Biogenic Crust Research Articles

Spatiotemporal analysis of dune stabilization in the Kyzylkum and Karakum sandy deserts

Sand seas and dune bedforms are climatic chronicles that have a wide range of scientific meanings. The Karakum and Kyzylkum sand seas in Central Asia span ∼500,000 km2, among the largest sand seas on Earth; yet, very little is known about their emergence and stabilization. Further, the internationally accessible literature lacks comprehensive studies on the interactions between contemporary climate and dune morphodynamics for this region. In this study, we applied the conventional approach for examining wind data—Fryberger’s drift equations and the latest Copernicus ERA5 wind reanalysis model—to demonstrate that the Karakum and Kyzylkum deserts had (and continue to have) low-energy environments during 1950–2019. Time-series multidimensional raster analysis and data mining indicated that 93% of surveyed desert areas were subjected to low-energy wind conditions during the last 70 years. The decrease in wind energy was further confirmed using the partitioning around medoids (PAM) unsupervised machine-learning clustering method and Getis-Ord Gi* statistics. Such an environmental setting promotes plant growth and biogenic crust development, and strengthens dune stability across the deserts. Furthermore, the results suggested that the spatial patterns of active dune morphologies (e.g., complex barchanoid ridges and overlaying superimpositions) were closely linked to the drift direction, power, and variability of contemporary winds, whereas stabilized aeolian formations (e.g., distinct formations of complex and compound vegetated linear dunes) indicated debatable disassociations. The relationship between the recognized orientation of the surveyed dune types and the computed resultant drift direction did not change significantly, suggesting that over time, the winds in these areas have most likely varied in strength, but not in direction. The calculated drift powers are not sufficient for the formation of registered mega profiles. Rather, they bolster dunes stability, stressing both deserts as indicative of earlier climatic eras that permitted aeolian sand activity and severe shifts that have initiated their steadiness. This is the first comprehensive study to statistically evaluate the links between the contemporary climate and dune morphologies of the Karakum and Kyzylkum deserts. Our study can serve as a foundation for future studies on climate change, dune mapping, and optically stimulated luminescence (OSL) dating, while offering a broad understanding of the region’s paleo and contemporary environmental systems dynamics.

Pleistocene Caves of Eastern Sicily Coast: Exceptional Archives to Reconstruct the History of the Island’s Biota

The distinctive features and fossil content of some caves from eastern Sicily (San Teodoro, Donnavilla, Fulco, Taormina, Tremilia, Spinagallo), altogether spanning from the middle Pleistocene until the beginning of the Holocene, are discussed. Although dating on vertebrate and/or invertebrate remains is available in few instances, coastal notches and marine terraces correlate with the caves, provide further chronological constraint. The San Teodoro and Spinagallo caves are the best known, whereas the Tremilia cave deserves to be better analysed. Most caves, but not the San Teodoro one (including only terrestrial faunas), testify to the transition from submarine coastal environments (documented by biogenic crusts, borings, shelly sediments), to continental conditions (vertebrate remains of the Paleoloxodon falconeri, Maccagnone and San Teodoro Faunistic Complexes). The fossil register preserved in these cavities represents a source of information useful to (1) reconstruct the palaeogeography of Sicily and its coastline, largely resulting from the interplay between tectonic and sea-level changes linked to climate fluctuations; and (2) the consequent evolution of the terrestrial biota, including the dominance of insular endemic taxa later replaced by species shared with continental Italy, after the establishment of temporary connection through the Messina Strait.

Sand dune vegetation-biocrust interaction as a source of spatial heterogeneity

Abstract Vegetation and biocrust play crucial roles in dune stability and mobility, and their interaction can lead to bistability, temporal oscillations, and hysteresis. We studied a two-dimensional (2D) mathematical model of vegetation and biogenic crust cover dynamics on sand dunes. Under a certain parameter range, the space-independent version of the model exhibited the bi-stability of an oscillatory state and a steady state, and we studied the 2D dynamics of the model under these parameters. The patterns developed by the 2D model showed a high degree of spatial heterogeneity and complexity depending on the initial conditions and on the state type across the front. The results suggest that spatial heterogeneity and complexity can evolve from the intrinsic dynamics between vegetation and biocrust, even without natural geodiversity and spatiotemporal climate fluctuations. In the real world, these two types of intrinsic and extrinsic heterogeneity processes interact such that it is difficult to distinguish between them.

Upper Triassic (Carnian) sponge reef mounds from South Canyon, central Nevada

An important interval for reef evolution occurs in the Triassic Period. However, Late Triassic reefs along the edge of the Panthalassa Ocean receive much less attention than their Tethys region counterpart. To improve our understanding of reef evolution along the Panthalassa, we present a quantitative microfacies analysis to characterize reef facies types from a central Nevada locality. We point counted thin sections to quantitatively assess the relative abundance of reef and interstitial components from six Carnian reef mounds. Reef mound formation occurs at three different stratigraphic intervals. Each interval records a different reef mound size and shape. The oldest stratigraphic interval consists of four separate reef mounds; each mound is approximately 3–12 m wide and 2–4 m high. The second youngest stratigraphic interval consists of one large ~ 10-m wide and 15.5-m high domal reef mound. The third, and youngest, reef mound is smaller in comparison (i.e., 1-m wide and 1.5-m high). We recognize two reef facies types within these reef mounds. Different calcareous sponges, bound together by microproblematica and clotted micrite, form the overall reef framework. We suspect that changes in relative sea level affect the initial colonization, different growth capacities, and overall preservation of the South Canyon reef mounds. When South Canyon reefs are compared to other Panthalassa reefs, it seems that “Wetterstein-type” reef–sponge bindstone facies containing biogenic crusts dominate and corals are less abundant and persist generally in both shallow and deeper water environments. However, significant differences in primary and secondary framebuilder abundances exist due to differences in where the reefs grew in relation to fair-weather wave base (FWWB). Thus, changes in relative sea level may affect the initial colonization, different growth capacities, and overall preservation of reef but water depth may also control the primary and secondary reef builders. Consequently, quantitative assessment of reef ecosystems within a sequence stratigraphic framework undoubtedly facilitates fewer problematic comparisons between reefs but it also enhances our understanding of reef development.

Composition and biostratinomy of sponge-rich biogenic crusts in submarine caves (Aegean Sea, Eastern Mediterranean)

Submarine caves constitute “natural laboratories” for studying biodiversity, community structure and inter-specific relationship in cryptic habitats. These unique systems are of strategic importance to reconstruct the complex biotic processes developed in cavities of skeletal frameworks through geologic time. In this study, the biogenic crusts in two submarine caves of the Aegean Sea were characterized with regards to the organisms involved in their formation. The crusts were examined with the aim to investigate the possible influence of environmental parameters and/or biotic associations on the framework. The walls and ceilings of the studied Fara and Agios Vasilios Caves (Lesvos Island, Greece) are covered mainly with sponges, coralline algae, scleractinian corals, serpulid polychaetes, and bryozoans. Skeletons of these organisms are often cemented together and form extensive crusts of variable thickness. Optical and electron microscopy were utilized to detect quantitative relationships among skeletal components inside the crusts. Coralline algae and corals dominate close to the opening of the caves, whereas serpulids, bryozoans and sponges are the main crust builders in the innermost cave sectors. Among skeletal components, the micrite (microcrystalline calcite) is a minor component of the crusts and consists mainly of an autochthonous fraction, mineralized directly inside the crust through organomineralization processes. Crusts show abundance of endolithic and insinuating sponges, whose organic tissue decay leaves borings filled with spicules. The abundance of sponges competing with carbonatogenetic bacteria for the same living cryptic spaces prevented the development of microbialites. This competition explains the morphological differences between the studied biogenic crusts and the large biostalactites, which are common in other Mediterranean caves (i.e. Sicily, Apulia and Cyprus) and are characterized by only a few sponges but abundant microbialites.

Modeling the bistability of barchan and parabolic dunes

Abstract Extensive areas in arid and semi-arid regions of the world are covered by sand dunes. Sand dunes can be active, semi-active, or stable, depending on, among other factors, their vegetation and biogenic crust covers. Vegetation growth on barchan dunes can induce a transformation to parabolic dunes with long trailing arms pointed upwind. Here we propose a vegetation dynamical model, coupled to a previously suggested 3D continuous dune morphology model (Duran and Herrmann, 2006). The modeled vegetation reduces sand flux, but it is also suppressed by erosion and by sand deposition. The coupling between the model for bare dunes and the model for vegetation growth is performed by reducing the shear stress due to the presence of vegetation. We use the suggested model to study the effect of vegetation on dune formation, concentrating on the previously simulated barchan-parabolic dune transition. Under the action of sufficiently strong unidirectional winds and a low vegetation growth rate, the model results in a barchan dune. When the vegetation growth rate is increased, the barchan dune turns into a stable parabolic dune. When, however, the growth rate is again decreased, the dune becomes an active barchan dune, only with a much lower growth rate, indicating the existence of bistability and hysteresis behavior of barchan and parabolic dunes under similar climatic (vegetation growth rate or precipitation) conditions.

Microdiagnostics of initial pedogenesis on a phosphogypsum dump

This paper presents the results of the study of initial pedogenesis on phosphogypsum dump rocks under dry steppe bioclimatic conditions (Balakovo, Saratov Region, Russia). It was shown that a soil crust about 3 cm thick was formed at the dump surface as a result of natural pedogenic processes over a period of 20-30 years. Such soil crusts act to cement the surface and protect the dump material from deflation and water erosion. The crust was shown to consist of two parts that can be distinguished by morphological features: an upper part (about 2 cm thick) of a more firmly bound material more grey in colour and a lower part (about 1 cm thick) with a looser consistency and lighter colour. The structural organisation is primarily determined by the presence of live roots of grasses and mosses, which is characteristic of a biogenic crust. The two parts of the crust were characterized at both macro- and micro-scales, by use of thin sections and tomographic imagery. The presence of humification features and porosity observed within the crust allowed for the diagnostics of initial pedogenesis.</p><p align="center"> </p><p align="center">

Sand Dune Albedo Feedback

Sand dunes cover substantial parts of desert areas. Fully active dunes are bare, while fixed dunes are stabilized by vegetation and biogenic crust, and the dune activity is affected by the wind. Here we suggest the following atmosphere-sand dune feedback: spatial differences in the dunes’ vegetation and biogenic crust cover lead to differences in albedo as the albedo of bare sand is larger than that of vegetation and biogenic crust. This leads to a higher temperature over the vegetated area, resulting in air flow from the bare dune area to the vegetated dune area, thus increasing the wind activity over the vegetated dune area. In turn, this leads to enhanced stress on the vegetation and enhanced dune activity and thus to a decrease in vegetation. These changes in vegetation cover affect the surface albedo, leading to a change in wind activity. We examined this feedback using an atmospheric general circulation model, Weather Research and Forecasting (WRF), in selected regions of the northwestern Negev Desert and the Sahara/Sahel region, and we show that changes in surface albedo do indeed lead to significantly enhanced wind activity over the lower albedo region. We then incorporated this feedback into a simple vegetated dune model, showing that the multiple states associated with active and fixed dunes can be obtained for a larger range of parameters and that the stables states become more extreme (i.e., the fixed dune state becomes more vegetated and the active dune state becomes less vegetated).

Organisms in wall ecosystems as biomonitors of metal deposition and bioavailability in urban environments.

Vegetated walls are common structures in urban environments, and aiming to test the hypothesis that the biogenic crusts and plant and animal communities inhabiting these vertical surfaces can be more reliable indicators of atmospheric metal deposition than plants or animals inhabiting urban soils, we analyzed the chemical composition of the wall crusts, moss cushions (Tortula muralis) and the shells, soft tissues and feces of the stonework snail Papillifera papillaris collected in three small towns in Tuscany (Central Italy). Crusts and mosses from the same stones or bricks indicated that Cd, Pb, and Zn are the main pollutants released by vehicular traffic, while Hg and Cu probably originate from other sources. The soft tissues of P. papillaris (purged of the gut contents) showed as well higher Cd, Pb, and Zn and lower Hg concentrations at more traffic-affected sites, while data from shells and feces suggested that this species probably ingests large amounts of Al, Cr, Fe, Mn, and Pb, and avoids eating mosses. Most lithophilic elements and Pb are scarcely absorbed in the snail digestive tract and soft tissues mainly accumulate Cd and essential elements such as Cu and Mn. This study definitively confirms the extraordinary Mn bioaccumulation in P. papillaris soft tissues and reports extraordinary Mn levels also in the shell. The shells also contain unusually high Cu, Fe, and Zn concentrations and this bioaccumulation likely remains after death, potentially providing a historical record of the snail exposure to metals over lifetime.

A Giant Underwater, Encrusted Stalactite from the Blue Hole, Lighthouse Reef, Belize, Revisited: a Complex History of Biologically Induced Carbonate Accretion Under Changing Meteoric and Marine Conditions

A late Pleistocene to Holocene submerged and encrusted speleothem exhibits a complex history including a meteoric phase and two marine phases. A combined study using petrography, mineralogy, and inorganic and organic geochemistry, as well as geochronology has shown that phototrophic and heterotrophic biological activity impacted carbonate precipitation during all phases of carbonate accretion. The stalactite formed ca. 30 m below modern sea level at a marginal overhang in the Blue Hole of Lighthouse Reef Atoll. Unlike purely meteoric speleothems, the Belize example consists of a meteoric core, a marine aragonite crust, and a serpulid-micrite-rich outer crust as a result of postglacial flooding of the karst cave. The core of the stalactite has a tufaceous texture, containing algal or microbial remains, and consists entirely of low-magnesium calcite, formed 19.55-10.68 kyr BP. The texture suggests that the stalactite formed at the cave entrance, and, hence, the former cave ceiling had apparently collapsed earlier during the Pleistocene. Oxygen (δ18O) and carbon (δ13C) isotopes across the core suggest a trend towards drier conditions and reduced soil and plant cover after the last glacial maximum. The marine aragonite crust consists of stacked botryoids in which individual crystals up to 700 lm have dark terminations enriched in high-magnesium calcite. This crust accreted from 10.82 to 9.95 kyr BP in warm shallow water during the early Holocene thermal optimum. Carbonate accretion rates were considerable and averaged 125 μm/yr. The crust has a dense, laminated texture on one side and a porous, shrubby texture on the other. The presence of n-C16:1ω5, n-C17:1ω6, and 10Me-C16 fatty acids in the laminated crust suggests that sulfate-reducing bacteria contributed to aragonite formation in an environment that was less open than the formation environment of the porous crust, where these biomarkers are lacking (n-C16:1ω5,n-C17:1ω6) or are less abundant (10Me-C16). Enrichment of 34S and 18O in carbonate-associated sulfate (CAS) relative to seawater sulfate also suggests sulfate reduction during carbonate formation. The greater contribution of heterotrophic processes to aragonite precipitation in the laminated crust is also reflected in δ13C values as low as -1.3%, whereas no such depletion is observed in the aragonite of the porous crust (δ13C values as low as 0.0%). A pronounced isotopic variability and excursions to positive δ13C values as high as +3.5%0 in the inner half of the laminated crust indicate an episodic, local impact of photosynthesis on aragonite precipitation, whereas the lack of such excursions in the porous crust (δ13C values as high as +1.5%0) is again best explained by a more open environment of formation. After a ca. 5 kyr hiatus, from 4.39 kyr BP, a biogenic crust of abundant serpulids and finely crystalline, microbial and detrital carbonate, consisting of high-magnesium calcite and aragonite, accreted on the outer surface of the stalactite. Outermost crust accretion was probably influenced by the inundation of the Lighthouse Reef lagoon that started to shed abundant fine-grained carbonate sediment into the Blue Hole. The stalactite broke off the cave ceiling either before or after the formation of the outermost crust, likely due to seismic movements along the nearby plate boundary. The study demonstrates that like speleothems from the terrestrial realm, submerged stalactites may have had complex histories with great potential as paleoenvironmental archives.

A Coupled Vegetation–Crust Model for Patchy Landscapes

A new model for patchy landscapes in drylands is introduced. The model captures the dynamics of biogenic soil crusts and their mutual interactions with vegetation growth. The model is used to identify spatially uniform and spatially periodic solutions that represent different vegetation-crust states, and map them along the rainfall gradient. The results are consistent extensions of the vegetation states found in earlier models. A significant difference between the current and earlier models of patchy landscapes is found in the bistability range of vegetated and unvegetated states; the incorporation of crust dynamics shifts the onset of vegetation patterns to a higher precipitation value and increases the biomass amplitude. These results can shed new light on the involvement of biogenic crusts in desertification processes that involve vegetation loss.

Exceptional record of submarine cave communities from the Pleistocene of Sicily (Italy)

An Early Pleistocene benthic community, discovered inside the Rumena Cave in NW Sicily, Italy, was studied. Analysis of the community led to the recognition of several encrusting species – notably scleractinians, bryozoans, serpuloideans, cirripeds, foraminifera and brachiopods – and borings mostly referable to the ichnogenus Gastrochaenolites. All fossils detected are typical of the present-day hard-surface submarine cave biota, at both high taxonomic rank and species level. The biogenic crust, restricted to a few sectors of the cave but locally up to few centimetres thick, largely consist of scleractinians, mainly represented by dendrophylliids. Bryozoans and serpuloideans are also present with Hippaliosina depressa and Spiraserpula massiliensis, locally forming multi-layered sheets and dense specimen aggregates, respectively. Basing mostly on the composition of the encrusting community and on morphological/morphometric features of some species, it has been hypothesized that at least part of the cave was blind when the crust formed, possibly at relatively shallow depth in a sheltered setting or, more probably, at higher depths, below the fair weather swell zone. Encrustations and borings on the rocky cave ceiling and on occasional speleothems broken surfaces document subsequent phases of cave submersion/colonization separated by emersion/erosion phases. The importance of the Early Pleistocene fossils of the Rumena Cave for the knowledge of submarine cave communities through time and for the understanding of sea-level variations and the uplift of the area has been remarked.

The effect of wind and precipitation on vegetation and biogenic crust covers in the Sde-Hallamish sand dunes

Vegetation and biogenic crust covers play an important role in sand dune stabilization, yet there is a lack of high temporal and spatial resolution data on sand dune cover. A field experiment, aimed at measuring the dynamics of biogenic crust and vegetation in sand dunes, was conducted at the Sde-Hallamish sand dunes in the northwestern Negev Desert, Israel, from July 2008 to August 2010. The climate of the Sde-Hallamish sand dunes is arid (the mean annual precipitation over the past 13 years is 61 mm), and the dunes are linear and partially stable, mainly due to the presence of biogenic crust and partially due to the presence of vegetation. In July 2008, 10 × 10 m plots on the four dune habitats (crest, interdune, north slope, and south slope) were treated as follows: (i) removal of vegetation and biogenic crust, (ii) removal of biogenic crust only, (iii) removal of vegetation only, (iv) partial removal of biogenic crust and vegetation, and (v) control plot. The surface coverage of sand, biogenic crust, and vegetation was monitored on a monthly basis, using a remote-sensing technique especially developed for the Sde-Hallamish sand dunes. It was found that strong wind events, with durations of several days, accounted for the coverage changes in biogenic crust and vegetation. The response to precipitation was much slower. In addition, no rehabilitation of biogenic crust and vegetation was observed within the experiment time period. The changes in biogenic crust cover were not necessarily related to changes in dune dynamics, since often an increase in biogenic crust cover is a result of wind erosion that exposes old crust that was buried under the sand; wind hardly erodes biogenic crust at all due to its high durability to wind action. The Sde-Hallamish dunes seem to have become more active as a result of a prolonged drought during the past several years. The field experiment reported here indicates that biogenic crust cover exhibits large seasonal variations that are not necessarily related to the growth of new crust but rather to the exposure of old buried crust.

Land-use change and land degradation in Turkmenistan in the post-Soviet era

The Central Asian Newly Independent States have experienced dramatic political and economic changes over the last three decades. Despite these changes, significant areas of the drylands in this region have not been studied since the 1980s. Landsat images acquired before and after the collapse of the Soviet Union, were analyzed to evaluate land-use/land-cover changes and desertification processes in northern Turkmenistan. Vegetation and crust indices, albedo, and spectral mixture analysis, supplemented by field work, were applied to estimate the long-term degradation/re-growing of vegetation cover.The major land-use change identified was an 86% increase in irrigated agricultural areas, equivalent to a loss of about 4500 km2 previously available for natural pastures. Pastures adjacent to the irrigated (and populated) areas were not affected, and in many places, increased vegetation cover was observed. The main degradation processes in these pastures are flooding and technogenic desertification; both occur around man-made structures. Remote pastures have experienced a higher degree of vegetation degradation, mainly due to the development of soil biogenic crust. These observations emphasize the controversy and variability of land degradation processes in this region: distant pastures show a degradation trend, while closer to populated areas, there are signs of rehabilitation.

Biogenic crust dynamics on sand dunes

Sand dunes are often covered by vegetation and biogenic crusts. Despite their significant role in dune stabilization, biogenic crusts have rarely been considered in model studies of dune dynamics. Using a simple model, we study the existence and stability ranges of different dune-cover states along gradients of rainfall and wind power. Two ranges of alternative stable states are identified: fixed crusted dunes and fixed vegetated dunes at low wind power; and fixed vegetated dunes and active dunes at high wind power. These results suggest a crossover between two different forms of desertification.

SERPULID-FRUTEXITES ASSEMBLAGE FROM SHADOW-CRYPTIC ENVIRONMENTS IN JURASSIC MARINE CAVES, BETIC CORDILLERA, SOUTHERN SPAIN

In the Middle–Upper Jurassic boundary of the External Subbetic, there are abundant discontinuities with neptunian dikes and sills composed of Callovian–lower Tithonian deposits. In cavities developed on a slope with escarpments, cryptobiontic communities were preserved in life position. These cavities were excavated beneath a hardground covering the upper surface of Bathonian oolitic limestones deposited in very shallow pelagic carbonate platforms. The biogenic crusts are composed mainly of serpulids and Frutexites—laminated dendrolitic microstructures—and, secondarily, by sessile foraminifera. The serpulids were pioneer organisms during colonization of the walls of small cavities in stressed shadowcryptic environments. Serpulid aggregates then grew downward from the top walls of the cavities. The colonization of serpulid tubes was mainly after the death of organisms, first by microborers, secondly by Frutexites, and later by sessile foraminifera. The preferential colonization of these cryptic environments by serpulids can be interpreted as due to possible photophobic behavior and or the possibility of avoiding space competition or predation.

Biogenic soil crusts and soil depth: a long-term case study from the Central Negev desert highland

Wind-blown soil degradation is a major problem in arid regions. Biogenic soil crust consists of a dense growth of many small organisms covering bare desert soil surfaces in arid regions worldwide. These organisms perform essential services in the ecosystem, for example, soil surface stabilization and carbon and nitrogen fixation. A unique service provided by biogenic crusts is the incorporation of large quantities of deposited atmospheric particles, leading to a significantly enhanced rate of increase in soil depth in windy and arid environments. A long-term study (over 42 months) was conducted to investigate the contribution of a biogenic crust to the accumulation of atmospheric particles in an arid zone. Undisturbed and treated biogenic crusts were studied for their capacity to incorporate deposited particles. Atmospheric particles were found to accumulate on marble dust collectors at a rate of 120 g m−2 year−1 and on sterilized crust at a rate of 208 g m−2 year−1, while the accumulation rate on live, intact crusts was 277 g m−2 year−1, suggesting a soil depth accretion rate on an undisturbed biogenic crust of 10 mm every 33 years. Maintenance of a healthy biogenic crust in dry land environments should, therefore, be a major consideration for improving soil quality and increasing soil depth in arid regions.

Quantitative estimation of land cover structure in an arid region across the Israel–Egypt border using remote sensing data

The clearly visible border between the Israeli Negev and the Egyptian Sinai in remote sensing imagery is a very interesting phenomenon that has long been studied. The widely accepted explanation to this observation is a viewpoint of anthropogenic impacts on the arid environmental ecosystem across the border. In order to examine the validity of this viewpoint, three methods were employed in this study to determine the quantitative structure of main land cover patterns (biogenic crust, bare sand, vegetation and playa) in the arid region: field observation, measurement on aerial photograph, and analysis of vegetation cover changes on Landsat Thematic Mapper (TM) and SPOT images. Field observation on the Israeli side indicated that vegetation covers ∼16% of the ground, biogenic crust ∼69%, sand ∼12% and playa 3%. Evidence from aerial photograph supported a sharp contrast of vegetation cover across the border, with ∼17% on the Israeli side and ∼6% on the Egyptian side. Analysis of the available TM/SPOT images indicated a high vibration of seasonal vegetation changes in the region. The Israeli side had a vegetation cover rate ranging from above 18% in the growing season and below 5% in the dry months. The rate on the Egyptian side changes from less than 2% in the dry season to ∼5% in the growing season. Therefore, it is reasonable to estimate surface composition structure of the region as follows: vegetation, biogenic crust, bare sand and playa account for 5–18%, 71–84%, 7.5% and 3.5%, respectively, on the Israeli side, and 2–5%, 12.5%, 79–82% and 3.5% on the Egyptian side, depending on the season. This estimate of land cover structure has been successfully used to model land surface temperature differences across the border, in order to understand arid ecosystem evolution in the region.

The reefal margin and slope of a Middle Triassic carbonate platform: the Latemar (Dolomites, Italy)

The Latemar is a mainly aggrading platform, but shows repeated backstepping during its entire development. The behaviour of the slope does not reflect accommodation changes and lateral consistencies of the lagoonal interior; the Latemar contemporaneously reveals different, even contrasting depositional characteristics. The slope of the late stage platform evolution corresponds at least partially to the “base-of-slope apron” model. Controlling factors on slope evolution are of tectonic (proximity of the Stava Line) and autocyclic (repeated oversteepening) nature. Other factors are insignificant and/or overprinted. The reef-facies at Latemar reveals a complex facies pattern; it varies along and across the margin and is rich in encrusting sponges, corals, biogenic crusts and “Microproblematica”. Some biota or fossil assemblages—e.g. foraminifers (Abriolina mediterranea, Turriglomina scandonei) or “Tubiphytes” multisiphonatus thrombolites—have not been described in the Dolomites before. Biostratigraphic evidence from the uppermost reef-facies confirms a mainly Anisian age of the outcropping platform interior.

Ground temperature measurement and emissivity determination to understand the thermal anomaly and its significance on the development of an arid environmental ecosystem in the sand dunes across the Israel–Egypt border

The Israel–Egypt border region composed of longitudinal sand dunes is a very unique arid environmental ecosystem in the world: the Israeli side with much more vegetation cover has notably higher land surface temperature (LST) during daytime than the Egyptian side where bare sand prevails. In order to understand this thermal anomaly and its scientific significance in the arid environmental ecosystem development, a series of intensive research activities have been conducted in the past several years, including remote sensing analysis and meteorological modeling. In the paper, we present part of the series studies on the issue: the ground temperature measurement and emissivity determination. The region is mainly composed of four basic surface patterns: biogenic crust, bare sand, vegetation and playa (physical crust). Our hypothesis to occurrence of the thermal anomaly is that it is the direct result of the different surface composition structures and ground emissivities on both sides. Results from our ground temperature measurements during 1997–1998 validate the hypothesis of a significant LST difference existing among the main surface patterns of the region. Biogenic crust covering 72% on the Israeli side and only about 12% on the Egyptian side has an average kinetic surface temperature of above 3°C higher than bare sand. Emissivity of the two most important surface patterns also presents a significant difference. Biogenic crust has an average emissivity ranging from 0.9671 at low temperature to 0.9725 at high temperature. Bare sand occupying above 80% of the surface on the Egyptian side and only about 7% on the Israeli side has an average emissivity between 0.9435 and 0.9543. On the basis of the ground temperature measurements, we use the estimated surface cover percentage to factor the emissivity for a simple simulation of average LST on both sides, which results in an outcome that strongly support the explanation of the thermal anomaly in the border region. Since biogenic crust that covers most surface of the region plays important functions in arid ecosystem development and is common in several deserts such as north Africa and central Australia, our documentation of its surface temperature change and determination of its emissivity, which have not been seen in the literature, will provide valuable scientific basis for other studies on arid environmental ecosystems.