The nature, distribution and formation of pans in arid zones

Goudie, Andrew; Wells, Gordon

doi:10.1016/0012-8252(94)00066-6

Cited by 157 publications

(111 citation statements)

References 62 publications

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“…The Bolivia sample was collected in the surroundings of the Laguna Verde in the southern part of Bolivia. The salt flats on the Altiplano including Laguna Verde are important dust sources in South America (Goudie and Wells, 1995;Washington et al, 2003).…”

Section: Statistical Evaluation Of Emulsion Measurementsmentioning

confidence: 99%

Ice nucleation efficiency of natural dust samples in the immersion mode

et al. 2016

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Abstract. A total of 12 natural surface dust samples, which were surface-collected on four continents, most of them in dust source regions, were investigated with respect to their ice nucleation activity. Dust collection sites were distributed across Africa, South America, the Middle East, and Antarctica. Mineralogical composition has been determined by means of X-ray diffraction. All samples proved to be mixtures of minerals, with major contributions from quartz, calcite, clay minerals, K-feldspars, and (Na, Ca)-feldspars. Reference samples of these minerals were investigated with the same methods as the natural dust samples. Furthermore, Arizona test dust (ATD) was re-evaluated as a benchmark. Immersion freezing of emulsion and bulk samples was investigated by differential scanning calorimetry. For emulsion measurements, water droplets with a size distribution peaking at about 2 µm, containing different amounts of dust between 0.5 and 50 wt % were cooled until all droplets were frozen. These measurements characterize the average freezing behaviour of particles, as they are sensitive to the average active sites present in a dust sample. In addition, bulk measurements were conducted with one single 2 mg droplet consisting of a 5 wt % aqueous suspension of the dusts/minerals. These measurements allow the investigation of the best icenucleating particles/sites available in a dust sample. All natural dusts, except for the Antarctica and ATD samples, froze in a remarkably narrow temperature range with the heterogeneously frozen fraction reaching 10 % between 244 and 250 K, 25 % between 242 and 246 K, and 50 % between 239 and 244 K. Bulk freezing occurred between 255 and 265 K. In contrast to the natural dusts, the reference minerals revealed ice nucleation temperatures with 2-3 times larger scatter. Calcite, dolomite, dolostone, and muscovite can be considered ice nucleation inactive. For microcline samples, a 50 % heterogeneously frozen fraction occurred above 245 K for all tested suspension concentrations, and a microcline mineral showed bulk freezing temperatures even above 270 K. This makes microcline (KAlSi 3 O 8 ) an exceptionally good ice-nucleating mineral, superior to all other analysed K-feldspars, (Na, Ca)-feldspars, and the clay minerals. In summary, the mineralogical composition can explain the observed freezing behaviour of 5 of the investigated 12 natural dust samples, and partly for 6 samples, leaving the freezing efficiency of only 1 sample not easily explained in terms of its mineral reference components. While this suggests that mineralogical composition is a major determinant of ice-nucleating ability, in practice, most natural samples consist of a mixture of minerals, and this mixture seems to lead to remarkably similar ice nucleation abilities, regardless of their exact composition, so that global models, in a first approximation, may represent mineral dust as a single species with respect to ice nucleation activity. However, more sophisticated representations of ice nucleation by mineral dusts...

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Section: Statistical Evaluation Of Emulsion Measurementsmentioning

confidence: 99%

Ice nucleation efficiency of natural dust samples in the immersion mode

et al. 2016

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“…For inland playas, catchment lithology and weathering processes are the main determinants of salts precipitated in their beds. Unlike coastal depressions, in inland depressions, airborne dust deposition only encompasses a secondary source of salts [3,4].…”

Section: Introductionmentioning

confidence: 99%

“…Both the water input and water on the playa's floor are ephemeral in nature [5,6], resulting in a negative balance between input (through direct rainfall and runoff accumulation) and output (evaporation and deep seepage) of water [3,4]. The extent, frequency and length of inundation are dependent on climatic, hydrologic, geologic and pedogenic conditions [6].…”

Section: Introductionmentioning

confidence: 99%

Ancient to Recent-Past Runoff Harvesting Agriculture in Recharge Playas of the Hyper-Arid Southern Israel

Stavi

Shem-Tov

Ragolsky

et al. 2017

Water

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Recharge playas are prevalent throughout the hyper-arid southern Negev and Arava Valley of Israel. While some of these playas are terminal, others were found to be not absolutely terminal, allowing, under extreme floods, the outlet of water from their beds to a draining, ephemeral channel. Indicators for ancient to recent-past agricultural practicing were recorded for two playas. In one of them, this included the archaeological remains of seven Byzantine-Age stone terraces across the playa bed, indicating ancient runoff harvesting agriculture. In another playa, the agricultural indicator included observations by key informants who reported the cropping of barley and wheat by Bedouin populations until the mid-1990s. This was supported by rare bibliographic sources, reporting the cropping of cereals at this site by Bedouins during the 1930s and 1940s. Agro-hydrological assessments of seven playas and their catchments were conducted, revealing a marginal agronomic potential under the current climatic conditions and only for a small number of them. The results highlight the profound environmental know-how of local populations that inhabited this harsh region. Furthermore, the results coincide with previous studies, which have reported drier climatic conditions at present compared to those in ancient times, and even compared to those during the mid-1990s.

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“…These are called lunette dunes. It has been demonstrated that asymmetries in the shape of these depressions are due to the effect of wind blowing from their concave and rough border towards their convex and smooth border (Goudie & Wells, 1995). The interpretation of V3 as lunette dunes could pertain to the case of Ontario Lacus, since Global Circulation Models (GCMs) predict that regional winds in this region blow from the SSW to the NNE (Tokano, 2008).…”

Section: Unit E: Lunette Dunes ? Evaporitic Deposits ?mentioning

confidence: 99%

Geomorphological significance of Ontario Lacus on Titan: Integrated interpretation of Cassini VIMS, ISS and RADAR data and comparison with the Etosha Pan (Namibia)

Cornet

Bourgeois

Mouëlic

et al. 2012

Icarus

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Ontario Lacus is the largest lake of the whole southern hemisphere of Titan, Saturn's major moon. It has been imaged twice by each of the Cassini imaging systems (Imaging Science Subsystem (ISS) in , Visual and Infrared Mapping Spectrometer (VIMS) in 2007 and RADAR in 2009. We compile a geomorphological map and derive a "hydrogeological" interpretation of Ontario Lacus, based on a joint analysis of ISS, VIMS and RADAR SAR datasets, along with the T49 altimetric profile acquired in December 2008. The morphologies observed on Ontario Lacus are compared to landforms of a semi-arid terrestrial analog, which resembles Titan's lakes: the Etosha Pan, located in the Owambo Basin (Namibia). The Etosha Pan is a flat-floored depression formed by dissolution, under semi-arid conditions, of a surface evaporitic layer (calcretes) controlled by groundwater vertical motions. We infer that Ontario Lacus is an extremely flat and shallow depression lying in an alluvial plain surrounded by small mountain ranges under climatic conditions similar to those of terrestrial semi-arid regions. Channels are seen in the southern part of Ontario Lacus in VIMS and RADAR data, acquired at a 2-years time interval. Their constancy in location with time implies that the southern portion of the depression is probably not fully covered by a liquid layer at the time of the observations, and that they most probably run on the floor of the depression. A shallow layer of surface liquids, corresponding to the darkest portions of the RADAR images, would thus cover about 53 % of the surface area of the depression, of which almost 70 % is located in its northern part. These liquid-covered parts of the depression, where liquid ethane was previously identified, are interpreted as topographic lows where the "alkanofer" raises above the depression floor. The rest of the depression, and mostly its southern part, is interpreted as a flat and smooth exposed floor, likely composed of a thick and liquid-saturated coating of photon-absorbing materials in the infrared. This hypothesis could explain its dark appearance both in the infrared and radar data and the persistence of channels seen on the depression floor over the time. Shorelines are observed on the border of Ontario Lacus suggesting past high-stand levels of the alkanofer table. The analogy with the Etosha Pan suggests that Ontario Lacus' depression developed at the expense of a soluble layer covering the region. Dissolution of this layer would be controlled by vertical motions of the alkanofer table over the time. During flooding events, liquid hydrocarbons covering the depression floor would dissolve the surface layer, increasing progressively the diameter of the depression on geological timescales. During drought episodes, liquid hydrocarbons of the underground alkanofer would evaporate, leading to crystallization of "evaporites" in the pores and at the surface of the substratum, and to the formation of the regional soluble layer. The presence of specific landforms (lunette dunes or evaporites) ...

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The nature, distribution and formation of pans in arid zones

Cited by 157 publications

References 62 publications

Ice nucleation efficiency of natural dust samples in the immersion mode

Ice nucleation efficiency of natural dust samples in the immersion mode

Ancient to Recent-Past Runoff Harvesting Agriculture in Recharge Playas of the Hyper-Arid Southern Israel

Geomorphological significance of Ontario Lacus on Titan: Integrated interpretation of Cassini VIMS, ISS and RADAR data and comparison with the Etosha Pan (Namibia)

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