ABSTRACT Clumped isotope (Δ 47 ) data from the shell aragonite of Praemytilus strathairdensis , a non‐marine Middle Jurassic mytilid from the Inner Hebrides of Scotland, presents a rare geological context for better understanding the effects of diagenesis on Δ 47 in skeletal aragonite. Nineteen P. strathairdensis shells gave Δ 47 temperatures between 23 ± 5°C and 48 ± 9°C despite having an identical burial/thermal history. During the early Palaeocene these rocks were briefly buried to temperatures warm enough (~50 to 80°C for <1 my) to sufficiently overcome the activation energy for bond breakage and diffusion in fossil molluscan aragonite. This caused mostly incomplete resetting of some Δ 47 derived temperatures to warmer values. As individual shells with the same thermal history record different Δ 47 an extrinsic defect regime associated with impurities is implied, possibly varying amounts of water, in the aragonite lattice. Seven P. strathairdensis Δ 47 derived temperatures, between 23°C and 30°C, overlap those of within‐sequence, early diagenetic calcitic concretion bodies that are not reset. While it is not certain these molluscan aragonite Δ 47 temperatures are wholly unaltered, they may represent a best estimate of Jurassic lagoon water temperatures.

A multi-proxy micropaleontological and geochemical study from Ocean Drilling Program (ODP) Site 738, a southern high-latitude site in the Indian Ocean, is presented. Variations in relative abundance and test size of the planktic foraminiferal species of the symbiotic upper mixed layer genera, Morozovella and Acarinina, and asymbiotic lower mixed layer genus, Subbotina, are analyzed across the Early Eocene Climate Optimum (EECO), a period associated with elevated atmospheric pCO(2) levels. During the early Eocene, Morozovella first decreased in abundance and finally locally disappeared, whereas Acarinina remained relatively abundant. Results indicate that the first early Eocene decline in relative abundance of morozovellids at Site 738 was probably earlier than in the northwest Pacific and Atlantic Oceans and southeast Atlantic Ocean. The early disappearance may have been due to the high paleolatitude of Site 738 (>60 degrees S), differences in the water column structure, and nutrient availability. Size-dependent carbon stable isotope values are recorded for three target species, Subbotina velascoensis, Acarinina soldadoensis and Morozovella subbotinae. They show a significant morphological shift for the symbiotic foraminifera with decreasing in maximum test size from just before the J Carbon Isotope Excursion (CIE) event, and a reduction in the delta C-13-test size gradient of the symbiotic monospecific foraminifera following the J CIE event. These changes may be due to reduced symbiotic activity ('bleaching events') driven by extreme environmental stress at the base of the EECO. However, test size of Acarinina soldadoensis returns toward its maximum size following the M CIE event.

The Arabian Desert experienced multiple periods of wetter and greener conditions that sustained human populations and allowed the dispersal of mammal fauna across the Arabian Peninsula. A recently published speleothem-based paleoclimate reconstruction of central Arabia extends the record of such recurrent short-lasting humid periods over at least the past 8 million years. Here, we applied multiple recently developed paleothermometers to this late Miocene to late Pleistocene speleothem record: Fluid inclusion stable isotopes, microthermometry and dual-clumped isotopes. The data indicate that in the late Miocene and Pliocene, wetter episodes in central Arabia were up to ~4 °C warmer than current Mean Annual Air Temperature (MAAT). These temperature estimates imply that potential evapotranspiration was significantly higher during the late Miocene and Pliocene than during the late Pleistocene. From these temperature estimates, we calculated Pliocene potential evapotranspiration and estimated precipitation amounts for the humid periods in central Arabia. All the evidence from the speleothems combined (temperature, precipitation, δ¹³C values) suggests that over the past 8 million years, the wetter phases in central Arabia typically led to savanna-like environments.Modern climate data show that our study area has already reached Pliocene MAATs in recent years due to anthropogenic warming. The concomitant drying trend in modern settings indicates that higher temperatures are not the key factor in creating wetter conditions on the Arabian Peninsula. Previously proposed orbital control on the incursion of monsoonal moisture from the south into the Arabian Peninsula remains the most important driver of humidity during these past humid periods. In the modern orbital configuration, monsoonal moisture advection is displaced to the south, and increasing temperatures will likely lead to increased potential evaporation and aridity in central Arabia.

Reconstructing the climate of central Europe during the Eemian serves a dual purpose. First, the Eemian represents the most recent pre-Holocene period of widespread climate warming, and its vegetation structure offers a potential natural baseline for temperate European vegetation, as it was unaffected by large-scale anthropogenic alterations. Second, because Neanderthals lived in Europe during this period, understanding the climate provides insights into their environmental adaptations. Here we examined seasonal climate variation at a sub-annual scale during the early Eemian (ca. 121 +/- 5 ka) by analyzing oxygen isotopes (delta O-18(CO3)) in tooth enamel of 14 serially sampled equid third molars from the Neanderthal occupation site of Neumark-Nord 2 (NN2), Germany. These specimens were retrieved from find level NN2/2B, which spans less than 500 years. Stable carbon (delta O-18(CO3)) and mineral-bound nitrogen isotopes (delta N-15(mb)) were measured in the same enamel aliquots to assess seasonal influences on diet. Intra-tooth delta O-18(CO3) values show clear sinusoidal seasonal patterns, indicating mean annual temperatures of 11 +/- 1 degrees C, which are closely aligned with previously published Eemian estimates and slightly higher than presentday values. However, modeled water delta O-18 suggest stronger seasonal contrasts than today, with summers similar to 5 degrees C warmer and similar winter conditions. delta O-13(CO3) values indicate a semi-open habitat and more annual precipitation than today. Notably, delta O-13(CO3) and delta N-15(mb) values show no seasonal variation, implying stable year-round equid diets and consistent plant availability despite pronounced climate seasonality.

Multi-isotope analyses of extant and extinct animals provide key insights into dietary ecology. Here, we examined mineral-bound nitrogen isotopes alongside carbonate carbon and oxygen stable isotope ratios in tooth enamel from sympatric chimpanzees, other primates (yellow baboons, red-tailed, and red colobus monkeys), herbivores, omnivores, and a radicivore from the miombo woodlands of the Issa Valley, Tanzania. Chimpanzees occupy a distinct isotopic niche characterized by low nitrogen and carbon isotope values and enriched oxygen isotope values relative to other primates. This unique isotopic niche likely reflects their reliance on termites as a major source of dietary protein. Our data indicate that termites contribute substantially to the chimpanzee’s nitrogen intake (at least 50%), consistent with nitrogen isotope values of chimpanzees. These findings from woodland-dwelling primates demonstrate the power of multi-isotope approaches for reconstructing modern and past dietary ecology and highlight their potential for interpreting ancient diets, including those of hominins.

Littorina littorea-the common periwinkle-is biogeographically widely distributed and occurs frequently in archaeological shell middens along the European Atlantic coast. Yet, its potential use as a recorder of palaeoclimate and the season-of-collection has not been rigorously assessed. Here, gaps of knowledge are addressed with a comprehensive dataset of 78 specimens collected from Skaill Farm, a Medieval and Post-medieval archaeological site on the island of Rousay, Orkney, UK, and the adjacent intertidal zone, and more than 3000 shell oxygen isotope data. Shell δ18O-based coastal summer water temperature deviated by only +0.18°C from the 1992/93-2022 average, but winter temperatures were overestimated by 2-5°C, provided proper sampling was applied. Modern summers are 0.7°C warmer than during the final centuries of the late Little Ice Age, but statistically indistinguishable from such during two Medieval intervals (14th-15th century). As the timing and rate of seasonal shell growth remains unchanged through the lifetime, the season of harvest can be faithfully determined from apertural δ18O profiles. During studied time intervals in the past, snails were predominantly collected in early spring and possibly functioned as a starvation food. Findings of this study may encourage future shell midden archaeological studies at sites where the common periwinkle occurs.This article is part of the theme issue 'Shifting seas: understanding deep-time human impacts on marine ecosystems'.

Europe experienced periods of significant climatic fluctuation during the late Pleistocene, which is likely to have led to environmental stress on many species, including the extinct cave bear Ursus spelaeus. We investigated temporal variation in carbon and oxygen isotopic values extracted from dental enamel of U. spelaeus specimens from multiple stratigraphic units within Scladina Cave, Belgium, in conjunction with dental morphology, which we quantified using 2D geometric morphometrics to test the hypothesis that Pleistocene climatic changes impact phenotypic variation and feeding ecology of extinct megafauna. Size and shape of the second lower molar differ in cave bears across several stratigraphic units, even for short temporal gaps between sediment depositions (similar to 3ky). Ursus spelaeus from Scladina exhibited low delta C-13 values comparable to that of contemporary herbivores from the same sequence, suggesting an herbivorous diet for the species throughout the temporal sequence. Climatic change had an impact on size and diet, with larger dentition relating to previously suggested colder environmental periods. The existence of these periods was further supported by our delta C-13 and S18O measurements. Warmer periods were indicated by higher delta O-18 values and correlated with lower delta C-13 values indicative of a diet enriched in plant sources from more forested environments. The environmental variation through the studied sedimentary units of Scladina Cave is discussed and interpreted alongside previously produced palynological results for units herein. Our results support previous suggestions that cave bears from Scladina Cave had a herbivorous diet, while further strengthening the current stratigraphic interpretation of the cave.

Extreme rainfall events are expected to become more frequent and intense worldwide due to climate change, as indicated by the Sixth Assessment Report from the Intergovernmental Panel on Climate Change. This includes the most populated region in South America, southern and southeastern Brazil, where several studies document a consistent pattern of intense rainfall increases. The increasing intensity and frequency of these events have a direct impact on society, triggering natural disasters such as flash floods and landslides, accounting for 74% of natural disaster-related deaths and an impact of 6.2 billion dollars between 2010 and 2019. The scarcity of available data and limitations to the instrumental period hamper assessments regarding the frequency and intensity of extreme rainfall events beyond this period. This limitation precludes the assessment of how larger-scale forcings, atmospheric circulation, and environmental changes can affect the frequency and magnitude of those events. Previous studies show that extreme rainfall events in the study area are caused by Extratropical Cyclones and Frontal Systems, as well as the South Atlantic Convergence Zone. Our 5-year cave flood monitoring indicates that extreme rainfall events are responsible for triggering the cave floods, therefore stalagmites subjected to those cave floodings can be used as a proxy for extreme rainfall events. In this context, we use a large set of Holocene stalagmites collected from two different caves (Lage Branca and Malfazido cave). Reconstructions are based on detrital layers within stalagmites identified using thin-section petrography. Records from Malfazido cave exhibit a higher sensitivity to high-frequency cave flood events (subdecadal to decadal frequency), as demonstrated by reconstructions. In contrast, Lage Branca records are sensitive to high-magnitude events (multidecadal, centennial, or multi-centennial frequency) due to their high topographic position (20-50 m above the underground river) and slow growth rate. We present new cave flood records for Malfazido and Lage Branca caves, covering the last 7000 years and 10000 years, respectively. Periods of increased occurrence of flood layers in the stalagmites are observed for both caves around 4.1 kyr during the transition from the Middle to Late Holocene. For higher-frequency events, a remarkable increase in cave flood frequency is observed during the Little Ice Age. To assess the mean climate state in which the changes in frequency are observed, a high-resolution multiproxy record based on stalagmites (δ13C, δ18O, trace elements) is used to reconstruct paleohydrology and environmental conditions. New paleoflood cave records from both caves are used to assess how the frequency of extreme rainfall events can vary over time, providing insights into how different forcings and climate changes, such as atmospheric circulation changes and variations in SSTs, can affect the frequency of those events.

The role that climate played in human evolution has been controversially discussed among scientists for decades. Inspired by these discussions, the Hominin Sites Paleolakes Drilling Project (HSPDP) conducted five deep drilling campaigns adjacent to key hominin fossil sites in eastern Africa, including the Chew Bahir Basin in southern Ethiopia. Analysis of the Chew Bahir lacustrine sedimentary record revealed that over the past 620,000 years, phases of environmental stability and instability occurred contemporaneously with milestones in human history, including pulsed dispersal events out of Africa coinciding with potential humid periods. Although proxies from Chew Bahir sediments have provided important qualitative information about relative changes in environmental conditions, we still lack quantitative information on water availability and an understanding of the dominant climatic forcings controlling water balance. Here we present the first radiogenic strontium isotope (87Sr/86Sr) record covering the past 50,000 years from four Chew Bahir sediment short cores (CB01, CB03, CB05, CB06) and one long core HSPDP-CHB-1A in a resolution of 100 to 1000 years measured on fish bones, endogenic calcites, and ostracods. We interpret the Sr isotope proxy to reflect water provenance changes, particularly controlled by the varying contribution of water overflowing from a series of lakes further north in Ethiopia. Our new Sr-isotope record shows a remarkable correlation with global sea level variability and does not show a pattern of precession paced cycles. Superimposed on this pattern, we see concurrent excursions in the Sr-isotope record of centennial- to millennial scale events such as Heinrich Event 1 (H1) or the Younger Dryas (YD). As Chew Bahir dominantly receives Indian Ocean moisture, the most likely driver of moisture availability in this part of eastern Africa is the temperature of western Indian Ocean surface water that varies in pace with glacial-interglacial climate change. Also on shorter time scales, reduced Indian Ocean surface temperatures correspond to reduced moisture in the tropical rainbelt resulting in dry conditions around H1 and the YD. Where other paleohydrological proxy data from lake fossils can be comparatively noisy because of the high spatial and seasonal variability in such tropical systems, the relatively conservative hydrochemistry of the Sr isotope signal in lakes like Chew Bahir makes this proxy relatively insensitive to seasonal variability while it faithfully captures decadal to longer time scale signals.

Over the past decade or so, laser spectrometric instruments have revolutionized the field of isotope analysis of water samples. These instruments do not require complex lab facilities, are easy to use and can provide hydrogen and oxygen isotope data at high precision and high throughput.One well-known shortcoming of these laser spectrometric analyzers is that individual measurements display significant sample-to-sample memory effects. Particularly at larger isotopic differences between samples, isotopic contamination by the previous sample can off-set the following measurements even after multiple injections. Therefore, it is common in many laboratories to run 7 or more replicate analyses of each sample, and discard the first 4 or so, to come to an accurate isotope value of that sample.Because the single-shot precision of these instruments is rather good, the sample replication is not so much necessary for obtaining better precision, but indeed mostly needed to flush out the memory effect on the isotope values. Therefore, any technical adaptation that decreases the memory effect of these analyzers, and thus reduces the number of replicate analyses required to come to an accurate isotope ratio, would greatly improve the sample throughput of these instruments.We here present an adapted injection interface system, coupled to a Picarro L2140i analyzer, that practically removes sample to sample memory effects. This effectively leads to accurate and high-precision isotope analysis of single-shot sample injections, even at large sample-to-sample isotope differences. Key to the removal of the memory effect is that the analyzer runs on a moisturized carrier gas, providing a constant water background upon which the injected samples are analyzed (De Graaf et al., 2021). We will present results of series of standard waters and natural samples (including seawaters) and discuss protocols that we developed for data calculation and quality control. Reference:de Graaf, S., Vonhof, H.B., Levy, E.J., Markowska, M., Haug, G.H., 2021. Isotope ratio infrared spectroscopy analysis of water samples without memory effects. Rapid Communications in Mass Spectrometry 35.

Drylands cover almost half of Earth’s land surfaces, supporting ~30% of the world’s population. The International Panel on Climate Change predicts increasing aridification and expansion of drylands over the course of this century. As we approach new climate states without societal precedent, Earth’s geological past may offer the best tool to understand hydroclimate change under previously, allowing us to elucidate responses to external forcing. Paleo-records from previously warm and high-CO2 periods in Earth’s past, such as the mid-Pliocene (~3 Ma), point towards higher humidity in many dryland regions. Here, we examine desert speleothems from the hyper-arid desert in central Arabia, part of the largest near-continuous chain of drylands in the world, stretching from north-western Africa to the northern China, to elucidate substantial and recurrent humid phases over the past 8 million years. Independent quantitative paleo-thermometers suggest that mean annual air temperatures in central Arabia were approximately between 1 to 5 °C warmer than today. The analyses of the isotopic composition (δ18O and δ2H) of speleothem fluid inclusion waters, representing ‘fossil rainwater’, reveal an aridification trend in Arabia from the Late Miocene to Late Pleistocene during Earth’s transition from a largely ‘ice-free’ northern hemisphere to an ‘ice-age’ world. Together, our data provide evidence for recurrent discrete wetter intervals during past warmer periods, such as the Pliocene. Data-model comparisons allow us to assess the agreement between our paleoclimate data and climate model output using the HadCM3 isotope-enabled model simulations during past ‘warmer worlds’ – namely the mid-Piacenzian warm period (3.264 to 3.025 Ma). To assess the hydroclimate response to external forcing, we examine model output from a series of sensitivity experiments with different orbital configurations allowing us to postulate the mechanisms responsible for the occurrence of humid episodes in the Arabian desert, with potential implications for other dryland regions at similar latitudes. Together, our approach unveils the long-term controls on Arabian hydroclimate and may provide crucial insights into the future variability.

Incorporation of animal-based foods into early hominin diets has been hypothesized to be a major catalyst of many important evolutionary events, including brain expansion. However, direct evidence of the onset and evolution of animal resource consumption in hominins remains elusive. The nitrogen-15 to nitrogen-14 ratio of collagen provides trophic information about individuals in modern and geologically recent ecosystems (<200,000 years ago), but diagenetic loss of this organic matter precludes studies of greater age. By contrast, nitrogen in tooth enamel is preserved for millions of years. We report enamel-bound organic nitrogen and carbonate carbon isotope measurements of Sterkfontein Member 4 mammalian fauna, including seven Australopithecus specimens. Our results suggest a variable but plant-based diet (largely C 3 ) for these hominins. Therefore, we argue that Australopithecus at Sterkfontein did not engage in regular mammalian meat consumption.

Speleothems (stalagmites, stalactites and flowstones) are a powerful archive for reconstructing past climate conditions. These are secondary calcium-carbonate deposits that form in caves from the adequate supply of rainwater, soil CO2 and dissolved bicarbonate. They have been used extensively in arid regions, such as SW Asia, to reconstruct and benchmark past hydroclimatic conditions. Analysis of the distribution of active and inactive speleothem deposition across the Negev desert suggested a precipitation threshold of ~300-350 mm yr-1 is required for speleothems to deposit. This threshold has been applied to the broader SW Asia region to understand the minimum rainfall during periods of climate amelioration but has lacked specific region-wide analysis. Here, we apply logistic regression techniques and machine-learning methods to understand the climatic parameters which predict speleothem deposition across SW Asia. We show a gradual, rather than threshold response between speleothem deposition and rainfall amount, suggesting 1) precipitation over 300-350 mm yr is not a simple predictor of speleothem deposition across SW Asia, and 2) sites specific climates/environments and processes play an important role. We then apply a Random Forest machine-learning algorithm to our dataset to create a prediction of speleothem deposition. We show that minimum and maximum monthly rainfall, elevation, and a terrain roughness index are the most important variables, suggesting that water availability and topography are important predictors of speleothem deposition. Climate indices associated with temperature and evaporation contribute but play a less important role in the prediction. We emphasise the need for additional monitoring of external and internal cave environments to refine the climatic predictors of speleothem deposition in SW Asia and understand the site-specific processes that lead to the activation or cessation of speleothem growth. Importantly, our prediction provides a model which includes a range of climate-environmental data and may be used by researchers to locate new speleothem-bearing cave sites for study.

The hydroclimate change in the hot and arid Arabian Desert under anthropogenic global warming is a subject of ongoing discussions. Climate models project rising mean annual temperatures coupled with decreasing precipitation averaged over Saudi Arabia with regional variance (Almazroui, 2020). Stable isotope analysis on a combined speleothem record from central Arabia revealed recurring local humid periods during globally warmer intervals over the past ~8 million years (Markowska et al., in review). The speleothem record showed a long-term drying trend towards present, which may potentially be controlled by temperature change. The present study aims to reconstruct mean annual air temperatures (MAATs) of central Arabia during humid periods. These temperatures provide valuable benchmark data for past and future climate models in a region where terrestrial climate archives are scarce. Recent advances in speleothem-based paleothermometry facilitate extracting robust MAATs. We present data from several independent paleothermometers: Fluid inclusion isotopes (de Graaf et al., 2020), TEX86 (Meckler et al., 2021; Wassenburg et al., 2021), fluid inclusion microthermometry (Krüger et al., 2011), and dual clumped isotopes (Bajnai et al., 2020). These reconstructions show that recurrent wet intervals during the Miocene to Pleistocene in the Arabian Peninsula occurred at warmer than modern MAATs. We note, however, that temperature is not the only driver of humidity in the Arabian Peninsula and that both dry and humid periods likely existed under a warmer than today’s climate. Therefore, these observations cannot directly be interpreted as indicator that anthropogenic global warming will lead to future wet conditions in Saudi Arabia. Overall, we provide novel quantitative paleoclimate parameters that can inform climate model experiments leading to improved predictions for future climate scenarios.

Foraminifera often form symbiotic relationships with photosynthetic algae, providing a host environment and inorganic nutrients in exchange for photosynthetic organic matter from the algal symbiont. To date, the history of this relationship has been studied in paleoceanographic records using the oxygen and carbon stable isotopes of foraminiferal calcite. More recently, photosymbiotic activity has been observed to impact the nitrogen isotope ratio (δ15N) of foraminiferal tissue and the organic matter incorporated into foraminiferal tests. Dinoflagellate symbiont-bearing species appear to be lower in δ15N than symbiont-barren species and more similar to their feeding sources, likely due to their retention of low-δ15N metabolic ammonium and thus a weaker amplitude for the “trophic enrichment factor”, the δ15N increase per trophic level that is widely observed in food webs. We report new glacial–interglacial foraminifera-bound δ15N (FB-δ15N) data from Deep Sea Drilling Program Site 516, located in the subtropical South Atlantic gyre, which contains multiple foraminifera species at adequately high abundance for interspecies comparison of foraminiferal nitrogen, carbon, and oxygen isotopes over a full glacial cycle. Our data show a conserved δ15N difference of 3 ‰–5 ‰ between dinoflagellate-bearing species and the other species, qualitatively consistent with, but greater in amplitude than, the δ15N difference observed in previous modern ocean and core-top studies. We propose that this greater amplitude at Site 516 is the result of the lateral transport of symbiont-barren species into the South Atlantic subtropical gyre, which appears to represent a small region of low thermocline nitrate δ15N surrounded by regions with higher thermocline nitrate δ15N. We demonstrate that FB-δ15N provides a clear signal of dinoflagellate endosymbiosis and that it may be able to identify other, weaker endosymbioses (e.g., with chrysophytes or pelagophytes). However, the data also suggest caution in regions with strong gradients, where species from contrasting environments may occur in a single sediment sample.

Unusually high delta N-15 values in the Neoarchean sedimentary record in the time period from 2.8 to 2.6 Ga, termed the Nitrogen Isotope Event (NIE), might be explained by aerobic N cycling prior to the Great Oxidation Event (GOE). Here we report strongly positive delta N-15 values up to +42.5 parts per thousand in similar to 2.75 - 2.73 Ga shallow-marine carbonates from Zimbabwe. As the corresponding deeper-marine shales exhibit negative delta N-15 values that are explained by partial biological uptake from a large ammonium reservoir, we interpret our data to have resulted from hydrothermal upwelling of 15N-rich ammonium into shallow, partially oxic waters, consistent with uranium isotope variations. This work shows that anomalous N isotope signatures at the onset of the NIE temporally correlate with extensive volcanic and hydrothermal activity both locally and globally, which may have stimulated primary production and spurred biological innovation in the lead-up to the GOE.

The Saharo-Arabian Desert is one of the largest biogeographical barriers on Earth, impeding dispersals between Africa and Eurasia, including movements of past hominins. Recent research suggests that this barrier has been in place since at least 11 million years ago 1 . In contrast, fossil evidence from the late Miocene epoch and the Pleistocene epoch suggests the episodic presence within the Saharo-Arabian Desert interior of water-dependent fauna (for example, crocodiles, equids, hippopotamids and proboscideans) 2–6 , sustained by rivers and lakes 7,8 that are largely absent from today’s arid landscape. Although numerous humid phases occurred in southern Arabia during the past 1.1 million years 9 , little is known about Arabia’s palaeoclimate before this time. Here, based on a climatic record from desert speleothems, we show recurrent humid intervals in the central Arabian interior over the past 8 million years. Precipitation during humid intervals decreased and became more variable over time, as the monsoon’s influence weakened, coinciding with enhanced Northern Hemisphere polar ice cover during the Pleistocene. Wetter conditions likely facilitated mammalian dispersals between Africa and Eurasia, with Arabia acting as a key crossroads for continental-scale biogeographic exchanges.

Geochemical anomalies within speleothems serve as crucial indicators of environmental changes. While research predominantly focuses on calcite-dominated formations, understanding the significance of aragonite is essential for a comprehensive grasp of past climate dynamics. This study presents high-resolution records, based on 230Th/U dating, stable isotopes (δ13C) and trace elements analysis in recent aragonite growth lamina near the calcite top in three speleothems from Mawmluh Cave, Meghalaya, India. Covering a total of 163 years (2022 to 1859 CE), the research explores the environmental impact on the cave system, especially in relation to nearby industrial activities. Laser Ablation-Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) was utilized to analyze trace elements (e.g., Mg, Sr, Ba, U, P, Y, Pb, Al, Th, etc.) in the recent aragonite growth lamina. Detected trace elements (Pb, Zn, Mn, etc.) at trace concentrations, alongside current δ13C values, may be linked to emissions from a nearby cement plant and open-cast mining activities, acting as potential indicators of anthropogenic influence. All three speleothems displayed transitions from calcite to aragonite near the top, suggesting a significant alteration in the cave system over time, potentially induced by human activities. Anthropogenic factors may contribute to this transition, with specific elements acting as key markers. Future studies on the geochemical signatures of aragonite formations promise to fill existing gaps, offering a nuanced perspective on paleoclimatic and paleoenvironmental conditions. Keywords: speleothems, aragonite formations, trace elements, stable isotopes, anthropogenic impact, Mawmluh Cave.

The Brujas cave is located in the eastern flank of the subtropical Andes, in the boundary between two major components of the climate system that drives precipitation variability over the South America: The South American monsoon system (SAMS) domain and the Southern hemisphere westerlies (SHW). As a result, the long-term hydroclimate variability in this region can be complex. Paleorecords from lake sediments and ice cores surrounding the area show meridional fluctuations of either the SAMS or the SHW, yet without long and high-resolution records, this area remains poorly constrained.The deglacial and Holocene are interesting periods in this regard, providing valuable information about the atmospheric circulation in the western sector of SAMS in response to millennial-scale events of the last glacial. Moreover, changing climate forcings associated with ice volume and greenhouse gases can impact hydroclimate at these latitudes by reorganizing atmospheric circulation during the onset of the interglacial boundary conditions. For instance, the expansion of the Hadley cell under current global warming severely affects the regional hydroclimate of the mid-latitudes. Yet, our knowledge of this region is limited compared to what we know about the core SAMS region or the SHW in southernmost South America. New records from this transitional zone can provide clarity on the extent of variability in space and intensity of the SAMS and the SHW, serving as useful benchmarks to assess the performance of climate models in such a sensitive zone, right in interphase between two systems.Here we present preliminary results from a stalagmite record (15,000 to 3,000 years) from Las Brujas cave, on the northern edge of the SHW domain. The westerlies transport moisture from the Pacific Ocean to the continent, where the Andes barrier induces orographic convection so that intense precipitation falls on the uphill side of the cordillera, over the Chilean Andes. The limited moisture that crosses the Andes and reaches the downslope area, produces precipitation over Las Brujas cave site during the cold months (April-September). Immediately north of Las Brujas cave, precipitation is concentrated in the warm season, produced by the South American low-level jet (SALLJ), a main component of the SAMS that transports moisture from the Amazon to northwestern Argentina. Given the proximity of both systems to our cave, precipitation contribution of either source is likely to have occurred in the past. Our multiproxy record can potentially show periods of rainfall dominated by the SAMS or the westerlies and the relationship unveil local temperature variations. We find evidence of a slight trend from dryer to wetter conditions from the mid-Holocene onwards and a large shift from dry to wet from the deglacial to the early Holocene.

The South American Monsoon System (SAMS) plays an important role in the hydroclimate variability and rainfall patterns across South America. Stemming from its convective core in the southwestern Amazon basin, the South Atlantic Convergence Zone (SACZ) is a southeastward convection band, being a critical component of SAMS responsible for large-scale moisture transport, particularly over Central Brazil. Previous paleoclimate studies suggest that SACZ has changed over time, usually associated with changes in the SAMS, and there are current debates regarding the nature of SACZ, shifts in position, size, and intensity, and their potential impacts on vegetation changes. Therefore, this study addresses these debates for the last 16,000 years based on a novel multi-proxy paleorecord of δ18O, δ13C, and Sr isotope ratios (87Sr/86Sr) from a stalagmite collected in São Mateus Cave at the northeast limits of SACZ in central Brazil. This site is therefore under the regime of SACZ, with a climate characterized as tropical semi-humid with a rainy summer season and a dry winter.The inclusion of Sr isotope data enhances our interpretation of past local climate variability since changes in 87Sr/86Sr can provide valuable information about the water residence in the epikarst and changes in soil composition. Furthermore, as São Mateus Cave lies within the Cerrado biome, it offers a unique insight into the past climate and environmental changes in central Brazil due to its distinct floral compositions influenced by factors such as location, soil, rainfall distribution, and fire frequency. Comparisons with other paleoclimate data from SACZ-influenced sites are made to access climate and vegetation changes in different locations within this convective band, particularly over larger time scales, such as the transition from the Late-Pleistocene to the Holocene and longer trends. We demonstrate that even though there is a common change in the regional δ18O signal connected with SACZ variations, differences in vegetation and local moisture between northern and southern SACZ limits are evident albeit being in the same biome. This multi-proxy approach, combining traditional stalagmite proxies with high-resolution LA-MC-ICP-MS Sr isotope analysis, offers a better understanding of SACZ changes and their implications for Central Brazil's climate and environment.