Using biomarkers to determine dispersion and cycling of organic matter from the Sepik River, Papua New Guinea

In January 2000, two sediment trap arrays consisting of five stainless steel cylinders (1 m long and 10 cm diameter) fitted into a weighted aluminium frame were deployed for 48 hours on a free drifting mooring in the Sepik Canyon (SC) at depths of 100 and 260 m. During deployment, the mooring drifted 19.5 km north west from the Canyon axis, but remained within the area of the river plume. The mooring was retrieved in approximately 380 m of water and the contents of the sediment traps were drained into 4 L glass bottles. The bottles were shaken and sub-sampled for particulate carbon and the remaining samples were then filtered through pre-weighed 0.45 µm GFF filters, rinsed with MilliQ water to remove salt, and were wrapped in pre-combusted foil, then stored at -20°C. Water samples for lipid analysis were collected with Infiltrex II (TM) high volume samplers. Samplers were attached to the sediment trap mooring at depths of 55, 180, 200 and 220 m. Depths were chosen to target layers of turbidity as detected with the CTD instruments. Each sampler pumped 388- 432 L of seawater before the filters clogged and the pumps shut down. At other offshore stations an Infiltrix sampler was attached to the hydrowire and lowered to sample at 220 m within the undercurrent while the ship drifted. These deployments were short in duration and only sampled about 90 L each time. Samples were collected at Vitiaz Strait (Vitiaz), a region not influenced by the river, and another station (S+2) to the northwest of the river, which may be influenced by it, to determine dispersion and potential entrainment in the 200 m undercurrents. Samples were also collected upstream of the small village of Kopar (SR), at a depth of 1 m below the river surface, in 4 L glass bottles and pumped through an Infiltrex II (TM) sampler on the deck of the vessel. Upon retrieval of the samplers, the GFF filters were removed and packed in glass jars with foil lined lids and stored at -20°C. The XAD2 columns were removed, resealed and stored at 4°C. Samples for marine dissolved lignin analysis were collected using 10 L Niskin bottles attached to a CTD system. Specific depths were targeted, which offshore included the chlorophyll maximum and the depth of the New Guinea Coastal Undercurrent (NGCUC1, NGCUC2) or the Equatorial Undercurrent (EUC1, EUC2) at 220 m. Upon retrieval the Niskin bottles were clamped shut, pressurised with N2 gas and the water was filtered through GFF filters into 4 L glass bottles. The filtered seawater was acidified to pH 2 with concentrated HCl and poured back into the 10 L Niskins. The bottles were again clamped and pressurized and the water forced through prepared cartridges of C18 silica for solid phase extraction of lignin. After sampling, the cartridges were re-wrapped in cleaned foil and stored at 4°C. Riverine dissolved lignin samples were collected using GFF filtration into 1 L glass bottles and frozen at dry ice temperature. In the laboratory, the water was removed using rotary evaporation, leaving a powder for lignin analysis. Surface sediment samples for lignin analysis were collected from 19 sites on the coastal margin (around SC) by gravity and Kasten corers.Additional water samples were collected using Niskin bottles for dissolved and particulate carbon (DOC, POC), nutrient and stable isotope analyses. Riverine samples, collected for lignin analysis, were also analysed to determine organic carbon, total nitrogen, stable carbon isotope ratios and stable nitrogen isotope ratios. Samples collected for lipid analysis were extracted and a subsample taken for determination of total extractable organic matter (EOM). The remaining extracts were reduced and saponified and the neutral lipids extracted and then separated into hydrocarbon and esters plus alcohol/sterol fractions on silica gel. The remaining extract was acidified and the fatty acids were extracted.Alkanes in the hydrocarbon fractions were determined using a gas chromatograph fitted with a flame ionization detector (GC-FID). Polynuclear aromatic hydrocarbon (PAH) analysis was carried out using selected ion monitoring gas chromatography-mass spectroscopy (SIM GC-MS). Sterols and n-alcohols were converted to TMS esters and analysed using full scan gas chromatography/mass spectroscopy (GC-MS). The fatty acid fraction was converted to methyl esters and analysed using GC-FID.Dried riverine and surface sediment samples for lignin analysis were converted to phenols and the lignin-derived phenols separated using GC-MS. Quantification was achieved using SIM GC-MS,
 This research was undertaken to describe the fate and cycling of organic matter input from the Sepik River into the near coastal waters using molecular markers and to investigate stable biomarkers that might be useful for tracing long range transport.
 This work is part of Project TROPICS (Tropical River Ocean Processes in Coastal Settings), a joint coastal oceanographic study by Australia, Indonesia, Papua New Guinea, and the USA.

Organization: Australian Ocean Data Network