Holocene glacier fluctuations in South America and Antarctica

Abstract

Glacial geologic evidence indicates that glaciers throughout the Andes and Antarctica fluctuated during the Holocene. Radiocarbon dating and other age determinations suggest that glaciers readvanced significantly only during the last 5 ka, reaching positions from several 100 m to a few kilometres beyond their present limits. In South America tenuous evidence from radiocarbon dates, with dendrochronological data and environmental interpretations from pollen analyses indicate four main periods of Neoglacial advance, culminating 5000-4000 BP, 3000-2000 BP, 1300-1000 BP, and 15th-late 19th centuries; smaller advances may have occurred at ca. 8400 BP, ca. 7500 BP, and ca. 6300 BP. The meagre data are consistent in indicating broad synchrony throughout the Andes during the last 5 ka, suggesting response to global climatic changes. Anomalies exist in Patagonia where some tide-water glaciers reached their maximal Holocene limits recently this century. The broad spectrum of differing Antarctic environments produces interesting contrasts. Some local glaciers in the McMurdo Sound area of the East Artarctic continent are more extensive now than during the global glacial maximum ca. 18 ka BP, when they were starved of precipitation. Consistent agreement among 14 radiocarbon dates from the South Shetland Islands indicates two main Holocene glacier advances, the most extensive (2–3 km) peaking in the 12th century, the other culminating in the 18th–19th century. Glaciers in South Georgia reached their most advanced Holocene limits before 2200 BP. Moraine Fjord glacier, which culminated as a 6 km advance between 1460–1700 radiocarbon BP, may have lagged 400–650 years behind the climatic forcing because it could only advance in its deep-water fjord by building a moraine bank. Smaller advances in South Georgia culminated in the 17th–19th centuries and during the 1920s-30s. There is no firm evidence of glacier advances before 3 ka BP in the Southern Ocean-sub-Antarctic domain, but broad synchrony in glacier advances during the last ca. 3000 years appears to have occurred throughout the Andes-Antarctic transect. Caution is required in the interpretation and correlation of moraines associated with calving glaciers and of those with poorly constrained dating.