C32C-05
Climatic Controls and Climate Proxy Potential of Lewis Glacier, Mt Kenya

Wednesday, 16 December 2015: 11:20
3005 (Moscone West)
Rainer Prinz1,2, Lindsey I Nicholson3, Thomas Mölg4, Wolfgang Gurgiser3 and Georg Kaser3, (1)University of Innsbruck, Institute of Atmospheric and Cryospheric Sciences, Innsbruck, Austria, (2)University of Graz, Department of Geography and Regional Science, Graz, Austria, (3)University of Innsbruck, Innsbruck, Austria, (4)University of Erlangen-Nuremberg, Institute of Geography, Erlangen, Germany
Abstract:
If their interaction with the atmosphere is understood, and their changes are documented or reconstructed, glaciers in the tropics can provide information about regional climate, its dynamics, and its evolution over decadal and centennial time scales. The glaciers on Mount Kenya capture a climate signal from the mid troposphere at about 5 km a.s.l., where our knowledge of climate change is scarce and controversial.

We use in-situ meteorological and glaciological observations to optimize and validate a physically-based, process-orientated energy and mass balance model to quantify the exchange processes between the glacier surface and the atmosphere above and to explore the sensitivity of energy and mass exchanges to changing climatic conditions. Currently the glacier loses mass due to the imbalance between insufficient accumulation and enhanced melt, because radiative energy gains cannot be compensated by turbulent energy sinks. Exchanging model input data with synthetic climate scenarios, which were sampled from the meteorological measurements and account for coupled climatic variable perturbations, reveal that the current mass balance is most sensitive to changes in atmospheric moisture (via its impact on solid precipitation, cloudiness and surface albedo). Scenarios with lower air temperatures are drier and associated with lower accumulation and increased net radiation due to reduced cloudiness and albedo.

If the scenarios currently producing positive mass balances are applied to Lewis Glacier's late 19th century maximum extent (L19), negative mass balances are the result, meaning that the conditions required to sustain the glacier in its L19 extent are not reflected in today’s observations. Alternatively, a balanced mass budget for the L19 extent can be explained by changing model parameters that imply a distinctly different coupling between the glacier’s local surface-air layer and its surrounding boundary layer. This result underlines the difficulty of deriving paleoclimates for larger glacier extents on the basis of modern measurements of small glaciers.

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