Benthic sediment surveys of inner Darwin Harbour (GA0358) and shallow water areas in and around Bynoe Harbour (GA0359) in 2017: Total sediment metabolism, carbonate, organic isotope and organic and inorganic element measurements on seabed sediments.

Brief description

Benthic sediment sampling of Inner Darwin Harbour (GA0358) and shallow water areas in and around Bynoe Harbour (GA0359) was undertaken between May 29 and June 19, 2017. Partners involved in the surveys included Geoscience Australia (GA), the Australian Institute of Marine Science (AIMS) and the Department of Environment and Natural Resources within the Northern Territory Government (NT DENR) (formerly the Department of Land and Resource Management (DLRM)). These surveys form part of a four year (2014-2018) science program aimed at improving knowledge about the marine environments in the regions around Darwin and Bynoe Harbour’s through the collection and collation of baseline data that will enable the creation of thematic habitat maps to underpin marine resource management decisions. This project is being led by the Northern Territory Government and is supported by the INPEX-led Ichthys LNG Project, in collaboration with - and co-investment from GA and AIMS. This dataset comprises total sediment metabolism, carbonate, organic isotope and organic and inorganic element measurements on seabed sediments.

Lineage

Maintenance and Update Frequency: asNeeded

Statement: Bottom sediments were collected using a Shipek grab. The surface sediments (0-2 cm) within each 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 water samples 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 0.2. The accuracy of the wet/dry weight used in the calculations were better than 1%. Bulk carbonate was determined on dried ground sediment using the carbonate bomb method. Data for duplicate samples are presented with the data. 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. Major and trace elements were determined in GA laboratories using X-Ray fluorescence (XRF; Phillips PW204 4kW sequential spectrometer) and ICP-MS (AGILENT 7500ce). Two Certified Reference Materials (CRMs) called CH-1 (Marine Sediment; Institute of Rock and Mineral Analysis, Beijing) and WG-1 (Woodstock Basalt; Australian National University, Canberra) were run in triplicate to calculate accuracy. Ten to twelve samples were also analysed in duplicate to measure precision. 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). Quality control information is presented with the accompanying datasets.