Geoscience Australia Marine Survey 282 Post-Survey Report: Shallow Gas and Benthic Habitat Mapping, Arafura Sea

Brief description

A range of geophysical indicators have been used to infer the presence of shallow gas in the Arafura Sea. The existence of shallow gas has been confirmed by the analysis of core material obtained during the survey. This sampled gas has a microbial origin related to decay of organic matter in Holocene mud-filled channels. However, geophysical data indicates that another source of gas exists in deeper parts of the sedimentary section and this gas appears to be migrating up from depth. Intense pockmark fields (~350/km2) are often developed above the mud-filled channels but they have also been recorded away from these channels. The development and density of the pockmark fields appears to be related to sea bed sediment type, microbial gas production within the mud-filled channels and supply of fluids from deeper within the sedimentary section. Correlation of sub-bottom profile data with conventional seismic data also indicates that there are links between deep first-order Proterozoic faults, second-order Jurassic faults and third-order faults to sea bed observed in sub-bottom profiles.

The detailed sea bed mapping carried out during the survey has also shown correlations between habitat and biodiversity of various benthic fauna. Areas of high biodiversity and abundance generally correlated with harder substrates. In these areas, sea whips and fans, soft corals, hydroids, crinoids and octocorals were frequently identified, with sessile benthos extending up to ~50cm in height. The extensive areas of soft substrate commonly exhibited low-relief benthos which often covered less than 5% of the surface area. Such areas were also frequently noted for pockmark fields and the general uniformity of the environment.

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