Rig Seismic Survey 112: Continuous Geochemical Tracers (CGT), Natural Processes and Anthropogenic Inputs to Seawater Off Sydney

A pilot project conducted in October 1991, from Rig Seismic (AGSO Survey 104), utilising the continuous geochemical tracer [CGT] capability, showed that theanalyses of oceanic waters for light hydrocarbon content provides a useful method for characterising pollutants from various sources (BMR Research Newsletter, 16). The offshore Sydney component of Survey 104 was conducted between Botany Bay and North Head. Light hydrocarbon anomalies were detected from each of the three deepwater ocean outfalls operated by the Water Board. The results suggested that the molecular compositions of different hydrocarbon mixtures may be useful indicators of hydrocarbon 'sources' mixed together in the coastal zone. A reprint of the BMR Research Newsletter article of the pilot survey is reproduced in Figure 1.1.

The usefulness of the CGT equipment, demonstrated during that pilot project, resultedin an additional survey (Survey 112), conducted on Rig Seismic during September/October 1992 (Heggie et al., 1992), which combined scientific staff from AGSO and the Water Board (Sydney). Scientific activities on Survey 112 included: (i)seafloor sampling, to gather environmental baseline information on the nutrient and contaminant (heavy metals and organochlorines) status of sediments, and also sedimentology of the nearshore region and, (ii) water column analyses, comprising approximately 500 line-km of CGT data (light hydrocarbons in seawater complemented with temperature, salinity, dissolved oxygen and pH) collected in the vicinity of the deepwater ocean outfalls.

The purposes of this Record are to: (i) provide a description of the edited hydrographic (temperature and salinity), oxygen and pH data and, (ii) combine these data with some of the light hydrocarbon (DHD) data. Sediment and DHD data collected during Survey 112 are addressed in other AGSO Records (Heggie et al., 1993a; Heggie et al., I993b). A separate part of Survey 112, conducted with scientific staff from Sydney University, the NSW Geological Survey and the Ocean Sciences Institute, between Newcastle and Wollongong provides a regional context for thoseobservations focussed about Sydney. The preliminary results of that part of Survey 112 are included in Bickford and Heggie et al. (1993).