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12 June 1998 |
Ref 98/140 |
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One hundred and fifty seven years ago a rough mark was cut into the sandstone cliffs of Port Arthur's Isle of the Dead.
Now the rise and fall of the sea is again being measured at the former prison colony, in a study which could add new information to the global warming debate.
In 1841, amateur meteorologist Thomas Lempriere - in the company of noted Antarctic explorer Captain Sir James Ross - cut what is believed to be one of earliest benchmarks in the world against which to measure scientific changes in sea level.
At the same time, a rudimentary tide gauge was operated by Lempriere, then the Deputy Assistant Commissary at Port Arthur. Records from this tide gauge were thought to have been lost but now three years of figures have now been located in the Royal Society, London
In 1998 - the International Year of the Ocean - and with the aid of navigational satellites, sophisticated tidal gauges, and precision surveying, scientists are hoping to establish a new fix on sea level change during the past 150 years.
A new tide gauge installed at Port Arthur has begun measuring tidal levels with the objective of providing comparative information relevant to changes in global climate during the period of industrialisation, and in the geology and geophysics of the Earth
"With a great deal of searching in Australia and in the UK, records of perhaps the oldest known tidal movements in the Southern Hemisphere have been tracked down," said Dr John Hunter, a researcher at CSIRO Marine Research.
"Now, we aim to ensure that the imaginative work begun by Lempriere in the days of sailing ships has a comparative value in these days of satellites and modern instrumentation.
"This program will indicate any significant change in mean sea level or tidal range over the 150 years that has elapsed since the benchmark was installed," he said.
Another study by Dr David Pugh, from the Southampton Oceanographic Centre, in the United Kingdom, compared changes in tides and sea level over a very similar period for a number of sites in Ireland. Dr Pugh concluded that such changes, although small, are probably real.
Also involved in the project are Dr Peter Morgan, from the University of Canberra, Dr Richard Coleman from the University of Tasmania, Mr Nick Bowden, from the Tasmanian Department of Environment and Land Management, and staff from the Port Arthur Historic Site Management Authority.
Supported by funding from the University of Canberra and CSIRO, the tidal gauge was installed on the Port Arthur shore, across the bay from the Isle of the Dead and not far from where researchers believe the original gauge was located.
The Isle of the Dead was selected by Ross to host the benchmark because of tidal observations already made by Lempriere. The benchmark - a broad arrow containing a horizontal line about 200 mm long - is still still clearly visible.
Following an investigation in 1985, another oceanographer, Dr Bruce Hamon, wrote: "we must admire the industry and foresight of men like Ross and Lempriere - and regret that so much of Lempriere's effort was in vain.
"The position of course would be different if Lempriere's original observations ever came to light," he concluded.
Dr Hamon and earlier researchers initiated numerous searches for the records in Australian and the United Kingdom. But without the records no scientific conclusions could be drawn.
Then, in a collaboration between Drs Hunter and Pugh, a fresh investigation was initiated leading to Dr Pugh discovering three years of Lempriere's tidal data from Port Arthur, written in Lempriere's own hand.
More information from:
- Craig Macaulay 0419 704 094
Bill Knox, 03-6250 2363
Port Arthur Historic Site Authority
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