Paleoenvironmental Studies Research Articles

Formation of halotrichite in the South Kerala Sedimentary Basin, SW India: Implications for Martian paleo-environmental studies

Formation of halotrichite in the South Kerala Sedimentary Basin, SW India: Implications for Martian paleo-environmental studies

The influence of weathering and pedogenesis on the geochemical record of Miocene marls and Plio-Quaternary sediments, Medvednica Mt., Croatia

The geochemical signature of weathering and pedogenesis in a temperate humid climate on two parent material types in the foothills of Medvednica Mt. was studied. Five soil profiles on Miocene marls and three sections of Plio-Quaternary (PlQ) proluvial sediments with overlying soil and weathered material were analyzed. The (clay) mineralogy of all profiles and sections had been determined in previous studies. The chemical composition of the samples was determined by inductively coupled plasma emission spectroscopy (ICP-OES) and inductively coupled plasma mass spectroscopy (ICP-MS). Poorly ordered Fe and Mn oxides were determined in the PlQ sediment and overlying soil samples by atomic absorption spectroscopy (AAS), after oxalate dissolution in the dark. The concentrations and element ratios were used to determine element enrichment/mobility and intensity of chemical weathering, material provenance, and to compare the geochemical signatures with previously obtained clay mineralogy results. Trace elements in the Miocene marls, including rare earth elements (REE), indicate the continental origin of the marl siliciclastic component, while more scattered geochemical data of the PlQ sediments reflect their proluvial/torrential nature. The mass transfer coefficient (τ) for major elements and element ratios of the Miocene marl profiles indicate chemical weathering and pedogenesis of lower intensity. The geochemistry of these samples shows homogeneity within the profiles. In the geochemical signature of the PlQ sections, a chaotic proluvial deposition of the material is visible, as well as the heterogeneity with the overlying soil and weathered material. Overall, the geochemistry results largely support the clay mineralogy of the samples and demonstrate how a multiproxy approach can help test hypotheses about past environments and provide valuable additional information for complex paleoenvironmental studies.

Exploring hydrogen isotope fractionation in lipid biomolecules of freshwater algae: implications for ecological and paleoenvironmental studies

ABSTRACT Understanding the stable hydrogen isotope (δ 2H) composition and fractionation in lipid biomolecules of primary producers, such as terrestrial and aquatic plants, is crucial for deciphering past environmental conditions, as well as applying compound-specific stable isotope analysis for the study of metabolic and ecological processes. We conducted a new tracer experiment to explore the δ 2H composition of algal fatty acid biomarkers, focusing on freshwater algae, which form the base of aquatic food webs. We selected a range of algal species widely found in freshwater ecosystems and cultivated them under controlled conditions. First, we added 2H2O to ambient water as a tracer to investigate the net hydrogen isotope fractionation during algal lipid synthesis at isotopic equilibrium, which is particularly informative for paleo-geochemical studies. Then, we conducted kinetic experiments to quantify the time needed for algal fatty acids to achieve isotopic steady-state conditions in response to the change in ambient water δ 2H values. Our findings revealed substantial variability in hydrogen isotope fractionation among different algal taxa and various fatty acids. Based on taxa, different fatty acids exhibited faster integration of water hydrogen than others, but they were not necessarily in the order of the biosynthetic pathway. This experiment underscores the complexity of hydrogen isotope fractionation and the requirement for controlled laboratory studies to properly apply compound-specific stable H isotope analysis techniques in ecological and paleo-environmental studies.

Exploring the acid-insoluble shell organic matrix of freshwater mussels (Unionoida) as a proxy for palaeodietary and paleoenvironmental studies

ABSTRACT The shells of freshwater mussels, commonly found at archaeological sites associated with the Kodjadermen-Gumelnița-Karanovo VI human groups (5th millennium BCE, Romania and Bulgaria), were a significant dietary component for this population. The organic matrix of these ancient shells is often well-preserved and can be analysed using stable isotopes. This study establishes the empirical relationship between the isotopic composition of the acid-insoluble shell organic matrix (AIM) and the soft tissues of modern Unio tumidus. A quality criterion for AIM (C:N ratio 3.6 (3.3–<3.8)) was defined, and isotopic offsets (Δ15NAIM-defatted body = +0.95‰, Δ13CAIM-defatted body = +0.93‰ for soft tissues; Δ15NAIM-muscle = +1.7‰, Δ13CAIM-muscle = +0.3‰ for the adductor muscle) were determined. Our data suggest that the Gumelnița mussels were omnivorous, with a similar trophic level to carp and pond turtles, sourced from diverse water bodies (rivers, lakes …) based on δ13C values.

Pleistocene to early Holocene paleoenvironmental evolution of the Abrolhos depression (Brazil) based on benthic foraminifera.

The paleoenvironmental evolution of the Abrolhos Depression (AD) on the southern Abrolhos Shelf during the global post-Last Glacial Maximum (LGM) transgression is investigated through benthic foraminifera analysis. Downcore sediment samples (core DA03A-5B) collected at a depth of 63m provide insights into the formation and paleoenvironmental variations of AD over the past 18 kyr BP. The core is divided into four biofacies based on foraminifera assemblages. At the base, the presence of carbonate concretions indicates a karstic surface, marking the initiation of the paleolagoon formation at approximately 13 kyr BP with low density of foraminifera, where species such as Elphidium sp. and Hanzawaia boueana (EH Biofacies) were more abundant. During the Younger Dryas (YD) (12.8-12.5 kyr BP), the AD exhibits two distinct phases: an initially confined lagoon environment with reduced circulation characterized by the dominance of the species Ammonia tepida (At Biofacies), followed by increased circulation characterized by higher density, richness, and diversity of benthic foraminifera. The end of the YD is identified by a significant biofacies change, indicative of a shallow marine environment, where the dominant species were A. tepida and Elphidium excavatum (AE Biofacies), supported by sedimentological and geochemical proxies. This paleoenvironmental shift is associated with Meltwater Pulse (MWP) -1B, suggesting a connection to a shallow marine environment. As sea levels continue to rise, the AD transitions into an open marine setting. However, around 8 kyr BP, a change occurs with the absence of A. tepida and the occurrence of planktonic and other benthic foraminifera typical of the outer shelf, indicating depths greater than 50m (HQ Biofacies). The findings highlight the complex interplay between climate fluctuations, sea-level changes, and the formation of coastal environments during the LGM transgression. This study contributes to our understanding of paleoenvironmental dynamics, adding valuable insights to the evolutionary history of AD. The results emphasize the importance of integrating benthic foraminifera analysis, radiocarbon dating, and geochemical proxies to reconstruct paleoenvironments accurately. Overall, this research enhances our knowledge of global continental shelf evolution during the post-LGM transgression and provides valuable information for future paleoenvironmental studies.

A dendroarchaeological tree-ring dataset of Abies alba Mill. from historic buildings in the French Pyrenees

Key messageThis article presents ring width chronologies derived from samples extracted from historical timber buildings in the French central Pyrenees. Two chronologies for fir (Abies alba Mill.) were dated for two periods: 1446–1655 and 1679–1952 AD. These chronologies are suitable for dendroarchaeological and paleoenvironmental studies, or for reconstructing past climates. Dataset access is at https://doi.org/10.48579/PRO/KH6HPC and associated metadata at https://metadata-afs.nancy.inra.fr/geonetwork/srv/fre/catalog.search#/metadata/edba546e-3769-4f06-959b-f0d8db7fbcdb.

The Origin of Magnetofossil Coercivity Components: Constraints From Coupled Experimental Observations and Micromagnetic Calculations

AbstractBiogenic magnetite crystals produced by magnetotactic bacteria (MTB) and associated magnetofossils in sediments are characterized by variable morphologies, grain sizes, and chain structures. Magnetofossils are widely used in paleomagnetic and paleoenvironmental studies, but the complex magnetofossil shapes and particle arrangements significantly affect magnetic properties, hampering their magnetic detection and proxy interpretation. Here we perform coupled experimental and micromagnetic modeling analyses of typical magnetofossil‐rich sediments, where the effects of magnetofossil crystal forms and microstructures on magnetic properties can be quantitatively separated. Since the in situ magnetofossil chain structures in sediments remain poorly known, we compare results from magnetic measurements and micromagnetic simulations based on realistic magnetofossil shapes and grain size distributions. Our results suggest that bullet‐shaped magnetofossils certainly contribute to the biogenic hard (BH) coercivity component with a minor contribution from elongated prismatic particles, and collapsed equidimensional grains to the biogenic soft (BS) component. Micromagnetic simulations with different collapse models of bullet‐shaped magnetofossils produce variable FORC (first‐order reversal curve) central‐ridge contributions with similar coercivity distributions. Sensitivity test suggests that samples containing different forms of magnetofossils can produce the BH coercivity component if the proportion of the bullet‐shaped particles is more than ∼2%. Magnetofossil assemblages with a higher proportion of bullet‐shaped particles have higher coercivities, squareness ratios, and larger BH contents. Our data shed new light on understanding the origin of magnetofossil coercivity components and the in situ magnetofossil microstructures in sediments, which is widely useful for interpreting magnetofossil proxy signals in geological records.

A New Method for the Detection of Siliceous Microfossils on Sediment Microscope Slides Using Convolutional Neural Networks

AbstractDiatom communities preserved in sediment samples are valuable indicators for understanding the past and present dynamics of phytoplankton communities, and their response to environmental changes. These studies are traditionally achieved by counting methods using optical microscopy, a time‐consuming process that requires taxonomic expertise. With the advent of automated image acquisition workflows, large image data sets can now be acquired, but require efficient preprocessing methods. Detecting diatom frustules on microscope images is a challenge due to their low relief, diverse shapes, and tendency to aggregate, which prevent the use of traditional thresholding techniques. Deep learning algorithms have the potential to resolve these challenges, more particularly for the task of object detection. Here we explore the use of a Faster Region‐based Convolutional Neural Network model to detect siliceous biominerals, including diatoms, in microscope images of a sediment trap series from the Mediterranean Sea. Our workflow demonstrates promising results, achieving a precision score of 0.72 and a recall score of 0.74 when applied to a test set of Mediterranean diatom images. Our model performance decreases when used to detect fragments of these microfossils; it also decreases when particles are aggregated or when images are out of focus. Microfossil detection remains high when the model is used on a microscope image set of sediments from a different oceanic basin, demonstrating its potential for application in a wide range of contemporary and paleoenvironmental studies. This automated method provides a valuable tool for analyzing complex samples, particularly for rare species under‐represented in training data sets.

Variations in Calcareous Nannofossil Assemblages and paleoenvironmental studies on the Danian – Selandian Succession at the Qreiya area, East Qena, Eastern Desert, Egypt

Variations in Calcareous Nannofossil Assemblages and paleoenvironmental studies on the Danian – Selandian Succession at the Qreiya area, East Qena, Eastern Desert, Egypt

Microbial hydrogenation of cholesterol to coprostanol by anaerobic bacteria: evidence from Antarctic lacustrine sediment

Fecal sterols are traditionally ascribed as important biomarkers for animal excrement, and have been widely used to identify the source of organic matter and to reconstruct paleoecological changes in Antarctic terrestrial, aquatic, and marine ecosystems. However, the in situ microbial hydrogenation of cholesterol to coprostanol could have significance as a proxy to infer paleoenvironmental studies in Antarctica, particularly in anoxic sediment. Here, we report that abundant coprostanol, which was traditionally deemed as a biomarker for human sewage contamination, was found in three anoxic sediment profiles (AC2, BI, and CH1), which were strongly influenced by animal excrement at North Victoria Land, western Ross Sea, Antarctica. Our results suggest that the high concentrations of coprostanol in these three sediment profiles were not due to animal excrement, since coprostanol is not present in penguin guano and is a minor component in seal excrement. Coprostanol/cholesterol and coprostanol/(coprostanol + cholestanol) ratios suggest that coprostanol in the sediment cores of AC2 and BI was primarily derived from bacterial hydrogenation of cholesterol introduced by penguin guano. Coprostanol in CH1 sediments is related to human sewage due to intensive research activities from 1968 to 2006 in this region. However, the low abundance of coprostanol and the ratios of coprostanol/cholesterol and coprostanol/(coprostanol + cholestanol) in a relatively oxidizing sediment core (IIL1) infer that coprostanol was likely contributed by seal settlement. Together with high-throughput sequencing of the 16S rRNA gene, the conversion of cholesterol to coprostanol by anaerobic bacteria (e.g., Eubacterium coprostanoligenes) could occur in anoxic aquatic systems. Our results suggest that the presence of coprostanol in Antarctic lacustrine sediment with anoxic conditions does not necessarily indicate seal activity and human waste as the microbial hydrogenation of cholesterol to coprostanol should also be considered.

Ocean bottom-water oxygenation across the Late Miocene–Early Pliocene biogenic bloom

The Late Miocene–Early Pliocene biogenic bloom (ca. 9–3.5 millions of years ago, My) represents a period of globally heightened marine biological productivity. Paleoenvironmental studies across this interval show alternating phases of low-oxygen eutrophic and well-oxygenated oligotrophic conditions. Here, we focus on the bottom water oxygenation changes during the biogenic bloom to assess the validity of the enhanced Benthic Foraminifera Oxygen Index (EBFOI). The index was calculated for three ocean drilling sites: Ocean Drilling Program Site 1085 (southeast Atlantic), and International Ocean Discovery Program sites U1506 (southwest Pacific) and U1488 (equatorial Pacific). The quantitative study of benthic foraminiferal assemblages from Site 1488 allowed us to infer the paleoenvironmental evolution across the biogenic bloom. At this site, we document a shift from stable oxygen concentrations and seasonal input of phytodetritus (8.7–4.3 My) to short-term fluctuations between low oxygen eutrophic conditions and well-oxygenated oligotrophic conditions (4.3–3.0 My). The EBFOI calculated at sites 1085 and U1506 was cross-referenced with the published paleoenvironmental conditions. While the EBFOI proves to be a valuable tool to infer paleoenvironmental changes at the seafloor, it has limitations, as evidenced by comparisons with paleoenvironmental interpretations of Site U1488, where it does not consistently align with inferred oxygen conditions.

Distributions of bacterial branched tetraether lipids associated with bacterial communities in hummock and hollow soils from Southern Tibetan peatland

Branched glycerol dialkyl glycerol tetraethers (brGDGTs), special membrane-spanning lipids derived from some bacteria, are widely used as molecular tools in paleoenvironmental studies to reconstruct terrestrial temperature and pH conditions. However, the impact of microtopography discrepancies on the accuracy and applicability of brGDGT-based proxies remains unclear. Here we investigated the distributional patterns of brGDGTs and bacterial communities within the hummock-hollow microtopography in the mid-southern Tibetan peatlands. Our results show that the methylation index of C5-methyl brGDGTs (MBT′5ME) values are significantly correlated with the local mean annual air temperature (MAAT). However, the peat-specific temperature calibration exhibits an underestimation of MAATpeat compared to the present MAAT. We find the MBT′5ME values are significantly lower in the moist hollows than that in the drier hummocks. This discrepancy could be primarily attributed to the shifts in bacterial communities and the physiological adaptation of brGDGT-producing bacteria driven by the high soil water content. These findings highlight the remarkable variability of MBT′5ME values at small spatial scales, which holds profound implications for paleotemperature reconstruction in alpine peatlands.

Provenance and paleoenvironmental studies of Bima and Dukul Formations in the Yola Basin, Northern Benue Trough, Nigeria.

Sedimentological studies of some areas located within latitudes 11035’E &amp; 12000’E, and longitudes 9014’N &amp; 9025’N were undertaken to delineate the surface lithologies of the Yola sub-basin, in the Northern Benue Trough. Field observations of the surficial deposits at Mayolope, Taana, Kpasam and Bille revealed that they are Bima Formation while the ones in Abare are Dukul Formation. Paleoenvironmental studies based on the characteristics of lithofacies of these exposed sections and laboratory assessments of some selected samples showed that the Bima Formation was deposited in a continental setting while the Dukul Formation was deposited in a low-energy marine setting. Petrographic studies of framework components showed that the samples of the Bima Formation were predominated by quartz minerals, leading to their identifications as sandstones and classifications as quartzarenites while the samples of the Dukul Formation were limestones and were classified as bioclastic packstones. Heavy mineral compositions of the sandstones revealed their provenance; Zircon and Tourmaline with a combined amount of 60.1% suggested igneous and low-grade metamorphic rocks while rutile and staurolite with a total amount of 27.7% indicated contributions from high-grade metamorphic rocks.

Progress in the taxonomy of Late Cretaceous high-latitude radiolarians: insights from the Horton River area, Northwest Territories, Canada

Abstract. Radiolarians have proven to be exceptional tools in biostratigraphic and paleoenvironmental studies despite their relatively low preservation potential in the sedimentary record. Reports of Upper Cretaceous radiolarians in high northern latitudes are scant, and their taxonomy is not often discussed in the few reports available in the literature. In this study, we describe one new genus and three new species of polycystine radiolarians from Upper Cretaceous strata of the northern mainland coast of Arctic Canada. The specimens were recovered from the Santonian–middle Campanian Smoking Hills Formation and the middle Campanian–Maastrichtian Mason River Formation and are assigned to the genus Canadasphaera n. gen. (Order Spumellaria) and the species Canadasphaera inuita n. sp., Kuppelella rusti n. sp., and Lithocampe? rara n. sp. The taxonomic notes provided in this study improve our understanding of Late Cretaceous radiolarians from high northern latitudes and serve as a foundation for future Cretaceous radiolarian research in Arctic regions. Canadasphaera: urn:lsid:zoobank.org:act:C6B7B702-4B74-472D-8893-0A41B93A5066, date of registration: 19 April 2024 Canadasphaera inuita: urn:lsid:zoobank.org:act:C30E555B-EE94-4680-87D1-5CE83E128461, date of registration: 19 April 2024 Kuppelella rusti: urn:lsid:zoobank.org:act:68ECB628-2E74-4748-ACA4-DD1A33B05837, date of registration: 19 April 2024 Lithocampe? rara: urn:lsid:zoobank.org:act:25E569B2-93A8-425F-BB7C-D29A0437763F, date of registration: 19 April 2024

Natural and anthropogenic influences on sterol geochemical characteristics in lake sediments and implications for using sterols as paleoenvironmental indicators

Sterol-based geochemical proxies are used to reconstruct the historical environmental evolution of lakes and their catchment areas. However, the reliability of these proxies remains challenging because the link between environmental drivers and sterol geochemical characteristics has not been fully assessed. In this study, the abundance and composition of sterols were determined in sediment cores from nine lakes with contrasting natural conditions and anthropogenic perturbations to establish the response pattern of sterol geochemical characteristics to environmental drivers, and the controlling mechanisms behind this phenomenon were also tentatively speculated. Our results revealed that cholesterol and total C27 sterols were consistently enriched in the sediment cores from deep lakes (Fuxian, Lugu, and Erhai). In contrast, sitosterol and total C29 sterols were consistently enriched in the sediment cores from shallow (Changdang, Taibai, Chaohu, and Liangzi) and alpine lakes (Heihai and Jiren). The variable sterol distribution can be attributed to different natural processes in these lakes. In deep lakes, the productive zooplankton, owing to the long water column, contributed to high cholesterol levels; in shallow lakes, the delivery of massive terrestrial organic matter through abundant inflowing rivers caused a large sitosterol influx. In alpine lakes, the rapid input of alpine meadows due to the dense growth of these plants on lake shores and adjacent areas resulted in the dominance of sitosterol. The significant influence of natural processes on sterol geochemical characteristics stated above implies that the lake natural background should be considered when sterol proxies were used in paleoenvironmental studies. Comparison of sterol ratios in sediments deposited in the oligotrophic and eutrophic phases of each lake revealed a marked influence of anthropogenic perturbations on sterol distribution. In particular, the cholesterol/brassicasterol ratio exhibited consistent and significant variation with nutrient enrichment in shallow or alpine lakes, but not in deep lakes, revealing the possibility of using this ratio as a nutrient indicator in the former two types of lakes.

Assessment of Porites microatolls for paleothermometry: Calibration for French Polynesia

Massive dome-shaped coral Porites are the predominant choice for paleoclimate studies due to their consistent and reliable growth. When growing close to sea level, they become limited in their vertical growth and form so-called ‘microatolls’. Microatolls have not yet been extensively explored for paleoclimate reconstruction. Here, we investigate how reliable modern Porites microatolls are against empirical sea-surface temperature using Sr/Ca, δ18O, Li/Mg and SrU paleothermometry methods on samples from the Society Islands, French Polynesia. Our results show Sr/Ca ratios have the lowest Standard Error of the Inverse Prediction (SEIP) at 0.415 °C (N = 41) with a calibration of Sr/Ca (mmol mol−1) = −0.082 ± 0.006 SST (°C) + 11.256 ± 0.170 and with high reproducibility across multiple corals. The reproducibility of δ18O was less good, with SEIP increasing to 0.829 °C (N = 41). Considering methods directly from the literature, Li/Mg ratio empirically corrected for Sr/Ca had the best balance between bias and precision where no local calibration could be available. This study independently evaluates and confirms the suitability of Porites microatolls from well-flushed environments for paleoclimate studies. Fossil dome-shaped Porites grow anywhere between near-surface and roughly 20 m depths which inherently incorporates uncertainty into any sea surface temperature reconstruction. This uncertainty is significantly reduced for microatolls due to their well-constrained bathymetry. The study represents a fundamental step in paleoclimate research targeting consistently near the water-air interface bringing reliability and, especially when combined with their ability to reconstruct past sea-level changes, microatolls have the potential to be central for future paleoenvironmental studies.

The Pleistocene ice-sheet dynamics in north-central Poland based on magnetic fabrics of tills and landform analysis

Abstract This research was carried out in north-central Poland, which was occupied by the ice sheet of the Saalian (Marine Isotope Stage [MIS] 6) and Upper Stadial of the Weichselian (MIS 2) glaciation. The application of the anisotropy of magnetic susceptibility (AMS) method supported by a digital elevation model (DEM) analysis of the orientation of glacial landforms allowed for the reconstruction of ice-sheet extent and ice movement directions of these two Pleistocene glaciations. The research used an innovative method of collecting AMS till samples from the glacial plateau areas. Based on the research, it was found that during the general recession of the ice sheet of the Saalian glaciation, a previously undescribed glacial transgression occurred, characterized by a different direction of ice-sheet movement. On the basis of detailed geomorphological studies of the area of terminal moraines, previously described in fragments, the maximum extent of the ice sheet during the Weichselian glaciation was clarified. The recession of the ice sheet of the Weichselian glaciation from the area of north-central Poland took place in four regressive or transgressive–regressive stages with variable directions of ice-sheet movement. The results obtained indicate the great potential of the AMS method in paleoenvironmental studies of glaciated areas.

Diatom-based paleoenvironmental research: global trends, regional disparities and the evolving role of South America

The use of diatoms in paleoenvironmental research is of the utmost importance for reconstructing past ecosystems because it provides crucial insights into the adaptability and resilience of these systems under ongoing climate change and increased human impacts. Maintaining a comprehensive dataset distribution is crucial to ensure the validity and relevance of these reconstructions on a global scale. This scientometric study aimed to analyze trends in diatom-based paleoenvironmental research on a global scale with an emphasis on South America. This study aimed to investigate disparities in the geographical distribution of diatom-based paleoenvironmental studies, collaboration networks in the field, and regions in which this research is lacking. The Scopus search criteria excluded certain types of publications, such as conference articles and notes. The search focused on articles, reviews, books and chapters of books using specific keywords aligned with the objectives of this study. Using the Scopus database, we identified 7,091 publications (1979-2023) that employed diatoms as a primary proxy for paleoenvironmental reconstruction. The results show significant changes in this field recent decades. The analysis highlights a marked upsurge in publication output during the 1980s and a substantial increase in publications after 2000. This upward trend in scientific documentation reflects the growing interest in and recognition of the importance of this field in the context of palaeoecology and environmental sciences. After 2011, the results revealed a shift in thematic focus from historical and geological reconstruction to ecological, anthropogenic, and climatic interactions. Key researchers, including Smol JP, Leng MJ, and Birks HJB, have been at the forefront of international collaborations. Since the 2000s, South American studies have focused primarily on lakes, climate change effects, and volcanic activity. In this region, researchers such as Maidana N.I., Urrutia, R., and García-Rodriguez, F. emphasized the significance of regional ecosystems and their paleoenvironmental history in the global context of the field. Despite its high biodiversity, South America contributed only 6.7% of the global research output, placing it 19th globally. Socioeconomic factors and other obstacles faced by researchers in the region could explain the observed disparity in scientific output in South America compared to other regions. To unlock South America’s vast potential for diatom-based paleoenvironmental research, which boasts the highest global biodiversity yet remains underrepresented in the field, stakeholders must implement equitable partnerships, increase funding and improve their academic infrastructure and opportunities. These strategies are crucial for advancing the global paleoenvironmental understanding, informing future conservation and environmental policies in South America, and promoting scientific progress on a global scale.

Preservation of chemical and isotopic signatures within the Weißseespitze millennial old ice cap (Eastern Alps), despite the ongoing ice loss

Alpine ice core research has long focused on a few suitable drilling sites at high elevation in the Western European Alps, assuming that the counterparts at lower elevation in the eastern sector are unsuitable for paleoenvironmental studies, due to the presence of melting and temperate basal conditions. However, it has been demonstrated that even in the Eastern Alpine range, below 4,000 m a.s.l., cold ice frozen to bedrock can exist. In fact, millennial-old ice has been found at some locations, such as at the Weißseespitze (WSS) summit ice cap (Ӧtztal Alps, 3,499 m a.s.l.), where about 6 kyrs appear locked into 10 m of ice. In this work, we present a full profile of the stable water isotopes (δ18O, δ2H), major ions (Na+, K+, Mg2+, Ca2+, NH4+, Cl−, NO3−, SO42−), levoglucosan, and microcharcoal for two parallel ice cores drilled at the Weißseespitze cap. We find that, despite the ongoing ice loss, the chemical and isotopic signatures appear preserved, and may potentially offer an untapped climatic record. This is especially noteworthy considering that chemical signals of other archives at similar locations have been partially or full corrupted by meltwater (i.e., Silvretta glacier, Grand Combin glacier, Ortles glacier). In addition, the impurity concentration near the surface shows no signs of anthropogenic contamination at WSS, which constrains the age at the surface to fall within the pre-industrial age.

Redox geochemical signatures in Mediterranean sapropels: Implications to constrain deoxygenation dynamics in deep-marine settings

Global warming and anthropogenic activity are boosting marine deoxygenation in many regions around the globe. Deoxygenation is a critical ocean stressor with profound implications for marine ecosystems and biogeochemical cycles. Understanding the dynamics and evolution of past deoxygenation events can enhance our knowledge of present-day and future impacts of climate change and anthropogenic pressure on marine environments. Many studies have reconstructed the evolution redox conditions of past deoxygenation events using geochemical proxies. In this regard, the present work focuses on understanding the paleoenvironmental significance of geochemical redox signals derived from the onset, evolution and termination of regional-scale deoxygenations in deep-marine settings, with a specific focus on sapropels in the Eastern Mediterranean (EM). Sapropels, rhythmic organic-rich sediments deposited in EM, offer a unique opportunity to investigate recent deoxygenation events linked to past climate changes. Sapropels serve as paleo-archives of past deoxygenation events and can provide insights into the potential impacts of ongoing climate change on marine ecosystems and biogeochemical cycles. By integrating previous sapropel geochemical studies with a detailed analysis of new geochemical data from five Quaternary sapropels (S1, S5, S6, S7 and S8) in three different EM deep-marine settings, this study enhances our understanding of the paleoenvironmental significance of geochemical redox signals produced by deoxygenation dynamics and postdepositional processes in different deep-marine settings. The study supports that certain trace elements, such as Mo, V, U, Co, and Ni, are identified as more reliable redox proxies compared to Cr, Cu, Pb, and Zn. Four recurrent geochemical intervals attributed to specific redox conditions and postdepositional processes have been identified. Moreover, internal calibration of redox proxies thresholds has been performed and demonstrates how local environmental conditions (e.g., productivity rate) and hydrogeographic features (e.g., water-depth, particulate-shuttling intensity, deep-water renewal and fluvial input) play crucial roles in controlling the authigenic uptake rates of redox-sensitive trace metals, and subsequently, redox thresholds values of geochemical redox proxies. The results also emphasize the importance of postdepositional processes to accurately interpret geochemical signals in paleoenvironmental studies. This research enhances our overall understanding of geochemical signals associated with regional-scale deoxygenation events in deep-marine settings, offering new insights into predicting biogeochemical changes in marine environments undergoing a transition towards anoxia. By comprehending the dynamics of past and present deoxygenation, we acquire valuable knowledge regarding the potential effects of climate variability in marine ecosystems.