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Alumni Newsletter: July '08 to July '09

Tropical Mountain Climates and Glacier Dynamics

The coring team (above), May, 2008 in Kilembe, Uganda. Geology's Professor Jim Russell is in the back row in the white shirt and graduate student Jessica Tierney is in the front second row, second from right.

Expedition to Rwenzori: The Rwenzori Mountains (the so-called Mountains of the Moon) are a small but spectacular mountain range in central Africa, on the border between Uganda and the Democratic Republic of the Congo The mountains were created in the Pliocene by uplift of crystalline rocks (mainly gneiss, amphibolite, granite and quartzite) that rose from within East Africa’s western rift valley. The uplifted mountain range has subsequently been sculpted by rivers and the repeated advance of glaciers during the Pleistocene ice age, resulting in six separate mountain peaks rising over 4,500 m above sea level, the tallest of which reaches 5109 m.

Until recently, glaciers covered all of the Rwenzori’s six major peaks, but glaciers now exist on only the three highest mountains. Extrapolation of the rates of this glacier recession suggests that permanent ice will disappear from the Rwenzori entirely within the next two decades. However, many aspects of both the present glacier recession as well as long-term climate and glacial history in the Rwenzori remain poorly understood, as there are virtually no observational climate or paleoclimate data available from these remote, rugged mountains. Luckily, the range is also dotted with numerous lakes occupying glacially excavated and moraine dammed basins whose sediments chronicle the history of both the Rwenzori’s glaciers (in the amount of glacial rock flour delivered by meltwater) as well as the region’s climate.

In order to understand the climatic controls of glacier recession, the relative impacts of human-induced global warming versus natural climate variability, and the long-term tropical mountain ecosystem and glacier stability in the Rwenzori, Professor Jim Russell (coring, right) and his team have made five expeditions to the Rwenzori between 2005 and present. The main goal of the team’s research is to investigate both modern and long-term variations in rainfall and temperature and their impacts on alpine glaciation and ecosystems in the Rwenzori through analysis of sediment records from lakes. To this end, they have:

  • Explored the physical, chemical, and biological limnology of virtually all lakes on the Ugandan side of the range, 28 lakes in total.
  • Installed and maintain a network of 25 in-situ air temperature and humidity loggers from multiple sites between 1,500-5,000 m asl to monitor current climate conditions. Local collaborators also monitor changes in river discharge and chemistry.
  • Calibrated sedimentological, geo-chemical and biological indicators of temperature and rainfall through analysis of their variation in the surface sediments of lakes and pools throughout the Rwenzori and East Africa’s other major mountain ranges.
  • Quantify the effects of temperature and rainfall amount on the isotopic composition of Rwenzori meteoric waters using field data and isotope-enabled climate models for quantitative reconstruction of changes in precipitation.
  • Recovered new, long sediment piston cores from 7 lakes in the Rwenzori Mountains. These cores span up to 10,000 years in time, and were obtained from lakes that currently receive glacial meltwater as well as lakes that do not so that they can distinguish changes in climate from changes in the lakes driven by the waxing and waning of the glaciers.
  • Sampled numerous moraines and other glacial deposits for cosmogenic isotope dating to determine the timing of late Pleistocene and Holocene glacial advances in the Rwenzori.
  • Documented aspects of the poorly known biodiversity of aquatic algae, insects and micro-crustacea in the unique setting of tropical high-elevation lakes. Apart from throwing light on the ecology and biogeography of the different groups of Afroalpine aquatic biota, the data will also provide a baseline against which to compare future ecological changes.

Ultimately, by comparing both sediment- based and moraine-based estimates of the timing of glacial advances with independent, lake sediment-based reconstructions of temperature, precipi-tation, and lake ecology, the team hopes to elucidate the relative importance of changes in air temperature (which controls melting) and precipitation (which “feeds” the glacier) in controlling Rwenzori glaciers, as well as the impacts of changes in climate and glaciers on this unique alpine ecosystem.

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