Observations of the sea ice near Mawson were carried out in 1980, concentrating on the thickness of the ice at several points, and the accumulation and ablation of snow/ice cover on the ice. The ablation measurements were carried out by laying 23 ablation stakes out in two fields - a set of eight stakes in a straight line, and a set of 15 in a triangle. Results from both sets of observations were recorded in a log book, currently archived at the Australian Antarctic Division.

This indicator is no longer maintained, and is considered OBSOLETE. 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.

This dataset contains 102 depth measurements of the water column in Long and Tryne fjords, which are in the northern Vestfold Hills, Prydz Bay, Antarctica. Sea ice thickness and snow thickness were recorded simultaneously. The motivation for this project has been to yield a description of the pupping and moulting habitat of Weddell seals. This information will assist the interpretation of 25+ years of data on seal distribution within that area. Our data were collected between 7th and 13th December 1999. The measurement sites were chosen according to geographical features; their exact location was determined by GPS with an accuracy of about 25m. At each site a 5cm diameter hole was drilled through the sea ice and a weighted measurement tape was lowered through the ice-hole to the bottom. Water depths were measured to the nearest centimetre; ice and snow thicknesses were measured to the nearest millimetre. A minimum depth of less than 3m was found in a narrow channel between small islands immediately west of Shirokaya Bay. The maximum depth of the water column was 222m in the middle basin of Long Fjord. The tidal range for the measured days was less than 0.5m, with tidal corrections applied to the raw data. Water samples were taken in Breid Basin and the middle basin of Long Fjord. These and water samples taken in Snezhnyy Bay [pers. comm. J. Laybourn-Parry, 1999] show aerobic and relatively fresh water for all upper basins. This indicates that even the far basins of both fjords are well mixed despite the drainage of large volumes meltwater from the Antarctic plateau into the fjords. See related URL for data and a spatial summary of the data. See Entry: long_tryne_bathy for an interpolation of bathymetry made using the Topogrid command within the ArcInfo GIS software, version 8.0.2. Coastline and spot height (heights above sea level) data, extracted from the Australian Antarctic Data Centre's Vestfold Hills topographic GIS dataset (see Entry: vest_hills_gis), was also used as input data to optimise the interpolation close to the coastline. The fields in this dataset are: day weighpoint lat(dd) long(dd) ice (cm) freeboard(cm) snow(cm) depth(m)