Porosity and Chlorins - 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 porosity, total chlorin and chlorin index data from the upper 2 cm of seabed sediments.

Lineage

Maintenance and Update Frequency: asNeeded

Statement: Bottom sediments were collected using a Smith McIntyre grab. Bulk sub-samples (6.5 ml) of surface sediment (0-2 cm) were extruded into vials which were wrapped in Al foil and immediately frozen. Porosity was determined by calculation of the wet volume as a percentage of the total volume, after freeze drying and correction for seawater salts. The accuracy of the wet/dry measurements were >1%. The precision of the volume measurements were >2%. The residual sediments were then ground under dark conditions and each successive sample was quickly returned to the freezer. Chlorins were then extracted from freeze-dried sediment using the method of Schubert et al. (2005). Relative standard deviations of the precisions on duplicate samples averaged 6.1 ± 8.2 for total chlorins and 3.1 ± 3.6 for chlorin indices (the data for each sample is provided).