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Clearing and construction activities related to the Maya Train (Tren Maya) project resulted in potential and inevitable impacts to archaeological caves sites in largely undeveloped areas of Quintana Roo. An effort coordinated by Mexico's National Institute of Anthropology and History (INAH) involved accelerated digital documentation of two caves – via SLAM-enabled mobile LiDAR scanning and targeted photogrammetry – to facilitate prompt visualization and evaluation of terrestrial and subterranean geospatial relationships. Mobile LiDAR is well suited to the challenges of capturing the complex, multilevel morphology of caves and was readily deployed across and through priority environments. Specific archaeological features – such as ancient Maya rock art and masonry shrines – were documented via photogrammetry, and the resulting higher-resolution models co-referenced with the georeferenced mobile LiDAR-generated point clouds of each cave and the surrounding topographic context. This integrative approach contributed to a more informed decision-making process, with respect to conservation and construction, and provided baseline data for future monitoring of the affected cave sites. [ABSTRACT FROM AUTHOR]

Cave carbonate minerals are an important terrestrial paleoclimate archive. A few studies have explored the potential for applying carbonate clumped isotope thermometry to speleothems as a tool for constraining past temperatures. To date, most papers utilizing this method have focused on mass-47 clumped isotope values (Δ 47) at a single location and reported that cave carbonate minerals rarely achieve isotopic equilibrium, with kinetic isotope effects (KIEs) attributed to CO 2 degassing. More recently, studies have shown that mass-47 and mass-48 CO 2 from acid digested carbonate minerals (Δ 47 and Δ 48) can be used together to assess equilibrium and probe KIEs. Here, we examined 44 natural and synthetic modern cave carbonate mineral samples from 13 localities with varying environmental conditions (ventilation, water level, pCO 2 , temperature) for (dis)equilibrium using Δ 47 -Δ 48 values, in concert with traditional stable carbon (δ13C) and oxygen (δ18O) isotope ratios. Data showed that 19 of 44 samples exhibited Δ 47 -Δ 48 values indistinguishable from isotopic equilibrium, and 18 (95 %) of these samples yield Δ 47 -predicted temperatures within error of measured modern temperatures. Conversely, 25 samples exhibited isotopic disequilibria, 13 of which yield erroneous temperature estimates. Within some speleothem samples, we find Δ 47 -Δ 48 values consistent with CO 2 degassing effects, however, the majority of samples with KIEs are consistent with other processes being dominant. We hypothesize that these values reflect isotopic buffering effects on clumped isotopes that can be considerable and cannot be overlooked. Using a Raleigh Distillation Model, we examined carbon and oxygen isotope exchange trajectories and their relationships with dual clumped isotope disequilibria. Carbon isotope exchange is associated with depletion of both Δ 47 and Δ 48 relative to equilibrium, while oxygen isotope exchange is associated with enrichment of both Δ 47 and Δ 48 relative to equilibrium. Cave rafts collected from proximate locations in Mexico exhibit the largest average departures from equilibrium ( Δ Δ 47 ¯ = −0.032 ± 0.007, Δ Δ 48 ¯ = −0.104 ± 0.035, where ΔΔ i is the measured value – the equilibrium value). This study shows how the Δ 47 -Δ 48 dual carbonate clumped isotope framework can be applied to a variety of tcave carbonate mineral samples, enabling identification of isotopic equilibria and therefore quantitative application of clumped isotope thermometry for paleoclimate reconstruction, or alternatively, constraining the mechanisms of kinetic effects. [ABSTRACT FROM AUTHOR]

The Astyanax mexicanus complex includes two different morphs, a surface‐ and a cave‐adapted ecotype, found at three mountain ranges in Northeastern Mexico: Sierra de El Abra, Sierra de Guatemala and Sierra de la Colmena (Micos). Since their discovery, multiple studies have attempted to characterize the timing and the number of events that gave rise to the evolution of these cave‐adapted ecotypes. Here, using RADseq and genome‐wide sequencing, we assessed the phylogenetic relationships, genetic structure and gene flow events between the cave and surface Astyanax mexicanus populations, to estimate the tempo and mode of evolution of the cave‐adapted ecotypes. We also evaluated the body shape evolution across different cave lineages using geometric morphometrics to examine the role of phylogenetic signal versus environmental pressures. We found strong evidence of parallel evolution of cave‐adapted ecotypes derived from two separate lineages of surface fish and hypothesize that there may be up to four independent invasions of caves from surface fish. Moreover, a strong congruence between the genetic structure and geographic distribution was observed across the cave populations, with the Sierra de Guatemala the region exhibiting most genetic drift among the cave populations analysed. Interestingly, we found no evidence of phylogenetic signal in body shape evolution, but we found support for parallel evolution in body shape across independent cave lineages, with cavefish from the Sierra de El Abra reflecting the most divergent morphology relative to surface and other cavefish populations. [ABSTRACT FROM AUTHOR]

Complex patterns of acoustic communication exist throughout the animal kingdom, including underwater. The river-dwelling and the Pachón cave-adapted morphotypes of the fish Astyanax mexicanus are soniferous and share a repertoire of sounds. Their function and significance is mostly unknown. Here, we explored whether and how sounds produced by blind cavefishes inhabiting different Mexican caves may vary. We compared "Clicks" and "Serial Clicks" produced by cavefish in six different caves distributed in three mountain ranges in Mexico. We also sampled laboratory-bred cavefish lines originating from four of these caves. Sounds were extracted and analyzed using both a manual method and a machine learning-based automation tool developed in-house. Multi-parametric analyses suggest wild cave-specific acoustic signatures, or "accents". An acoustic code also existed in laboratory cavefish lines, suggesting a genetic basis for the evolution of this trait. The variations in acoustic parameters between caves of origin did not seem related to fish phenotypes, phylogeography or ecological conditions. We propose that the evolution of such acoustic signatures would progressively lead to the differentiation of local accents that may prevent interbreeding and thus contribute to speciation. [ABSTRACT FROM AUTHOR]

Speleothems (cave stalagmites) contain inorganic and organic substances that can be used to infer past changes in local and regional paleoenvironmental conditions. Specific biomarkers can be employed to elucidate the history of past fires, caused by interactions among climate, regional hydrology, vegetation, humans, and fire activity. We conducted a simple solid–liquid extraction on pulverised carbonate samples to prepare them for analysis of 16 polycyclic aromatic hydrocarbons (PAHs) and three monosaccharide anhydrides (MAs). The preparation method requires only small samples (0.5–1.0 g); PAHs and MAs were measured by GC–MS and LC–HILIC–MS, respectively. Detection limits range from 0.05–2.1 ng for PAHs and 0.01–0.1 ng for MAs. We applied the method to 10 samples from a ∼ 400-year-old stalagmite from Cenote Ch'en Mul, at Mayapan (Mexico), the largest Postclassic Maya capital of the Yucatán Peninsula. We found a strong correlation (r = 0.75, p < 0.05) between the major MA (levoglucosan) and non-alkylated PAHs (Σ 15). We investigated multiple diagnostic PAH and MA ratios and found that although not all were applicable as paleo-fire proxies, ratios that combine PAHs with MAs are promising tools for identifying different fire regimes and inferring the type of fuel burned. In the 1950s and 1960s, levoglucosan and Σ 15 concentrations roughly doubled compared to other times in the last 400 years, suggesting greater fire activity at Mayapan during these two decades. The higher concentrations of fire markers may have been a consequence of land clearance at the site and exploration of the cave by Carnegie Institution archaeologists. [ABSTRACT FROM AUTHOR]

Large bell‐shaped calcite formations called "Hells Bells" were discovered underwater in the stratified cenote El Zapote on the Yucatán Peninsula, Mexico. Together with these extraordinary speleothems, divers found a white, cloudy turbid layer into which some Hells Bells partially extend. Here, we address the central question if the formation of the turbid layer could be based on microbial activity, more specifically, on microbially induced calcite precipitation. Metagenomic and metatranscriptomic profiling of the microbial community in the turbid layer, which overlaps with the pelagic redoxcline in the cenote, revealed chemolithoautotrophic Hydrogenophilales and unclassified β‐Proteobacteria as the metabolic key players. Bioinformatic and hydrogeochemical data suggest chemolithoautotrophic oxidation of sulfide to zero‐valent sulfur catalyzed by denitrifying organisms due to oxygen deficiency. Incomplete sulfide oxidation via nitrate reduction and chemolithoautotrophy are both proton‐consuming processes, which increase the pH in the redoxcline favoring authigenic calcite precipitation and may contribute to Hells Bells growth. The observed mechanism of microbially induced calcite precipitation is potentially applicable to many other stagnant sulfate‐rich water bodies. [ABSTRACT FROM AUTHOR]

Reconstructing hydroclimate over the Common Era is essential for understanding the dominant mechanisms of precipitation change and improving climate model projections, which currently suggest Northeast Mexico will become drier in the future. Tree‐ring reconstructions have suggested regional rainfall is primarily controlled by Pacific sea‐surface temperatures (SSTs). However, tree ring records tend to reflect winter‐spring rainfall, and thus may not accurately record total annual precipitation. Using the first multiproxy speleothem record spanning the last millennium, combined with results from an atmospheric general circulation model, we demonstrate mean annual rainfall in Northeast Mexico is highly sensitive to Atlantic SST variability. Our findings suggest future precipitation in Northeast Mexico is more dependent upon the warming of Tropical Atlantic SSTs relative to the Tropical Pacific. Plain Language Summary: We use geochemical markers of past rainfall in a rock from a cave (speleothem) to show that warming in Atlantic sea‐surface temperatures (SSTs) increases the amount of precipitation in Northeast Mexico. These finding are surprising, since previous rainfall reconstructions using tree rings have suggested a warmer Atlantic decreases precipitation in the region. We used a climate model to show that warming in the Atlantic increases precipitation during the summer but decreases precipitation during the winter. Although winter precipitation only accounts for 8% of annual rainfall in this region, tree rings are more reflective of the winter precipitation response. This is the first speleothem record from NE Mexico over this time‐period and suggests that projections of future rainfall should emphasize relative changes in Atlantic SST variability because it has a major impact on annual precipitation. Key Points: We present the first speleothem record spanning the last millennium from NE Mexico using multiple geochemical proxiesIn contrast to tree ring reconstructions, we suggest regional precipitation is primarily controlled by Atlantic sea‐surface temperatures (SSTs)We utilize results from a forced‐SST climate model to further support our interpretation [ABSTRACT FROM AUTHOR]

Hourly temperature was measured for approximately one year at 17 stations in three caves in Quintana Roo, Mexico. Thirteen of these stations were in the extensive twilight zones of all three caves. All seventeen stations showed seasonality in temperature with a 3°C drop during the Nortes season. Two of the caves, Muévelo Sabrosito and Muévelo Rico, showed greater variability during the winter months while in Río Secreto (Tuch) variability was greatest during the rainy season. Río Secreto is less open to the surface than the other two. All sites also showed a daily temperature cycle, although it was very faint in some Río Secreto (Tuch) sites. While temperature variability is diminished relative to surface variation, its temporal pattern is worthy of further study. [ABSTRACT FROM AUTHOR]

This study examines the oxygen isotopic composition (δ18O values) of drip water, rainfall, and groundwater in the Río Secreto cave system, located in the Yucatán Peninsula, Mexico. The main motivation of this study was to determine the implications of drip water hydrology for the reconstruction of rainfall, droughts and tropical cyclone activity from stalagmite δ18O records. Monitoring of environmental and isotopic conditions was conducted for two years, from June 2017 to April 2019. This study provides the first instrumental evidence of an "amount effect" on interannual timescales in the Yucatán Peninsula. Observed bi-weekly to interannual variability in drip water δ18O values can be explained for individual drips by different integrations of rainfall amount in the time domain. Drip sites in two chambers (Stations A and B) integrate 4–15 months of rainfall accumulation. In a third chamber (Station LF) one drip site reflects the annual rainfall isotopic cycle with a positive offset and another, the largest rainfall events. During epikarst infiltration, the integration of rainfall amount by drip water source reservoirs determines the degree to which they "dilute" a tropical cyclone (TC) isotopic signature. TCs can be detected particularly when: (1) the water volume of the reservoir is low, such as during a persistent meteorological drought, and; (2) TCs have a sufficiently distinct isotopic signal relative to that of the reservoir prior to the event. TC isotopic signals can be masked or attenuated when drip water samples integrate more than a week and if significant rainfall events proceed the TC. In Río Secreto cave, reconstructing precipitation amount and detecting the TC isotopic signatures from stalagmite δ18O records is possible. Our analysis shows that stalagmite δ18O records are more likely to underestimate the magnitude of annual-scale droughts following normal hydroclimate conditions and more likely to record TCs during multiyear droughts than during normal or wet periods. Drip water monitoring results suggest that available stalagmite δ18O records from the Maya lowlands might be underestimating the intensity of paleo-drought events, such as the Terminal Classic droughts associated with the disintegration of the Maya civilization. This study complements the results from Lases-Hernandez et al. (2019) comparing two different sampling protocols of drip water collection. This study shows that a discrete sampling protocol is expected to approximate the amount-weighted isotopic composition of a drip, as long as it is conducted at a temporal resolution higher than the rainfall integration time by the drip reservoir. We highlight the importance of conducting multiyear monitoring of drip water and rainfall in order to interpret stalagmite δ18O as a paleoclimate proxy. [ABSTRACT FROM AUTHOR]

Pac Chen Lake is located on the Yucatan Peninsula, Mexico and is ~ 42 km from the coast and ~ 22 km NE of Coba. It has an area of ~ 36,735 m2 and maximum depth of 25 m. Four sediment cores along a depth transect provide a 4-ka record of the evolution of the eastern deep basin (core PC1 at 25 m depth) and the shallow margin (cores PC2–4 at 0.25–5 m depth). PC1 shows the effect of water-level rise and flooding of the shallow margin (2.8–1.8 ka) through a lithological (organic to carbonate) and geochemical (μXRF; decreased Ti, Fe, K and Ca) change along with a reduction in sediment accumulation (~ 0.2927 to 0.0343 cm year−1). This change in sedimentation matches basal ages of PC2 and PC4 at 2.5 and 1.8 ka respectively, indicating water-level rise and flooding of the shallowly sloped margin which is within estimates of Holocene sea-level rise thus indicating connection with the aquifer. Corroborating evidence for connection with the aquifer comes from water-level monitoring (30 min intervals; 6 months December 12, 2018 to June 6, 2019) which shows a semi-diurnal tidal fluctuation (1–1.5 cm). Droughts have been thoroughly discussed as a proponent of the decline of the Classic Maya, with lakes being inferred to be isolated from the aquifer and experiencing water level drawdown. However, during the Classic Maya droughts lake drawdown in Pac Chen would be minimal, and there is no evidence of a water level drop in our lake margin stratigraphy (PC2–4). Water mass characteristics measured in March 2016 (temperature, conductivity) indicate some hydrological isolation from the aquifer. This isolation would have allowed for recording of environmental changes, but also likely changed through time as flooding of the lake progressed. The shallow margin core PC4, however, recorded several rapid drops in K and Fe from ~ 1100 to 975, and 925–875 yr BP, which we interpret as periods of reduced inputs of terrigenous weathering during times of reduced rainfall and runoff. These periods are consistent with other regional paleoclimate records (lake and speleothem) of the Classic Maya droughts (1200–850 yr BP). [ABSTRACT FROM AUTHOR]

• Species delimitation methods and morphology validated a new species of cave brittle star. • Successful colonisation of anchihaline caves by brittle stars has been very rare. • The origin of Ophionereis commutabilis does not conform fully to models on the origin of cave taxa. • Cave brittle stars do not share convergent morphological traits association with cave-life. Caves are a useful system for testing evolutionary and biogeographic hypotheses, as they are isolated, and their environmental conditions have resulted in adaptive selection across different taxa. Although in recent years many more cave species have been discovered, cave-dwelling members of the class Ophiuroidea (brittle stars) remain scarce. Out of the more than two thousand species of brittle stars described to date, only three are regarded as true cave-dwellers. These occurrences represent rare colonising events, compared to other groups that are known to have successfully diversified in these systems. A third species from an anchihaline cave system in the Yucatan Peninsula, Mexico, has been previously identified from cytochrome oxidase I (COI) barcodes. In this study, we reassess the species boundaries of this putative cave species using a phylogenomic dataset (20 specimens in 13 species, 100 exons, 18.7 kbp). We perform species delimitation analyses using robust full-coalescent methods for discovery and validation of hypotheses on species boundaries, as well as infer its phylogenetic relationships with species distributed in adjacent marine regions, in order to investigate the origin of this cave-adapted species. We assess which hypotheses on the origin of subterranean taxa can be applied to this species by taking into account its placement within the genus Ophionereis and its demographic history. We provide a detailed description of Ophionereis commutabilis n. sp., and evaluate its morphological characters in the light of its successful adaptation to life in caves. [ABSTRACT FROM AUTHOR]

Unique bell-shaped underwater speleothems were recently reported from the deep (∼ 55 m) meromictic El Zapote sinkhole (cenote) on the Yucatán Peninsula, Mexico. The local diving community has termed these speleothems as Hells Bells because of their shape and appearance in a dark environment in ∼ 28–38 m water depth above a sulfidic halocline. It was also suggested that Hells Bells form under water, yet the mystery of their formation remained unresolved. Therefore, we conducted detailed hydrogeochemical and geochemical analyses of the water column and Hells Bells speleothems including stable carbon isotopes. Based on the comprehensive results presented in this study we deduce that both biogeochemical processes in the pelagic redoxcline and a dynamic halocline elevation of El Zapote cenote are essential for Hells Bells formation. Hells Bells most likely form in the redoxcline, a narrow 1–2 m thick water layer immediately above the halocline where a pelagic chemolithoautotrophic microbial community thrives from the upward diffusion of reduced carbon, nitrogen and sulfur species released from organic matter degradation in organic-rich debris. We hypothesize that chemolithoautotrophy, in particular proton-consuming nitrate-driven anaerobic sulfide oxidation, favors calcite precipitation in the redoxcline and hence Hells Bells formation. A dynamic elevation of the halocline as a hydraulic response to droughts, annual tidal variability and recharge events is further discussed, which might explain the shape of Hells Bells as well as their occurrence over a range of 10 m water depth. Finally, we infer that highly stagnant conditions, i.e., a thick halocline, a low-light environment and sufficient input of organic material into a deep meromictic cenote are apparent prerequisites for Hells Bells formation. This might explain their exclusivity to only a few cenotes in a restricted area of the northeastern Yucatán Peninsula. [ABSTRACT FROM AUTHOR]

We here report on a type of meter-sized pendant speleothem growing under water in the submerged El Zapote sinkhole (cenote) west of Puerto Morelos on the Mexican Yucatán Peninsula. These conical, mantle-shaped downward expanding and diverging calcareous structures, here termed as Hells Bells, are yet unreported in the scientific literature. They are characterized by bell- or trumpet shaped longitudinal and circular, elliptical or horse-shoe-like horizontal cross-sections. Hells Bells grow downward, based on the downward divergence of the structures and the horizontally laminated internal texture of both blade-shaped spar calcite and microspar laminae. Age dating confirms that Hells Bells are young (< 4500 yr) and formed in a subaquatic environment. They grow under lightless conditions in a stratified water body, which is characterized by a fresh water body overlying a salt water body with a stagnant transition zone (halocline) of several meters. We hypothesize that the growth of these structures is mediated by specific physical and biogeochemical conditions above and in the halocline. Stagnant hydraulic conditions led to extensive diffusion profiles of several nutrients including calcium originating from the salt water body. Dissolved organic carbon from the fresh water is microbially oxidized in the upper part of the halocline, where a distinct redox zonation was identified from oxic to anoxic conditions. Degradation processes combined with slightly alkaline pH values as well as the diffusive transport of calcium into this zone may induce an increase in calcite oversaturation. Phylogenetic analysis of the community on the surface of the Hells Bells suggests the presence of microorganisms involved in the nitrogen-cycle, from which some potentially have the capability to increase the pH by autotrophic growth and denitrifying activity, thus supporting calcite precipitation. The growth of Hells Bells is strictly dependent on the elevation of the halocline. This offers a wide potential for the use of Hells Bells as archives of paleo-hydrological conditions during the Holocene, e.g. the variation of thickness of the fresh water lens on the Yucatán Peninsula. [ABSTRACT FROM AUTHOR]

Las Karmidas Cave (Puebla State, Mexico) is an unusual type of pseudokarstic cavity generated by piping and erosive processes within the contact of a diamicton and an overlying Quaternary ignimbrite. Morphological evidence suggests that the cave was developed in two stages: a phreatic stage and a vadose stage. The latter was characterized by the formation of carbonate speleothems. The absolute upper-age limit for the cave (168 +7.1/-7.5 ka) was established by U-Th dating of zircons grains extracted from the overlying ignimbrite, whilst a minimum age for the transition from a phreatic to vadose regime (95.6 ± 2.1 ka) was constrained by U-Th dating of carbonate speleothems within the cave. The geochronological results indicate a very rapid evolution of this pseudokarstic system, and suggest that similar systems might evolve and degrade at a very fast pace; consequently, making them hard to be preserved. Despite this, and considering the rather common geological context in which this system was developed, it is likely that similar pseudokarstic systems are yet to be detected worldwide. [ABSTRACT FROM AUTHOR]

Methane (CH4) is an economic resource and a greenhouse gas, but its migration through rocks is not immediately associated with speleogenesis. Sulfuric-acid speleogenesis is a cave-forming mechanism that has produced a variety of economically important oil fields and aquifers, and is theorized to be related to the oxidation of CH4 and hydrocarbons. Despite hypotheses that the oxidation of CH4 may provide a basis for the generation of sulfides during sulfuric-acid speleogenesis, evidence from active systems has not yet been obtained. In this study, we address how CH4 influences the development of sulfidic cave systems by sampling the CH4, H2S, and CO2 concentrations, as well as δ1313CCH4 , δ2HCH4 , and δ13CCO2 values, in a cave currently forming by sulfuric-acid speleogenesis, Cueva de Villa Luz. CH4, H2S, and CO2 concentrations were highest directly above springs in the cave, showing that all three gases enter by means of the spring water. The δ13CCH4 and δ2HCH4 in the air of CVL ranged from -47.92 ±15 to -35.47 ±12 % (VPDB) and -117 to -83 % (VSMOW), respectively. Keeling plots suggest that CH4 with δ13CCH4-24 ± 3 % and δ2HCH4-40 ± 50 % was outgassing from spring water. This stable-isotope signature does not fall within traditional published δ13CCH4 versus δ2HCH4 fields. Our data suggest that the CH4 entering Cueva de Villa Luz is the remnant of a larger thermogenic CH4 flux that is incompletely oxidized in the subsurface as it travels to Cueva de Villa Luz. Our data support links between the processes forming Cueva de Villa Luz and the proposed mechanisms for other caves associated with sulfuric acid. [ABSTRACT FROM AUTHOR]

Abstract: Climate oscillations have significantly contributed to the planet''s evolution, including volcanic activity. Major glaciations have been considered not only as a triggering mechanism for large magmatic eruptions but also inducing volcano instability. Generally, volcano instability can be inferred from detailed volcanological and structural studies of a volcano and its associated depositional sequence, but the triggering mechanism has been always difficult to infer. In this paper, we present evidence of how climatic variations during the Late Pleistocene could have forced sector collapses of the main Mexican stratovolcanoes and enhanced the mobility of associated massive flows inducing the transformation of debris avalanche into debris flows. In particular, the climatic record based on atmospheric moisture content from robustly dated lake record from Guatemala and a U/Th dated speleothem from New Mexico are used here as indicators of summer and winter precipitation. Depositional sequences associated with Late Pleistocene sector collapses of Volcán de Colima, Nevado de Toluca, Citlaltépetl (Pico de Orizaba) and Cofre de Perote volcanoes are here analyzed. Comparing the timing of the event with the climatic record, a combination of summer and/or winter pluvial conditions could have forced and triggered the failure of already unstable volcanoes, even during glacier advances (as for the Citlaltépetl event). Independent of the main cause of the volcano instability (magmatic or tectonic) it is important to highlight that the climatic factor played an important role in enhancing the volcano instability and promoted the lateral transformation of debris avalanches, which under dry conditions would have affected more limited areas. [Copyright &y& Elsevier]

Some of the most outstanding hypogenic gypsum speleothems worldwide have been recently discovered in the Naica mines. The Cueva de las Espadas (Swords Cave), which lies at 120 m depth, hosts a rare type of speleothem called "espada" ("sword"). This study contributes to the understanding of the mineralogical composition of these singular speleothems, by means of their examination using micro-Raman spectroscopy, FT-IR spectroscopy and EDX microprobe. Our data revealed a complex mineralogy comprising a high-purity selenite core covered by several layers of calcite, aragonite and gypsum. Solid inclusions of polymetallic oxides (Mn-Pb-Zn) and graphite were also detected. The position of the water table during the genesis of the "espada" speleothems (over the past 60 kyr) was deduced from their mineralogy. Water level fluctuations at around -120 m depth led to environmental changes within the Cueva de las Espadas. The selenite core and gypsum layers were precipitated under biphasic (water-rock) conditions when the cave was submerged under hydrothermal water. The aragonite precipitation required triphasic (air-water-rock) conditions and occurred when the water table intercepted the cave, allowing the CO2 exchange necessary for carbonate precipitation. Solid inclusions were trapped in an aerobic environment when the gypsum-aragonite boundary condition occurred. A thin calcite layer was precipitated under vadose conditions after the water table definitively moved out of the cave. [ABSTRACT FROM AUTHOR]

Abstract: A paleoclimate reconstruction for the Holocene based upon variations of δ18O in a U–Th dated stalagmite from southwestern Mexico is presented. Our results indicate that the arrival of moisture to the area has been strongly linked to the input of glacial meltwaters into the North Atlantic throughout the Holocene. The record also suggests a complex interplay between Caribbean and Pacific moisture sources, modulated by the North Atlantic SST and the position of the ITCZ, where Pacific moisture becomes increasingly more influential through ENSO since ~4.3ka. The interruption of stalagmite growth during the largest climatic anomalies of the Holocene (10.3 and 8.2ka) is evidenced by the presence of hiatuses, which suggest a severe disruption in the arrival of moisture to the area. The δ18O record presented here has important implications for understanding the evolution of the North American Monsoon and climate in southwestern Mexico, as it represents one of the most detailed archives of climate variability for the area spanning most of the Holocene. [ABSTRACT FROM AUTHOR]

Lakes and speleothems from Mexico's Yucatan Peninsula have been used extensively over the past decades for paleoclimate studies, however aquifer condition and its response to climate change has received little attention. Cenotes (sinkholes) and coastal caves have been shown to record the paleohydrology of the aquifer, but there is little information on sedimentation in these cave systems and its response to climate change. Newly developed μXRF instrumentation for the analysis of cores can achieve subannual resolution due to small measurement increments, but short period studies examining weathering inputs and rainfall have not yet been undertaken, hindering paleoenvironmental interpretations of lake and cave sediment records. This study examines the spatial and temporal relationship of cave sediment geochemistry in the anchialine cave system of Yax Chen (Quintana Roo, Mexico). Sediment traps (n = 51) were placed at seventeen stations along the 2.7 km flooded cave system, which transitions from mangrove to upland forest terrain, with cenotes of variable size and frequency along its length. Sediment traps were collected every ~6 months from May 2013–May 2017 along with rainfall and groundwater level data. There are distinct responses of lithogenic (Fe, Ti, Sr - limestone weathering) and biogenic influenced (Si, K, S - phytoplankton and mangrove sediment) elements in the sediment samples associated with seasonal rainfall and hurricanes. While lithogenic elements (Ti/K) show a direct relationship seasonal rainfall, the sedimentation of biologically influenced (Si/Ti) elements exhibit a 6–12 month lagged response with large rainfalls such as Hurricane Ingrid in 2013 and other tropical storms throughout the study period. • 4 years of μXRF data offers interpretation of paleo-rainfall from sediment cores • Lithogenic elements (Fe, Ti, Sr) correlate to seasonal rainfall. • Biogenic elements (K, S, Si) have a seasonally lagged response to hurricanes. • Ti/K and Si/Ti are suitable proxies for paleo-rainfall in karst basins. • Intense rainfall can increase metal release from mangrove to the aquifer and coast. [ABSTRACT FROM AUTHOR]