Sediment Profile Research Articles

Identifying the Vertical Stratification of Sediment Samples by Visible and Near-Infrared Spectroscopy

Vertical stratification in marine sediment profiles indicates physical and chemical sedimentary processes and, thus, is the first step in sedimentary research and in studying their relationship with global climate change. Traditional technologies for studying vertical stratification have low efficiency; thus, new technologies are highly needed. Recently, visible and near-infrared spectroscopy (VNIR) has been explored to rapidly determine sediment parameters, such as clay content, particle size, total carbon (TC), total nitrogen (TN), and so on. Here, we explored vertical stratification in a sediment column in the South China Sea using VNIR. The sediment column was 160 cm and divided into 160 samples by 1 cm intervals. All samples were classified into three layers by depth, that is, 0–50 cm (the upper layer), 50–100 cm (the middle layer), and 100–160 cm (the bottom layer). Concentrations of TC and TN in each sample were measured by Elementa Vario EL III. Visible and near-infrared reflectance spectra of each sample were collected by Agilent Cary 5000. A global model and several classification models for vertical stratification in sediments were established by a Support Vector Machine (SVM) after the characteristic spectra were identified using Competitive Adaptive Reweighted Sampling. In the classification models, K-means clustering and Density Peak Clustering (DPC) were employed as the unsupervised clustering algorithms. The results showed that the stratification was successful by VNIR, especially when using the combination of unsupervised clustering and machine learning algorithms. The correct classification rate (CCR) was much higher in the classification models than in the global model. And the classification models had a higher CCR using K-means combined with SVM (94.8%) and using DPC combined with SVM (96.0%). The higher CCR might be derived from the chemical classification. Indeed, similar results were also found in the chemical stratification. This study provided a theoretical basis for the rapid and synchronous measurement of chemical and physical parameters in sediment profiles by VNIR.

Climatic Oscillations and Dynastic Trends: A Multiproxy analysis of the past two millennia in the Indian Subcontinent

The study examines centennial-scale climatic oscillations over the past two millennia in the monsoon-dominated Indian subcontinent by multiproxy analysis of pollen along with stable carbon isotope, total organic carbon, magnetic susceptibility, and grain size from a 274 cm deep sediment profile in Sarsapukhra Lake, Varanasi, in the Central Ganga Plain (CGP) to portray vegetation changes and their impact on rise and fall of dominant dynasties. Between ∼1800 to 1600 cal yr BP, the coarser silty sand with few Poaceae and Asteraceae pollen with other proxy data, indicate that the region experienced a strong Indian Summer Monsoon (ISM). Subsequently, from ∼1600 to 1350 cal yr BP, presence of mixed moist deciduous taxa such as Shorea robusta, Madhuca indica, Rubiaceae, Morus alba, Syzygium, and Moraceae indicate a moderate ISM while between 1350 to 1200 cal yr BP, the dominance of dry deciduous taxa viz. Acacia sp., Bombax ceiba, Holoptelea, Rutaceae, Madhuca indica, Mangifera indica etc. suggested weak ISM conditions. A pulsative ameliorating trend from ∼1200 to 1030 cal yr BP showed the dominance of deciduous taxa such as Holoptelea, Rutaceae, Ziziphus, Rubiaceae, Maytenus and Acanthaceae etc. indicating warm and moist climatic conditions, followed by a weak ISM until ∼900 cal yr BP and improved ISM until 620 cal yr BP. Subsequently, an improving trend in the ISM from ∼620 to 450 cal yr BP was observed, with increased dominance of wetland taxa, followed by acute dry climate beyond ∼450 cal yr BP indicating poor ISM conditions.Additionally, the alternating warm and cold episodes had a direct impact on vegetation, forcing human civilizations to migrate from their original locations and contributing to the downfall of prominent dynasties. Furthermore, this study lays the foundation for future research into issues related to vegetation change, the amount of ISM shift, and human culture−climate relationship.

The environmental consequences of rapid urbanization in central Florida reconstructed with high resolution 241Am and 210Pb dating in lake sediments

Throughout the 20th century, Florida was one of the fastest growing states in the US, putting unique environmental stress on the region. Accurately dated lake sediments can provide invaluable records of environmental change that extend beyond monitoring records. Here, we analyze profiles of americium-241 (241Am), cesium-137 (137Cs), lead (Pb), zinc (Zn), and uranium-series radionuclides in Lake Bonny in Lakeland, Florida. The 241Am peak is sharp in the sediment profile, while the 137Cs peak is broader and spread evenly across two layers. The measured 137Cs inventory of ~448Bq/m2 is less than half of the expected inventory from atmospheric deposition (accounting for decay since deposition), indicating significant losses. The reliability of 137Cs as a chronological tool can be complicated in environments with low quantities of 2:1 clays and low available potassium (K), characteristic of Florida and the U.S. southeast. Using a piecewise constant rate of supply 210Pb model verified by 241Am, we reconstruct sedimentation and chemical change in this lake. Highest sedimentation rates in the lake occur during decades of peak population growth in the mid-20th century. Uranium (U) and radium-226 (226Ra) inputs to the lake reach a maximum in the 1960s, consistent with expansion of local phosphate mines and elevated groundwater pumping during that time in response to drought conditions. Total Pb in the sedimentary record captures the rise and fall of the use of leaded gasoline, but Zn inputs to the lake remain nearly two orders of magnitude above background levels in the last decade. Our high-resolution chronology of the lake reveals regional impacts on water and lake quality in central Florida during a period of rapid population growth.

Late Holocene extraordinary palaeoflood events and their climatological context in the Shahe River, Huaihe River Basin, China

Palaeoflood events represent immediate hydrological responses to extreme climate change. A loess-paleosol sedimentary profile containing three overbank flood deposits (OFD1, OFD2, and OFD3) layers that recorded palaeoflood events was discovered on the platform scarp of the Shahe River, a tributary of the Huaihe River through a field investigation. Sediment samples were collected, and their physicochemical properties, as well as optically stimulated luminescence (OSL) dating, were analyzed. The results indicated that OFD1, OFD2, and OFD3 were indeed overbank flood deposits influenced by hydrodynamic forces. However, OFD3 and OFD1 consisted primarily of sand (>60 %) in terms of particle size composition, whereas paleosol (S0), transitional loess (Lt), and Malan loess (L1) mainly comprised silt (>70 %). Moreover, the magnetic susceptibility values of OFD3 and OFD1 exceeded those of S0, Lt, and L1. The contents of Na2O, K2O, and SiO2 were higher, while their contents of Al2O3 and Fe2O3 were lower in OFD3 and OFD1. These suggested that OFD3 and OFD1 may originate from weathered bedrock materials transported from the upper reaches of the Shahe River under significant hydrodynamic forces. The particle size composition, magnetic susceptibility value, and geochemical element composition of OFD2 were similar to those of S0, Lt, and L1 but diverged significantly from those of OFD1 and OFD3, indicating that OFD2 originated from loess and soil sediments widely distributed on both sides of the valley. Through OSL dating and stratigraphic chronological framework of the sedimentary profile, these three extraordinary palaeoflood events in the Huaihe River Basin occurred during the late Holocene, ∼1470 a. The analysis of high-resolution climate proxy indicators, atmospheric circulation factors, and global mean temperature demonstrated a direct correlation between these extreme flood events and abrupt climate changes during ∼ 1470 a. This period corresponded to severe climate deterioration during the Northern and Southern Dynasties (589–420 CE) in China. These findings are crucial for enhancing our understanding of regional hydrological climate responses to global changes.

Integrating short- and full-length 16S rRNA gene sequencing to elucidate microbiome profiles in Pacific white shrimp (Litopenaeus vannamei) ponds.

Despite their immense economic value as a key aquaculture species, the production of Pacific white shrimp (Litopenaeus vannamei) faces significant challenges from intensive farming practices and disease outbreaks. Routine microbial profiling for disease surveillance could be a promising approach to anticipate and control disease outbreaks. To achieve this, accuracy in microbial profiling in shrimp ponds is crucial for enabling targeted action and prevention. Extensive documentation emphasizes that, beyond biological factors (related to the host, diet, or health status during the rearing period), technical elements, including sequencing techniques significantly influence bacterial community profiling. This study investigated the influence of short- and long-read sequencing of 16S rRNA genes on the microbial profiles in shrimp intestines, water, and sediments. The origin of the samples (intestine or environmental) in shrimp culture ponds primarily drove the observed differences in core microbial species. The ecological niches accounted for 56% of bacterial community variations in culture ponds. Both sequencing approaches showed consistent results in identifying higher-rank taxa and assessing alpha and beta diversity. However, at the species level, full-length 16S rRNA gene sequences provided better resolution than V3-V4 sequences. For routine microbial profiling in shrimp culture ponds, our study suggests that short-read sequences were sufficient for determining overall bacterial community.IMPORTANCEThis interdisciplinary study investigated the influence of sequencing techniques on bacterial communities profiling within Pacific white shrimp (Litopenaeus vannamei) ponds. By integrating aquaculture, microbiology, and environmental science, we revealed the role of ecological niches and factors like salinity and pH on microbiota diversity and composition in shrimp intestines, pond water, and sediment. Additionally, we compared the taxonomic resolution using partial versus full-length 16S rRNA gene sequences, highlighting the value of longer amplicons for precise identification of key taxa. These findings provide novel insights into microbial dynamics underlying environmental effects in shrimp aquaculture. Comprehensive characterization of the pond microbiome could lead to management strategies that promote shrimp health and productivity. Furthermore, the potential of a multi-omics approach for integrating complementary data streams to elucidate environment-microbiome-host interactions was highlighted.

Vertical growth rate of planted vegetation controls dune growth on a sandy beach

The integration of coastal dunes planted with vegetation and dikes combines traditional infrastructure with dynamic aeolian sediment and ecological processes to enhance coastal resilience. The functioning of such dune-dike hybrid Nature-based Solution strongly depends on aeolian sediment transport and the vertical growth rate of vegetation. We used the AeoLiS numerical model to investigate the relative importance of aeolian and vegetation dynamics in the evolution of a 120 m long and 20 m wide marram grass-planted dune field on a Belgian sandy beach backed by a seawall, constructed in 2021. AeoLiS proved to be a promising tool for predicting these systems, effectively capturing aeolian sediment deposition, vegetation growth, and profile development three years post-construction. Seasonal variations in vegetation trapping efficiency, driven by sediment burial, and seasonal plant growth emerged as important factors controlling dune growth. Profile development discrepancies were attributed to unaccounted biotic and abiotic factors, highlighting the complexity of coastal eco-geomorphological processes. Dunes planted with vegetation wider than 20 m were identified to enhance sediment trapping without an increase in dune height. These findings offer actionable insights for coastal management, promoting strategic dune design and planting approaches to reinforce shoreline resilience. Additionally, the findings underscore the necessity for advancing eco-morphodynamic models and deepening our knowledge of coastal dune dynamics.

Specialists regulate microbial network and community assembly in subtropical seagrass sediments under differing land use conditions

Microorganisms in the sediment play a pivotal role in the functioning and stability of seagrass ecosystems and their dynamics are influenced by the nutrient acquisition strategies of host plants. While the distinct impacts of microbial generalists and specialists on community dynamics are recognized, their distribution patterns and ecological roles within seagrass ecosystems remain largely unexplored. To address this issue, we conducted an analysis of community assembly processes and co-occurrence relationships of both microbial generalists and specialists within sediment profiles (0–100 cm) from seagrass habitats subjected to differing land use conditions. The results revealed that seagrasses in Yifeng Estuary experienced the large proportion of cultivated land and exhibited higher organic carbon content in the 0–20 cm surface sediment layer. Nitrogen-cycling bacteria were predominantly associated with seagrasses from Yifeng Estuary, whereas Vibrio spp. was more prevalent in seagrasses from Liusha Bay. Notably, seagrass Halophia beccarii (YHB) in Yifeng Estuary harbored higher niche breadths for both microbial generalist and specialist compared to Halodule uninervis (LHU) and Halophia ovalis (LHO) from Liusha Bay. Stochastic processes were pivotal in shaping seagrass sediment microbial communities, with a higher immigration rate observed in YHB, suggesting greater microbial turnover in this area. Additionally, YHB sediment presented lower drift and higher dispersal limitation among generalists compared to LHU and LHO, whereas the pattern was reversed among specialists. Specialists were found to play a crucial role in shaping microbial interactions within YHB sediment, with genera Halioglobus identified as keystone species in the network. The specialists were further found to significantly influence microbial β-diversity in seagrass sediment directly. Overall, our findings illustrated how microbial generalists and specialists were distributed in seagrass sediments in response to land use changes and provided new insights into the potential roles of microbial regulation in degraded seagrass ecosystems.

Late Holocene vegetation history and monsoonal climate change from the Core Monsoon Zone of India

To understand the vegetation response to climate change and the Indian Summer Monsoon rainfall (ISMR) variability during the Late Holocene (approx. 2.5 ka), pollen analysis was conducted on a 1.2-m-long lacustrine sediment profile from the Korba District of Chhattisgarh, central India, within the core monsoon zone (CMZ). The pollen evidence suggest that between approx. 2500 and 1950 cal yr BP, open tropical deciduous forest vegetation occupied the landscape under a warm and relatively less humid climate, coupled with decreased ISMR. Between approx. 1950 and 1035 cal yr BP, a warm and relatively more humid climate prevailed, along with moderate ISMR, leading to the transition of the existing vegetation to an open mixed tropical deciduous forest. Between approx.1035 and 220 cal yr BP (CE 915–1730), the mixed tropical deciduous forest became established under a warm and humid climate with increased ISMR, coinciding globally with the Medieval Climatic Anomaly (MCA). Mixed tropical deciduous forest expanded and transformed into a dense mixed tropical deciduous forest between approx. 220 cal yr BP to the present (CE 1730 onwards). This transformation occurred under a warm and relatively more humid climate, accompanied by intensified ISMR, aligning with the Current Warm Period (CWP). Gradual forest transformation from open vegetation to dense mixed tropical deciduous forests, as well as in the ISMR has been observed since the last approx. 2.5 ka in central India. Cereal-based agricultural practices and other anthropogenic activities have been documented in the study area since approx. 2.5 ka, with an accelerated pace observed from 1035 cal yr BP to the present.

Record of microplastic deposition revealed by ornithogenic soil and sediment profiles from Ross Island, Antarctica

Microplastics (MPs) are a global concern as an emerging pollutant, and the investigation on MPs in Antarctic aids in informing their global pollution assessments. Therefore, there are urgent scientific concerns regarding the environmental behavior, origins, influencing factors, and potential hazards of MPs in Antarctica. This study presents the characteristics of MPs from one ornithogenic sediment profile (coded CC) and two ornithogenic soil profiles (coded MR1 and MR2) from ice-free areas on Ross Island, Antarctica. We explored the potential sources of MPs and the main influencing factors for deposition based on their distribution with depth in the profiles. Through laser-infrared imaging spectroscopy (LDIR), a total of 30 polymer types were identified in all samples, with polyethylene terephthalate (PET) and polyvinyl chloride (PVC) as the dominant types, accounting for more than 70% of the total. The abundance of MPs in the CC sediment profile ranged from 2.83 to 394.18 items/g, while in MR1 and MR2 soil profiles, the abundance ranged from 2.25 to 1690.11 and 8.24 to 168.27 items/g, respectively. The size of MPs was mainly concentrated in the range of 20–50 μm, and possible downward movement of certain polymer types was revealed. From the perspective of temporal variation, we suggest that MPs were heavily influenced by local human activities including scientific research, fishing, and tourism, balanced by protective regulations, while no solid evidence was obtained to support strong influence from biological transport through penguins. This research enhances our understanding on the environmental behavior of MPs in the terrestrial systems of remote polar regions.

Sedimentation of heterogeneous particles in a porous material

Filtration of suspensions and colloids in porous materials occurs during the construction and operation of hydraulic structures, tunnels and underground storage facilities. Filtration models are used to calculate the penetration of grout into loose soil, when treating drinking water and industrial wastewater. During the filtration process, suspended particles pass through large pores and get stuck at the entrance of small-diameter pores. The trapped particles form a stationary deposit. A model of filtration of a polydisperse suspension in a porous material is considered. The purpose of the work is to study sediment profiles – the dependence of the concentration of deposited particles on the distance to the porous material inlet at a fixed time. An exact solution to the model was constructed using the method of characteristics. It has been shown that when filtering a polydisperse suspension, the distribution of sediment differs for different types of particles. The sediment profile of the largest particles always decreases monotonically, but the sediment profile of the smallest particles is not monotonic. It decreases at short times, then a maximum point appears on the graph, moving along the porous medium as time increases. After the maximum point reaches the porous material exit, the sediment profile becomes monotonically increasing. The sediment profiles of intermediate size particles and the total sediment profile are either monotonic or non-monotonic depending on the model parameters. The behavior of maximum points of non-monotonic profiles has been studied.

Temperature changes of the Mid-Late Holocene transition in North China and their implications for regional cultural succession

Evaluating the influence of temperature on cultural successions in North China during the Mid-Late Holocene transition (MLHT) is a significant research problem. We used a lacustrine sedimentary profile (BG-2019) from Lake Baiyangdian, in the hinterland of the North China Plain, to quantitatively reconstruct temperature changes during the MLHT, using branched glycerol dialkyl glycerol tetraethers (brGDGTs). We then integrated this record with selected quantitative paleotemperature records from North China to explore the effects of temperature change on the evolution of Neolithic cultures in this region. The results show that the mean annual temperature (MAT) in the hinterland of the North China Plain during the MLHT averaged ∼15.7 °C (∼3.6 °C higher than today); and that three significant cooling events occurred (the 5.3 ka event, 4.8 ka event, and 4.2 ka event), at ∼5300-5100 cal yr BP, 4800 cal yr BP, and ∼4500-4300 cal yr BP, respectively, with cooling between −2.1 °C and −3.4 °C. Integration of our results with other regional quantitative paleotemperature records shows that these three cooling events are well documented in North China, with spatial consistency in their magnitude and onset of cooling. These cooling events are temporally correlated to two cultural transitions in North China: the cooling event at ∼5300-4800 cal yr BP corresponds to the decline of the Yangshao culture in the Central Plains region, and the decline of the Hongshan culture in the Yanliao region, which evolved into the Xiaoheyan culture. Additionally, we suggest that the cooling event at ∼5300-4800 cal yr BP, combined with the weakening of the summer monsoon, contributed to the end of the Yangshao culture and the rise of the Longshan culture in the Central Plains region, and that it accelerated the end of the Xiaoheyan culture and the rise of the Xiajiadian Lower Culture in the Yanliao region.

Cyanobacteria decay alters CH4 and CO2 produced hotspots along vertical sediment profiles in eutrophic lakes

Cyanobacteria-derived organic carbon has been reported to intensify greenhouse gas emissions from lacustrine sediments. However, the specific processes of CH4 and CO2 production and release from sediments into the atmosphere remain unclear, especially in eutrophic lakes. To investigate the influence of severe cyanobacteria accumulation on the production and migration of sedimentary CH4 and CO2, this study examined the different trophic level lakes along the middle and lower reaches of the Yangtze River. The results demonstrated that eutrophication amplified CH4 and CO2 emissions, notably in Lake Taihu, where fluxes peaked at 929.9 and 7222.5 μmol/m2·h, mirroring dissolved gas levels in overlying waters. Increased sedimentary organic carbon raised dissolved CH4 and CO2 concentrations in pore-water, with isotopic tracking showing cyanobacteria-derived carbon specifically elevated CH4 and CO2 in surface sediment pore-water more than in deeper layers. Cyanobacteria-derived carbon deposition on surface sediment boosted organic carbon and moisture levels, fostering an anaerobic microenvironment conducive to enhanced biogenic CH4 and CO2 production in surface sediments. In the microcosm systems with the most severe cyanobacteria accumulation, average CH4 and CO2 concentrations in surface sediments reached 6.9 and 2.3 mol/L, respectively, surpassing the 4.7 and 1.4 mol/L observed in bottom sediments, indicating upward migration of CH4 and CO2 hotspots from deeper to surface layers. These findings enhance our understanding of the mechanisms underlying lake sediment carbon emissions induced by eutrophication and provide a more accurate assessment of lake carbon emissions.

Effects of cable bacteria on vertical redox profile formation and phenanthrene biodegradation in intertidal sediment responded to tide

Periodic oxygen permeation is critical for pollutant removal within intertidal sediments. However, tidal effects on the vertical redox profile associated with cable bacterial activity is not well understood. In this study, we simulated and quantified the effects of tidal flooding, exposing, and their periodic alternation on vertical redox reactions and phenanthrene removal driven by cable bacteria in the riverbank sediment. Results show that electrogenic sulfur oxidation (e-SOx) mediated by cable bacteria during exposing process drove the vertical permeation of oxidation potential characterized by a decrease in Fe(II) and sulfide concentrations. The sulfate produced was observed in deep sediment (5–10 mm) and served as an electron acceptor for anaerobic oxidation, thereby triggering the functional succession of microbial community. About 78.2 % and 80.8 % of phenanthrene was degraded in deep sediment where cable bacteria grew well under exposing and tidal conditions. Anaerobic processes during tidal flood were also found to be important for the survival of cable bacteria. Higher cable bacteria abundance (up to 1.5 %) was observed under tidal conditions compared to that under continuous exposing conditions and flooding conditions. This might be attributed to lower oxidation stress and sulfide replenishment via sulfate reduction while flooding. Under tidal conditions, the cable bacteria interacted with sulfate reduction bacteria (e.g. Desulfobacca spp. and Desulfatiglans spp.) and maintained the dynamic balance of HS− and SO42− in sediment profiles. This HS−-SO42− cycle could serve as a “redox connector” that continuously delivers oxidation potential to deep sediments, resulting in the removal of organic pollutants. The findings provide preliminary evidence of the self-purification mechanisms within intertidal sediments and suggest a potential strategy for sediment remediation.

Assessing the potential of n-alkyl amides and n-alkyl nitriles in the arid sedimentary strata of northwestern China as environmental indicators

Recent advancements in the application of lipid biomarkers as paleoenvironmental indicators have provided invaluable insights into the dynamics of climatic variations, vegetative histories, and anthropogenic impacts. However, our current understanding of nitrogen-containing lipid biomarkers (NCLBs) in sedimentary deposits remains limited, notwithstanding their potential significance in global nitrogen cycling. To bridge this research gap, a comprehensive study was conducted to characterize the distribution patterns of n-alkyl amides (NAAs) and n-alkyl nitriles (NANs) in representative paleo-lake and loess sedimentary profiles from the arid region of northwestern China (NWC). The widespread occurrence of these NCLBs across late Quaternary strata, with distinct distribution patterns observed in various settings, suggests their formation under diverse environmental conditions. The prevalence of NAAs in arid sedimentary deposits can primarily be attributed to the diverse array of local biota, including vascular plants, algae, and fungi, rather than being solely associated with biomass burning, as commonly assumed. Furthermore, the distribution patterns of NANs closely align with those of NAAs, indicating their formation through thermally induced dehydration of precursor NAAs. Both groups of NCLBs exhibit significant preservation potential in sediments within NWC, which is believed to be intimately linked to the region's arid and cold climate as well as its neutral or weakly alkaline depositional setting. These findings underscore the prospective use of NAAs as indicators of environmental changes and NANs as potential markers of past fire-related activities, making them valuable tools for paleoenvironmental reconstructions of late Quaternary strata, especially in arid, cold, and weakly alkaline regions.

Habitat-driven otolith shape morphology in Oreochromis niloticus (pelagic) and Chrysichthys nigrodigitatus (benthic) from distinct zones of a tropical coastal lagoon system

This study explored the morpho-functional variations in the otoliths of Oreochromis niloticus (ON) and Chrysichthys nigrodigitatus (CN) across the Ikorodu (IKL) and Epe (EPL) regions in Nigeria's southern coastal lagoon system, with monthly sampling over twelve months. Digitized otoliths provided shape descriptors, and bathymetric analysis was conducted using the depth invariance index (DII). Remotely sensed reflectance (RSR) at 469 nm, 531 nm, and 555 nm assessed habitat productivity. Morpho-functional variations were evaluated using discriminant analysis (DA) and principal component analysis (PCA). Bathymetric analysis revealed that EPL has a deeper and more heterogeneous substratum than IKL. Additionally, Epe exhibited consistently higher RSR values than IKL. Sediment analysis showed higher clay and silt percentages in IKL and increased coarse sand in EPL, indicating distinct terrains. DA accuracy was high (ON: 92.0 %, CN: 90.8 % in cross-validation), highlighting variables such as area and circumference for ON and area, circularity, and compactness for CN. DA emphasized ellipticity, rectangularity, and roundness for ON, and form factor, compactness, circularity, and aspect ratio for CN. Higher reflectance values at EPL than at IKL indicate distinct ecological characteristics, with greater nutrient cycling and trophic productivity at EPL. Sediment analysis revealed distinct ecological heterogeneity and hydrological effects, with finer sediments in IKL indicating calmer conditions and EPL exhibiting higher energy conditions. Visualizing normal curve distributions for otolith shape descriptors in ON and CN populations revealed skewness patterns indicative of divergent adaptive features, possibly associated with habitat heterogeneity and productivity. The key otolith variables identified by DA and PCA suggest relative ecological opportunity and underscore the intricate relationships between otolith morphology and habitat variables (heterogeneity, productivity, sediment profile) in Nigeria's tropical southern lagoon system.

The northernmost Polish Eemian palaeolake near Łęczyce − Stratigraphic and palaeoecological implications for a MIS 6a − MIS 5d sediment record

We report the results of high-resolution multi-proxy studies of a 10 m thick sedimentary profile from Łęczyce, Poland. It reveals a continuous lacustrine succession from the Eemian Interglacial. On this basis, we have distinguished seven sedimentary units (U7a-U7f) and ten local palynological zones (LPAZ Lec 1 − Lec 10), revealing the evolution of the lake from the moment of dead-ice melting, through the continuous filling of the lake basin with organic mud, to the final stage of shallowing and transformation into a peat bog. This northernmost known Eemian site was investigated for the first time, therefore, the reconstructed changes in local conditions were correlated with global changes from the final phase of the penultimate glaciation through the Eemian Interglacial to the beginning of the last glaciation. The results show that the melting of dead ice blocks at this site was delayed compared to central Poland, with lacustrine processes starting as glaciolimnic sedimentation. Furthermore, the delayed start of vegetation development around the lake resulted in the absence of a Pinus-Betula-Ulmus E2 level. During the Eemian, local conditions were generally stable, and sedimentation took place in a relatively deep basin with well-defined epilimnion and hypolimnion zones. Climatic instability at the end of the Eemian resulted in reduced vegetation cover. During the first climatic deterioration in the Weichselian (presumably the Herning Stadial), lacustrine sedimentation was reduced and the deposition of fine-grained mineral material predominated. This was followed by the complete drying out of the lake and the development of soil formation. The subsequent climatic warming (Brørup Interstadial?) recorded in the uppermost part of the profile (U7f) was characterised by the plant community Lec 10 (Carpinus-Corylus-Picea) and was presumably warmer than commonly assumed. Multi-proxy studies show that the development of the lake was more similar to that of southern Scandinavia than to that of Poland.

Holocene paleoclimatic records from Chakrata area, Northwest Himalaya

We present monsoon variability records for the Holocene using multi-proxy approach (environmental magnetism, carbon isotope, and total organic carbon) from a 146 cm thick sedimentary profile in the Kotikanasar meadow (Chakrata), Northwest Himalaya. The chronology of the record was constrained by five AMS 14C ages. The carbon isotope (δ13C) and Total Organic Carbon (TOC) data highly variable which vary between -26.62‰ and -22.46‰ (C3-plants) and 0.1 to ∼4%, respectively, indicating paleo-vegetation history and productivity of the studied area. The environmental magnetics indicates highly fluctuating in the Early Holocene with high concentrations of magnetic minerals during high monsoon conditions and vice-versa. Intense Indian Summer Monsoon (ISM) phases were identified during the Early and Late Holocene i.e., ∼9.2 to 7.4 ka, and ∼4.8 ka to Modern which shows warm and wet climate. While decline in the ISM intensity during ∼7.4 to 4.8 ka which indicates cold and dry climatic condition in the Northwest Himalayan regions. From ∼9.2 to 7.4 ka highly fluctuating climate linked with the Early Holocene warming. Sediment profile exhibits aridity in climate accompanying with the high influence of mid-latitude westerlies during ∼7.4 to 4.8 ka from Northwest Indian regions (Enzel et al., 1999). Hence the long-term fluctuation in the climate governed by the changes in the North Atlantic Ocean circulation as well as variations in the incoming solar radiations.

Geology, mineralogy, geochemistry and genesis of volcano-sedimentary hosted Lake Abiyata diatomite in central main Ethiopian Rift

The Abiyata Diatomite deposit is located in the Main Ethiopian Rift, which is characterized by strong extensional tectonics. The deposit is mostly made up of diatomaceous earth, which is a sedimentary rock made up of the fossilized remnants of diatoms, which are tiny algae. Diatomite's geological, geochemical, and mineralogical features, as well as its formation, are discussed in this research. To characterize diatomite from Abiyata, chemical, mineralogical, technological, and micro paleontological examinations were conducted on samples collected from outcrops and stream sections. The XRD characteristic peaks of diatomite demonstrate that it is primarily made up of Opal A silica, however certain crystalline phases were discovered in adequate amounts. Quartz and feldspar were the predominant crystalline phases, with lesser amounts of Calcite, Cristobalite, Illite, Mordinite, Wairakite, Halloysite, Clinoaptilolite, Adularia, and Tridymite. From SEM photomicrographs diatomites are primarily formed of benthic freshwater diatom species such as Staurosirella pinnata, Staurosira construens, Pseudostaurosira brevistriata, Epithemia Sorex and surirella pinnata. Diatom species, sedimentary profile sections and mineralogical data suggest that diatomite was deposited in lacustrine-type freshwater shallow lake environment. Chemical data obtained from 10 diatomite samples show that while silica is the bodybuilding material for diatomite. i.e., Silica (SiO2), 76.9 %; Alumina (Al2O3), 3.49 %; Sodium Oxide (Na2O), 1.52 %; Potassium Oxide (K2O), 1.107 %; Iron Oxide (Fe2O3), 1.1 %; Loss on ignition (LOI) 13.7 and other oxides are below 1 %. Studies from technological properties like physical tests, chemistry, and mineralogy and micropaleontology of Abiyata diatomite suggest that calcined diatomite can be used for waste treatment processes in the filter aid industry and as filler material.

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.

Ornithogenic sedimentary profiles of n-alkanes and PAHs constrain breeding penguin population dynamics at Cape Bird, Ross Island, Antarctica, over the past 1,500 years

Ornithogenic sediment may contain important paleoecological information concerning past bird population dynamics. In this paper, we analyse the distribution of n-alkanes and polycyclic aromatic hydrocarbons (PAHs) in two sedimentary profiles collected from abandoned penguin colonies at Cape Bird, Ross Island, Antarctica. The geochronology of the sediment profiles was determined using 210Pb and AMS 14C dating techniques, and spans the past 1500 years. We observe low levels of n-alkanes (0.93–2.67 μg g−1) and PAHs (20.5–46.8 ng g−1) concentrations dominated by short-chain n-alkanes, low-molecular-weight and alkyl PAHs. Principal Component Analysis (PCA) shows that the PC 1 scores for n-alkanes and PAHs are significantly correlated with the input intensity of penguin guano and penguin bioelements. Using these proxies in combination with Generalized Additive Model (GAM), we reveal that breeding penguin population growth reaches a historical peak during the Medieval Climate Anomaly (MCA) prior to 1550 CE. This growth in population size corresponds to the extent of sea ice cover and the activity of the local atmospheric-ocean circulation. Warming induced by El Niño and the positive phase of the Southern Annular Mode, along with the expansion of ice-free zones and increased oceanic nutrient and food availability, are considered primary factors contributing to the growth of breeding penguin populations. Additionally, variations in sea ice extent and Amundsen Sea Low significantly influence penguin population dynamics. Our study suggests that n-alkanes and PAHs may be valuable organic proxies for reconstructing historical changes in breeding penguin populations, with the local sea ice extent and atmospheric-oceanic circulation exerting a major influence on Antarctic penguin population dynamics.