2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 40-37
Presentation Time: 9:00 AM-5:30 PM


JACKSON, Margaret S.1, KELLY, Meredith A.1, RUSSELL, James M.2, HOWLEY, Jennifer A.1, DOUGHTY, Alice M.1, BABER, Margaret B.1, LOOMIS, Shannon E.3 and ZIMMERMAN, Susan H.4, (1)Department of Earth Sciences, Dartmouth College, HB 6105 Fairchild Hall, Hanover, NH 03755, (2)Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI 02912, (3)Geological Sciences, University of Texas, Austin, TX 78712, (4)Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore, CA 94550, margaret.s.jackson.gr@dartmouth.edu

As the locus of global water vapor production and atmospheric convergence, the tropics have a strong influence on global climate. Whether the tropics played a role in millennial-scale climate changes during late-glacial time is not well established. In an effort to improve the understanding of late glacial climate changes in the tropics, we are developing records of past glacial extents at high altitude (2600-4000 m asl) in the Rwenzori Mountains (~1ºN, 30ºE) of Uganda. Here we present a chronology of glacier extents from the Last Glacial Maximum (LGM) to early Holocene time using 10Be dating. Glaciers in the Bujuku and Mubuku Valleys in the central Rwenzori Mountains reached their maximum extents at ~23.4 and ~20.1 ka, similar to the timing of LGM glacier extents in the Northern Hemisphere. In a valley to the south, the maximal glacier extent during the last glacial period was reached at ~17.2 ka, similar to the timing of Heinrich Stadial 1. Glacier recession in the Bujuku Valley subsequent to the LGM stalled, or was interrupted by a readvance, at ~13.8-13.4 ka. Subsequently, ice receded ~1.5 km upvalley to another moraine position dated at ~11.1 ka. This date is coeval with 10Be ages of moraines in the Nyamugasani Valley, located in the southern Rwenzori Mountains. There, glacier recession occurred between ~11.5 and 10.5 ka. No additional moraines occur in either the Bujuku or Nyamugasani Valleys between the early Holocene moraines and estimated late Holocene age moraines upvalley. We compare the chronology of glacial extents in the Rwenzori Mountains with similar datasets from tropical South America. There is a broad synchrony in the timing of glacier fluctuations during late glacial time in tropical South America and Africa suggesting that these glaciers responded to a common driver during the late glacial period.