INDICATOR DEFINITION Regular measurements of the thickness of the fast ice, and of the snow cover that forms on it, are made through drilled holes at several sites near both Mawson and Davis.
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 Each season around the end of March, the ocean surface around Antarctica freezes to form sea ice. Close to the coast in some regions (e.g. near Mawson and Davis stations) this ice remains fastened to the land throughout the winter and is called fast ice.
The thickness and growth rate of fast ice are determined purely by energy exchanges at the air-ice and ice-water interfaces. This contrasts with moving pack ice where deformational processes of rafting and ridging also determine the ice thickness. The maximum thickness that the fast ice reaches, and the date on which it reaches that maximum, represent an integration of the atmospheric and oceanic conditions.
Changes in ice thickness represent changes in either oceanic or atmospheric heat transfer. Thicker fast ice reflects either a decrease in air temperature or decreasing oceanic heat flux. These effects can be extrapolated to encompass large-scale ocean-atmosphere processes and potentially, global climate change.
DESIGN AND STRATEGY FOR INDICATOR MONITORING PROGRAM Spatial Scale: At sites near Australian Antarctic continental stations: Davis; Mawson.
Frequency: at least weekly, reported annually
Measurement Technique: Tape measurements through freshly drilled 5 cm diameter holes in the ice at marked sites.
RESEARCH ISSUES To more effectively analyse the changes in Antarctic fast ice a detailed long-term dataset of sea ice conditions needs to be established. This would provide a baseline for future comparisons and contribute important data for climate modelling and aid the detection of changes that may occur due to climate or environmental change.
LINKS TO OTHER INDICATORS SOE Indicator 1 - Monthly mean air temperatures at Australian Antarctic stations SOE Indicator 40 - Average sea surface temperatures in latitude bands 40-50oS, 50-60oS, 60oS-continent SOE Indicator 41 - Average sea surface salinity in latitude bands: 40-50oS, 50-60oS, 60oS-continent SOE Indicator 42 - Antarctic sea ice extent and concentration
The fast ice data are also available as a direct download via the url given below. The data are in word documents, and are divided up by year and site (there are three sites (a,b,c) at each station). Snow thickness data have also been included. A pdf document detailing how the observations are collected is also available for download.
At Davis, where the water depth near the station is relatively shallow, there is little heat transfer from the ocean to the ice, and the thickness is largely determined by atmospheric conditions, predominantly temperature and snow cover. At Mawson, where ocean depths are over 200 m, interannual variability of ice thickness is also influenced by changes in oceanic heat flux.
... Long-term statistics are maintained for each site of the date of ice formation, maximum thickness, date of maximum thickness, date of any mid-season breakouts, and date of final breakout of the fast ice. Incomplete historical records exist for Mawson back to 1954 and for Davis back to 1958.
Simple (e.g. Allison, 1981) or more complex (Heil et al., 1996) thermodynamic modelling of the growth of the ice cover can be used to estimate seasonal and interannual variations in the oceanic heat flux.
These data are publicly available for download from the URL given below.
A pdf document detailing how the data are collected is also available for download from the provided URL.