Australasian Hydrographic Society
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Australasian Hydrographic Society

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Australasian Hydrographic Society
Lydia Taylor, AHS Education Award winner for Academic Year 2004, has reported on her participation in the scientific cruise led by Geoscience Australia in May 2004. The aim of the cruise was to look at the geology of a large, submerged continental block, the Kenn Plateau lying off the Queensland coast. The cruise was conducted on board CSIRO Research Vessel, the Southern Surveyor and involved extensive seismic, multi-beam, gravity, magnetic measurements and dredge samples across the plateau in order to investigate its evolution, structure and hydrocarbon potential. Her further research in 2004 involved the use of geological and geophysical data from the Queensland and Marion Plateaux and the Norfolk Basin, north east of Australia to investigate the origin of anomalous tectonic subsidence and igneous activity in the area within the context of mantle convection.

Evidence from seismic reflection data, dredges, mantle tomography and geodynamic modelling supported the hypothesis that the Norfolk Basin formed as a backarc basin (zone of extension behind a subduction zone) in a plume-influenced subduction setting, rather than by subduction driven mantle flow. This accounts for an irregular progression of back-arc spreading. Seismic reflection data revealed the first volcanic margins described from a back-arc basin, found here because of the unusual association of subduction in a mantle-plume setting. Tectonic subsidence analysis, mantle tomography and geodynamic modelling indicate that anomalous subsidence on the Queensland and Marion plateaux is consistent with the hypothesis it was caused by a passing subducted slab as it passed beneath the margin in the late Tertiary era.

In the second half of 2004 Lydia went to Los Angeles to study at the California Institute of Technology (Caltech) where she finished her thesis. This is entitled ‘Surface expressions of mantle convection north and east of Australia during the Tertiary: A synthesis of observations from wells and seismic data with seismic tomography and geody-namic models’. She worked with Professor Michael Gurnis on producing geodynamic models, all of which has inspired her to progress with a PhD in marine geophysics in 2005.

AHS Education Award Scheme Presentation
At a luncheon ceremony on Tuesday 8th February, Michael Daly was presented with his cheque for Aus$2500 and a framed certificate as the winner of the AHS Education Award for Academic year 2005. Michael, an undergraduate in the School of Biological, Earth and Environmental Sciences at the University of New South Wales, is undertaking his Honours Year for a Baccalaureate in Environmental Science (Marine) under the tutelage of Dr Robert Brander. His chosen research is ‘The Sensitivity of Fringing Reef Flats and Shorelines to Climate Change’.

The response of reef flats and reef island shorelines to possible future rises in sea level is one of the major concerns in global climate change research. Chronic shoreline erosion resulting from both increased water depth and wave energy across reefs is envisaged, as manmade stress and global warming inhibit future reef growth. Australia will suffer major impact as she has one sixth of the world's reefs, the most common type of which are fringing reefs. Australia has 26% fringing reefs around islands or along coastal mainland in the approximately 1,000 miles-long Great Barrier Reef (GBR). At present there is little understanding of fringing-reef top and shoreline morpho-dynamics. Daly's research is ultimately aimed at remedying this situation by investigating wave patterns, currents and sediment transport across reefs in both low and high energy environments, and monitoring the response of fringing-reef shorelines (beaches) to process-regime changes (waves, currents) and boundary controls (wind, waves, tides, sediment). In addition, the sensitivity of fringing-reef shorelines to sudden shifts in climate change and energy forcing (storms, seasonality) will be monitored and a morphodynamic model will be developed for modal short-term (Springs/Neaps) conditions.

The fringing reefs of the GBR are an integral element of one of the most diverse and productive ecosystems in the world. They, and the shoreline they protect, are morphologically very sen-sitive to short-term climate change such as storms and seasonal shifts and will be extremely vulnerable to longer-term adjustments in oceanic and climatic boundary conditions, such as sea-level rise and increases in wave height and energy. It is obvious that beaches behind the fringing reefs are of major importance as these are the final impact zone for wave energy and the protector of terrestrial resources.

The first phase of Daly's research will occur in 2005, involving the continental island fringing reef at Lizard Island in Queensland waters, 300 kilometres north of Cairns. This site is only 19 kilometres from the outer reef boundary and subject to a higher energy wave climate. The data collection will embrace complete Spring/Neap tidal cycles, starting at the end of May 2005. The site and timing have been chosen in order to monitor the effects of high-energy exposure to the reef flat processes, beach form and sediment composition. Lizard Island in late May and June should be experiencing consistent Trade Winds of Force 3 to Force 4 over a long fetch, when steady moderate to high wave activity can be guaranteed. The research from this data will build upon August 2002 experiments at Warraber Island (Sue Islet) at the northern end of the GBR, and February 2002 and July 2003 experiments at Lady Elliot Island at the southern end. Both of these earlier studies monitored reef flat and shoreline hydrodynamics during Spring/Neap tidal cycles on reef flats around coral reef islands. It is hoped to follow up the Lizard Island work with comparative research on a wide, mainland fringing reef in a low-energy wave environment to gain more understanding of the morpho-dynamic relationships existing between fringing-reef flats and reef shorelines. No such study has been attempted to date.

Laser Airborne Depth Sounder Flight
The Royal Australian Navy's Laser Airborne Depth Sounder Flight, operating from Broome, Western Australia, recently completed a successful and unusual mission involving a survey of the remote and environmentally sensitive Ashmore Reef. This reef and its sand bay provide a rookery for seabirds, so the LADS team was required to plan sorties extremely carefully in order to comply with strict regulations to ensure that aircraft activities did not disturb this important habitat.

Contact
Australasian Hydrographic Society
Att. E.R. Whitmore
4/6 Carrington Street
Wahroonga, New South Wales
2076
Australia
Tel: +61 2 94892091
Fax: +61 2 94892048

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