Coronavirus pandemic: an opportunity to study the anthropogenic impact on micro-climate conditions and CaCO3 crystal morphology in the Nerja Cave (SE Spain)

Following the declaration of the COVID-19 pandemic, the Spanish Government restricted non-essential movements of all citizens and closed all public spaces, such as the Nerja Cave, until May 31, 2020. This particular condition of the closure of the cave provided a unique opportunity to study the micro-climate conditions and carbonate precipitation in this tourist cave without the presence of visitors. Our results show the significant effect of visitors on the air isotopic signature of the cave and on the genesis of the extensive dissolution features affecting the carbonate crystals formed in the tourist sector of the cave, alerting us to the possible corrosion of the speleothems located there. The movement of visitors within the cave also favours the mobilisation of aerial fungi and bacterial spores and their subsequent sedimentation simultaneously with the abiotic precipitation of carbonates from the drip water. The traces of these biotic elements could be the origin of the micro-perforations previously described in the carbonate crystals formed in the tourist galleries of the cave, but they are subsequently enlarged due to abiotic dissolution of the carbonates through these weaker zones.It is financed by the Nerja Cave Foundation, co-ordinated by its Research Institute and authorized by the Consejería de Cultura (Junta de Andalucía). This study is also a contribution to the Research Groups RNM-308 and RNM-126 of the Junta de Andalucía and to the Projects PID2021-125619OB-C21, PID2021-125619OB-C22, TED2021-130549B-I00 funded by MCIN/AEI/10.13039/ 501100011033. Funding for open access charge: Universidad de Málaga / CBUA

Microstratigraphic Analysis of a Speleothem from the Nerja Cave (Málaga, Southern Spain)

Congreso realizado en Málaga en junio de 2022.[EN] The microstratigraphic analysis in speleothems allows to identify and characterize the stratigraphic elements and limiting surfaces. The textural variations are related to the availability of dripping water, the nature of the flow, and the transport of water and/or evaporation. The different phases of growth therefore respond to the different physicochemical conditions that existed during their formation and even to possible post-sedimentary processes, constituting true paleoclimatic indicators. Fluid inclusions formed during crystal growth may harbor existing karst water in the cave during precipitation. Verification by petrographic studies of the genetic relationship between the fluid inclusion and the surrounding calcite allows defining the type of fluid inclusions based on the temporal relationship with the calcite (primary or secondary), the spatial relationship with the calcite crystals (inter- or intra-crystalline), and their morphology. In this work, a microstratigraphic–petrographic characterization of the carbonate fabrics and textures is presented, as well as the type of fluid inclusions of a calcitic–aragonitic stalagmite from the Cueva de Nerja (Málaga, Southern Spain). The most recognized fluid inclusions appear in the columnar textures which are formed in conditions close to equilibrium.This work has been carried out within the project Contract Technological Support between the CSIC (IACT) and the Nerja Cave Foundation “Speleothems and archaeological records of the Nerja Cave as indicators of paleoclimatic and paleoenvironmental change” (2018–2021) and PID20231-125619OB-C22 project.Peer reviewe

Isotopic composition of the waters in the Hydrogeological Unit Yunquera-Nieves (Province of Malaga)

The isotopic composition of the waters sampled in the Hydrogeological Unit Yunquera-Nieves are from Mediterranean and Atlantic origin. The lsO and 2H contents define a local meteoric water line with lower slope than mundial meteoric water line, because of the evaporation process. The mineralization and isotopic composition of the waters decreases with the altitude, which allow us delimite the recharge surface of the main springs of the Unit. The mineralization and the isotopic composition of rainwater vary inversely to the amount of precipitation. The springwaters deplete their mineralization and isotopic content in response to the outflow increase because of the important winter precipitations. Anyway, the responses are quick, which probe the karstic behaviour of the spring

Estimation of spatio-temporal recharge of aquifers in mountainous karst terrains: application to Sierra de las Nieves (Spain)

We describe a method for estimating the daily, spatially distributed recharge of aquifers in mountainous karst terrains using a water balance. Water recharge into an aquifer is a highly variable process over both time and space. Many methods have been developed to assess aquifer recharge although most have been applied to detrital aquifers. Many karst aquifers, especially in Mediterranean areas, occur in mountainous environments where rainfall and evapotranspiration can vary considerably over space and time and where there are usually few rainfall and temperature monitoring stations. We have used an advanced geostatistical method to estimate daily rainfall and temperature. The method involves kriging with an external drift using a climatological semi-variogram model inferred by modified maximum-likelihood. The depth of the soil–epikarst layer is estimated from remote sensing and terrain analysis data together with field observations and electrical resistivity tomography. Because of the karst nature of the mountainous terrain, concentrated infiltration is allowed for in some places. The parameters are calibrated against the cumulative discharge of various springs. The method is illustrated by a case study of the Sierra de las Nieves aquifer in the mountainous karst region of southern Spain.Instituto Geológico y Minero de España, EspañaFaculty of Engineering, Computer and Mathematical Sciences, University of Adelaide, AustraliaDepartamento de Geología, Universidad de Málaga, Españ

Development and collapse of karstic cavities in folded marbles: Geomorphological and geophysical evidences in Nerja Cave (southern Spain)

Karstic evolution leads to the growth and collapse of cavities by the interaction between geological structures and the hydrogeological framework. Nerja Cave developed within marbles belonging to the Alpujarride complex of the Internal Zones in the Betic Cordillera of Spain. The residual gravity anomaly map of the karstified areas –surrounding the known Nerja Cave– may indicate a likely elongated parallel cave system, N-S oriented, unknown up to present, and formed by both small shallow and large deep caves below a nearby hill located north-westwards to the known cave. At the east hillside, a moderate gravity anomaly minimum and geomorphological evidence (vertical walls and sunken terrains) suggest the presence of an old collapsed cave. At the west hillside, a marked gravity minimum is associated with a strongly folded marble layer without evidence of collapse. An electrical resistivity tomography (ERT) profile across the hill –in the E-W direction– supports an interpretation of several voids, two of the bigger ones located on either side of the hill. The combination of geomorphological, ERT and gravity forward modelling indicate the location of unknown caves, one of them partially collapsed. These caves, located at a higher topographic level than the known Nerja Cave, may represent an early stage of cave development, and suggest the preferred dissolution of some layers in the folded marbles. This field example provides new insights on the interaction of structure in the karstic evolution that determines the cavity stability.info:eu-repo/semantics/publishedVersio

Consideraciones sobre el funcionamiento hidrogeológico y la vulnerabilidad a la contaminación de la Sierra de las Nieves (Málaga) a partir de un ensayo de trazador en condiciones de estiaje

A tracer test during low-flow conditions was carried out in the karstic aquifer of Sierra de las Nieves (Málaga) in order to assess its hydrogeological functioning and vulnerability to contamination. Two kilogrammes of Eosine were injected in an active siphon located in the Sima del Aire cave shaft (-640 m) at the end of August 2003. The springs were sampled until November 2003. For more than 50 days, the tracer was not detected at any of the springs. After several rainfall events in October 2003, a signal was observed in the two Río Grande springs. The first arrival of Eosine appears before the increase of spring discharge and the dilution effect of the most important rainfalls (86 mm, October 25th). The calculated groundwater velocities (below 4 m/hour) are not representative of the dry period because rainfall forced the Eosine transport. However, they give an idea about the long residence time if a contamination event occurs during low-flow conditions

Groundwater temperature and electrical conductivity as tools to characterize flow patterns in carbonate aquifers: The Sierra de las Nieves karst aquifer, southern Spain

In carbonate massifs, flow patterns are conditioned by karstification processes which develop a conduit network and preserve low permeability microfractured blocks. The Sierra de las Nieves karst massif (southern Spain) is subjected to a given climatic and geological context, and thus it is possible to analyse the spatial and temporal variability of the water temperature and electrical conductivity at its main karst outlets, which display different responses to rainfall episodes. In this experimental field area, conduit flow and diffuse flow drainage patterns have been distinguished by combining groundwater temperature and electrical conductivity data. Both parameters show large variations in water coming from conduit flow systems and low variations in water drained by springs draining diffuse flow systems. However, groundwater temperature displays the smallest variations, which seems to indicate that this parameter is less sensitive as regards characterising the degree of karstification, which is a key question in characterising the aquifer functioning