Recent Tropical Andes Glacier Retreat Unprecedented in the Holocene

Abstract

Glaciers in the tropics have retreated over recent decades, but whether the magnitude of this retreat has exceeded the bounds of past Holocene fluctuations is unclear. In this study, we measure cosmogenic 10Be and 14C concentrations from recently exposed bedrock at the margin of five glaciers in the tropical Andes, including four small glaciers and the Quelccaya Ice Cap, the world’s largest tropical ice mass. Concentrations at the Quelccaya Ice Cap margin suggest there was extended exposure during the first half of the Holocene, but that the site was covered by ice for the last 5 kyr. In contrast, nuclide concentrations are strikingly low in all samples at the margins of the four small glaciers, equivalent to ~200 years of 14C and 50 years of 10Be accumulation at surface production rates. These data suggest that the small tropical glaciers are now smaller than they have been at any point during the Holocene, whereas the Quelccaya Ice Cap has not yet retreated to its smallest extent of the Holocene, likely due to its larger size and slower response time.