The average %RSD across the elements and the 4 sets of duplicates was 20 +/- 25% and thus was quite variable. The accuracy and precision information is presented on an element by element basis in accompanying spreadsheet. Limits of detection and limits of quantitation are also included as a separate spreadsheet. De-carbonated powders were sent to Environmental Isotopes Pty Ltd (Sydney) for isotopic analysis by mass spectrometry. Samples were back-corrected to account for the carbonate removal, using carbonate concentrations derived from the bomb method (this dataset). Error estimates for the C and N isotope values are ±0.15. Thanks to the crew of the RV Tangaroa for help with sample collection.