Monitoring of Sierra Nevada Caves Reveals the Potential for Stalagmites to Archive Seasonal Variability

In the southwestern United States, California (CA) is one of the most climatically sensitive regions given its low (≤250 mm/year) seasonal precipitation and its inherently variable hydroclimate, subject to large magnitude modulation. To reconstruct past climate change in CA, cave calcite deposits (stalagmites) have been utilized as an archive for environmentally sensitive proxies, such as stable isotope compositions (δ18O, δ13C) and trace element concentrations (e.g., Mg, Ba, Sr). Monitoring the cave and associated surface environments, the chemical evolution of cave drip-water, the calcite precipitated from the drip-water, and the response of these systems to seasonal variability in precipitation and temperature is imperative for interpreting stalagmite proxies. Here we present monitored drip-water and physical parameters at Lilburn Cave, Sequoia Kings Canyon National Park (Southern Sierra Nevada), CA, and measured trace element concentrations (Mg, Sr, Ba, Cu, Fe, Mn) and stable isotopic compositions (δ18O, δ2H) of drip-water and for calcite (δ18O) precipitated on glass substrates over a two-year period (November 2018 to February 2021) to better understand how chemical variability at this site is influenced by local and regional precipitation and temperature variability. Despite large variability in surface temperatures and precipitation amount and source region (North Pacific vs. subtropical Pacific), Lilburn Cave exhibits a constant cave environment year-round. At two of the three sites within the cave, drip-water δ18O and δ2H are influenced seasonally by evaporative enrichment. At a third collection site in the cave, the drip-water δ18O responds solely to precipitation δ18O variability. The Mg/Ca, Ba/Ca, and Sr/Ca ratios are seasonally responsive to prior calcite precipitation at all sites but minimally to water-rock interaction. Lastly, we examine the potential of trace metals (e.g., Mn2+ and Cu2+as a geochemical proxy of recharge and find that variability in their concentrations has high potential to denote the onset of the rainy season in the study region. The drip-water composition is recorded in the calcite, demonstrating that stalagmites from Lilburn Cave, and potentially more regionally, could record seasonal variability in weather even during periods of substantially reduced rainfall.

Cave monitoring in Hungary: An overview

In this study, already published and new monitoring data are compiled from the Baradla and Béke caves in the Aggtelek Karst, from the Vacska Cave in the Pilis Mountains as well as from the Szemlőhegy and Pálvölgy caves in the Buda Hills. Recent investigations (2019–2020) include monitoring of climatological parameters (e.g., temperature, CO2) measured inside and outside the caves, and the chemical, trace element and stable isotopic compositions of drip waters. In the Baradla Cave, the main focus of the investigation was on the stable isotope composition and the temperature measurements of drip water. In the Vacska Cave, which belongs to the Ajándék-Ariadne cave system, CO2 measurements and drip water collection were conducted in order to perform chemical and stable isotope measurements. In the Szemlőhegy and Pálvölgy caves, the chemical and stable isotope compositions of drip waters at six sites were determined. These datasets were used to characterize the studied caves and the hydrological processes taking place in the karst, and to trace anthropogenic influences. Climatological investigation revealed seasonality in CO2 concentration related to outside temperature variation, indicating a variable ventilation regime in the caves. In addition, the contributions of the winter and summer precipitation to the drip water were also estimated, in order to evaluate the main infiltration period. The knowledge of these parameters plays a crucial role in constraining the carbonate precipitation within the cave. Thus, the dataset compiled in this study can provide a basis for the interpretation of speleothem-based proxies.

Analysis of the Three-Dimensional Fluorescence Spectroscopy Characteristics of Dissolved Organic Matter in Groundwater from a Subtropical Cave in Dry Season—Daxiao Cave in South China Karst

Groups in dissolved organic matter (DOM) emit fluorescence information at characteristic wavelengths when irradiated by excitation waves, which can reveal the geochemical behavior of dissolved organic matter in the environment and its sources, but there are few relevant studies in cave groundwater systems. In order to investigate the relationship between drip hydrochemistry characteristics and DOM in cave systems after subsurface leakage, in this study, from the perspective of dissolved organic matter in the karst cave water system, the groundwater in the dry season of Daxiao Cave was selected as the research object. Five drip points and one water pool (DX-1, DX-2, DX-3, DX-4, DX-5, and DX-C) in Daxiao Cave were monitored and consecutively sampled for four months. The parallel factor analysis method (PARAFAC), three-dimensional (3D) fluorescence parameters, and excitation-emission matrix fluorescence spectroscopy (EEM), combined with the hydrochemistry characteristics of the drip water and correlation analysis, were used to analyze the 3D fluorescence spectral characteristics of the DOM of the drip water of Daxiao Cave and their influencing factors. The results show that (1) the hydrochemistry type of the drip water in Daxiao Cave was within the Ca–Mg–HCO3 type, and Ca2+, Mg2+, and HCO3- were the dominant ions in Daxiao Cave; (2) the fluorescence fractions of drip water in dry season caves were dominated by C1 (humus-like), C2 (tryptophan-like), and C3 (tyrosine-like), and the fluorescence fractions of drip water DOM were controlled by protein fluorophores; (3) the DOM in the drip water of Daxiao Cave in the dry season was controlled in part by subsurface leakage and was largely the result of microbial degradation; and (4) the DOM of the drip water may be influenced by the chemical composition of the water, but the exact process is not clear.

Hydrogeochemical Responses of Cave Drip Water to the Local Climate in Liangfeng Cave, Southwest China

The hydrogeochemistry of cave drip water is an important environmental index in cave systems, and drip water monitoring may be an essential solution for paleoclimate reconstructions. We measured the hydrogeochemical properties of the seasonal and perennial drip water and CO2 concentrations from 2015 to 2019 in Liangfeng Cave, Guilin, Southwest China. This study identified the difference in the regional environmental records in perennial and seasonal drip water. By comparing the regional climate data recorded by the drip water, the results showed the perennial drip water recorded regional climate information throughout the year, while the seasonal drip water only recorded the high precipitation periods. The precipitation during the 2015 dry season was abnormally high, which not sure what index is higher than the values in other rainy seasons. This indicates that hydrogeochemistry only represents changes in precipitation and not the alternation of dry and rainy seasons during this period.

Last glacial millennial-scale hydro-climate and temperature changes in Puerto Rico constrained by speleothem fluid inclusion δ¹⁸O and δ²H values

We present speleothem fluid inclusion δ18Of and δ2Hf values from Larga Cave, Puerto Rico, that covers the interval between 46.2 to 15.3 ka before present on millennial scale, including the Last Glacial Maximum (LGM) and several stadial and interstadial cycles. The dataset can be divided in two main clusters of stable isotope compositions of the fluid inclusion water with respect to the global meteoric water line which coincide with strong variations in the water content of the stalagmite. In particular, this clustering is found to be climate related, where the first cluster comprises samples from cold and dry periods, such as Heinrich and Greenland stadials, as well as parts of the LGM, which exhibit very high δ18Of and δ2Hf values. We interpret this enrichment as caused by evaporation inside the cave due to enhanced cave ventilation during these colder and drier times. In contrast, in most samples corresponding to warmer and wetter Greenland interstadials, but also for some from Heinrich Stadial 2 and 3, the δ18Of and δ2Hf values plot on the meteoric water line and modification of fluid inclusion water due to “in-cave” evaporation is found negligible. Consequently, variations of last glacial hydro-climate and temperature in the western tropical Atlantic can be constrained. In general, δ18Of values from fluid inclusions are up to 3 ‰ higher than those of modern drip water, which is interpreted as a weaker atmospheric convective activity during the last glacial period. In addition, reconstructed temperatures suggest an average cooling of c. 3 °C during the LGM compared to modern cave temperature. During Heinrich Stadials 2 and 3, reconstructed cave temperatures yield an additional cooling of 2.9 ± 2.6 °C and 4.4 ± 0.6 °C, respectively. Higher δ18Of values of these samples further suggest that the drip water was dominated by orographic rainfall and/or cold fronts, along with weak or even absent convective activity. In contrast, during interstadial phases, reconstructed temperatures reached nearly modern values, and convective activity was comparable or only slightly weaker than today.

Isolation and Screening for Ureolytic Bacteria from Bukilat Cave, Camotes Islands, Cebu

Microbial-induced calcite precipitation (MICP) is an eco-friendly technique used in creating better soil substrate often for engineering purposes. This is done through the application of the ureolytic pathway of certain bacteria. This study aims to discover whether any of these bacteria can be found in Bukilat Cave, Camotes Islands, Cebu. Samples from the pools of water, drip water, and swabs of the walls of the cave were collected, cultured, and then tested using Christensen’s agar for their ability to undergo the ureolytic pathway. The rate at which they undergo the ureolytic pathway was then measured and compared between different sources and to the positive control, Bacillus megaterium. The results showed that there was no significant difference between the rate at which bacteria from the different sources underwent ureolysis. There was also no significant difference between the rate at which the collected bacteria underwent ureolysis and the rate of the positive control (2.588 mM/min). Finally, the species with the fastest rate of ureolysis was identified to be Bacillus cereus NR 074540 with a rate of 3.033 mM/min. However, it is not ideal for MICP purposes because of its potential pathogenicity.

Sources, Distribution and Paleoenvironmental Application of Fatty Acids in Speleothem Deposits From Krem Mawmluh, Northeast India

Integrated multiproxy geochemical studies are essential to reconstruct the paleoenvironment through different time scales. Pristine terrestrial archives such as speleothems provide an excellent opportunity to study these changes by measuring the stable isotope and biomarker trends preserved in these records. Here, we investigated fatty acids in drip water, moonmilk, and a stalagmite (KM-1) retrieved from Krem Mawmluh in northeast India to constrain the sources and distribution of these compounds. Besides, we tested their compatibility with established glycerol dialkyl glycerol tetraethers and stable isotope proxies in KM-1 to probe the use of fatty acid-derived proxies for paleoclimate reconstruction. We observe a similar composition of fatty acids in drip water as well as the cave deposits with significantly higher concentrations of fatty acids in drip water (10.6–124 μg/L) and moonmilk (1.32–16.5 μg/g) compared to the stalagmite (0.67–2.09 μg/g). In KM-1 stalagmite, fatty acids and the presence of azelaic acid transported from surface soils indicate that these compounds are derived from bacterial activity both within the cave and the overlying soil cover. The branched C15 fatty acid index (iso+anteiso C15/nC15) increases during the Holocene, suggesting enhanced microbial production under warm/wet conditions. Fluctuations in the fatty acid indices coincide with abrupt shifts in the TEX86 and BIT proxies reflecting the warm/wet Holocene and cold/dry Late Pleistocene. These trends imply the potential use of fatty acids for reconstructing past climate changes in speleothems but need more analytical reference points to provide statistical data.

Farmed calcite δ18O, δ13C, and Δ47 at Ascunsă cave, Romania

<p>Ascunsă cave (Romania) is the subject of a monitoring program since 2012. While the cave air temperature was very stable around 7°C for most of the time, it experienced in 2019 a 3°C rise, and remained high until the present.</p><p>We present here δ<sup>18</sup>O, δ<sup>13</sup>C, and clumped isotope results from calcite farmed at two drip points inside the cave (POM X and POM 2). POM X has a slower drip rate than POM 2 and deposits calcite more continuously. Calcite deposition has been shown to depend on cave air CO<sub>2</sub> concentration, which controls the drip water pH and, further, the calcite saturation index.</p><p>In 2019, δ<sup>18</sup>O values at both sites quickly shifted to lower values as a response to the increase in temperature. At POM X, values were situated between approximately -7.2‰ and -7.6‰ before this transition, whereas in 2019 they shifted to -7.8‰ - -8.0‰. At POM 2, where values were generally lower, they shifted from -7.5‰ to -7.8‰ to -8.0‰.</p><p>Clumped isotope temperature estimates mostly agree, within measurement error, with measured cave temperature. This agreement is notable given that strong offsets are commonly observed in mid-latitude caves, reflecting kinetic fractionation effects. However, intervals with deviations from cave temperature are also observed, suggesting variations in isotopic disequilibrium conditions with time.</p><p>Here we will discuss these isotope changes in relation to cave air temperature and CO<sub>2</sub> concentration, drip water isotope values and elemental chemistry, as well as in relation to drip rates, in order to improve our understanding of calcite precipitation and isotope effects in caves.</p>

Investigating cave responses to regional climate change: an approach to calibrate speleothem proxies in Madagascar

<p>Caves are an excellent natural laboratory for understanding the transfer processes of the region’s environmental signals to speleothems. At least eight speleothems have produced high resolution paleoclimate and paleoenvironment records from Anjohibe Cave, NW Madagascar. However, due to the remote and difficult access to many caves in Madagascar, no studies have yet been done to understand the transfer of climate and environmental changes of the region to the cave. This is the first monitoring study to understand the linkage between regional climatology and various responses in Anjohibe Cave. We monitored (1) the drip water pH, TDS, EC, temperature, δ<sup>13</sup>C<sub>DIC</sub>, δ<sup>18</sup>O<sub>w</sub>, δ<sup>2</sup>H<sub>w</sub>, and elemental (Ca, Mg, Sr) composition, and (2) the cave atmosphere <em>p</em>CO<sub>2</sub>, relative humidity and temperature. Results show that air-to-air transfer is fast, and the internal parameters closely vary with the regional climatology. In contrast, rainfall to drip signal transfer is not immediate, and it can take few months to one season for the signals to be detected in the drip water due to the “epikarst storage effect”. The deposition of CaCO<sub>3</sub> is inferred to occur late in the dry austral winter season, during which prior carbonate precipitation was also detected. Since the growth of speleothems is influenced by numerous cave-specific factors, this study, although preliminary, indicates that Anjohibe Cave drip waters are capable of registering changes in its surrounding environment. A longer monitoring study is expected in the future to constrain the timing and the mode of transfer.</p>