Microchemistry of small desert varnish samples, western New South Wales, Australia

Dragovich, Deirdre

doi:10.1002/(sici)1096-9837(199805)23:5<445::aid-esp859>3.0.co;2-e

Cited by 10 publications

(4 citation statements)

References 26 publications

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“…5E) to penetrate deep into rocks thus protecting themselves from environmental stresses. In this sense, the visible portion of melanized MCF is like the tip‐of‐the‐iceberg, because the hyphae can rapidly penetrate several mm to cm into hard rocks in search of more protected environments and; the ability to create a multitude of varnish‐like like coatings, skins and shells that arise from the impregnation of the extracellular matrix and melanin layers with minerals (Dragovich, 1984; 1993; 1998; Gorbushina, 2003). …”

Section: Diversity and Biological Interactions Of Sabmentioning

confidence: 99%

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Life on the rocks

Gorbushina¹

2007

Environmental Microbiology

568

418

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SummaryBiofilms 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, selfsufficient, 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.

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Section: Diversity and Biological Interactions Of Sabmentioning

confidence: 99%

“…the ability to create a multitude of varnish‐like like coatings, skins and shells that arise from the impregnation of the extracellular matrix and melanin layers with minerals (Dragovich, 1984; 1993; 1998; Gorbushina, 2003).…”

Section: Diversity and Biological Interactions Of Sabmentioning

confidence: 99%

Life on the rocks

Gorbushina¹

2007

Environmental Microbiology

568

418

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“…2001; Dorn and DeNiro 1985; Dorn and Oberlander 1981; Dorn et al. 1992; Dragovich 1998; Flood et al. 2003; Garvie et al.…”

Section: The Past Present and Futurementioning

confidence: 99%

The Rock Varnish Revolution: New Insights from Microlaminations and the Contributions of Tanzhuo Liu

Dorn

2009

Geography Compass

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Rock varnish is a coating composed of clay minerals cemented to rock surfaces by oxides of manganese and iron. Although this dark brown-to-black accretion is most noticeable in arid regions, it occurs in all terrestrial weathering environments. Scholarly varnish research started with Alexander von Humboldt, when he asked how this external accretion forms and why manganese concentrations in varnish are 10 1 -10 2 greater than in potential source materials. In the ensuing two centuries, investigations into rock varnish have been characterized by researchers studying only a handful of samples who have often used limited data to draw general conclusions. In contrast, nearly two decades of work by Tanzhuo Liu of Columbia University has yielded more than 10,000 varnish microstratigraphies obtained from rock depressions, analyses of which have provided new insights into the origin of rock varnish and the nature of climatic change in deserts, in addition to opening new research avenues in geomorphology and geoarchaeology.

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“…The former include deterioration of microenvironmental conditions required to sustain varnish development while the latter involve post-depositional modification of varnish through leaching of cations (Pineda et al, 1990;Dragovich, 1998;Dorn, 1998). Evidence tends to suggest that this destruction is triggered by a breach in the varnish cover thus facilitating ingress of salt and moisture into the hitherto protected limestone substrate.…”

Section: Rock Varnishmentioning

confidence: 99%

Limestone weathering in contemporary arid environments: a case study from southern Tunisia

Smith

Warke

Moses

2000

Earth Surf. Process. Landforms

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Weathering features are described from a meteorologically arid area in southern Tunisia. Active weathering is concentrated in topographic lows (pits and pans) that concentrate available moisture and are associated with endolithic and epilithic algae responsible for algal boring, plucking and etching of the limestone substrate. Deposits of gypsum have concentrated through evaporation within hollows and occur as isolated patches of tabular crystals indicating an additional weathering agent characteristic of arid environments. The active development of a complex microkarst and associated salt weathering are combining to destroy linear karstic features such as rillenkarren, widespread case‐hardening and in places patches of iron‐ and manganese‐rich rock varnishes. The complexity of active and inherited weathering features belies the perceived simplicity and lack of weathering opportunities associated with aridity. Instead it focuses on the need to consider the nature of microclimatic conditions at the rock/air interface especially when seeking to define desert weathering environments. It also highlights the difficulties of interpreting polygenetic landforms and the importance of microscale studies for identifying the impact of contemporary climatic conditions. Copyright © 2000 John Wiley & Sons, Ltd.

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Microchemistry of small desert varnish samples, western New South Wales, Australia

Cited by 10 publications

References 26 publications

Life on the rocks

Life on the rocks

The Rock Varnish Revolution: New Insights from Microlaminations and the Contributions of Tanzhuo Liu

Limestone weathering in contemporary arid environments: a case study from southern Tunisia

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