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Glaciers on the world's highest tropical mountains are among the most sensitive components of the cryosphere, yet the climatic controls that influence their fluctuations are not fully understood. Here we present the first 10Be ages of glacial moraines in Africa and use these to assess the climatic conditions that influenced past tropical glacial extents. We applied 10Be surface exposure dating to determine the ages of quartz-rich boulders atop moraines in the Rwenzori Mountains (~1°N, 30°E), located on the border of Uganda and the Democratic Republic of Congo. The 10Be ages document expanded glaciers ca. 23.4 and 20.1 ka, indicating that glaciers in equatorial East Africa advanced during the global Last Glacial Maximum (ca. 26-19.5 ka). A comparison of these moraine ages with regional paleoclimate records indicates that Rwenzori glaciers expanded contemporaneously with dry and cold conditions. Recession from the moraines occurred after ca. 20.1 ka, similar in timing to a rise in air temperature documented in East African lake records. Our results suggest that, on millennial time scales, past fluctuations of Rwenzori glaciers were strongly influenced by air temperature. [ABSTRACT FROM AUTHOR]

The last glacial-interglacial transition (ca. 18--11 ka) was interrupted by abrupt climate events that differed in each hemisphere. During the Antarctic Cold Reversal (ca. 14.5--12.9 ka), the Southern Hemisphere high and mid latitudes cooled, while the Northern Hemisphere warmed. The pattern of change then reversed during the Younger Dryas (ca. 12.9--11.7 ka), which was characterized by cold conditions in much of the Northern Hemisphere. Well-dated paleoclimate records serve to reveal the possible mechanisms for these events. Here we present a reconstruction of the late glacial fl uctuations of Quelccaya Ice Cap, located in the southern tropics, based on 38 new radiocarbon ages. Quelccaya was retreating from its Last Glacial Maximum (ca. 21 ka) extent by ca. 17.2 ka, and was located upvalley from its late glacial moraines by 13.6--12.8 ka. Quelccaya experienced a signifi cant readvance that culminated at 12.5--12.4 ka, and then receded several kilometers to near, or within, its late Holocene extent by ca. 11.6 ka. This record provides the most detailed evidence yet of glacier fl uctuations in the southern tropics during late glacial time. [ABSTRACT FROM AUTHOR]

Tropical glaciers have retreated alongside warming temperatures over the past century, yet the way in which these trends fit into a long-term geological context is largely unclear. Here, we present reconstructions of Holocene glacier extents relative to today from the Quelccaya ice cap (Peru) and the Rwenzori Mountains (Uganda) based on measurements of in situ 14C and 10Be from recently exposed bedrock. Ice-extent histories are similar at both sites and suggest that ice was generally smaller than today during the first half of the Holocene and larger than today for most, if not all, of the past several millennia. The similar glaciation history in South America and Africa suggests that large-scale warming followed by cooling of the tropics during the late Holocene primarily drove ice extent, rather than regional changes in precipitation. Our results also imply that recent tropical ice retreat is anomalous in a multimillennial context. [ABSTRACT FROM AUTHOR]