Glacier inventories reveal an acceleration of Heard Island glacier loss over recent decades

Abstract. Glacier inventories provide baseline data for understanding and evaluating past, current, and future changes in glacier extent in response to climate changes. We present a multi-year, manually mapped glacier inventory for sub-Antarctic Heard Island, a remote glacier-covered volcano in the southern Indian Ocean. Glacier outlines are presented for 1947, 1988, and 2019, derived from large-scale topographical maps (1:50,000), cloud-free medium-resolution SPOT, and high-resolution Pléiades satellite orthoimages. ASTER and Pléiades digital surface elevation models for 2000 and 2019 were also used to determine topographic parameters for individual glaciers. Heard Island glacier area reduced from 289.4±6.1 km² in 1947 to 260.3±6.3 km² in 1988, further decreasing to 225.7±4.2 km² in 2019. The rate of annual glacier area loss between the two observation periods (1947–1988 and 1988–2019) almost doubled from −0.25 % yr⁻¹ to −0.43 % yr⁻¹. Glaciers on the eastern slopes of Heard Island experienced much higher retreat rates than glaciers elsewhere on the island. The maximum retreat observed between 1947 and 2019 was ~5.8 km for the east-facing Stephenson Glacier, where collapse of the terminus led to the formation of a large lagoon during recent decades. Surface debris cover on Heard Island glaciers increased from 7.0±6 % (18.1 km²) in 1988 to 12.8±5.5 % (29.0 km²) in 2019. We also observed an upward shift (4.2 m yr⁻¹) in the maximum elevation of debris cover from 285±20 m a.s.l. (above sea level) to 605±20 m a.s.l., during this time. Direct climate observations from Heard Island are scarce, but reanalysis climate data show that the decline in glaciers is associated with a rising temperature of 0.7 °C Many questions about the behaviour of Heard Island glaciers remain unanswered. Our inventory dataset will be freely available in the GLIMS glacier database to facilitate further analysis and modelling of Heard Island glaciers.