In this study, we show that moonmilk subaerial speleothems in Altamira Cave (Spain) consist of a network of fiber calcite crystals and active microbial structures. In Altamira moonmilks, the study of the typology and distribution of fiber crystals, extracellular polymeric substances, and microorganisms allowed us to define the initial stages of fiber crystal formation in recent samples as well as the variations in the microstructural arrangement in more evolved stages. Thus, we have been able to show the existence of a relationship among the different types of fiber crystals and their origins. This allowed us to outline a model that illustrates the different stages of formation of the moonmilk, developed on different substrata, concluding that microbes influence physicochemical precipitation, resulting in a variety of fiber crystal morphologies and sizes.

Fossil evidence from the Iberian Peninsula is essential for understanding Neandertal evolution and history. Since 2000, a new sample Ϸ43,000 years old has been systematically recovered at the El Sidró n cave site (Asturias, Spain). Human remains almost exclusively compose the bone assemblage. All of the skeletal parts are preserved, and there is a moderate occurrence of Middle Paleolithic stone tools. A minimum number of eight individuals are represented, and ancient mtDNA has been extracted from dental and osteological remains. Paleobiology of the El Sidró n archaic humans fits the pattern found in other Neandertal samples: a high incidence of dental hypoplasia and interproximal grooves, yet no traumatic lesions are present. Moreover, unambiguous evidence of human-induced modifications has been found on the human remains. Morphologically, the El Sidró n humans show a large number of Neandertal lineage-derived features even though certain traits place the sample at the limits of Neandertal variation. Integrating the El Sidró n human mandibles into the larger Neandertal sample reveals a north-south geographic patterning, with southern Neandertals showing broader faces with increased lower facial heights. The large El Sidró n sample therefore augments the European evolutionary lineage fossil record and supports ecogeographical variability across Neandertal populations. dental hypoplasia ͉ geographic patterning ͉ geometric morphometrics ͉ mandible ͉ Neandertal diversity

The walls and ceiling of Altamira Cave, northern Spain, are coated with different coloured spots (yellow, white and grey). Electron microscopy revealed that the grey spots are composed of bacteria and bioinduced CaCO(3) crystals. The morphology of the spots revealed a dense network of microorganisms organized in well-defined radial and dendritic divergent branches from the central area towards the exterior of the spot, which is coated with overlying spheroidal elements of CaCO(3) and CaCO(3) nest-like aggregates. Molecular analysis indicated that the grey spots were mainly formed by an unrecognized species of the genus Actinobacteria. CO(2) efflux measurements in rocks heavily covered by grey spots confirmed that bacteria-forming spots promoted uptake of the gas, which is abundant in the cave. The bacteria can use the captured CO(2) to dissolve the rock and subsequently generate crystals of CaCO(3) in periods of lower humidity and/or CO(2). A tentative model for the formation of these grey spots, supported by scanning electron microscopy and transmission electron microscopy data, is proposed.

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In recent years, methane (CH 4 ) has received increasing scientific attention because it is the most abundant non-CO 2 atmospheric greenhouse gas (GHG) and controls numerous chemical reactions in the troposphere and stratosphere. However, there is much that is unknown about CH 4 sources and sinks and their evolution over time. Here we show that near-surface cavities in the uppermost vadose zone are now actively removing atmospheric CH 4 . Through seasonal geochemical tracing of air in the atmosphere, soil and underground at diverse geographic and climatic locations in Spain, our results show that complete consumption of CH 4 is favoured in the subsurface atmosphere under near vapour-saturation conditions and without significant intervention of methanotrophic bacteria. Overall, our results indicate that subterranean atmospheres may be acting as sinks for atmospheric CH 4 on a daily scale. However, this terrestrial sink has not yet been considered in CH 4 budget balances. M ethane (CH 4 ) is currently the most abundant non-CO 2 greenhouse gas (GHG) in the atmosphere, reaching a global average concentration of B1,800 p.p.b. at midnorthern latitudes 1 . Despite significant research progress in recent years, large uncertainties remain about the CH 4 budget and its evolution over time because there is a lack of knowledge about CH 4 sinks and sources [2][3][4][5] . Superimposed on the long-term trend of increasing atmospheric CH 4 , there is significant interannual variability 1,6,7 , and the sources of variation remain controversial 8 .Current CH 4 estimates account for B22% of the total forcing potential of all long-lived GHGs 9 . By weight, CH 4 is 28 times more effective at trapping heat in the atmosphere than CO 2 over a 100-year period 10 . Sensible mitigation strategies also require a quantitative understanding of the CH 4 budget regarding emissions and sinks 11 . The total global emissions of CH 4 are constrained reasonably well by atmospheric observations and estimates of its lifetime, based on multiple atmospheric CH 4 inversion models (top-down studies). However, the uncertainties concerning emissions/consumption from individual sources/ sinks 12 are greater, and they are poorly constrained by the current atmospheric observation network 6 . Some unaccounted sinks (or sources) could contribute the global CH 4 budget and its long-term variations.The Earth's surface exerts its influence on the free atmosphere through the atmospheric boundary layer. This lowest portion of the atmosphere ranges from a few tens of metres to 1-2-km deep 13 . The subsurface atmosphere is usually overlooked as an important part of this boundary layer. At the top of the subsurface layer in the vadose zone (below the subsoil and above the groundwater table) highly specific biogeochemical processes occur, which may act as regulators of gas exchanges between the surface and the free atmosphere.The uppermost part of the vadose zone may contain large amounts of underground air, that is, a CO 2 -rich air reservoir permeating the unsaturated...

The paintings from Tomba della Scimmia, in Tuscany, are representative of the heavy bacterial colonization experienced in most Etruscan necropolises. The tomb remained open until the late 70′s when it was closed because of severe deterioration of the walls, ceiling and paintings after decades of visits. The deterioration is the result of environmental changes and impacts suffered since its discovery in 1846. We show scanning electron microscopy and molecular studies that reveal the extent and nature of the biodeterioration. Actinobacteria, mainly Nocardia and Pseudonocardia colonize and grow on the tomb walls and this process is linked to the availability of organic matter, phyllosilicates (e.g. clay minerals) and iron oxides. Nocardia is found metabolically active in the paintings. The data confirm the specialization of the genera Nocardia and Pseudonocardia in the colonization of subterranean niches.

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Despite evidence of damaging human impacts, cave paintings may again be threatened if visitors are allowed access.