Optical rock properties and weathering processes in polar environments (with special reference to Antarctica)
Résumé
Abstract: As a result of the “ freeze-thaw dogma ”, the polar scientific community has, for a long time, emphasized the importance of physical properties of rocks (porosity, jointing, etc) as a primary control on rock weathering. More recently, due to growing interest in chemically-driven processes operating in cold areas, attention has been drawn to the chemical rock properties. Surprisingly, the optical properties of rocks have either been ignored or only alluded to in most rock weathering studies. Based on the available Antarctic biological and geomorphological literature, it is now appropriate to consider these optical properties as exerting a potentially significant influence and to promote a Manichean view in which the light-coloured and translucent rocks (e.g. the emblematic Beacon sandstones) are considered from the perspective of biogenic weathering, while the dark rocks (e.g. the dolerites of the Dry Valleys) are viewed as being influenced by thermal weathering. Field observations and monitoring carried out from Labrador to Antarctica lead, however, to a much more subtle appreciation, for it appears necessary to: (1) integrate the optical properties within a corpus of rock properties (within which some operate synergistically and others antagonistically with those optical properties), (2) to take into account the impact of scale (e.g. macro vs. micro) and (3) to consider the nature and role of lithophytic communities involved in bioweathering.