Isle of the Dead gives up clues

Dr Hunter worked in the sea at the Isle of the Dead

By Brady Haran BBC News Online

Scientists in Australia and the UK have learned about rising sea levels by investigating a carving at an old convict burial ground.

The Isle of the Dead is a creepy place, surrounded in mystery and the subject of ghost stories.

It is located in waters just off the Port Arthur convict colony in Tasmania, Australia.

But researcher John Hunter is not interested in the 1,000 convicts buried there - he is fixated on a small carving on rocks near the waterline.

Etched in stone more than 160 years ago, the carving has yielded information about the history of sea levels.

Lempriere carved his arrow 160 years ago

The marker - a benchmark carved in a vertical rock face - was made by amateur meteorologist Thomas Lempriere.

It is thought to be one of the earliest benchmarks cut in the world and probably the first in the Southern Hemisphere.

However the benchmark was useless until its accompanying records were recently uncovered in the archives at the Royal Society, in London.

It had previously been thought the records, detailing levels in 1841 and 1842, were burned.

The information gives an indication of water levels before global warming, and can be compared with current measurements.

Dr Hunter, from the University of Tasmania, said it was an honour to use Lempriere's old records.

Rising seas

The first ideas that the volume of the sea could be altered by changes in the amount of ice on the earth were only recorded in about 1842

Dr John Hunter

"When working with Lempriere's data, my over-riding feeling was one of privilege - the privilege of putting these records to use after such a long time.

"We have no evidence that Lempriere's sea level observations were ever taken seriously by the Admiralty in the United Kingdom or ever put to any practical use, until now."

The records, when carefully compared with current sea levels and movement of the cliff face itself, indicate an overall rise in the ocean level of 1mm a year - totalling between 16cm and 17cm.

Tidal expert Dr David Pugh, from the UK's Southampton Oceanography Centre, was also involved in the project.

He said: "This is an important result for the Southern Hemisphere, and especially for Australia, providing a benchmark against which Australian regional sea levels can be measured in 10, 50 or 100 years time."

Interestingly, Lempriere's work was not concerned with sea levels, but with attempting to monitor land movement.

Dr Hunter said: "The concept of the sea actually moving up or down in an absolute sense was only just being formed (in Lempriere's era).

"The first ideas that the volume of the sea could be altered by changes in the amount of ice on the earth were only recorded in about 1842, the year after the striking of the benchmark.

"It took decades for these ideas to take hold."