Typical Crust Research Articles

Environmental determinants of biocrust carbon fluxes across Europe: possibilities for a functional type approach

Due to the well-known importance of biocrusts for several ecosystem properties linked to soil functionality, we aim to go deeper into the physiological performance of biocrusts components. Possible functional convergences in the physiology of biocrust constituents would facilitate the understanding of both species and genus distributional patterns and improve the possibility of modelling their response to climate change. We measured gas exchange in the laboratory under controlled conditions of lichen- and moss-dominated biocrusts from four environmentally different locations in Europe. Field data were used to determine the natural hydration sources that drive metabolic activity of biocrusts. Our results show different activity drivers at the four sites. Within site analyses showed similar C fixation for the different crust types in the three sites without hydric stress whilst light use related parameters and respiration at 15 °C were similar in the between sites analyses. There were significant differences in water relations between the biocrusts types, with moss-dominated crusts showing higher maximum and optimum water contents. The functional type approach for biocrusts can be justified from a physiological perspective when similar values are found in the within and between site analyses, the latter indicating habitat independent adaptation patterns. Our multi-site analyses for biocrusts functional performance provide comparisons of C fluxes and water relations in the plant-soil interface that will help to understand the adaptation ability of these communities to possible environmental changes.

Ecophysiological characterization of early successional biological soil crusts in heavily human-impacted areas

Abstract. Ecophysiological characterizations of photoautotrophic communities are not only necessary to identify the response of carbon fixation related to different climatic factors, but also to evaluate risks connected to changing environments. In biological soil crusts (BSCs), the description of ecophysiological features is difficult, due to the high variability in taxonomic composition and variable methodologies applied. Especially for BSCs in early successional stages, the available datasets are rare or focused on individual constituents, although these crusts may represent the only photoautotrophic component in many heavily disturbed ruderal areas, such as parking lots or building areas with increasing surface area worldwide. We analyzed the response of photosynthesis and respiration to changing BSC water contents (WCs), temperature and light in two early successional BSCs. We investigated whether the response of these parameters was different between intact BSC and the isolated dominating components. BSCs dominated by the cyanobacterium Nostoc commune and dominated by the green alga Zygogonium ericetorum were examined. A major divergence between the two BSCs was their absolute carbon fixation rate on a chlorophyll basis, which was significantly higher for the cyanobacterial crust. Nevertheless, independent of species composition, both crust types and their isolated organisms had convergent features such as high light acclimatization and a minor and very late-occurring depression in carbon uptake at water suprasaturation. This particular setup of ecophysiological features may enable these communities to cope with a high variety of climatic stresses and may therefore be a reason for their success in heavily disturbed areas with ongoing human impact. However, the shape of the response was different for intact BSC compared to separated organisms, especially in absolute net photosynthesis (NP) rates. This emphasizes the importance of measuring intact BSCs under natural conditions for collecting reliable data for meaningful analysis of BSC ecosystem services.

Ecophysiological properties of three biological soil crust types and their photoautotrophs from the Succulent Karoo, South Africa

Background and AimsBiological soil crusts cover about one third of the terrestrial soil surfaces in drylands, fulfilling highly important ecosystem services. Their relevance to global carbon cycling, however, is still under debate.MethodsWe utilized CO2 gas exchange measurements to investigate the net photosynthetic response of combined cyanobacteria/cyanolichen-, chlorolichen- and moss-dominated biocrusts and their isolated photoautotrophic components to light, temperature, and water. The results were compared with field studies to evaluate their compatibility.ResultsDifferent biocrust types responded similarly, being inhibited by limited and excess water, saturated by increasing light intensities, and having optimum temperatures. Cyanobacteria/cyanolichen-dominated biocrusts reached their water optimum at lowest contents (0.52–0.78 mm H2O), were saturated at highest light intensities, and had a comparably high temperature optimum at 37 °C. Chlorolichen-dominated crusts had a medium water optimum (0.75–1.15 mm H2O), medium saturating light intensities and a moderate temperature optimum of 22 °C. Moss-dominated biocrusts had the highest water optimum (1.76–2.38 mm H2O), lowest saturating light intensities, and a similar temperature optimum at 22 °C. Isolated photoautotrophs responded similar to complete crusts, only isolated moss stems revealed much lower respiration rates compared to complete crusts.ConclusionsIn addition to their overall functional similarities, cyanobacteria/cyanolichen-dominated biocrusts appeared to be best adapted to predicted climate change of increasing temperatures and smaller precipitation events, followed by chlorolichen-dominated biocrusts. Moss-dominated biocrusts needed by far the largest amounts of water, thus likely being prone to anticipated climate change.

Crustal structure of the conjugate Equatorial Atlantic Margins, derived by gravity anomaly inversion

Abstract The crustal structure of the Equatorial Atlantic conjugate margins (South America and West Africa) has been investigated using 3D gravity anomaly inversion, which allows for (1) the elevated geothermal gradient of the lithosphere following rifting and break-up and (2) magmatic addition to the crust during rifting and break-up. It is therefore particularly suitable for the analysis of rifted margins and their associated ocean basins. Maps of crustal thickness and conjugate-margin stretching, derived from gravity anomaly inversion, are used to illustrate how the Equatorial Atlantic opened as a set of stepped rift-transform segments, rather than as a simple orthogonal rifted margin. The influence of the transform faults and associated oceanic fracture zones is particularly clear when the results of the gravity anomaly inversion are combined with a shaded-relief display of the free-air gravity anomaly. A set of crustal cross-sections has been extracted from the results of the gravity inversion along both equatorial margins. These illustrate the crustal structure of both rifted-margin segments and transform-margin segments. The maps and cross-sections are used to delineate crustal type on the margins as (1) inboard, entirely continental, (2) outboard, entirely oceanic and (3) the ocean–continent transition in between where mixed continental and magmatic crust is likely to be present. For a given parameterization of melt generation the amount of magmatic addition within the ocean–continent transition is predicted by the gravity inversion. One of the strengths of the gravity-inversion technique is that these predictions can be made in the absence of any other directly acquired data. On both margins anomalously thick crust is resolved close to a number of oceanic fracture zones. On the South American margin we believe that this thick crust is probably the result of post-break-up magmatism within what was originally normal-thickness oceanic crust. On the West African margin, however, three possible origins are discussed: (1) continental crust extended oceanwards along the fracture zones; (2) oceanic crust magmatically thickened at the fracture zones; and (3) oceanic crust thickened by transpression along the fracture zones. Gravity inversion alone cannot discriminate between these possibilities. The cross-sections also show that, while ‘normal thickness’ oceanic crust ( c. 7 km) predominates regionally, local areas of thinner ( c. 5 km) and thicker ( c. 10 km) oceanic crust are also present along both margins. Finally, using maps of crustal thickness and thinning factor as input to plate reconstructions, the regional palaeogeography of the Equatorial Atlantic during and after break-up is displayed at 10 Ma increments.

Postseafloor Spreading Volcanism in the Central East South China Sea and Its Formation Through an Extremely Thin Oceanic Crust

AbstractP wave velocity models were obtained by forward and inverse modeling from 38 ocean bottom seismometers deployed in the central East subbasin of the South China Sea (SCS). Four types of crust have been defined: (a) thin oceanic crust (<5 km), (b) typical oceanic crust (5–6 km), (c) thick oceanic crust hosting postspreading volcanoes (>6 km) with significant intrusive roots, and (d) thick oceanic crust with enhanced spreading features (>6 km) but without significant roots. Within the central East subbasin, the thin oceanic crust, only identified inside an 80 km wide zone, is located within an overall 150 km wide domain characterized by N055° seafloor spreading trends. The postspreading volcanoes were formed during a N‐S tensional episode around 6–10 Ma, several millions of years after seafloor spreading ceased in the SCS. Seafloor spreading (N055° and N145°) and postspreading (N000° and N090°) features are observed in the morphology of some of these volcanoes. The rupture of the brittle thin oceanic crust was focused where the crust was the weakest, i.e., at the intersection of the extinct spreading ridge with former fracture zones. From geological and geophysical arguments, we suggest that the postspreading volcanism might have been influenced by the Hainan plume activity through a buoyancy‐driven partial melting mechanism.

Surface mineral crusts: a potential strategy for sampling for evidence of life on Mars

AbstractSurface mineral crusts on Earth are highly diverse and usually, contain microbial life. Crusts constitute an attractive target to search for life: they require water for their formation, they efficiently entrap organic matter and are relatively easy to sample and process. They hold a record of life in the form of microbial remains, biomolecules and carbon isotope composition. A miniaturized Raman spectrometer is included in the ExoMars 2020 payload as it is sensitive to a range of photosynthetic pigments. Samples from the Haughton Impact Structure, Canadian High Arctic and others, shows the preservation of pigments in a range of crust types, especially supra-permafrost carbonate crusts and cryptogamic crusts. The Raman spectral signatures of these crusts are shown along with biomarker analysis to showcase these techniques prior to the ExoMars 2020 mission. Carotenoids and other photoprotective microbial pigments are identified in the Haughton surface crusts using Raman spectroscopy. Gas chromatography-mass spectrometry analyses show a distribution of fatty acids which are most likely from a cyanobacterial source. The successful demonstration of these analyses in the Haughton Impact structure shows the biosignature of surface mineral crusts can be easily extracted and provides an excellent target for sampling evidence of life on Mars.

Photoautotrophic organisms control microbial abundance, diversity, and physiology in different types of biological soil crusts

Biological soil crusts (biocrusts) cover about 12% of the Earth’s land masses, thereby providing ecosystem services and affecting biogeochemical fluxes on a global scale. They comprise photoautotrophic cyanobacteria, algae, lichens and mosses, which grow together with heterotrophic microorganisms, forming a model system to study facilitative interactions and assembly principles in natural communities. Biocrusts can be classified into cyanobacteria-, lichen-, and bryophyte-dominated types, which reflect stages of ecological succession. In this study, we examined whether these categories include a shift in heterotrophic communities and whether this may be linked to altered physiological properties. We analyzed the microbial community composition by means of qPCR and high-throughput amplicon sequencing and utilized flux measurements to investigate their physiological properties. Our results revealed that once 16S and 18S rRNA gene copy numbers increase, fungi become more predominant and alpha diversity increases with progressing succession. Bacterial communities differed significantly between biocrust types with a shift from more generalized to specialized organisms along succession. CO2 gas exchange measurements revealed large respiration rates of late successional crusts being significantly higher than those of initial biocrusts, and different successional stages showed distinct NO and HONO emission patterns. Thus, our study suggests that the photoautotrophic organisms facilitate specific microbial communities, which themselves strongly influence the overall physiological properties of biocrusts and hence local to global nutrient cycles.

生物土壤结皮碳释放对水热因子的响应

在室内控制条件下，以腾格里沙漠东南缘1964年人工固沙植被区藻类、混生和藓类结皮为对象，研究了3个温度梯度(15℃、25℃和35℃)和7个水分梯度(3%、5%、10%、15%、20%、25%和30%质量含水量)条件下其碳释放特征。在相同水分条件下，BSCs和流沙呼吸速率随着温度的增加而增加，35℃时BSCs和流沙呼吸速率达到最大值。藓类结皮的呼吸速率显著高于其他土壤类型土壤呼吸。藓类结皮Q10为1.40~3.17，藻类结皮为0.81~3.07，混生结皮为0.55~3.84，流沙为1.19~2.16。BSCs类型、水分和温度显著影响BSCs碳释放量(P < 0.001)。水分含量较高的条件下，藻类和混生结皮的呼吸速率受到了明显抑制，而对藓类结皮的呼吸速率影响不显著。 The carbon release of different types of biological soil crusts (BSC) covered soil was measured under different temperatures condition (15˚C, 25˚C and 35˚C) and different soil water content conditions (3%, 5%, 10%, 15%, 20%, 25% and 30%) in fixed sand dunes at the re-vegetated area in Tengger Desert, Northern China. In the same soil water content condition, the carbon release rate of BSCs and sand were increased with temperature increasing, the highest carbon release rate occurred at 35˚C. The carbon release rate of moss crust was significantly higher than other soil types. Q10 value of moss crust was 1.40 - 3.17, algae crust was 0.81 - 3.07, mixed crust was 0.55 - 3.84 and sand was 1.19 - 2.16. BSCs types, soil water content and temperature were significantly affected on carbon release rate (P < 0.001). The results showed that the respiration rate of the algal crust and mixed crust were significantly restrained by higher soil water content; however, moss crust was not significantly influenced.

МОРФОСТРУКТУРНЫЙ АНАЛИЗ ПРИ РЕШЕНИИ ГЕОЛОГИЧЕСКИХ ПРОБЛЕМ ВОСТОКА АЗИИ, "Геоморфология"

Окраинные моря Западно-Тихоокеанской зоны перехода континент-океан рассматриваются как вихревые структуры. В Япономорском регионе (ЯР) применение линеаментного анализа (комплекса геоморфологических, геологических и геофизических методов) позволило выявить в континентальной части Япономорского региона рудоконтролирующие зоны (эндогенного оруденения, месторождений алмазов и др.), скрытых разломов фундамента и магматических очаговых структур, а на дне Японского моря разломных структур. В регионе: 1) выявлены три литосферные вихревые морфоструктуры - Япономорская (ЯМ), Нижнеамурская (НА) и Сунляо (СЛ), 2) выделены два структурных этажа: мантийный и литосферный, включающие, соответственно, тектонический каркас и вихревые структуры, тесно связанные с подстилающей астеносферой. ЯМ морфоструктура отражает процесс раскрытия Японского моря - как результат взаимодействия Евроазиатской и Тихоокеанской плит; НА - соответствует межгорная впадина, с которой на западе сочленяется нефтегазоносная депрессия Сунляо вихревого типа. В ЯР развиты нефтегазоносные мезокайнозойские осадочные бассейны, представляющие литосферные вихри. Линеаментный анализ позволит по-новому прогнозировать характер миграции углеводородов в земной коре и выявлять предполагаемые места их скопления. Этот метод может быть использован в процессе подготовительного этапа при исследовании нефтегазоносности Западно-Тихоокеанских окраинных морей, а также Арктических бассейнов.

Evidence of synsedimentary microbial activity and iron deposition in ferruginous crusts of the Late Cenomanian Utrillas Formation (Iberian Basin, central Spain)

Ferruginous sandstones and crusts are prominent sedimentary features throughout the continental (braided)-coastal siliciclastic (estuarine-tidal) wedges of the Late Cenomanian Utrillas Formation in the Iberian Basin. Crust types recognized are: Ferruginous sandy crusts (Fsc) with oxides-oxyhydroxides (hematite and goethite) concentrated on sandstone tops presenting a fibro-radial internal structure reminding organic structures that penetrate different mineral phases, suggesting the existence of bacterial activity in crust development; Ferruginous muddy crusts (Fmc) consisting of wavy, laminated, microbial mats, being composed mainly of hematite. On the other hand, a more dispersed and broader mineralization included as Ferruginous sandstones with iron oxides and oxyhydroxides (hematite and goethite) representing a limited cement phase on these sediments. The presence of microbial remains, ferruginous minerals, Microbially-induced sedimentary structures, microbial laminites and vertebrate tracks preserved due to the presence of biofilms suggest firstly a direct evidence of syn-depositional microbial activity in these sediments; and, secondly, that iron accumulation and ferruginous crusts development occurred immediately after deposition of the host, still soft sediments. Ferruginous crusts cap sedimentary cycles and they represent the gradual development of hard substrate conditions, and the development of a discontinuity surface at the top of the parasequence sets, related to very low sedimentary rates; the overlying sediments record subsequent flooding of underlying shallower environments; crusts are, consequently, interpreted as boundaries for these higher-order cycles in the Iberian Basin.

Active Magmatic Underplating in Western Eger Rift, Central Europe

AbstractThe Eger Rift is an active element of the European Cenozoic Rift System associated with intense Cenozoic intraplate alkaline volcanism and system of sedimentary basins. The intracontinental Cheb Basin at its western part displays geodynamic activity with fluid emanations, persistent seismicity, Cenozoic volcanism, and neotectonic crustal movements at the intersections of major intraplate faults. In this paper, we study detailed geometry of the crust/mantle boundary and its possible origin in the western Eger Rift. We review existing seismic and seismological studies, provide new interpretation of the reflection profile 9HR, and supplement it by new results from local seismicity. We identify significant lateral variations of the high‐velocity lower crust and relate them to the distribution and chemical status of mantle‐derived fluids and to xenolith studies from corresponding depths. New interpretation based on combined seismic and isotope study points to a local‐scale magmatic emplacement at the base of the continental crust within a new rift environment. This concept of magmatic underplating is supported by detecting two types of the lower crust: a high‐velocity lower crust with pronounced reflectivity and a high‐velocity reflection‐free lower crust. The character of the underplated material enables to differentiate timing and tectonic setting of two episodes with different times of origin of underplating events. The lower crust with high reflectivity evidences magmatic underplating west of the Eger Rift of the Late Variscan age. The reflection‐free lower crust together with a strong reflector at its top at depths of ~28–30 km forms a magma body indicating magmatic underplating of the late Cenozoic (middle and upper Miocene) to recent. Spatial and temporal relations to recent geodynamic processes suggest active magmatic underplating in the intracontinental setting.

Pb–Pb isotopic systematics of orogenic gold deposits of the Baikal–Patom fold belt (Northern Transbaikalia, Russia) and estimation of the role of neoproterozoic crust in their formation

The paper reports the results of Pb isotope study of several gold deposits of the Russia’s largest metallogenic province of Northern Transbaikalia. Potential sources of the ore material are considered by the example of new and previously published Pb–Pb data on nine deposits and occurrences of different scales. The comparison of Pb–Pb isotope-geochemical characteristics of ores, Paleozoic granitoids, as well as metamorphic pyrite from barren metasedimentary sequences shows that the Neoproterozoic terrigenous–carbonate rocks of the Baikal–Patom fold belt (BPB) served as the main source of lead and other components in the mineral-forming systems of the deposits. Significant variations of Pb isotope ratios typical in general of the considered deposits of the BPB reflect the initial isotopic heterogeneity of Pb source. This heterogeneity is caused by mixing of two geochemical types of continental crust during sedimentation: old (Early Precambrian) crust of the Siberian craton with long-term geochemical evolution and newly formed Late Precambrian crust. Pb–Pb data serve in support of the hydrothermal–metamorphogenic hypothesis of the formation of gold deposits of the BPB.

Earth’s crust composition of the Ingul megablock of the Ukrainian Shield (types of crust) and patterns of location of ore mineral resources

Within the Ingul Megablock of the Ukrainian Shield, according to the data of three-dimensional density modeling, at the scale of 1 : 200 000, the thickness of conditionally allocated “granite”, “diorite”, “basalt” layers, which abroad have the name of the upper, middle and lower crust, are determined and their characteristic is given. In relation to the thickness of each layer to the total crust, which is expressed in parts, four types of crust are distinguished: granite, diorite, leuco-basalt, basalt. Since the composition of the Earth’s crust is an important factor in assessing the prospects for minerals, a comparison of the location of the ore deposits of manifestations of hydrothermal and hydrothermal-metasomatic genesis with a real composition scheme is made. It is established that most of the deposits of minerals are confined to blocks of granitic-diorite and diorite types of crust, and the smaller — gravitates to blocks of leuco-basalt and basalt types.

The major tectonic boundaries of the Northern Red Sea rift, Egypt derived from geophysical data analysis

AbstractIn the present study, we have attempted to map the plate boundary between Arabia and Africa at the Northern Red Sea rift region including the Suez rift, Gulf of Aqaba-Dead Sea transform and southeastern Mediterranean region by using gravity data analysis. In the boundary analysis method which was used; low-pass filtered gravity anomalies of the Northern Red Sea rift region were computed. Different crustal types and thicknesses, sediment thicknesses and different heat flow anomalies were evaluated. According to the results, there are six subzones (crustal blocks) separated from each other by tectonic plate boundaries and/or lineaments. It seems that these tectonic boundaries reveal complex structural lineaments, which are mostly influenced by a predominant set of NNW–SSE to NW–SE trending lineaments bordering the Red Sea and Suez rift regions. On the other side, the E–W and N–S to NNE–SSW trended lineaments bordering the South-eastern Mediterranean, Northern Sinai and Aqaba-Dead Sea transform regions, respectively. The analysis of the low pass filtered Bouguer anomaly maps reveals that the positive regional anomaly over both the Red Sea rift and South-eastern Mediterranean basin subzones are considered to be caused by the high density of the oceanic crust and/or the anomalous upper mantle structures beneath these regions whereas, the broad medium anomalies along the western half of Central Sinai with the Suez rift and the Eastern Desert subzones are attributed to low-density sediments of the Suez rift and/or the thick upper continental crustal thickness below these zones. There are observable negative anomalies over the Northern Arabia subzone, particularly in the areas covered by Cenozoic volcanics. These negative anomalies may be attributed to both the low densities of the surface volcanics and/or to a very thick upper continental crust. On the contrary, the negative anomaly which belongs to the Gulf of Aqaba-Dead Sea transform zone is due to crustal thickening (with limited heat flow values) below this region. Additionally in this study, the crustal thinning was investigated with heat flow, magnetic and free air gravity anomalies in the Northern Red Sea rift region. In fact, the crustal thinning of the study area was also proportional to the regions of observable high heat flow values. Finally, our results were found to be well correlated with the topography, free air, aeromagnetic and heat flow dataset profiles crossing most of the study area.

A preliminary study on ore-forming environments of Xianglushan-type iron deposit and the weathering mineralization of Emeishan basalt in Guizhou Province, China

Xianglushan-type iron deposits are one of the new types of iron deposits found in the Weining Area of Western Guizhou. The iron-bearing rock system is a paleo-weathered crustal sedimentary (or accumulating) stratum between the top of the Middle-Late Permian Emeishan basalt formation and the Late Permian Xuanwei formation. Iron ore is hosted in the Lower-Middle part of the rock system. In terms of the genesis of mineral deposit, this type of deposit should be a basalt paleo-weathering crustal redeposit type, very different from marine sedimentary iron deposits or continental weathering crust iron deposits. Based on field work and the analytical results of XRD Powder Diffraction, Electron Probe, Scanner Electron Microscope, etc., the geological setting of the ore-forming processes and the deposit features are illustrated in this paper. The ore-forming environment of the deposit and the Emeishan basalt weathering mineralization are also discussed in order to enhance the knowledge of the universality and diversity of mineralization of the Emeishan Large Igneous Province (ELIP), which may be a considerable reference to further research for ELIP metallogenic theories, and geological research for iron deposits in the paleo-weathering crust areas of the Emeishan basalt, Southwestern, China.

Understanding the tectonic history offshore Southern Gabon with high resolution seismic, gravity and magnetics

Having produced oil since 1957, Gabon has several proven petroleum systems, both onshore and offshore. Over the last decade interest has moved towards the deep offshore area where a number of early exploration wells have been successful in finding hydrocarbons, but also highlighted the need to answer questions about trap formation, source maturation and timing of charge in this new area. Following this exploration trend, and aiming to answer these key questions, a recent 3D broadband seismic survey was acquired in conjunction with shipborne gravity and magnetic data in the southern deep offshore area of Gabon. Understanding the tectonic evolution of the basin and its impact on the petroleum systems, requires the integration of seismic with the concurrently acquired gravity and magnetic data. Potential fields data provide deep crustal information where it may be challenging for seismic to resolve deep geological features, and vice versa for the shallower sedimentary section. One of the key objectives of the potential fields study was to model crustal types and thicknesses for input into basin modelling. Upper and lower crust ratios, as well as the crustal characteristics and processes in the continental-oceanic transition zones, are important for understanding the temperature regimes undergone by potential source and reservoir rocks. Knowing the distribution of lower- or higher-density crust, and zones of higher susceptibility, provides insight into the characteristics and timing of formation/deformation of the crust along the margin.

Metabolic activity duration can be effectively predicted from macroclimatic data for biological soil crust habitats across Europe

Biological soil crusts (BSC) perform several important environmental functions such as soil erosion prevention, soil nutrient enrichment through photosynthesis and nitrogen fixation, and are receiving growing interest due to their importance in some changing habitats with soils under degradation risk. Primary producers within BSC (cyanobacteria, lichens, algae and bryophytes) are all poikilohydric and active only when wet, meaning that knowledge of the period of metabolic activity is essential to understand growth and adaptation to environment. Finding links with macroclimatic factors would allow not only prediction of activity but also the effects of any climate change over these communities. Metabolic activity and microclimate of BSC at four sites across Europe with different soils from semi-arid (Almeria, SE Spain) to alpine (Austria) was monitored during one year using a chlorophyll fluorometer. Local climatic data were also recorded. Mean monthly activity of crust within each site were strongly linked irrespective of crust type whilst, using the data from all sites, highly significant linear relationships (mean monthly values) were found for activity with incident light, air temperature and air relative humidity, and a nonlinear response to rainfall saturating at about 40mm per month. Air relative humidity and air temperature were the best predictors of metabolic activity duration. The links observed are all highly significant allowing climate data to be used to model activity and to gain inferences about the effects of climate change over BSC communities, soil structure and fertility. Linear relationships mean that small changes in the environment will not produce massive alterations in activity. BSC also appear to behave as a single functional group, which is helpful when proposing general management policies for soil ecosystems protection.

Cryostratigraphy and the sublimation unconformity in permafrost from an ultraxerous environment, University Valley, McMurdo Dry Valleys of Antarctica.

The cryostratigraphy of permafrost in ultraxerous environments is poorly known. In this study, icy permafrost cores from University Valley (McMurdo Dry Valleys, Antarctica) were analyzed for sediment properties, ground-ice content, types and distribution of cryostructures and presence of unconformities. No active layer exists in the valley, but the ice table, a sublimation unconformity, ranges from 0 to 60 cm depth. The sediments are characterized as a medium sand, which classifies them as low to non-frost susceptible. CT scan images of the icy permafrost cores revealed composite cryostructures that included the structureless, porous visible, suspended and crustal types. These cryostructures were observed irrespective of ground-ice origin (vapour deposited and freezing of snow meltwater), suggesting that the type and distribution of cryostructures could not be used as a proxy to infer the mode of emplacement of ground ice. Volumetric ice content derived from the CT scan images underestimated measured volumetric ice content, but approached measured excess ice content. A paleo-sublimation unconformity could not be detected from a change in cryostructures, but could be inferred from an increase in ice content at the maximum predicted ice table depth. This study highlights some of the unique ground ice processes and cryostructures in ultraxerous environments.

Comparison of Meniscal Cell-Mediated and Chondrocyte-Mediated Calcification.

Background:Chondrocytes have been traditionally thought to be responsible for calcium crystal deposits within osteoarthritic knees. Increasing recent experimental evidence suggests that menisci may also play a role. However, the calcifying potential of chondrocytes and meniscal cells derived from same OA patients, and the genes associated with meniscal calcification have never been fully examined.Objective:Examine and compare the calcifying potential of articular chondrocytes and meniscal cells derived from same OA patients and identify the calcium crystal type(s) and selected gene expression in OA menisci.Methods:Chondrocytes and meniscal cells were isolated from articular cartilage and menisci of OA patients undergoing total knee arthroplasty. Chondrocyte- and meniscal cell-mediated calcification was examined using both monolayer and micromass culture-based assays. Crustal types were examined with histological staining. Levels of Type X Collagen, MMP-13, and ANKH in OA menisci were examined using immunohistochemistry.Results:Primary human OA meniscal cells produced calcified deposits at a similar rate compared to OA chondrocytes in-vitro. Histological examinations indicate that both BCP crystals and CPPD crystals are present in the meniscal tissue. Type X collagen, MMP-13, and ANKH were found in human OA menisci and their levels increased with OA severity. In addition, type X collagen was co-localized with calcium crystals.Conclusion:These findings suggest that OA meniscal cells have a similar calcifying potential as OA chondrocytes, supporting a pathogenic role of OA menisci in OA.

Nitrogen fixation and diurnal changes of photosynthetic activity in Arctic soil crusts at different development stage

Nitrogen fixation and photosynthesis provided by microbial phototrophs (cyanobacteria and eukaryotic microalgae) are important processes occurring in Arctic soil crusts. Here, we describe and compare these processes in biological soil crusts from Central Svalbard at different stages of development. The gradient from poorly-developed to well-developed soil crusts was accompanied by the changes in biovolume of microbial phototrophs, nitrogenase and photosynthetic activity. The lowest biovolume of microbial phototrophs was detected in poorly-developed soil crusts as a consequence of the initial stage of soil colonization. The biovolume initially increased during the soil crust development but decreased in well-developed lichenized soil crusts. However, nitrogenase activity decreased from poorly to more developed soil crusts. Diurnal courses of photosynthetic activity differed among the soil crust types showing shifts in diurnal minima and maxima; the poorly-developed soil crust reacted faster to changes in temperature and PAR. In spite of different microclimatic conditions during the measurements, temperature was the main factor influencing photosynthetic activity while the effect of PAR was not significant. Higher temperatures led to inhibition of photosynthetic activity and increased energy dissipation, indicating acclimation/adaptation of the soil crust photosynthetic microorganisms to a cold environment.