Outer Darwin Harbour Marine Survey 2015: Grain size data of 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: Sediment grabs typically recovered about 0.1 cubic metres of undisturbed sediment from which a 250- 500 g sub-sample was taken to a depth of ~5 cm. Sub-samples were described from visual inspection, noting grain size, sorting, composition and Munsell colour then stored in plastic bags and refrigerated. In the laboratory, two different grain size measurements were undertaken. In the first method, sediments were first wet sieved to determine mud (<63 microns), sand (63-2000 microns) and gravel (>2000 microns) fractions as percentage of dry weight. Sediment > 63 um diameter were then dried, and subsequently dry sieved at whole phi values between 4 and -4 phi: these correspond to the Wentworth (1922) grain size boundaries between the major sediment classes representing the range from the base of very fine sand (63 um) to the base of coarse pebbles (16 mm). In the second method, a separate sub-sample (~1g) was used for laser diffraction measurement of the <1.4 mm fraction using a Malvern Mastersizer 2000 to derive statistics including the arithmetic mean, standard deviation, skewness and kurtosis.