Colored microbial coatings in show caves from the galapagos islands (Ecuador): first microbiological approach

The Galapagos Islands (Ecuador) have a unique ecosystem on Earth due to their outstanding biodiversity and geological features. This also extends to their subterranean heritage, such as volcanic caves, with plenty of secondary mineral deposits, including coralloid-type speleothems and moonmilk deposits. In this study, the bacterial communities associated with speleothems from two lava tubes of Santa Cruz Island were investigated. Field emission scanning electron microscopy (FESEM) was carried out for the morphological characterization and detection of microbial features associated with moonmilk and coralloid speleothems from Bellavista and Royal Palm Caves. Microbial cells, especially filamentous bacteria in close association with extracellular polymeric substances (EPS), were abundant in both types of speleothems. Furthermore, reticulated filaments and Actinobacteria-like cells were observed by FESEM. The analysis of 16S rDNA revealed the presence of different bacterial phylotypes, many of them associated with the carbon, nitrogen, iron and sulfur cycles, and some others with pollutants. This study gives insights into subsurface microbial diversity of the Galapagos Islands and further shows the interest of the conservation of these subterranean geoheritage sites used as show caves.Ministerio del Ambiente de Ecuador (Parque Nacional Galápagos)-PC-65-14Ministerio de Economía y Competitividad de España (MINECO) y el Fondo Europeo de Desarrollo Regional de la Unión Europea (FEDER)-CGL2016-75590-PPortuguese Foundation for Science and Technology. Fundação para a Ciência e a Tecnologia (FCT)-UID/Multi/04449/2019 HERCULES/U

Physical weathering of carbonate host-rock by precipitation of soluble salts in caves: A case study in El Orón-Arco Cave (Region of Murcia, SE Spain)

The dissolution of carbonate host-rock by freshwater in phreatic or vadose conditions is the most common mechanism for the formation of caves; however, circulation of saline solutions through carbonate materials and precipitation of soluble salts may also play an important role. We studied the stable isotope composition (δ18O and δ34S of sulfate, δ18O and δD of structurally-bound gypsum hydration water and 87Sr/86Sr) and salinity of fluid inclusions in gypsum speleothems found in El Orón-Arco Cave (Cartagena, SE Spain). We suggest that physical weathering of carbonate host-rock was driven by precipitation of soluble sea-salts (mostly gypsum and halite), and this process controlled the recent geomorphological evolution of the cave. The Triassic carbonate host-rock shows clear evidence for salt weathering, including gypsum/halite infillings in cracks of the bedrock, mechanical spalling of the carbonate, and detachment of rock fragments that lead to the formation cave voids and in-situ accumulations of piles of unsorted rubble. Sulfur and oxygen isotopes of gypsum sulfate (3.0‰ < δ18O < 11.6‰ and 16.7‰ < δ34S < 20.7‰) are generally lower than modern seawater sulfate and suggest contributions from a 34S-depleted source (i.e. oxidation of pyrite). The δ18O and δD of gypsum hydration water are relatively low compared to expected values for the evaporation of pure seawater to gypsum saturation, suggesting that gypsum precipitation involved a secondary calcium-sulfate source or recycling of gypsum from previous stages, along with mixing of seawater and meteoric water seepage to the cave. The 87Sr/86Sr in gypsum shows intermediate values between modern seawater and Triassic carbonate values because of interaction between the solution and the bedrock. The salinities of the speleothem-forming solutions are relatively high (13.2 ± 3.2 wt% eq. NaCl) compared to gypsum formed from evaporated brackish solutions (i.e. ~4–8 wt% eq. NaCl) and indicate dissolution of earlier evaporites before secondary gypsum precipitation. This cave-forming mechanism, which is related to saline water circulation and precipitation of evaporitic minerals, may be common in other coastal caves

Quantification of drought during the collapse of the classic Maya civilization.

The demise of Lowland Classic Maya civilization during the Terminal Classic Period (~800 to 1000 CE) is a well-cited example of how past climate may have affected ancient societies. Attempts to estimate the magnitude of hydrologic change, however, have met with equivocal success because of the qualitative and indirect nature of available climate proxy data. We reconstructed the past isotopic composition (δ18O, δD, 17O-excess, and d-excess) of water in Lake Chichancanab, Mexico, using a technique that involves isotopic analysis of the structurally bound water in sedimentary gypsum, which was deposited under drought conditions. The triple oxygen and hydrogen isotope data provide a direct measure of past changes in lake hydrology. We modeled the data and conclude that annual precipitation decreased between 41 and 54% (with intervals of up to 70% rainfall reduction during peak drought conditions) and that relative humidity declined by 2 to 7% compared to present-day conditions.ERC 339694 (Water Isotopes of Hydrated Minerals

Karst: a very diverse concept

La gran diversidad intrínseca del karst y la variedad de campos científicos desde los que ha sido estudiado este medio ha generado un espectacular aumento de su conocimiento. Ese avance ha venido acompañado también de nuevas incógnitas y nuevos planteamientos. El presente trabajo trata de recoger una pequeña muestra de esa amplia diversidad, asociada a un elevado grado de especialización, que de forma integrada permite completar el puzzle del karst. Inicialmente, se presenta una revisión sintética del concepto de karst, del proceso de karstificación y de las morfologías asociadas al mismo. Seguidamente, y planteado a partir de una serie de interrogantes, se muestran algunos aspectos y curiosidades relacionadas con el karst. Las características microclimáticas subterráneas, el karst no tradicional o los depósitos y mineralizaciones asociados al karst, son algunos de los temas que se incluyen en este trabajo y que puede interesar a los docentes que imparten docencia sobre el karst.The great intrinsic diversity of karst and the variety of scientific fields in which it has been studied has generated a dramatic increase in our knowledge about it. This advance has also been accompanied by new questions and issues that open the door to new approaches. Our work intends to show a small sample of the wide diversity, often associated with a high degree of specialization, which allows completing the karst puzzle. In the first place, this paper provides a synthetic review of the concept of karst, the karstification process and the morphologies associated with it. Next, starting with a few questions, it shows some aspects and curiosities related to karst. The features of the underground microclimate, the non-traditional karst or deposits and mineralization associated with karst, are some of the topics included in this work, which can be interesting for the teachers dealing with the topic of karst in their classes

Colored Microbial Coatings in Show Caves from the Galapagos Islands (Ecuador): First Microbiological Approach

The Galapagos Islands (Ecuador) have a unique ecosystem on Earth due to their outstanding biodiversity and geological features. This also extends to their subterranean heritage, such as volcanic caves, with plenty of secondary mineral deposits, including coralloid-type speleothems and moonmilk deposits. In this study, the bacterial communities associated with speleothems from two lava tubes of Santa Cruz Island were investigated. Field emission scanning electron microscopy (FESEM) was carried out for the morphological characterization and detection of microbial features associated with moonmilk and coralloid speleothems from Bellavista and Royal Palm Caves. Microbial cells, especially filamentous bacteria in close association with extracellular polymeric substances (EPS), were abundant in both types of speleothems. Furthermore, reticulated filaments and Actinobacteria-like cells were observed by FESEM. The analysis of 16S rDNA revealed the presence of different bacterial phylotypes, many of them associated with the carbon, nitrogen, iron and sulfur cycles, and some others with pollutants. This study gives insights into subsurface microbial diversity of the Galapagos Islands and further shows the interest of the conservation of these subterranean geoheritage sites used as show caves

Colored Microbial Coatings in Show Caves from the Galapagos Islands (Ecuador): First Microbiological Approach

The Galapagos Islands (Ecuador) have a unique ecosystem on Earth due to their outstanding biodiversity and geological features. This also extends to their subterranean heritage, such as volcanic caves, with plenty of secondary mineral deposits, including coralloid-type speleothems and moonmilk deposits. In this study, the bacterial communities associated with speleothems from two lava tubes of Santa Cruz Island were investigated. Field emission scanning electron microscopy (FESEM) was carried out for the morphological characterization and detection of microbial features associated with moonmilk and coralloid speleothems from Bellavista and Royal Palm Caves. Microbial cells, especially filamentous bacteria in close association with extracellular polymeric substances (EPS), were abundant in both types of speleothems. Furthermore, reticulated filaments and Actinobacteria-like cells were observed by FESEM. The analysis of 16S rDNA revealed the presence of different bacterial phylotypes, many of them associated with the carbon, nitrogen, iron and sulfur cycles, and some others with pollutants. This study gives insights into subsurface microbial diversity of the Galapagos Islands and further shows the interest of the conservation of these subterranean geoheritage sites used as show caves

Karst: un concepto muy diverso

La gran diversidad intrínseca del karst y la variedad de campos científicos desde los que ha sido estudiado este medio ha generado un espectacular aumento de su conocimiento. Ese avance ha venido acompañado también de nuevas incógnitas y nuevos planteamientos. El presente trabajo trata de recoger una pequeña muestra de esa amplia diversidad, asociada a un elevado grado de especialización, que de forma integrada permite completar el puzzle del karst. Inicialmente, se presenta una revisión sintética del concepto de karst, del proceso de karstificación y de las morfologías asociadas al mismo. Seguidamente, y planteado a partir de una serie de interrogantes, se muestran algunos aspectos y curiosidades relacionadas con el karst. Las características microclimáticas subterráneas, el karst no tradicional o los depósitos y mineralizaciones asociados al karst, son algunos de los temas que se incluyen en este trabajo y que puede interesar a los docentes que imparten docencia sobre el karst

Archaeological and environmental cave records in the Gobi-Altai Mountains, Mongolia

Though hundreds of caves are known across Mongolia, few have been subject to systematic, interdisciplinary archaeological surveys and excavations to understand Late Pleistocene and Holocene environments. Previous cave excavations in Mongolia have demonstrated their potential for preservation of archaeological and biological material, including Palaeolithic assemblages and Holocene archaeology, particularly burials, with associated organic finds. In other cases, cave surveys found that stratigraphic deposits and archaeological materials are absent. The large number of caves makes the Mongolian Altai Mountain Range a potentially attractive region for human occupation in the Pleistocene and Holocene. Here we present the results of an interdisciplinary survey of caves in four carbonate areas across the Gobi-Altai Mountains. We report 24 new caves, some of which contain archaeological material recovered through survey and test excavations. Most caves presented limited sedimentation, and some were likely too small for human habitation. Six caves showed evidence of palaeontological remains, mostly from likely late Holocene and recent periods. The most notable anthropogenic findings included petroglyphs at Gazar Agui 1 & 13. Gazar Agui 1 also contained lithics and a bronze fragment. Tsakhiryn Agui 1 contained 31 wooden fragments that include an unused fire drilling tool kit and items commonly found in association with medieval burials. We observed that the caves remain in contemporary use for religious and economic purposes, such as the construction of shrines, mining and animal corralling. Water samples from the caves, and nearby rivers, lakes, and springs were analysed for their isotopic compositions (δ18O, δD, δ17O, 17Oexcess, d-excess) and the data, combined with backward trajectory modelling revealed that the Gobi-Altai region receives moisture mainly from western sources. These results form a baseline for future archaeological, paleoclimate and palaeoecological studies about regional seasonality and land use

Physical weathering of carbonate host-rock by precipitation of soluble salts in caves: A case study in El Orón-Arco Cave (Region of Murcia, SE Spain)

The dissolution of carbonate host-rock by freshwater in phreatic or vadose conditions is the most common mechanism for the formation of caves; however, circulation of saline solutions through carbonate materials and precipitation of soluble salts may also play an important role. We studied the stable isotope composition (δ18O and δ34S of sulfate, δ18O and δD of structurally-bound gypsum hydration water and 87Sr/86Sr) and salinity of fluid inclusions in gypsum speleothems found in El Orón-Arco Cave (Cartagena, SE Spain). We suggest that physical weathering of carbonate host-rock was driven by precipitation of soluble sea-salts (mostly gypsum and halite), and this process controlled the recent geomorphological evolution of the cave. The Triassic carbonate host-rock shows clear evidence for salt weathering, including gypsum/halite infillings in cracks of the bedrock, mechanical spalling of the carbonate, and detachment of rock fragments that lead to the formation cave voids and in-situ accumulations of piles of unsorted rubble. Sulfur and oxygen isotopes of gypsum sulfate (3.0‰ < δ18O < 11.6‰ and 16.7‰ < δ34S < 20.7‰) are generally lower than modern seawater sulfate and suggest contributions from a 34S-depleted source (i.e. oxidation of pyrite). The δ18O and δD of gypsum hydration water are relatively low compared to expected values for the evaporation of pure seawater to gypsum saturation, suggesting that gypsum precipitation involved a secondary calcium-sulfate source or recycling of gypsum from previous stages, along with mixing of seawater and meteoric water seepage to the cave. The 87Sr/86Sr in gypsum shows intermediate values between modern seawater and Triassic carbonate values because of interaction between the solution and the bedrock. The salinities of the speleothem-forming solutions are relatively high (13.2 ± 3.2 wt% eq. NaCl) compared to gypsum formed from evaporated brackish solutions (i.e. ~4–8 wt% eq. NaCl) and indicate dissolution of earlier evaporites before secondary gypsum precipitation. This cave-forming mechanism, which is related to saline water circulation and precipitation of evaporitic minerals, may be common in other coastal caves.Proyecto MINECO Retos de la Sociedad. Ref. ESP2017-87690-C3-1-

Quantification of drought during the collapse of the classic Maya civilization

The demise of Lowland Classic Maya civilization during the Terminal Classic Period (~800 to 1000 CE) is a well-cited example of how past climate may have affected ancient societies. Attempts to estimate the magnitude of hydrologic change, however, have met with equivocal success because of the qualitative and indirect nature of available climate proxy data. We reconstructed the past isotopic composition (d18O, dD, 17O-excess, and d-excess) of water in Lake Chichancanab, Mexico, using a technique that involves isotopic analysis of the structurally bound water in sedimentary gypsum, which was deposited under drought conditions. The triple oxygen and hydrogen isotope data provide a direct measure of past changes in lake hydrology. We modeled the data and conclude that annual precipitation decreased between 41 and 54% (with intervals of up to 70% rainfall reduction during peak drought conditions) and that relative humidity declined by 2 to 7% compared to present-day conditions.</p