In 1841 Captain James Clark Ross, on his Southern Antarctic expedition, undertook scientific excursions on the Tasman Peninsula.
Accompanied by Lieutenant-Governor John Franklin, he visited Port Arthur.
One reason for this visit was to establish a permanent sea level benchmark based on tidal observations initiated by Franklin and continued by Thomas James Lempriere, Deputy Assistant Commissary General of Port Arthur.

Lempriere had taken on the duties of recording meteorological and tidal observations following the drowning of the Surveyor for the Royal Navy, Lieutenant Thomas Burnett in May 1837.
He recorded observations with a thermometer, water barometer, rain and tide gauge from 1 July 1837 to 30 June 1841.
These charts were then sent to the Royal Society through the Colonial Office.

Captain Ross describes in his book, A Voyage of Discovery and Research in the Southern and Antarctic Regions during the Years 1839–43, that the Isle of the Dead was chosen for the placement of the benchmark as it was near to the tide register.
The benchmark was then struck following Franklin giving Lempriere the workers he needed to have the mark cut deeply in the rock where Lempriere's “tidal observations indicated as the mean level of the ocean”.

The benchmark was carved into a north facing vertical rock on the Isle of the Dead on 1 July 1841.
The standard British ordnance survey benchmark of a broad arrow was used with the horizontal line measuring 50cm across.
A small stone tablet was also installed above the benchmark recording the date the benchmark was struck and the measurements used to determine its position.
The tablet remained until the early 20th century when it was reported missing.

The Isle of the Dead benchmark, including the related surviving records up until 1848, were placed on the Australian National Heritage List in June 2005 for having “exceptional historical and scientific significance in the international field of climate research”.

The benchmark is believed to be one of the oldest sea level benchmarks installed in the world.
It is one of the first and few remaining early sea level measurements in existence in the Southern Hemisphere.
It is also estimated to be the first benchmark made to measure “relative land-sea vertical movements at an ocean site”.
The Isle of the Dead sea level benchmark together with Lempriere's records and those taken since that time, cover the longest time span of any sea level observations in the Southern Hemisphere.
In 1841 Captain James Clark Ross, on his Southern Antarctic expedition, undertook scientific excursions on the Tasman Peninsula. Accompanied by Lieutenant-Governor John Franklin, he visited Port Arthur. One reason for this visit was to establish a permanent sea level benchmark based on tidal observations initiated by Franklin and continued by Thomas James Lempriere, Deputy Assistant Commissary General of Port Arthur.
Lempriere had taken on the duties of recording meteorological and tidal observations following the drowning of the Surveyor for the Royal Navy, Lieutenant Thomas Burnett in May 1837. He recorded observations with a thermometer, water barometer, rain and tide gauge from 1 July 1837 to 30 June 1841. These charts were then sent to the Royal Society through the Colonial Office.
Captain Ross describes in his book, A Voyage of Discovery and Research in the Southern and Antarctic Regions during the Years 1839–43, that the Isle of the Dead was chosen for the placement of the benchmark as it was near to the tide register. The benchmark was then struck following Franklin giving Lempriere the workers he needed to have the mark cut deeply in the rock where Lempriere's “tidal observations indicated as the mean level of the ocean”.
The benchmark was carved into a north facing vertical rock on the Isle of the Dead on 1 July 1841. The standard British ordnance survey benchmark of a broad arrow was used with the horizontal line measuring 50cm across. A small stone tablet was also installed above the benchmark recording the date the benchmark was struck and the measurements used to determine its position. The tablet remained until the early 20th century when it was reported missing.
The Isle of the Dead benchmark, including the related surviving records up until 1848, were placed on the Australian National Heritage List in June 2005 for having “exceptional historical and scientific significance in the international field of climate research”.
The benchmark is believed to be one of the oldest sea level benchmarks installed in the world. It is one of the first and few remaining early sea level measurements in existence in the Southern Hemisphere. It is also estimated to be the first benchmark made to measure “relative land-sea vertical movements at an ocean site”. The Isle of the Dead sea level benchmark together with Lempriere's records and those taken since that time, cover the longest time span of any sea level observations in the Southern Hemisphere.
Isle of the Dead (Tasmania)