Holocene glaciation in the Rwenzori Mountains, Uganda

Abstract. Tropical glaciers are retreating rapidly, threatening alpine ecosystems across the low latitudes. Understanding how tropical glaciers responded to past periods of warming is crucial for predicting and adapting to future climate change, yet relatively little is known about glacial fluctuations in tropical regions during the recent past (i.e., the Holocene Epoch). This is particularly true in the African tropics, where data constraining the timing and magnitude of Holocene glacial fluctuations in the region are sparse and where temperatures during the middle Holocene were perhaps as warm as or warmer than today. Here we present new beryllium-10 surface-exposure ages that constrain Holocene glacial extents in the equatorial Rwenzori Mountains, Uganda. These results document rapid Early Holocene (~11.7–8.2 ka) glacial retreat in two separate catchments and indicate that Late Holocene (~4.2 ka-present) deposits mark the greatest expansion of Rwenzori glaciers during the last ~11 ka. Holocene glacial fluctuations elsewhere in tropical Africa and in tropical South America are broadly similar to those in the Rwenzori, with most tropical glaciers retreating rapidly during the Early Holocene and remaining near or inboard of their Late Holocene positions through much of Holocene time. The similarity of Holocene glacial fluctuations across the tropics implies that low-latitude glaciers responded to a common forcing mechanism, most likely temperature. Although the drivers of Holocene temperature changes in the tropics remains enigmatic, these data help constrain the expression of tropical temperature changes in the low latitudes.