Paleolimnological records of recent glacier recession in the Rwenzori Mountains,Uganda-D. R. Congo |
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| Authors: | J Russell H Eggermont R Taylor D Verschuren |
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| Institution: | (1) Department of Geological Sciences, Brown University, Box 1846, Providence, RI 02912, USA;(2) Limnology Unit, Department of Biology, Ghent University, K. L. Ledeganckstraat 35, Ghent, 9000, Belgium;(3) Department of Geography, University College London, Gower Street, London, WC1E 6BT, UK |
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| Abstract: | The status of tropical glaciers is enormously important to our understanding of past, present, and future climate change,
yet lack of continuous quantitative records of alpine glacier extent on the highest mountains of tropical East Africa prior
to the 20th century has left the timing and drivers of recent glacier recession in the region equivocal. Here we investigate
recent changes (the last 150–700 years) in lacustrine sedimentation, glacier extent, and biogeochemical processes in the Rwenzori
Mountains (Uganda- Democratic Republic of Congo) by comparing sedimentological (organic and siliciclastic component determined
by loss-on-ignition; LOI) and organic geochemical profiles (carbon and nitrogen abundance, ratio, and isotopic composition
of sedimentary organic matter) from lakes occupying presently glaciated catchments against similar profiles from lakes located
in catchments lacking glaciers. The siliciclastic content of sediments in the ‘glacial lakes’ significantly decreases towards
the present, whereas ‘non-glacial lakes’ generally show weak trends in their siliciclastic content over time, demonstrating
that changes in the siliciclastic content of glacial lake sediments primarily record fluctuations in glacier extent. Radiometric
dating of our sediment cores indicates that prior to their late 19th-century recession Rwenzori glaciers stood at expanded
‘Little Ice Age’ positions for several centuries under a regionally dry climate regime, and that recession was underway by
1870 AD, during a regionally wet episode. These findings suggest that the influence of late 19th century reductions in precipitation
in triggering Rwenzori glacier recession is weaker than previously thought. Our organic geochemical data indicate that glacier
retreat has significantly affected carbon cycling in Afroalpine lakes, but trends in aquatic ecosystem functioning are variable
among lakes and require more detailed analysis. |
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| Keywords: | Alpine glaciers East Africa Climate forcing Loss-on-ignition Global warming |
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