The Ejulve cave speleothemic record:from monitoring control to abrupt climate changes during the Pleistocene in the Eastern Iberian Range (Teruel)

La presente tesis engloba un completo estudio en la Cueva de El Recuenco (Ejulve, Cordillera Ibérica, NE Península Ibérica) sobre la espeleogénesis de la cueva, la dinámica espeleotémica actual y la reconstrucción de cambios climáticos abruptos durante el Pleistoceno a partir de sus registros espeleotémicos. La cueva de Ejulve, situada a 1240 m.s.n.m., es una cueva relativamente pequeña en el sector suroriental de la Cordillera Ibérica. Se encuentra desarrollada en calizas dolomíticas y dolomías de la formación Mosqueruela, del Cretácico Superior, y está afectada por el arco de cabalgamientos de Portalrubio-Vandellós, estructurado durante el Oligoceno y Mioceno Inferior. El paisaje está dominado por amplias y deformadas superficies de erosión situadas a gran altitud (Superficie de Erosión Fundamental de la Cordillera Ibérica), que terminó de formarse en el Plioceno. El origen de la cueva debería situarse antes de la fase final de desarrollo de la Superficie de Erosión Fundamental. La identificación de ciertas morfologías de la cueva, muy características, como son el boxwork, los tubos con cúpulas ascendentes en el techo, pendants y cups, spongework y rasgos de micro-corrosión, sugieren un origen hipógeno de la misma. Por lo tanto, la karstificación hipógena ocurriría tentativamente durante el Mio-Plioceno, y se explicaría por al ascenso de agua subterránea debido a gradientes hidráulicos en un acuífero confinado, generando así las galerías en forma de laberinto y las morfologías características mencionadas previamente. Adicionalmente, el análisis del boxwork sugiere una fase previa, probablemente durante el Mioceno Superior, en la que calcita y dolomita rellenaron las discontinuidades existentes en el epikarst, todo ello bajo condiciones freáticas. Después de la karstificación, la cueva tuvo una transición a condiciones epigénicas sin confinamiento, debido a la reactivación de los procesos regionales de levantamiento y doming. Después de la tectónica extensional durante el Plioceno-Cuaternario, se produciría la fase de la incisión fluvial. Así, una vez el karst queda exhumado y se da paso a la fase vadosa, comienza la precipitación de espeleotemas, al menos desde hace 650.000 años antes del presente. El estudio de la dinámica actual de la cueva, incluyendo el muestreo de lluvia, goteo y carbonato precipitado, fue llevado a cabo durante cuatro años (2013-2016). El principal factor que controla el d18O de la lluvia es la temperatura (r2 = 0.82, p-value > 0.001), mostrando un patrón estacional con valores más bajos en invierno y más altos en verano. Tanto el área de origen de la precipitación (junto al componente de la lluvia) y la cantidad de lluvia, actúan como controles secundarios. El uso de la infiltración neta resulta crucial para evaluar la recarga del epikarst en las condiciones semi-áridas propias del área de estudio. De hecho, el uso de la infiltración neta revela que el efecto de cantidad de lluvia ejerce escasa influencia en la variabilidad isotópica del agua de goteo, en contraste con la influencia moderada que ejercía sobre el d18O de la lluvia anual. El muestreo de 12 goteos a lo largo de la cueva evidenció que tanto los goteos estacionales como los no estacionales muestran similares valores de d18O en el agua de goteo. La estacionalidad vista en el d18O del agua de lluvia, es también observada en el agua de goteo, aunque atenuada y con cierto retardo, por lo tanto, no hay un proceso completo de homogeneización de las aguas en el epikarst. La respuesta hidrológica de la cueva a la lluvia externa es rápida, con un incremento en las tasas de goteo en pocas semanas en ambos grupos de goteos durante las lluvias estacionales de otoño. No obstante, el retardo visto en el d18O de las lluvias de otoño-invierno asciende hasta un máximo de 21 semanas. Estos resultados sugieren la existencia del ‘efecto pistón’, según el cual el agua ‘nueva’ presiona en sentido descendente el agua ‘antigua’ pre-existente en el epikarst, a través de la red de fracturas existentes.El carbonato precipitado muestra una escasa variación total de un 0.11 ‰ en el d18O, con una variabilidad similar entre los goteos estacionales y los no estacionales. El d18O del carbonato depende del d18O del agua de goteo, con una escasa influencia de la tasa de goteo. La variación del d13C es de un 0.22 ‰, y muestra estacionalidad con valores más altos en verano y otoño, y más bajos en invierno y primavera. El d13C es más positivo en los goteos no estacionales, los cuales, debido a una mayor desgasificación, registran una variabilidad que asciende hasta el 0.42 ‰, comparado con el 0.29 ‰ de los goteos estacionales. Estas diferencias entre diferentes tipos de goteo están explicadas por la alta correlación entre el d13C y la tasa de goteo. Por lo tanto, los valores altos de d13C en el carbonato precipitado en la cueva de Ejulve se explican por la mayor desgasificación y menor disponibilidad hídrica, mientras que los valores bajos de d13C se registrarían cuando hay más actividad microbiana, mayor productividad vegetal y más disponibilidad hídrica. La ventilación de la cueva desde finales del otoño hasta la primavera, favorece una mayor precipitación de carbonato. De esta manera, tanto la hidroquímica de las aguas de goteo como la tasa de goteo quedan como controles secundarios de la tasa de precipitación de carbonato actual.La reconstrucción de los cambios climáticos en el pasado utilizado registros espeleotémicos de la cueva de Ejulve se ha centrado en dos períodos: (1) durante la transición de MIS 8 a MIS 7 a través de la estalagmita ARTEMISA, y (2) durante los períodos MIS 5, 4 y 3 a través de la estalagmita ANDROMEDA. Los indicadores usados han sido d18O, d13C y Mg/Ca.La estalagmita ‘ARTEMISA’ creció durante el período 262.7 - 217.9 ka, incluyendo la respuesta climática a la Terminación Glacial III (T-III), una transición glacial-interglacial escasamente conocida, en contraposición a las Terminaciones II y I. La respuesta del d13C y Mg/Ca a los eventos abruptos áridos en el desarrollo de la T-III es realmente pronunciada. Por lo tanto, se han identificado dos eventos de escala milenial (S8.1 y S8.2) que estarían explicados por debilitamientos de la AMOC durante MIS 8. La sensibilidad de la Península Ibérica a los cambios en la AMOC, debido a su posición latitudinal y geográfica, ya ha sido demostrada previamente durante la Terminación I y MIS 3. La variabilidad en d18O del registro marca el último evento (S8.1) con un cambio en el d18O del agua en el área fuente de la precipitación, probablemente asociado a la llegada de agua dulce en el Atlántico norte. Tras una comparación entre la T-III, T-II y T-I, los dos eventos estadiales que han sido propuestos tienen semejanzas con los eventos Heinrich (HS) 1 y 2. Estas similitudes se basan en las intensas descargas de IRD, la dominancia de taxones semidesérticos durante los eventos áridos, y la similar señal del d18O de los foraminíferos bentónicos marinos. No obstante, los cambios en el nivel del mar y en la insolación durante S8.1, lo hacen más similar al YD que a HS-1, impidiendo por lo tanto concluir que el YD es un evento único de la última terminación.La estalagmita ‘ANDROMEDA’ crece de manera continua durante el intervalo de 118.9 a 36.9 ka. Durante MIS 5, los valores de d18O estaban regidos por control orbital, con picos de baja precisión que dan paso a condiciones húmedas. En contraste, durante MIS 4 y 3, los valores de d18O se desacoplan de la precesión, y covarían con el d13C, sugiriendo así un control común en ambos isótopos, debido a una mayor desgasificación del agua de goteo durante los períodos áridos. En general, el d13C exhibe una clara respuesta a los eventos fríos marinos desde el C26 hasta el C23, así como a las oscilaciones Dansgaard-Oeschger (D-O) y a los eventos Heinrich. Este registro apoya los resultados de estudios previos que mostraban un final tardío del Eemiense en el sur de Europa, y ofrece nuevas fechas para dicha finalización, desde 108.6 ± 0.3 a 108.3 ± 0.3 ka para esta área. La respuesta a los eventos Heinrich se establece en dos períodos distintivos en forma de ‘W’ en el patrón de variabilidad del d13C. Esos períodos se caracterizan por la respuesta del d13C a los débiles eventos D-O 15 y 18. La variabilidad en el d13C es similar en ambos eventos, no así su desarrollo, siendo más largo el primer evento, contemporáneo a HS-6. En el evento W más antiguo (~67-60 ka) han sido identificadas dos fases, la primera caracterizada por un patrón frío-árido antes de 63 ka, y una segunda de patrón húmedo-frío de 63 ka en adelante. El evento W más moderno (~57-53 ka) está en concordancia con un refuerzo de los vientos alisios en el NE (fase NAO+), provocando así unas condiciones de clima árido en el sur de Europa. Por otro lado, la correlación positiva entre el d13C y Mg/Ca en los períodos estudiados (Terminación III y MIS 5, 4 y 3) está en concordancia con mayor disponibilidad hídrica, más productividad vegetal y actividad microbiana sobre la cueva, como sugieren los resultados de la monitorización expuestos anteriormente.En resumen, la presente tesis muestra un modelo inusual de espeleogénesis en la Cordillera Ibérica propuesto para la cueva de Ejulve, un completo y detallado conjunto de datos procedentes de la monitorización de la dinámica espeleotémica actual, y la reconstrucción de interesantes cambios climáticos pasados. Esas características la convierten en la primera compilación de datos de este tipo en una cueva de la Cordillera Ibérica. Asimismo, conviene recalcar el gran interés de los resultados paleoclimáticos procedentes de estalagmitas de esta cueva, especialmente en cambios climáticos abruptos. La clara respuesta que exhibe durante el final de los períodos glaciares (Terminaciones), durante las oscilaciones D-O o los eventos Heinrich, y la clara vinculación con otros registros clave como las estalagmitas procedentes de cuevas de China, hacen a la cueva de Ejulve un lugar extraordinario para realizar estudios paleoclimáticos. The present dissertation addresses a complete study of Ejulve cave (Iberian Range, NE Spain) related to the speleogenesis of the cave, the current speleothemic dynamics and the reconstruction of past Pleistocene abrupt climate changes based on its speleothem record. Ejulve cave, located at 1240 m.a.s.l., is a relatively small cave in the southeastern sector of the Iberian Range. The cave is developed in dolomitic limestones and dolostones of the Mosqueruela Fm., Upper Cretaceous in age, affected by the thrust fronts of Portalrubio-Vandellós system, structured during Oligocene and Low Miocene. The landscape is dominated by extensive high-altitude deformed planation surfaces (Main Planation Surface of the Iberian Chain), finally shaped during the Pliocene. The origin of the cave is expected to have occurred before the final phase of the Main Planation Surface development. The identification of some characteristic cave morphologies such as boxwork, tubes with rising ceiling cupolas, pendants and cusps, spongework and micro-corrosion features, suggests a hypogene karst setting during this time. Hence, the hypogene karstification, tentatively occurred during the Mio-Pliocene, could be explained by ascending water flows driven by hydraulic gradients in a confined aquifer, generating a maze network and the characteristic cave morphologies listed above. Additionally, the analysis of the boxwork suggests an earlier stage, probably during the Upper Miocene, of calcite and dolomite infills hosted in discontinuities of the bedrock, formed under phreatic conditions. After the karstification, the cave underwent a transition to epigenic unconfined conditions, driven by the regional uplift and doming mechanisms. After the extensional tectonics during Pliocene-Quaternary, there was the subsequent fluvial incision. Once the exhumation of the karst leads to the vadose phase, it is the starting point for the precipitation of carbonate speleothems, at least from 650 kyr BP. The study of the cave speleothemic dynamics, including sampling of rainfall, drip waters and farmed calcite, was conducted during four years (2013-2016). The main factor that controls the d18O of the rainfall are the temperature effect (r2 = 0.82, p-value > 0.001), showing a seasonal pattern of lower values in winter and higher in summer. Both source effect (together with the rainfall component) and amount effect act as secondary controls. The use of the effective infiltration is crucial to evaluate the recharge of the epikarst, in the semi-arid conditions of the study area. In fact, the use of the effective infiltration reveal that the amount effect exerts a scarce influence on the isotopic variability of the drip waters, in contrast with the moderate influence that it exerts on the annual d18O in rainfall. The sampling of 12 drips throughout the cave indicated that seepage and seasonal drips featured similar d18O in dripwaters. The d18O seasonality seen in rainfall was also observed in dripwater d18O, albeit attenuated and lagged, so the homogeneisation process of the waters in the epikarst was not complete. The hydrological response of the cave to the external rainfall is fast, with an increase of drip rates within few weeks in both seasonal and seepage drips during the seasonal rainfall in autumn. However, the lag seen in the d18O of autumn-winter rainfall is as long as 21 weeks. These results suggest the existence of a ‘piston effect’, in which the ‘new’ water pushed down the ‘old’ pre-existent water in the epikarst through the fracture network. The farmed calcite shows a small variation of 0.11 ‰ in d18O, with similar variability between seasonal and seepage sites. The d18O of the calcite showed dependence on the d18O of the dripwaters, with a weak influence of drip rate. The variation in d13C is of 0.22 ‰, and exhibit seasonality with higher values during summer and autumn, and lower in winter and spring. The d13C was more positive in seepage sites, enhanced by degassing kinetics, up to 0.42 ‰ compared to the 0.29 ‰ observed in the seasonal sites. These differences between drip sites are explained by the high correlation of the d13C with the drip rate. Therefore, the high d13C in the farmed calcite of Ejulve cave was explained by enhanced degassing and low water availability, while low d13C values were in concordance with more microbial activity, vegetation productivity, and greater water availability. The ventilation of the cave during late autumn through spring favored the higher calcite deposition rates found during that time. Dripwater chemistry and drip rate exerts as secondary controls on carbonate growth rate. The reconstruction of past climate changes using stalagmites from Ejulve cave was focused in two main periods: (1) during the transition MIS 8 - MIS 7 using the stalagmite ARTEMISA, and (2) during the periods MIS 5, 4 and 3, using the stalagmite ANDROMEDA. The proxies used were d18O, d13C and Mg/Ca. The stalagmite ‘ARTEMISA’ covered the interval 262.7 to 217.9 kyr BP, including the response to the Termination III (T-III), a poorly known glacial-interglacial transition, in contrast to Terminations II and I. The response of the d13C and Mg/Ca to the abrupt arid events in the timing of the T-III was clear. Hence, we identify two millennial-scale events (S8.1 and S8.2) that are related to AMOC slowdowns during MIS 8. The sensitivity of the Iberian Peninsula to AMOC changes, due to its latitudinal and geographical location, has been demonstrated previously during Termination I and MIS 3. The variability in d18O in the record also marks the latest event (S8.1) with a change in the d18O composition of the sea water in the source of moisture, probably associated with the entrance of freshwater in north Atlantic. After a comparison between T-III, T-II and T-I, the two stadial events we propose have some similarities with Heinrich stadial (HS) 1 and 2. These similarities are supported by intense IRD discharges, the dominance of semidesert taxa in the arid intervals, and the similar phasing of the benthic d18O. However, the changes in sea level and insolation during S8.1, makes it more similar to the YD than HS-1, precluding the identification of the YD as a unique feature of the most recent termination. The stalagmite ‘ANDROMEDA’ covers continuously the interval from 118.9 to 36.9 kyr. During MIS 5, the d18O were controlled by orbital pacing, with low precession peaks leading wet conditions. In contrast, during MIS 4 and 3, the d18O fluctuations were decoupled from precession, and co-varies with d13C, suggesting a common control of both isotopes by enhanced degassing of drip waters during dry periods. In general, d13C exhibit a clear response to the cold marine events C26 to C23, as well as Dansgaard-Oeschger (D-O) oscillations and Heinrich events. This record supports previous studies showing a late demise of the Eemian forest stage in southern Europe, and offer new dates from 108.6 ± 0.3 to 108.3 ± 0.3 in this area. The response to Heinrich events were identified by two periods with a marked ‘W-shape’ pattern in the d13C. These periods were characterized by the response of the d13C to the weak D-O cycles 15 and 18. The variability in the d13C is similar between both events, but a different timing is seen, longer in the first event contemporary with HS-6. Two phases were identified within the older W-event (~ 67-60 kyr), a first one with dry-cold conditions before 63 kyr BP, and a second one with wet-cold conditions afterwards. The younger W-event (~ 57-53 kyr) is in concordance with the reinforcement of the northeasterly trade winds (NAO+ phase) giving rise to a dry climate in Southern Europe at that time. On the other hand, the positive correlation seen between d13C and Mg/Ca, in both periods (Termination III and MIS 5, 4 and 3), is expected to reflect water availability, vegetation productivity and microbial activity over the cave, such as was suggested by the monitoring results above. In summary, the present dissertation shows an unusual speleogenesis model in the Iberian Range proposed for Ejulve cave, a complete and careful detailed dataset related to the monitoring of present-day speleothem dynamics, and the reconstruction of interesting past climate changes. Those features make it the first compilation of such outstanding new brand data in a cave from the Iberian Range. Likewise, it is worth noting the high interest of the paleoclimatic results using speleothems from this cave, especially in the abrupt climate changes. The clear response exhibited during the end of Glacial periods (Terminations), to D-O oscillations and Heinrich events, and the clear link with other key records such as the speleothems from caves in China, makes Ejulve cave an outstanding site for paleoclimatic studies. <br /

Extracting dimer structures from simulations of organic-based materials using QM/MM methods

The functionality of weakly bound organic materials, either in Nanoelectronics or in Materials Science, is known to be strongly affected by their morphology. Theoretical predictions of the underlying structure–property relationships are frequently based on calculations performed on isolated dimers, but the optimized structure of the latter may significantly differ from experimental data even when dispersion-corrected methods are used for it. Here, we address this problem on two organic crystals, namely coronene and 5,6,11,12-tetrachlorotetracene, concluding that it is caused by the absence of the surrounding monomers present in the crystal, and that it can be efficiently cured when the dimer is embedded into a general Quantum Mechanics/Molecular Mechanics (QM/MM) geometry optimization scheme. We also investigate how the size of the MM region affects the results. These findings may be helpful for the simulation of the morphology of active materials in crystalline or glassy samples.This work is supported by the “Ministerio de Economía y Competitividad” of Spain and the “European Regional Development Fund” through project CTQ2014–55073-P

Theoretical study of stability and charge-transport properties of coronene molecule and some of its halogenated derivatives: A path to ambipolar organic-based materials?

We have carefully investigated the structural and electronic properties of coronene and some of its fluorinated and chlorinated derivatives, including full periphery substitution, as well as the preferred orientation of the non-covalent dimer structures subsequently formed. We have paid particular attention to a set of methodological details, to first obtain single-molecule magnitudes as accurately as possible, including next the use of modern dispersion-corrected methods to tackle the corresponding non-covalently bound dimers. Generally speaking, this class of compounds is expected to self-assembly in neighboring π-stacks with dimer stabilization energies ranging from –20 to –30 kcal mol−1 at close distances around 3.0–3.3 Å. Then, in a further step, we have also calculated hole and electron transfer rates of some suitable candidates for ambipolar materials, and corresponding charge mobility values, which are known to critically depend on the supramolecular organization of the samples. For coronene and per-fluorinated coronene, we have found high values for their hopping rates, although slightly smaller for the latter due to an increase (decrease) of the reorganization energies (electronic couplings).This work is supported by the “Ministerio de Educación y Ciencia” of Spain and the “European Regional Development Fund” through Project No. CTQ2011-27253

Theoretical Insights for Materials Properties of Cyclic Organic Nanorings

The synthesis of new carbon nanoforms with remarkable and fine‐tuned bulk properties still represents a formidable challenge, with cyclic organic nanorings emerging in recent years for the template‐driven design of this kind of systems. The design and engineering of these materials can be first controlled at the molecular scale, to further induce their specific self‐assembly toward tailored properties at the nanoscale. Theoretical studies have lately contributed to the understanding of the underlying physical effects, the development of synthetic strategies, and the rationalization of novel materials properties, employing a variety of methods ranging from accurate calculations of isolated molecules to atomistic molecular dynamics simulations of a large sample of molecules in realistic conditions, which will be reviewed here with a focus on the transition from single‐molecule to supramolecular properties.Computational resources were provided along the years by projects CTQ2014-55073-P and PID2019-106114GB-I00 (“Ministerio de Ciencia e Innovación”) and AICO/2018/175 (“Generalitat Valenciana”)

Determining the cohesive energy of coronene by dispersion-corrected DFT methods: Periodic boundary conditions vs. molecular pairs

We investigate the cohesive energy of crystalline coronene by the dispersion-corrected methods DFT-D2, DFT-D3, and DFT-NL. For that purpose, we first employ bulk periodic boundary conditions and carefully analyze next all the interacting pairs of molecules within the crystalline structure. Our calculations reveal the nature and importance of the binding forces in every molecular pair tackled and provide revised estimates of the effects of two- and three-body terms, leading to accurate results in close agreement with experimental (sublimation enthalpies) reference values.Financial support by the “Ministerio de Economía y Competitividad” of Spain and the “European Regional Development Fund” through Project No. CTQ2011-27253. The work in Mons was supported by the “Programme d’Excellence de la Région Wallonne” (OPTI2MAT project) and FNRS-FRFC

The diene isomerization energies dataset: A difficult test for double-hybrid density functionals?

We have systematically analyzed the performance of some representative double-hybrid density functionals (including PBE0-DH, PBE-QIDH, PBE0-2, XYG3, XYGJ-OS, and xDH-PBE0) for a recently introduced database of diene isomerization energies. Double-hybrid models outperform their corresponding hybrid forms (for example, PBE0-DH, PBE0-2, and PBE-QIDH are more accurate than PBE0) and the XYG3, XYGJ-OS, and xDH-PBE0 functionals perform excellently, providing root mean square deviation values within “calibration accuracy.” XYGJ-OS and xDH-PBE0 also rival the best performing post-Hartree-Fock methods at a substantially lower cost.The work in Alicante is supported by the “Ministerio de Economía y Competitividad” of Spain and the “European Regional Development Fund” through Project No. CTQ2014-55073P. The work at IMDEA was supported by the Campus of International Excellence (CEI) UAM+CSIC. M.W. thanks the European Commission for his Marie Curie Fellowship (Grant No. FP7-PEOPLE-2012-IEF-331795)

Range-separated hybrid density functionals made simple

In this communication, we present a new and simple route to derive range-separated exchange (RSX) hybrid and double hybrid density functionals in a nonempirical fashion. In line with our previous developments [Brémond et al., J. Chem. Theory Comput. 14, 4052 (2018)], we show that by imposing an additional physical constraint to the exchange-correlation energy, i.e., by enforcing to reproduce the total energy of the hydrogen atom, we are able to generalize the nonempirical determination of the range-separation parameter to a family of RSX hybrid density functionals. The success of the resulting models is illustrated by an accurate modeling of several molecular systems and properties, like ionization potentials, particularly prone to the one- and many-electron self-interaction errors.E.B. thanks ANR (Agence Nationale de la Recherche) and CGI (Commissariat à l’Investissement d’Avenir) for their financial support for this work through Labex SEAM (Science and Engineering for Advanced Materials and devices) ANR 11 LABX 086, ANR 11 IDEX 05 02. The authors acknowledge the GENCI-CINES for HPC resources (Project Nos. AP010810360 and A0040810359)

Communication: Double-hybrid functionals from adiabatic-connection:The QIDH model

A new approach stemming from the adiabatic-connection (AC) formalism is proposed to derive parameter-free double-hybrid (DH) exchange-correlation functionals. It is based on a quadratic form that models the integrand of the coupling parameter, whose components are chosen to satisfy several well-known limiting conditions. Its integration leads to DHs containing a single parameter controlling the amount of exact exchange, which is determined by requiring it to depend on the weight of the MP2 correlation contribution. Two new parameter-free DHs functionals are derived in this way, by incorporating the non-empirical PBE and TPSS functionals in the underlying expression. Their extensive testing using the GMTKN30 benchmark indicates that they are in competition with state-of-the-art DHs, yet providing much better self-interaction errors and opening a new avenue towards the design of accurate double-hybrid exchange-correlation functionals departing from the AC integrand.J.C.S.G. and A.J.P.J. thank the “Ministerio de Educación y Ciencia” of Spain and the “European Regional Development Fund” through project CTQ2011-27253 for financial and computational support

La Cueva de El Recuenco (Ejulve, Teruel): Espeleogénesis y registro de cambios climáticos rápidos durante el Holoceno

Este estudio ha consistido en (1) investigar la espeleogénesis de la cueva de El Recuenco (Ejulve, Teruel) analizando su contexto geológico, y geomorfológico; (2) realizar un seguimiento instrumental de la dinámica espeleotémica actual (lluvia, goteo y carbonato precipitado) y (3) reconstruir la variabilidad climática durante el Holoceno Medio en la región a partir de los análisis geoquímicos de alta resolución realizados en una estalagmita. La cueva estudiada presenta un desarrollo de galerías de 794 m con una profundidad de 55 m y su morfología y topografía están controladas fundamentalmente por la red de fracturas en la roca soporte. El seguimiento de su dinámica actual revela una temperatura constante de 11 ºC, humedad relativa del 100% y mayor concentración de CO2 en la parte más interna de la cueva, aumentando la ventilación en los meses de invierno. A pesar de que se observa una falta de respuesta hidrológica de la cueva a la precipitación, los análisis de isótopos estables en goteos y vidrios revelan un claro patrón estacional, con valores más negativos en invierno respecto a primavera. La estalagmita estudiada cuenta con un preciso marco cronológico (23 dataciones) y una resolución analítica decadal, idóneas para la reconstrucción climática de los últimos milenios. Se observa un hiato durante el Holoceno Temprano y un crecimiento continuo entre 9969 y 2715 años BP. Además, el registro isotópico (d18O y d13C) y de elementos traza (relaciones Ba/Ca, Sr/Ca y Mg/Ca) permite identificar dos eventos de aridificación entre 5.2-4.7 ka BP y 3.8-3.6 ka BP, coincidentes con períodos cálidos de los ciclos de Bond. Así, a pesar de que estudios previos del Holoceno en latitudes medias y altas asociaban períodos áridos con fases frías de Bond, en esta región la asociación frío – aridez no es válida para el Holoceno

Nature (Hole or Electron) of Charge-Transfer Ability of Substituted Cyclopyrenylene Hoop-Shaped Compounds

We theoretically investigate here by means of DFT methods how the selective substitution in cyclic organic nanorings composed of pyrene units may promote semiconducting properties, analyzing the energy needed for a hole- or electron-transfer accommodation as a function of the substitution pattern and the system size (i.e., number of pyrene units). We choose to study both [3]Cyclo-2,7-pyrenylene ([3]CPY) and [4]Cyclo-2,7-pyrenylene ([4]CPY) compounds, the latter already synthesized, with substituents other than hydrogen acting in ipso and ortho positions, as well as the effect of the per-substitution. As substituents, we selected a set of electroactive halogen atoms (F, Cl, and Br) and groups (CN) to disclose structure–property relationships allowing thus to anticipate the use of these systems as organic molecular semiconductors.A.J.P.-J. and J.C.S.-G. acknowledge the project AICO/2018/175 from the Regional Government (GVA/FSE). M.M. acknowledges the E2TP-CYTEMA-SANTANDER program. A.N. acknowledges “Consejería de Economía y Conocimiento, Junta de Andalucía” (FQM-337) and “Acción 1-Plan 2017-18” (Universidad de Jaén, Spain)