Outer Darwin Harbour Marine Survey 2015: Porosity and Chlorins in seabed sediments.

Brief description

This resource contains surface sediment data for Outer Darwin Harbour collected by Geoscience Australia (GA), the Australian Institute of Marine Science (AIMS) and the Northern Territory Government (Department of Land Resource Management) during the period from 28 May and 23 June 2015 on the RV Solander (survey SOL6187/GA0351). This project was made possible through offset funds provided by INPEX-led Ichthys LNG Project to Northern Territory Government Department of Land Resource Management, and co-investment from Geoscience Australia and Australian Institute of Marine Science. The intent of this four year (2014-2018) program is to improve knowledge of the marine environments in the Darwin and Bynoe Harbour regions by collating and collecting baseline data that enable the creation of thematic habitat maps that underpin marine resource management decisions. The specific objectives of the survey were to: 1. Obtain high resolution geophysical (bathymetry) data for outer Darwin Harbour, including Shoal Bay; 2. Characterise substrates (acoustic backscatter properties, grainsize, sediment chemistry) for outer Darwin Harbour, including Shoal Bay; and 3. Collect tidal data for the survey area. Data acquired during the survey included: multibeam sonar bathymetry and acoustic backscatter; physical samples of seabed sediments, underwater photography and video of grab sample locations and oceanographic information including tidal data and sound velocity profiles. A detailed account of the survey is provided in: Siwabessy, P.J.W., Smit, N., Atkinson, I., Dando, N., Harries, S., Howard, F.J.F., Li, J., Nicholas, W.A., Potter, A., Radke, L.C., Tran, M., Williams, D. and Whiteway, T., 2015. Outer Darwin Harbour Marine Survey 2015: GA0351/SOL6187 Post-survey report. Record 2016/008. Geoscience Australia, Canberra. http://dx.doi.org/10.11636/Record.2016.008

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 4 ± 2.7 for total chlorins and 3 ± 2.1 for chlorin indices (the data for each sample is provided). Schubert, C.J., Niggemann, J., Klockgether, G., and Ferdelman, G., 2005. Chlorin Index: A new parameter for organic matter freshness in sediment. Geochemistry Geophysics and Geosystems 6(3), 1-12. Thanks to the crew of the RV Solander for help with sample collection.