Hydrocarbons in surface sediments from the north Queensland coast and Great Barrier Reef after tropical Cyclone Winifred

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Reef sediments were collected from the lagoons of Feather Reef, Gilby Reef and Potter Reef on 7-8 February 1986, about 5 days after Cyclone Winifred had passed through the region. Sediments were collected by divers, who scraped the surface layer (0-2 cm) into clean glass jars. The sediments were covered with a thin (1-2 mm) layer of light brown flocculant material. Samples of the upper 10-15 cm of the seabed were also collected before (8-20 January) and after the cyclone (9-10 February) in nearshore and innershelf locations (1 to 36 km offshore), using a frame supported Van Veen grab sampler. A sample of the surface layer (0-2 cm) was collected from each grab sample and transferred to clean glass jars. All sediment samples were quickly frozen in the shipboard laboratory and stored frozen until analysis, when samples were freeze-dried, sieved to remove coarse (>2.0 mm) material and ground to a fine powder in an agate ring mill. Lipids were extracted twice from 5-10 g of sediment by vigorous agitation with hexane:isopropanol:water (HIP) 3:2:0.13 The extracts were combined and partitioned against 0.5 M Na2SO4, and the resulting upper hexane-rich layer was reduced to ~1 ml using a rotary evaporator and transferred to a glass vial. The total lipid extract was taken to a few µl under a stream of nitrogen, and immediately dissolved in a known volume of HIP. The total lipid yield was determined by weighing aliquots (2 µl) on a microbalance.Total lipids were then fractionated on columns (10 mm i.d. x 300 mm) of aluminum oxide (3.5 g; Ajax 70-200 mesh; activated at 110°C) over silica (7.0 g; Merck 70-230 mesh, activated at 80°C) prepared by slurry packing in n-hexane. Aliphatic hydrocarbons (alkanes and alkenes) were eluted with n-hexane (25 ml), polycyclic aromatic hydrocarbons (PAH) with toluene:hexane 1:1 (25 ml), and polar lipids with HIP-HOH 3:4:7 (30 ml). Each fraction was transferred to clean glass vial and stored at 4°C.All hydrocarbon fractions were analyzed by flame ionization gas chromatography on a Hewlett-Packard 5840 gas chromatograph equipped with an on-column injector (SGE Pty Ltd). Individual alkanes and alkenes were quantified using the peak area of the internal injection standard chlorotetradecane. Selected hydrocarbon samples were analyzed by capillary GC-MS using a Hewlett-Packard 5970B mass selective detector attached to a Hewlett-Packard 5792A gas chromatograph equipped with an on-column injector (Hewlett-Packard).The organic carbon content of carbonate free sediment was measured directly using a Beckman Tocamaster Model 915B total carbon analyzer. Total carbon was determined using a Leco CHN Analyzer.For carbon isotope analyses, two gram subsamples of the ground sediment were acidified with 20-100 ml of 0.75 M HC1 to remove carbonates. The residue was centrifuged and rinsed with distilled water (3-6 times) until a pH of 5-6 was reached. After the final rinse, the samples were freeze-dried. The residues were combusted with excess CuO and Ag wire in evacuated silica tubes for 6 h at 900°C. The evolved CO2 was analyzed with a modified MS-12 triple-collector mass-spectrometer. All isotope ratios are reported relative to the Cretaceous Peedee belemnite (PDB) standard. We determined an overall analytical uncertainty of 0.2 ppt for replicate combustion and isotopic analyses of the same sediment sample.
This research was undertaken to investigate the short term biogeochemical effects of terrestrial river discharge into waters in the Innisfail region after Cyclone Winifred. Analyses of sediments collected from nearshore and innershelf locations and reefs up to 50km from the coast were carried out to investigate possible transport of terrestrial organic matter to the reef tract.
Tropical Cyclone Winifred crossed the north Queensland coast south of Innisfail on the evening of 1 February 1986. Wind speeds were estimated to reach in excess of 180 km/hr and rainfall exceeded 500 mm in coastal areas over the 5 day period that the cyclone was in the region.

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Statement: Statement: The method for extraction of lipids is described in:Hara A and Radin N S (1978) Lipid extraction of tissues with a low-toxicity solvent. Anal. Biochem. 90, 420-426.The method used for analysis of organic carbon content is described in:Sandstrom MW, Tirendi F and Nott A (1986) Indirect determination of organic carbon in modern reef sediments and calcareous organisms after dissolution of carbonate. Mar. Geol. 70, 321-329.The precision of the method is better than ±0.02 wt % organic carbon.Gas chromotography:A 50 m x 0.32 mm i.d. crosslinked methylsilicone fused silica capillary column (Hewlett-Packard) was used for all analyses. The column was temperature programmed from 80 to 120°C at 10°C/min and then from 120 to 280°C at 4 C/min after an initial 2 min isothermal period. Hydrogen was used as carrier gas at a linear flow velocity of 40 cm/s.Recovery and extraction efficiency of hydrocarbons was determined by spiking a preextracted sediment with a mixture of standard hydrocarbons. Recovery was better than 85% for n-alkanes in the range C15-C32.Gas chromatography-mass spectrometry (GC-MS):Chromatography was performed on a 50 m x 0.33 m i.d. fused silica column coated with methylsilicone fluid (Hewlett-Packard). The temperature was programmed from 80 to 290°C at 5°C/min after an initial 3 min wait. The mass spectrometer scanned masses from 50 to 450 amu at a speed of 380 amu/s.

Notes

Credit
Sandstrom, Mark W, Dr (Co Investigator)

Credit
Gagan, Michael K, Dr (Co Investigator)