Using a SPATIAL INS/GNSS MEMS Unit to Detect Local Gravity Variations in Static and Mobile Experiments: First Results.

In this study, we present the feasibility of using gravity measurements made with a small inertial navigation system (INS) during in situ experiments, and also mounted on an unmanned aerial vehicle (UAV), to recover local gravity field variations. The INS operated is the SPATIAL one developed by Advanced Navigation, which has three-axis accelerometers. When the temperature bias is corrected, these types of INS are powerful enough to present the periodic signal corresponding to the solid Earth tides. There is also a clear correlation with the data measured at different altitudes by a CG5 gravimeter. However, these data were recorded on static points, so we also studied the INS in a moving platform on a UAV. Because there are a lot of vibrations recorded by the INS (wind, motor, on-board computer), the GPS and accelerometric data need to be filtered extensively. Once the data are corrected so they do not show thermal bias and low-pass filtered, we take the second derivative of the altitude (GPS) data to find the radial accelerometry of the drone and compare it to the radial accelerometry measured directly by the INS, in order to isolate the accelerometric signal that is related to the area that is being studied and the altitude. With a high enough precision, this method could be used to obtain the gravity variations due to the topography and density variations in the ground.

The use of copper isotopes for understanding metal transfer mechanisms within the continuum mine-river-dam (Huelva Region, Spain).

Mining areas and in particular those containing massive sulfides have left a heavy environmental legacy with soils and hydrographic networks highly contaminated with metals and metalloids as for example in the Iberian Pyrite Belt (Huelva, Spain). Here, we present new data on copper (Cu) isotopic composition of waters and solids collected along a continuum Mine (Tharsis)-River (Meca)-Lake (Sancho) in the Iberian Pyrite Belt. Our results show that the isotopic signature of pit lakes is spatially variable, but remains stable over the seasons; this signature seems to be controlled by water-rock interaction processes. The data obtained on the Meca River imply a number of attenuation processes such as decrease in the metal concentration by precipitation of secondary minerals. This is accompanied by preferential retention of the heavy isotope (65Cu) with a possibility of living organisms (e.g., algae) participation. The terminal Sancho lake demonstrated constant isotopic signature over the entire depth of the water column despite sizable variations in Cu concentrations, which can be tentatively explained by a superposition of counter-interacting biotic and abiotic processes of Cu fractionation. Overall, the understanding of the isotopic variations along the hydrological continuum is useful for a better understanding of metal element transfer within mining environments and surrounding surface waters.

Signatures of Life Detected in Images of Rocks Using Neural Network Analysis Demonstrate New Potential for Searching for Biosignatures on the Surface of Mars.

Microorganisms play a role in the construction or modulation of various types of landforms. They are especially notable for forming microbially induced sedimentary structures (MISS). Such microbial structures have been considered to be among the most likely biosignatures that might be encountered on the martian surface. Twenty-nine algorithms have been tested with images taken during a laboratory experiment for testing their performance in discriminating mat cracks (MISS) from abiotic mud cracks. Among the algorithms, neural network types produced excellent predictions with similar precision of 0.99. Following that step, a convolutional neural network (CNN) approach has been tested to see whether it can conclusively detect MISS in images of rocks and sediment surfaces taken at different natural sites where present and ancient (fossil) microbial mat cracks and abiotic desiccation cracks were observed. The CNN approach showed excellent prediction of biotic and abiotic structures from the images (global precision, sensitivity, and specificity, respectively, 0.99, 0.99, and 0.97). The key areas of interest of the machine matched well with human expertise for distinguishing biotic and abiotic forms (in their geomorphological meaning). The images indicated clear differences between the abiotic and biotic situations expressed at three embedded scales: texture (size, shape, and arrangement of the grains constituting the surface of one form), form (outer shape of one form), and pattern of form arrangement (arrangement of the forms over a few square meters). The most discriminative components for biogenicity were the border of the mat cracks with their tortuous enlarged and blistered morphology more or less curved upward, sometimes with thin laminations. To apply this innovative biogeomorphological approach to the images obtained by rovers on Mars, the main physical and biological sources of variation in abiotic and biotic outcomes must now be further considered.

Tillandsia usneoides as biomonitors of trace elements contents in the atmosphere of the mining district of Cartagena-La Unión (Spain): New insights for element transfer and pollution source tracing.

Nowadays, atmospheric pollution has a major impact on the human health and the environment, encouraging the development of biomonitors of the air quality over a wide zone. In this study, the relevance of the epiphyte plants Tillandsia usneoides is studied to estimate the transfer of metal(loid)s from a former Zn and Pb mining zone in the Southeast of Spain (Cartagena-La Unión) to the local atmosphere. Biomonitoring was performed by installing plants in 5 sites along a transect from the main mining area to the urban and the coastal zones. An aliquot of plants was collected in every site every 2 months over 1 year. The Tillandsia usneoides have been observed with SEM-EDX, and analysed by ICP-MS to determine trace element concentrations, magnetic susceptibility signals and Zn and Pb isotopes ratios. Results show that atmospheric particles are distributed homogeneously at the plant surface. By comparing elemental contents in Tillandsia usneoides with regard to the values of the geochemical background of the region of Murcia, significant enrichments are observed in the epiphyte plants for Sb, As, Cd, Zn and Pb. The statistical analyses (decentred PCA and PLS) also suggest that the kinetics of dust deposition is slower for the urban and coastal sites compared to the mining sites and highlight an influence of agricultural activities in Cu deposition. The similarity of isotopic compositions (Zn and Pb) between Tillandsia usneoides, soils and atmospheric particles also put in evidence that these plants could be a powerful tool to trace the source of matter in the atmosphere. Finally, this experiment provides new insight to better understand the foliar absorption mechanisms.

Accumulation of heavy metals in phytoliths from reeds growing on mining environments in Southern Europe.

In Southern Europe, soil contamination by heavy metals (HM) due to mining and industrial activities is a long-known problem. Yet, despite soils being widely contaminated through decades, some plants are still able to grow. Some of these plants, like giant reed (Arundo donax) or common reed (Phragmites australis) are capable of accumulating substantial amount of HM. These reeds also contain small silica structures in their shoots, called phytoliths. However, the role of phytoliths in reducing stress caused by these HM remains unknown. The aim of this work is then to determine if phytoliths represent a preferential structure for the bioacccumulation of HM in plants. Therefore, plants from mining-contaminated sites in Spain and France were sampled and HM concentrations in total plant shoots were compared to those in phytoliths for eight metal(oid)s: As, Cd, Cu, Mn, Pb, Sb, Sn and Zn. Results show that Arundo donax and Phragmites australis tend to accumulate Cd, Sb and Sn but limit the uptake of As, Cu, Mn, Pb and Zn in plant shoots despite that the concentration of these HM in soil is quite high. Therefore, reeds appear as tolerant to high metal concentrations in soils, and phytoliths are identified as preferential structures for encapsulation of As, Cu, Mn, Pb and Zn, while Cd, Sb and Sn were mainly found to be accumulated in organic tissues rather than in phytoliths.

The Search for a Signature of Life on Mars: A Biogeomorphological Approach.

Geological evidence shows that life on Earth evolved in line with major concomitant changes in Earth surface processes and landforms. Biogeomorphological characteristics, especially those involving microorganisms, are potentially important facets of biosignatures on Mars and are generating increasing interest in astrobiology. Using Earth as an analog provides reasons to suspect that past or present life on Mars could have resulted in recognizable biogenic landforms. Here, we discuss the potential for, and limitations of, a biogeomorphological approach to identifying the subsets of landforms that are modulated or created through biological processes and thus present signatures of life on Mars. Subsets especially involving microorganisms that are potentially important facets of biosignatures on Mars are proposed: (i) weathering features, biocrusts, patinas, and varnishes; (ii) microbialites and microbially induced sedimentary structures (MISS); (iii) bioaccumulations of skeletal remains; (iv) degassing landforms; (v) cryoconites; (vi) self-organized patterns; (vii) unclassified non-analog landforms. We propose a biogeomorphological frequency histogram approach to identify anomalies/modulations in landform properties. Such detection of anomalies/modulations will help track a biotic origin and lead to the development of an integrative multiproxy and multiscale approach combining morphological, structural, textural, and geochemical expertise. This perspective can help guide the choice of investigation sites for future missions and the types and scales of observations to be made by orbiters and rovers.

Atmospheric dust characterisation in the mining district of Cartagena-La Unión, Spain: Air quality and health risks assessment.

Nowadays, air pollution has a major impact on the environment and human health. Owen gauges allow the sampling of atmospheric depositions in polluted sites for further characterisation. This paper shows the study of the air particles of an old mining zone in Cartagena-La Unión (South-east of Spain) in order to quantify their potential risk on human health. There were 4 strategic sites monitored: the main mining tailing (Avenque), the urban area (La Unión), an agricultural zone (formerly mining) and a site in the Mediterranean coast. Physico-chemical and mineralogical characterisation was applied to atmospheric fallouts. The granulometry revealed a dust particle size around 15 µm, with the coarsest particles in the urban area and the thinnest at the tailing site. XRD analyses showed the presence of quartz, carbonates, sulphides and sulphates. Observations with SEM-EDX confirmed chemical spectra and allowed us to classify the particles into well-crystallised minerals and heterogeneous dusts. Total metal content determination was carried out by ICP-MS analyses and results showed Zn, Pb, As and Cd fluxes (respectively 2549, 1275, 68 and 7 µg·m-2·d-1) exceeding the limit values set by European legislations in the mining area. The fluxes of Zn, Pb and As also exceed these standards in the urban area whereas the coastal zone only exceeds the thresholds in the case of As. Inhalation health risk (defined by US EPA, 2009) was quantified in the sites using total and bioaccessible metal contents of the dusts. Risk calculations using total metal content considering a residential scenario showed acceptable risk for all sites except for the mining tailing which presented non-acceptable cancer and hazard risk mainly due to the total As and Pb contents. When considering the bioaccessible fraction of As and Pb, the risk diminished to acceptable values, demonstrating the overestimation produced when using total metal contents.

GLORI: A GNSS-R Dual Polarization Airborne Instrument for Land Surface Monitoring.

Global Navigation Satellite System-Reflectometry (GNSS-R) has emerged as a remote sensing tool, which is complementary to traditional monostatic radars, for the retrieval of geophysical parameters related to surface properties. In the present paper, we describe a new polarimetric GNSS-R system, referred to as the GLObal navigation satellite system Reflectometry Instrument (GLORI), dedicated to the study of land surfaces (soil moisture, vegetation water content, forest biomass) and inland water bodies. This system was installed as a permanent payload on a French ATR42 research aircraft, from which simultaneous measurements can be carried out using other instruments, when required. Following initial laboratory qualifications, two airborne campaigns involving nine flights were performed in 2014 and 2015 in the Southwest of France, over various types of land cover, including agricultural fields and forests. Some of these flights were made concurrently with in situ ground truth campaigns. Various preliminary applications for the characterisation of agricultural and forest areas are presented. Initial analysis of the data shows that the performance of the GLORI instrument is well within specifications, with a cross-polarization isolation better than -15 dB at all elevations above 45°, a relative polarimetric calibration accuracy better than 0.5 dB, and an apparent reflectivity sensitivity better than -30 dB, thus demonstrating its strong potential for the retrieval of land surface characteristics.