“…Acidification of temperate rock surfaces results in the dissolution of rock varnish as exemplified by acid fog in Southern California [138] and industrial emissions in Western Australia [139]. In contrast, the reduction of acidity in the Khumbu region of Nepal from deforestation of acid-producing plants had the opposite effect on rock coatings.…”
Section: Anthropogenic Geochemical Impacts On Cold-climate Rock Surfacesmentioning
Conventional scholarship long held that rock fracturing from physical processes dominates over chemical rock decay processes in cold climates. The paradigm of the supremacy of cold-climate shattering was questioned by Rapp’s discovery (1960) that the flux of dissolved solids leaving a Kärkevagge, Swedish Lapland, watershed exceeded physical denudation processes. Many others since have gone on to document the importance of chemical rock decay in all cold climate landscapes, using a wide variety of analytical approaches. This burgeoning scholarship, however, has only generated a few nanoscale studies. Thus, this paper’s purpose rests in an exploration of the potential for nanoscale research to better understand chemical processes operating on rock surfaces in cold climates. Samples from several Antarctica locations, Greenland, the Tibetan Plateau, and high altitude tropical and mid-latitude mountains all illustrate ubiquitous evidence of chemical decay at the nanoscale, even though the surficial appearance of each landscape is dominated by “bare fresh rock.” With the growing abundance of focused ion beam (FIB) instruments facilitating sample preparation, the hope is that that future rock decay researchers studying cold climates will add nanoscale microscopy to their bag of tools.
“…Acidification of temperate rock surfaces results in the dissolution of rock varnish as exemplified by acid fog in Southern California [138] and industrial emissions in Western Australia [139]. In contrast, the reduction of acidity in the Khumbu region of Nepal from deforestation of acid-producing plants had the opposite effect on rock coatings.…”
Section: Anthropogenic Geochemical Impacts On Cold-climate Rock Surfacesmentioning
Conventional scholarship long held that rock fracturing from physical processes dominates over chemical rock decay processes in cold climates. The paradigm of the supremacy of cold-climate shattering was questioned by Rapp’s discovery (1960) that the flux of dissolved solids leaving a Kärkevagge, Swedish Lapland, watershed exceeded physical denudation processes. Many others since have gone on to document the importance of chemical rock decay in all cold climate landscapes, using a wide variety of analytical approaches. This burgeoning scholarship, however, has only generated a few nanoscale studies. Thus, this paper’s purpose rests in an exploration of the potential for nanoscale research to better understand chemical processes operating on rock surfaces in cold climates. Samples from several Antarctica locations, Greenland, the Tibetan Plateau, and high altitude tropical and mid-latitude mountains all illustrate ubiquitous evidence of chemical decay at the nanoscale, even though the surficial appearance of each landscape is dominated by “bare fresh rock.” With the growing abundance of focused ion beam (FIB) instruments facilitating sample preparation, the hope is that that future rock decay researchers studying cold climates will add nanoscale microscopy to their bag of tools.
“…The polygenetic model of varnish formation (Figure 2) combines three types of abiotic processes with budding bacteria as the main agent of Mn and Fe enhancement (Dorn, 1998, 2007, 2009, 2019; Krinsley et al, 2013, 2017). The polygenetic model starts with an abiotic step that allows raw varnish ingredients to attach to surfaces, such as van der Walls force or the presence of cations that can flocculate clays.Figure 2.The polygenetic hypothesis starts with an abiotic step that attaches raw varnish ingredients to surfaces.…”
Section: Testing the Polygenetic Hypothesis Of Varnish Formation Invo...mentioning
Investigators seeking to solve the mystery of rock varnish formation have yet to embrace hypothesis testing. Thus, this paper presents nine tests that assess the validity of the eight hypotheses proposed over the last four decades to explain varnish formation. An almost singular focus on manganese (Mn)-enrichment by many in varnish research may have led to six of the eight hypotheses failing to explain iron (Fe)-enrichment, as well as why clay minerals dominate the composition of rock varnish. Many varnish researchers displayed a sampling bias by collecting samples only from hot and dry deserts; thus, it should be of no surprise that four hypotheses failed a test of explaining varnishes in different climates; five hypotheses failed to explain varnishes in subsurface locations; and seven hypotheses failed to explain differences in varnish growth rates in hot deserts versus wetter locations. In the end, seven of eight proposed hypotheses to explain varnish formation failed more than five tests, any one of which would falsify the hypothesis. Only one hypothesis “passed” all nine tests.
“…Rock art, in the form of petroglyphs and pictograms, is found worldwide and has an undoubtedly immense value as it is considered one of the first forms of expression of ancient societies and the prehistoric precursor to art [1][2][3][4]. As part of the natural landscape, petroglyphs are constantly exposed to anthropogenic and natural weathering processes [5][6][7], but despite this, knowledge regarding preservation and conservation of this valuable cultural heritage is limited.…”
Section: Introductionmentioning
confidence: 99%
“…It is composed of clay minerals and amorphous silica (~70%) in a matrix of poorly crystallized manganese (Mn) and iron (Fe) oxides and hydroxides [17][18][19]. Despite the fact that geochemical aspects of rock varnish have been thoroughly investigated [19][20][21][22][23][24] and it is believed that its primary source of material is airborne dust, there is an ongoing debate about the exact process of formation and specifically whether or not microorganisms are involved in this process [5,25,26]. In a recent study, Lingappa et al [27] proposed a new hypothesis for varnish formation.…”
Petroglyph sites exist all over the world. They are one of the earliest forms of mankind’s expression and a precursor to art. Despite their outstanding value, comprehensive research on conservation and preservation of rock art is minimal, especially as related to biodeterioration. For this reason, the main objective of this study was to explore the factors involved in the degradation of petroglyph sites in the Negev desert of Israel, with a focus on biodegradation processes. Through the use of culture-independent microbiological methods (metagenomics), we characterized the microbiomes of the samples, finding they were dominated by bacterial communities, in particular taxa of Actinobacteria and Cyanobacteria, with resistance to radiation and desiccation. By means of XRF and Raman spectroscopies, we defined the composition of the stone (calcite and quartz) and the dark crust (clay minerals with Mn and Fe oxides), unveiling the presence of carotenoids, indicative of biological colonization. Optical microscopy and SEM–EDX analyses on thin sections highlighted patterns of weathering, possibly connected to the presence of biodeteriorative microorganisms that leach the calcareous matrix from the bedrock and mobilize metal cations from the black varnish for metabolic processes, slowly weathering it.
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