Microbial signatures in sabkha evaporite deposits of Chott el Gharsa (Tunisia) and their astrobiological implications

This study investigates the geomicrobiological potential of Upper Pleistocene evaporite deposits of the Chott el Gharsa, a wide continental sabkha in southern Tunisia. Organic and inorganic-derived biosignatures are mostly contained in microcrystalline, laminated gypsum lithofacies consisting of light/dark alternations of concordant laminae, which have precipitated from high salt concentrated waters. These biosignatures include mineralized microbial-interpreted morphologies, such as mucilage, rods, and microfibers, and dumbbell morphologies in the hollow cores of dolomite crystals that are associated with sulfates. Mineral products that are induced by microbial activity and their organic compounds lead to the formation of lenticular-shaped gypsum crystals, with a high length/width ratio, dolomite precipitation and formation of pyrite framboids. Morphological and structural aspects of these biosignatures, and their composition, in laminated, dolomite-rich sulfate deposits could be detected through microscopic investigations and micro-analyses performed by the instrumentation that is planned for ongoing Mars sample return missions.     

Interpreting the role of proximity on Industrial District competitiveness using a complexity science-based view and Systems Dynamics simulation

The paper investigates how proximity affects Industrial District competitiveness. We adopt the complexity theory by analyzing the influence of the proximity on the Industrial District adaptive capacity. Our argument in fact is that the more adaptive the Industrial District, the more the competitive success. Based on the complexity theory, we identify the structural features that allow Industrial District adaptation and their best values. Then, by developing a computational model based on the Systems Dynamics, we conduct a simulation analysis to evaluate the influence of proximity on the values of Industrial District structural features affecting its adaptive capacity. Results show that too much proximity is detrimental for the Industrial District competitiveness.     

Endolithic microorganisms from spring mound evaporite deposits (southern Tunisia)

This paper investigates endolithic microorganisms in modern gypsum crusts located in arid and saline areas of southern Tunisia. In arid regions, the endolithic mode of life facilitates the survival of the microorganisms and protects them from extreme environmental conditions. The gypsum crusts are the product of evaporite precipitation atop spring mounds developed at the margins of the Chott el Jerid, a saline lake close to the Algerian border. The early mineral precipitation has prevented the complete degradation of these microorganisms and their metabolic products because of the rapid sealing provided by the gypsum crusts. The spring mound structures of the Chott el Jerid offer an opportunity to study the endolithic communities in evaporite and arid environments. An understanding of where and how life survives in such extreme conditions, and how life signal prints in the rocks may help in search for life in the geological record and for astrobiological purposes.     

Astrobiological significance of the sabkha life and environments of southern Tunisia

In high-salinity and water-scarce environments, such as in hot and dry deserts, species develop adaptive strategies that are necessary for living in such harsh conditions. Continental ephemeral salt lakes (sabkhas) with periodic flooding from subsurface groundwater followed by high salt concentrations, such as the ones of the northern Africa Chotts, rank among the geological settings wherein the combined effect of salt concentration and fluctuation of water availability make the environment unstable and can thereafter lead to extreme changes. The present study investigates the continental sabkha environments of southern Tunisia, in which ecological niches (i.e. water and salt precipitates, including halite, gypsum, and dolomite) host microbial life. Halophilic microorganisms can be trapped in the extensive saline crusts of halite and gypsum, which can be regarded as the first step of their delivery to the fossil record. The study of halophiles can provide clues for the understanding of life strategies in extreme terrestrial environments, such as sabkhas, which are potential good terrestrial analogs for evaporite-bearing Martian deposits.     

A new implementation of narrowband interference detection,characterization, and mitigation technique for a software-defined multi-GNSS receiver

Due to the very low power of satellite signals when reaching the earth’s surface, global navigation satellite system receivers are vulnerable to various types of radio frequency interference, and, therefore, countermeasures are necessary. In the case of a narrowband interference (NBI), the adaptive notch filtering technique has been extensively investigated. However, the research on the topic has focused on the adaptation of the notch frequency, but not of the notch width. We present a fully adaptive solution to counter NBI. The technique is capable of detecting and characterizing any number of narrow interfered bands, and then optimizing the mitigation process based on such characterization, namely the estimates of both interference frequency and width. Its full adaptiveness makes it suitable to cope with the unpredictable and diverse nature of unintentional interfering events. In addition to a thorough performance evaluation of the proposed method, which shows its benefits in terms of signal quality improvement, an analysis of the impact of different NBI profiles on GPS L1 C/A and Galileo E1 is also conducted.     

Continental evaporites and the search for evidence of life on Mars

Continental evaporites are deposits that originate from the evaporation of saline waters in the low areas of saline lakes from all continents, except Europe, and mainly consist of chloride, sulphate and potash minerals. In recent years, the discovery on the Martian surface of hydrated salt minerals, including sulphates and chlorides, interpreted as deriving from the desiccation of preexisting large bodies of water, such as lakes, has provided further convincing evidence of liquid water activity on the surface of Mars and, consequently, it has reinforced the plausibility of finding life. Because evaporites require short‐term aqueous processes for their formation, they can trap and preserve over geologic times a biological record made up of halophilic extremophiles—such as microalgae, bacteria, and their remains—that recent research on Earth has shown to be characterized by unexpectedly high biodiversity. This record may consist of varying types of fossils, including morphological fossils, chemofossils and biominerals. As a consequence, continental evaporite environments and their saline deposits are now a primary target for the near future astrobiology missions devoted to the search for fossil Martian life. Lacustrine evaporite deposits and minerals have, therefore, been identified as primary targets for the NASA–ESA joint programme of the Mars sample return, planned for the end of the current decade. Copyright © 2011 John Wiley & Sons, Ltd.