Recent glacier changes and climate trends on South Georgia

Frontal positions for a sample of 36 out of a potential ca. 160 glaciers on the subantarctic island of South Georgia have been mapped, georeferenced in ArcGIS and analysed for 20th century fluctuations from a variety of satellite, aerial and oblique photographs, ground surveys and historical sources. Of these glaciers, 2 are currently advancing, 28 are retreating and 6 are stable or show a complex, ambiguous response. Most glaciers on the north-east coast of the island attained more advanced positions during the late 19th century. Since then, smaller mountain and valley glaciers have progressively receded. Although showing more variable behaviour, larger tidewater and sea-calving valley and outlet glaciers generally remained in relatively advanced positions until the 1980s. Since then, however, most glaciers have receded; some of these retreats have been dramatic and a number of small mountain glaciers will soon disappear. The response of these glaciers can be related to the direct effects of synoptic-scale warming on glacier mass balance, particularly since the 1950s. However, individual long-profile geometry also appears to be a significant influence on the response and sensitivity characteristics of these glaciers. Thus the delayed and varied behaviour of the larger glaciers may in part reflect their longer response time compared to small glaciers, but the combination of both larger and higher-elevation basins, potentially exposed to enhanced orographic-driven accumulation, is a critical factor that cannot be discounted, especially for the few calving glaciers that have recently advanced. Our observations indicate that glacier recession on the windward south-west coast, where precipitation is significantly higher, is less widespread.