Glacier retreat has been widespread on Heard Island, an isolated 2745-m-high volcano in the southern Indian Ocean, since the first observations in 1947. This study represents the first quantification of the mass loss of a Heard Island glacier. Brown Glacier is 4.8 km long and is land terminating. A digital elevation model for the glacier was developed using a combination of static and kinematic differentially corrected GPS surveys and hand-held GPS elevations, and together with ground penetrating radar, was used to estimate the glacier's catchment area boundary. The 1947 extent of the glacier was estimated from an aerial photograph. The total ice covered area has decreased from an estimated 6.18 × 106 m2 in 1947 to 4.38 × 106 m2 in 2004. This corresponds to a loss of ∼29% of the original area. During the same period the ice volume decreased by an estimated 1.743 × 108 m3 (∼3.06 × 106 m3 a−1), equating to an average thickness change of −0.50 m a−1. The mass loss is consistent with limited temperature observations in the area that indicate a 0.9 °C warming over the same time span. Meteorological observations combined with an energy balance model demonstrate the impact of foehn winds on the mass balance of the upper slopes of the glacier. Between December 2000 and December 2003, repeat differentially corrected GPS surface surveys revealed an average surface change of −9.9 m in the ablation area and −5.9 m in the accumulation area, translating to an ice loss of ∼8.0 × 106 m3 a−1, or more than double the 57 year average rate. There is no indication of an increase in geothermal heat flux that could explain an ice loss of this magnitude. The increase in the rate of ice loss suggests the glacier is reacting to ongoing changes in climatic conditions rather than approaching steady state.
