Organic matter of fossil origin in the amberine speleothems from El Soplao Cave (Cantabria, Northern Spain)

Unusual amberine-coloured speleothems were recently found in El Soplao Cave (Cantabria, Spain). Chromophore elements such as Fe, Mn, Cd, Co or Ti were not present in significant quantities. Rather, our data show that their colour comes from leachates of fossilized organic material hosted in the carbonaceous Urgonian facies of the host rock. These leachates are related to the Cretaceous amber deposit that has been recently discovered in the vicinity of El Soplao Cave. The presence of humic and fulvic acids of fossil origin were confirmed by IR and Raman spectroscopic analysis of the carbonaceous strata and the speleothems. In addition, the mineralogy of the amberine speleothems was studied. Alternating bands made of calcite and aragonite reveal that periods of humidity and aridity occurred within the cave during the speleothem genesis

Precise and accurate isotope fractionation factors (α17O, α18O and αD) for water and CaSO4·2H2O (gypsum)

Gypsum (CaSO4·2H2O) is a hydrated mineral containing crystallization water, also known as gypsum hydration water (GHW). We determined isotope fractionation factors (α17O, α18O and αD) between GHW and free water of the mother solution in the temperature range from 3 °C to 55 °C at different salinities and precipitation rates. The hydrogen isotope fractionation factor (αDgypsum-water) increases by 0.0001 units per °C between 3 °C and 55 °C and salinities <150 g/L of NaCl. The αDgypsum-water is 0.9812 ± 0.0007 at 20 °C, which is in good agreement with previous estimates of 0.981 ± 0.001 at the same temperature. The α18Ogypsum-water slightly decreases with temperature by 0.00001 per °C, which is not significant over much of the temperature range considered for paleoclimate applications. Between 3 °C and 55 °C, α18Ogypsum-water averages 1.0035 ± 0.0002. This value is more precise than that reported previously (e.g. 1.0041 ± 0.0004 at 25 °C) and lower than the commonly accepted value of 1.004. We found that NaCl concentrations below 150 g/L do not significantly affect α18Ogypsum-water, but αDgypsum-water increases linearly with NaCl concentrations even at relatively low salinities, suggesting a salt correction is necessary for gypsum formed from brines. Unlike oxygen isotopes, the αDgypsum-water is affected by kinetic effects that increase with gypsum precipitation rate. As expected, the relationship of the fractionation factors for 17O and 18O follows the theoretical mass-dependent fractionation on Earth (θ = 0.529 ± 0.001). We provide specific examples of the importance of using the revised fractionation factors when calculating the isotopic composition of the fluids

Origin of double-tower raft cones in hypogenic caves

In the present paper, we describe the genetic mechanism that causes the precipitation of raft cones in caves. These speleothems usually form in a hydrothermal and epiphreatic environment where dripwater, dripping repeatedly over the same spot, sinks calcite rafts that were floating on the water surface of a cave pool. In particular, the paper describes a new variety of raft cones that were recently discovered in the Paradise Chamber of the Sima de la Higuera Cave (Murcia, south-eastern Spain) based on their morphological and morphometric characteristics. These speleothems, dubbed ‘double-tower cones’, have a notch in the middle and look like two cones, one superimposed over the other. The genetic mechanism that gave rise to the double-tower cones must include an intermediate stage of rapid calcite raft precipitation, caused by a drop in the water table and by changes in cave ventilation leading to greater carbon dioxide (CO2) degassing and evaporation over the surface of the thermal lake where these speleothems formed. Calcite rafts were deposited in Paradise Chamber, completely covering many of the cones. Later, conditions for slower calcite raft precipitation were restored and some of the cones continued to grow at the same points. When the water table finally fell below the level of Paradise Chamber, the tower cones became exposed, as the incongruent deposits of calcite rafts were dissolved and mobilized to lower cave levels

In situ Raman characterization of minerals and degradation processes in a variety of cultural and geological heritage sites

Wetest the capabilities of in situ Raman spectroscopy for non-destructive analysis of degradation processes in invaluable masterpieces, as well as for the characterization of minerals and prehistoric rock-art in caves. To this end, we have studied the mechanism of decay suffered by the 15th-century limestone sculptures that decorate the retro-choir of Burgos Cathedral (N Spain). In situ Raman probe detected hydrated sulfate and nitrateminerals on the sculptures, which are responsible for the decay of the original limestone. In addition, in situ Raman analyses were performed on unique speleothems in El Soplao Cave (Cantabria, N Spain) and in the Gruta de las Maravillas (Aracena, SWSpain). Unusual cavemineralswere detected in El Soplao Cave, such as hydromagnesite (Mg5(CO3)4(OH)2·4H2O), as well as ferromanganese oxides in the black biogenic speleothems recently discovered in this cavern. In the Gruta de las Maravillas, gypsum (CaSO4·2H2O) was identified for the first time, as part of the oldest cave materials, so providing additional evidence of hypogenic mechanisms that occurred in this cave during earlier stages of its formation. Finally, we present preliminary analyses of several cave paintings in the renowned “Polychrome Hall” of Altamira Cave (Cantabria, N. Spain). Hematite (Fe2O3) is the most abundant mineral phase, which provides the characteristic ochre-reddish color to the Altamira bison and deer paintings. Thus, portable Raman spectroscopy is demonstrated to be an analytical technique compatible with preserving our cultural and natural heritage, since the analysis does not require physical contact between the Raman head and the analyzed items

The role of cave ventilation in the triple oxygen and hydrogen isotope composition of condensation waters in Altamira Cave, northern Spain

In cave environments, water vapor condensation occurs naturally when warmer/wet air masses flow close to colder cave surfaces. Artificial microclimate perturbations in show caves can enhance this process, leading to potential deterioration of rock art and degradation of speleothems. Here we investigate the triple oxygen and hydrogen isotopic compositions of condensation water in Altamira Cave (Cantabria, northern Spain) to evaluate the potential of stable isotopes in the study of condensation mechanisms in caves. We assess the role of cave ventilation in the spatiotemporal isotopic variability of condensation water in Altamira Cave. To this end, water drops that condense naturally on artificial supports in different parts of the cave were collected for 7 years and their isotopic compositions (?17O, ?18O, ?D and derived parameters 17O-excess and d-excess) were compared to those of droplets with no apparent dripping taken from the cave ceiling (i.e. presumably condensation water) and fast dripping points (i.e. infiltration water) during the same period. Condensation waters in the outmost cave sectors, closer to the entrance, show higher ?17O, ?18O and ?D values during the cave ventilation period (June to October) compared to the rest of the year. This seasonal pattern can be explained by changes in the contributions of two moisture sources for condensation: advection of allochthonous water vapor from outside during the cave ventilation period and recycling of autochthonous vapor generated from cave dripwater during the stagnation period. In contrast, the isotopic values of condensation waters in the inner cave sectors are similar to those of infiltration water, with insignificant seasonal variability. This suggests that water condensation in the inner cave sectors is sourced by autochthonous vapor, with no significant contributions of external moisture, even during the cave ventilation period. We conclude that allochthonous water vapor condenses preferentially in the Entrance Hall and does not affect significantly the rest of the cave. These results are relevant for the management of Altamira Cave and for future investigations on condensation mechanisms in cavities elsewhere.The authors are grateful to the Altamira Cave Research Centre and Museum staff for their help and support during the sampling surveys in the cave. The image of the ceiling of the Polychrome Hall was provided by the Altamira Cave Research Center. This work was supported by the Ministry of Education, Culture and Sport of Spain (MECD) [grant number J180052] under the Project “Servicio de control y seguimiento de las condiciones ambientales y del biodeterioro de la Cueva de Altamira”, and also with the support of the Cantabrian International Institute for Prehistoric Research (IIIPC) under the project entitled “Control y seguimiento de las condiciones ambientales, del agua de infiltracion ´ y de las emisiones de gas radon, de la cueva de Altamira”. The authors thanks Professor David A. Hodell for the isotopic analysis of 15 water samples. Dr. Fernando Gazquez ´ was financially supported by the HIPATIA research program of the University of Almería and by a Ramon ´ y Cajal Fellowship (RYC2020-029811-I) of the Spanish Government (Ministerio de Ciencia e Innovacion). ´ The authors are grateful to four anonymous reviews, who contributed to improve the original manuscript

Spatiotemporal distribution of δ¹³C-CO₂ in a shallow cave and its potential use as indicator of anthropic pressure

This study deals with the spatiotemporal dynamics of CO₂ and its isotopic composition (δ¹³C-CO₂) in the atmosphere of Altamira Cave (northern Spain) over two annual cycles. In general terms, the cavity shows two distinct ventilation modes, acting as a CO₂ reservoir from October to May (recharge stage), while actively exchanging gases with the outside atmosphere between July and September (discharge stage). In recharge mode, the in-cave air shows higher and relatively homogeneous CO₂ values (3332 ± 521 ppm) with lower δ¹³C-CO₂ ( 23.2 ± 0.4‰). In contrast, during the discharge stage, the CO₂ concentrations are lower and relatively more variable (1383 ± 435 ppm) and accompanied by higher δ¹³C-CO₂ (up to 12‰). This seasonal pattern is controlled by the distinct rates of exchange of air masses with the external atmosphere through the annual cycle, as well as by changes in the production of CO₂ in the soil and natural fluctuations in the concentration of dissolved inorganic carbon transported by drip water into the cave. In contrast to the interpretations of previous studies in Altamira Cave, no local air intakes into the deepest cave sections were flagged by our δ¹³C measurements. This finding is also supported by analyses of CO₂ and ²²²Rn in air, density of airborne particles and air temperature. In addition, preliminary experiments examining the visitor-produced disturbances on δ¹³C-CO₂ were conducted during the various cave ventilation stages to explore the potential use of this parameter as an indicator of anthropic pressure in caves. Our data show that visits (overall stay of 60-85 min; i.e., 4 people for 20 min) significantly affected δ¹³C-CO₂ (up to Δδ¹³C~-2‰) in the Polychrome Hall of Altamira Cave under conditions of low natural CO₂ (discharge stage), whereas it remained almost unaltered under circumstances of high CO₂ concentration (recharge stage). This demonstrates that δ¹³C-CO₂ is sensitive to perturbations produced by visitors during certain periods.The authors express warm thanks to the Altamira Cave Research Centre and Museum staff for their help and support during the sampling surveys in the cave. This research was founded by the Project entitled “Estudios analíticos para una propuesta de accesibilidad pública de la Cueva de Altamira” funded by the Spanish Ministry of Education, Culture and Sport (92522100). Sarah Steines is also thanked for revising the English

Coupled Mg/Ca and clumped isotope analyses of foraminifera provide consistent water temperatures

The reliable determination of past seawater temperature is fundamental to paleoclimate studies. We test the robustness of two paleotemperature proxies by combining Mg/Ca and clumped isotopes (Δ47) on the same specimens of core top planktonic foraminifera. The strength of this approach is that Mg/Ca and Δ47 are measured on the same specimens of foraminifera, thereby providing two independent estimates of temperature. This replication constitutes a rigorous test of individual methods with the advantage that the same approach can be applied to fossil specimens. Aliquots for Mg/Ca and clumped analyses are treated in the same manner following a modified cleaning procedure of foraminifera for trace element and isotopic analyses. We analysed eight species of planktonic foraminifera from coretop samples over a wide range of temperatures from 2 to 29°C. We provide a new clumped isotope temperature calibrations using subaqueous cave carbonates, which is consistent with recent studies. Tandem Mg/Ca–Δ47 results follow an exponential curve as predicted by temperature calibration equations. Observed deviations from the predicted Mg/Ca-Δ47 relationship are attributed to the effects of Fe-Mn oxide coatings, contamination, or dissolution of foraminiferal tests. This coupled approach provides a high degree of confidence in temperature estimates when Mg/Ca and Δ47 yield concordant results, and can be used to infer the past δ18O of seawater (δ18Osw) for paleoclimate studies

Insights into speleothems from lava tubes of the Galapagos Islands (Ecuador): mineralogy and biogenecity

Different types of hard and soft speleothems (stalactites, stalagmites, columns, crusts, flowstones, micro-gours and botryoidal coralloids) have been observed throughout lava tubes in the Galapagos archipelago, Ecuador. Three lava tubes were studied in this work: Gallardo and Royal Palm volcanic caves (Santa Cruz Island) and Sucre Cave (Isabela Island). The studied speleothems were mainly formed by opal, calcite and clay minerals, including plagioclase and pyroxenes from the basaltic host rock. Rarely, iron oxides, gypsum were found in some speleothems, which were interpreted as alteration products of the primary volcanic materials. Field emission scanning electron microscopy revealed abundant filamentous 17th International Vulcanspeleology Symposium 2 bacteria, and reticulated filaments similar to those recently observed in others lava tubes around the world. These filaments are associated with EPS and mineral deposits rich in Si, Ca or Fe. The identified minerals and the evidence of biosignatures suggest a biological contribution to speleothem development within Gallardo, Royal Palm and Sucre lava tubes

Magnetic Mesoporous Silica Nanorods Loaded with Ceria and Functionalized with Fluorophores for Multimodal Imaging

Multifunctional magnetic nanocomposites based on mesoporous silica have a wide range of potential applications in catalysis, biomedicine, or sensing. Such particles combine responsiveness to external magnetic fields with other functionalities endowed by the agents loaded inside the pores or conjugated to the particle surface. Different applications might benefit from specific particle morphologies. In the case of biomedical applications, mesoporous silica nanospheres have been extensively studied while nanorods, with a more challenging preparation, have attracted much less attention despite the positive impact on the therapeutic performance shown by seminal studies. Here, we report on a sol-gel synthesis of mesoporous rodlike silica particles of two distinct lengths (1.4 and 0.9 μm) and aspect ratios (4.7 and 2.2) using Pluronic P123 as a structure-directing template and rendering ∼1 g of rods per batch. Iron oxide nanoparticles have been synthesized within the pores yielding maghemite (γ-FeO) nanocrystals of elongated shape (∼7 nm × 5 nm) with a [110] preferential orientation along the rod axis and a superparamagnetic character. The performance of the rods as T-weighted MRI contrast agents has also been confirmed. In a subsequent step, the mesoporous silica rods were loaded with a cerium compound and their surface was functionalized with fluorophores (fluorescamine and Cyanine5) emitting at λ = 525 and 730 nm, respectively, thus highlighting the possibility of multiple imaging modalities. The biocompatibility of the rods was evaluated in vitro in a zebrafish (Danio rerio) liver cell line (ZFL), with results showing that neither long nor short rods with magnetic particles caused cytotoxicity in ZFL cells for concentrations up to 50 μg/ml. We advocate that such nanocomposites can find applications in medical imaging and therapy, where the influence of shape on performance can be also assesse

Mountain permafrost in the Central Pyrenees: insights from the Devaux ice cave

Ice caves are one of the least studied parts of the cryosphere, particularly those located in inaccessible permafrost areas at high altitudes or high latitudes. We characterize the climate dynamics and the geomorphological features of Devaux cave, an outstanding ice cave in the Central Pyrenees on the French–Spanish border. Two distinct cave sectors were identified based on air temperature and geomorphological observations. The first one comprises well-ventilated galleries with large temperature oscillations likely influenced by a cave river. The second sector corresponds to more isolated chambers, where air and rock temperatures stay below 0 ∘C throughout the year. Seasonal layered ice and hoarfrost occupy the first sector, while transparent, massive perennial ice is present in the isolated chambers. Cryogenic calcite and gypsum are mainly present within the perennial ice. During winter, the cave river freezes at the outlet, resulting in a damming and backflooding of the cave. We suggest that relict ice formations record past damming events with the subsequent formation of congelation ice. δ34S values of gypsum indicate that the sulfate originated from the oxidation of pyrite present in the bedrock. Several features including air and rock temperatures, the absence of drips, the small loss of ice in the past 7 decades, and the location of ice bodies in the cave indicate that the cave permafrost is the result of a combination of undercooling by ventilation and diffusive heat transfer from the surrounding permafrost, reaching a thickness of ∼ 200 m.</p