Conference papers

New evidence for drowned shelf edge reefs from the northern Great Barrier Reef, Australia

Authors: Webster, J.M., Ludman, D., Wust, R., Beaman, R.J., Renema, W., Moss, P.

Year: 2007

Publication: Hydro 2007 - The International Conference on Hydrography, 21-24 Nov 2007. Australasian Hydrographic Society, Cairns, Australia.

Abstract

We present new high-resolution multibeam bathymetry datasets from the shelf edge of the northern Great Barrier Reef (GBR). Analysis of these data, combined with Chirp sub-bottom profiles and submersible observation data provides a fresh insight into the detailed morphology and spatial distribution of submerged reefs and terraces at the shelf edge. The reefs will be the focus of a major expedition in Oct 2007.

Multibeam survey datasets collected along the GBR margin by the Royal Australian Navy, James Cook University and Scripps Institute of Oceanography were spatially analysed in 3D visualisation software and a Geographic Information System. Underwater imagery provided ground truth of the modern biota on the drowned reefs.

An extensive and persistent line of drowned shelf edge reefs exist on the GBR margin in approx. 40 to 70 m. They appear as barrier reefs up to approx. 200 m wide and comprising twin parallel ridges of rounded pinnacles. Subtle yet consistent terrace and step features lie between 78 to 114 m seaward of the shelf edge reefs. The drowned reefs now provide a favorable hard substrate for a covering of live soft corals and algae. They form a consistent and extensive seabed habitat that extends for possibly 900 km along the GBR shelf edge.

Based upon these results, we present a hypothesis that attributes reef demise to not just sea-level rise alone but to a significant reduction in water quality caused by an increase in sedimentation at 12 to 10 ka, as the sea flooded the GBR shelf and mobilised massive amounts of siliciclastic sediments.

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