Biofilms are interface micro-habitats formed by microbes that differ markedly from those of the ambient environment. The term 'subaerial biofilm' (SAB) was coined for microbial communities that develop on solid mineral surfaces exposed to the atmosphere. Subaerial biofilms are ubiquitous, self-sufficient, miniature microbial ecosystems that are found on buildings, bare rocks in deserts, mountains, and at all latitudes where direct contact with the atmosphere and solar radiation occurs. Subaerial biofilms on exposed terrestrial surfaces are characterized by patchy growth that is dominated by associations of fungi, algae, cyanobacteria and heterotrophic bacteria. Inherent subaerial settlers include specialized actinobacteria (e.g. Geodermatophilus), cyanobacteria and microcolonial fungi. Individuals within SAB communities avoid sexual reproduction, but cooperate extensively with one another especially to avoid loss of energy and nutrients. Subaerial biofilm metabolic activity centres on retention of water, protecting the cells from fluctuating environmental conditions and solar radiation as well as prolonging their vegetative life. Atmospheric aerosols, gases and propagatory particles serve as sources of nutrients and inoculum for these open communities. Subaerial biofilms induce chemical and physical changes to rock materials, and they penetrate the mineral substrate contributing to rock and mineral decay, which manifests itself as bio-weathering of rock surfaces. Given their characteristic slow and sensitive growth, SAB may also serve as bioindicators of atmospheric and/or climate change.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1462-2920.2007.01301.x

Life on the rocks.

Weathering in cold regions has primarily focused on the notion of ‘cold’, such that process and landform theory have generally used this both as the developmental criterion and as the outcome of palaeoenvironmental reconstructions based on landforms or sediments. As a result of this approach, the process focus in terms of weathering has been that mechanical processes predominate, with freeze-thaw weathering as the prime agent, and that chemical processes are temperature-inhibited, often to the point of nonoccurrence. Here a reconsideration of the whole conceptual framework of weathering in cold environments is undertaken. It is shown that, contrary to popular presentations, weathering, including chemical weathering, is not temperature-limited but rather is limited by moisture availability. Indeed, summer, and oft-times even winter, rock temperatures are more than adequate to support mechanical and chemical weathering if water is present. Where water is available it is clearly shown that chemical weatherin...

Weathering in cold regions: some thoughts and perspectives

A critique of Phanerozoic climatic models involving changes in the CO2 content of the atmosphere

Volumetric calculations of slope deposits, direct measurements of rockwall retreat and chronological control based on lichenometry provide a wide range of rockwall retreat rates in Svalbard (0–1580 mm ka−1) that appears consistent with previous evaluations from other Arctic areas. In northwest and central Spitsbergen (79°N), a triple-rate rockwall retreat is suggested for the last two millennia: very slow biogenic flaking (2 mm ka−1), moderate retreat due to frost shattering (100 ka−1) and rapid retreat associated with post-glacial stress relaxation (c. 1000 mm ka−1). Examination of the distribution of various processes indicates that the Holocene retreat of most rockwalls has not exceeded one or two metres. Bedrock conditions appear to be the main control on retreat rates. The massiveness of igneous and metamorphic outcrops, widespread in Arctic shield areas, largely accounts for the slowness of rockwall retreat, which on these lithologies is primarily due to chemical and biological processes. More rapid rates are usually associated with stress relaxation following glacial surges or with local frost susceptibility of bedrock, often where faulting has induced high joint density. At such sites, rockwall retreat rates are of the same order of magnitude as those reported from Alpine areas (1000–3000 mm ka−1) where both bedrock weakening due to tectonic stresses and the greater height of steep rockwalls account for the more rapid rockwall retreat rate. © 1997 by John Wiley & Sons, Ltd.

Holocene Rockwall Retreat in Svalbard: A Triple-Rate Evolution

Ecological perspectives on rock surface weathering : towards a conceptual model

Observations on a number of nunataks of the Juneau Icefield indicate that chasmolithic algae play a major role in the breakdown of granitic rock. Expansion and contraction of the algal mucilage, caused by wetting and drying episodes, results in the surface flaking of the rock. Available data suggest that the average mass of material lost per year from 1 m2 of rock could be as high as 562 g. It is suggested that biological weathering may be a major destructive mechanism of the granitic lithologies.



Des observations sur plusieurs nunataks du glacier Juneau indiquent que des algues chasmolithiques jouent un rǒle capital dans la rupture des roches granitiques. L'expansion et la contraction du mucilage algaire, dues a des periodes de secheresse et d'humidite entrainet la detachement de plaques superficielles de roche. Les donnees disponibles suggerent que la masse de materiau perdue par an sur une surface de 1 m2 de roche peut atteindre une valeur aussi elevee que 562 g. Il est suggere que cette alteration biologique peut ětre un mecanisme de desagregation capital pour des roches granitiques.

Wulf Otte

Papers

A note on biological weathering on nunataks of the juneau icefield, Alaska