Paper No. 6-8
Presentation Time: 11:30 AM
ASPECT-DEPENDENT MECHANICAL WEATHERING RATES IN THE ANTARCTIC DRY VALLEYS AND THE EVOLUTION OF TOPOGRAPHIC ASYMMETRY
Topographic asymmetry between north- and south-facing hillslopes is a common phenomenon across terrestrial landscapes. In the absence of structural, stratigraphic or lithological forcing, asymmetric hillslope evolution is commonly attributed to variability in solar insolation resulting in aspect-dependent vegetation, fluvial, colluvial, soil development, and frost-weathering processes that ultimately link to differential rock weathering and/or sediment transport rates. Here, we investigated the development of topographic asymmetry in the Antarctic Dry Valleys (ADV), where hyper-arid, extremely cold and barren conditions effectively exclude the mechanisms described above for aspect-dependent slope asymmetry. We show that slope asymmetry in the ADV links to higher rock-weathering rates on north-facing hillslopes, where higher frequencies of diurnal thermal-stress cycling occur due to insolation geometry. These higher weathering rates, which exceed the otherwise extremely low weathering rate of ADV landscape, appear to be facilitated by excess moisture sourced from snow-melt and/or salt deliquescence. Beyond the context of slope asymmetry in the ADV, we propose salt deliquescence as a possibly overlooked mechanism for effective conversion of atmospheric humidity to moisture available for rock-weathering processes in otherwise hyper-arid environments on Earth and possibly Mars.
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