Abstract:
INDICATOR DEFINITION
This indicator reports on the deviation of the annual mean sea level from the long-term sea level record.
TYPE OF INDICATOR
There are three types of indicators used in this report:
1.Describes the CONDITION of important elements of a system;
2.Show the extent of the major PRESSURES exerted on a system;
3.Determine RESPONSES to either condition or changes in the condition of a
... system.
This indicator is one of: CONDITION
RATIONALE FOR INDICATOR SELECTION
The climate of Antarctica is affected by complex interactions between the atmosphere and the ocean. The sea level is determined by these interactions, as well as by tidal forces. The enhanced greenhouse effect is expected to lead to a global increase in sea level, as the upper ocean expands and land ice melts due to global warming. By carefully observing the sea level around Antarctica, we can detect trends and attempt to identify their causes. The observed trends around Antarctica need to be compared with global values in order to separate local and large-scale features.
DESIGN AND STRATEGY FOR INDICATOR MONITORING PROGRAM
Spatial Scale: NTC Australia currently undertakes analysis of sea level data from Macquarie Island, Casey, Davis and Mawson for the AAD.
Macquarie Island (lat 54 degrees 37' 59.9& S, long 158 degrees 52' 59.9& E)
Casey (lat 66 degrees 16' 54.5& S, long 110 degrees 31' 39.4& E)
Davis (lat 68 degrees 34' 35.8& S, long 77 degrees 58' 02.6& E)
Mawson (lat 67 degrees 36' 09.7& S, long 62 degrees 52' 25.7& E)
Frequency: Data are continuously logged (Antarctic mainland: continuous ten minute averages, Macquarie Island: continuous three minute averages) on site and sent to NTC Australia once the record has been retrieved. Due to the nature of the environment this occurs on an irregular basis.
Data collection began in 1992, and since 1993 continuous records with very few gaps have been obtained with the submerged gauges. The records from the acoustic and pressure gauges at Macquarie contain many gaps until recently.
Measurement Technique: Casey, Davis and Mawson employ Platypus Engineering bottom mounted pressure gauges. Macquarie Island employs both an Aquatrak acoustic and Druck pressure gauges. Air pressure data are also collected at all sites.
Measurements are made using modern precise sensors in bottom or shore mounted gauges at the Antarctic stations of Mawson, Davis, Casey, Zhong Shan and the sub-Antarctic station of Macquarie Island.
Air pressure is reduced to MSL and subtracted from the Antarctic base sea level data whilst the pressure gauge data from Macquarie Island is reduced to MSL prior to being sent to NTC Australia.
The tide gauge data set contains averaged sea levels relative to mean sea level. The averaging period is 10 minutes for the bottom mounted pressure gauges and 3 minutes for the shore mounted acoustic and pressure gauges.
Pressure and height data are processed by the National Tidal Centre, (NTC), South Australia, to produce sea level records and predictions. These are available in graphical form via the Web or in tabular form by request from NTC.
RESEARCH ISSUES
Through careful observation of the sea level around Antarctica, we can detect trends and attempt to identify their causes. The observed trends around Antarctica need to be compared with global values in order to separate local and large-scale features. 
