Rising tide of interest in sea level rise

The tide gauge installed at Cape Denison in 1912 and operated by Captain Robert Bage
The tide gauge installed at Cape Denison in 1912 and operated by Captain Robert Bage (Photo: Mitchell Library, NSW)
The modern tide gauge installation on Macquarie Island.The bottom-mounted mooring with tide gauge at Davis station. The white cylinder at the end of the cable is a communications coil that will be placed over the tide gauge to download the data.A typical Macquarie Island tide recording and notes on graph paper from the Australasian Antarctic Expedition era. Tidal recordings from a modern electronic data logger come out as a series of numbers which may then be plotted on a graph.

4 June 2010

The approaching centenary of Douglas Mawson's Australasian Antarctic Expedition (1911–1914) will be celebrated in part for its contributions to science, particularly in the fields of geology and meteorology. A perhaps lesser-known scientific contribution, but a significant one given the challenges that face us today, was the establishment of tide gauges at Cape Denison and Macquarie Island in 1912.

Thanks to measurements from these gauges, modern-day scientists have a benchmark for sea level 100 years ago. This has allowed them to detect a rise in sea level, as a result of climate change, of 2.0 ±1.3mm/year at Cape Denison and 2.0 ±0.8 mm/year at Macquarie Island (approximately 200 mm over 100 years).

According to Australian Antarctic Division Mapping Officer, Henk Brolsma, just as important as the installation of these gauges was the proper documentation of the measurements in a scientific publication.

'The notes on the Cape Denison tide gauge were prepared by Captain Robert Bage, with Doodson, in 1939, documenting important datum information which is critical for sea level studies today; and the original graph paper showing the tidal records was archived at the Mitchell Library in NSW,' Mr Brolsma says.

'It's an important message for all scientists. You never know what your data will be used for, so it's important to document it correctly. Mawson's team weren't necessarily looking at sea level change when they made these measurements, but 100 years on, the tidal data has played a critical role in detecting sea level rise as a result of climate change.'

As there are very few tide gauges in the southern hemisphere compared to the northern hemisphere, the tidal data from Mawson's two gauges continue to make an important contribution to regional sea level rise observations and estimates (sea level rise varies amongst geographic regions due to a range of climatic and oceanographic effects).

Scientists at the Australian Antarctic Division have also gathered about 15 years of tide gauge measurements at Casey, Davis, Mawson and Macquarie Island. Due to natural events (such as El nino) and annual variability, a minimum of 15 years of data is required before sea level changes can begin to be accurately detected. The data is, however, useful for tidal predictions and the calibration of satellite altimeters. After the 2004 Aceh earthquake and subsequent tsunami, tide gauges detected an increase in tide height of about 500 mm at Mawson, 600 mm at Casey and 200 mm at Macquarie Island (Australian Antarctic Magazine 8: 13, 2005). These Antarctic and subantarctic gauges will continue to contribute to both a global and Southern Ocean network of gauges well beyond Mawson's expedition centenary.