Rich Sediments Research Articles

Columnar jointing in Paleoproterozoic carbon-bearing rocks (Onega Basin, NW Russia): implications for carbon migration in sedimentary rocks

ABSTRACT Columnar jointing occurs commonly in igneous rocks and rarely in sedimentary rocks. We report the results of combined field and petrological studies, Raman spectroscopy and column geometry analysis of columnar jointing in Paleoproterozoic carbon-bearing rocks, Eastern Fennoscandian Shield, NW Russia. The columnar rocks occur near the contact with the saucer-shaped dolerite sill emplaced in the unconsolidated organic rich sediments. Columnar jointing aureole (1 to 7 m) and column architecture strongly depends on the contact morphology. Columnar jointing is caused by the contraction of organic-rich sediments due to generation and further release of gas and oil rich fluid. The results of integrated studies indicate that fluidization driving the jointing is associated with not only the dehydration, but also with the mobilization of gas and oil rich fluid due to the thermal maturation of organic matter. Columnar jointing is associated with intensive fluid circulation and devolatilization evidenced by the numerous veins, globules, and vugs filled with migrated carbonaceous matter and secondary minerals in the columnar rocks as well as high vesicularity of dolerites near the contact. The redistribution of the mobile elements (K, Rb, LREE) along with the significant enrichment of S near the contact also indicates the intensive fluid circulation. The study contributes to understanding of mechanism of columnar jointing in sedimentary rocks and formation the fracture networks in organic-rich sediments.

Acoustic Rapid Detection Technology and Its Application for Rare Earth Element (REE)-Rich Sediments in the Pigafetta Basin of the Western Pacific

This study aims to investigate the stratigraphic features and rare earth element (REE) mechanisms of deep-sea REE-rich sediments in the West Pacific Pigafetta Basin using acoustic rapid detection technology. Through an analysis of sub-bottom profile data and synthesis of existing studies, this study reveals the acoustic properties and thickness distribution of the REE-rich sediments. Acoustic spectral records identify three distinct acoustic facies: opaque (O), transparent (T), and laminated (L). This study maps the thickness and spatial distribution of the REE-rich sediment layer in the research area, ranging from approximately 6 to 36 m in thickness. Regions with REE-rich sediments exceeding 30 m in depth are identified, showing concentrated distribution along the northwest–southeast axis and a contiguous zone in the southwest corner of the study area. The method employed in this study can determine the potential bottom boundary of the REE-rich layer by assessing the thickness range of the sedimentary layer, overcoming limitations of traditional sampling methods. Furthermore, the thickness distribution characteristics of the REE-rich sedimentary layer in the study area provide valuable insights for future research on resource evaluation and estimation.

Combined measures in lake restoration – A powerful approach as exemplified from Lake Groote Melanen (the Netherlands)

Controlling lake eutrophication is a challenge. A case-specific diagnostics driven approach is recommended that will guide to a suite of measures most promising in restoration of eutrophic lakes as exemplified by the case of the shallow lake Groote Melanen, The Netherlands. A lake system analysis identified external and internal nutrient load as main reasons for poor water quality and reoccurring cyanobacterial blooms in the lake. Based on this analysis, a package of restoration measures was implemented between January 2015 and May 2016. These measures included fish removal, dredging, capping of peat rich sediment with sand and an active barrier (lanthanum-modified bentonite), diversion of two inlet streams, reconstruction of banks, and planting macrophytes. Dredging and sand capping caused temporarily elevated turbidity and suspended solids concentrations, while addition of the lanthanum-modified clay caused a temporary exceedance of the Dutch La standard for freshwaters. Diversion of inflow streams caused 35 % less water inflow and larger water level fluctuations, but the lake remained water transporting with strongly improved water quality as was revealed by comparing five years pre-intervention water quality data with five years’ post-intervention data. Total phosphorus concentration in the water column was reduced by 93 % from 0.47 mg P l-1 before the intervention to 0.03 mg P l-1 after the intervention, total nitrogen by 66 % from 1.27 to 0.21 mg N l-1, total chlorophyll-a by 75 % from 68 to 16 µg l-1, cyanobacteria chlorophyll-a by 88 % from 32 to 4 µg l-1. Turbidity had declined by 58 % from 23.5 FTU to on average 9.9 FTU. No cyanobacteria blooms were recorded over the entire post-intervention monitoring period (2016–2021). Submerged macrophytes increased from complete absence before intervention to around 10 %–15 % coverage after intervention. Repeated fish removal lowered the fish stock to below 100 kg ha-1 with 12 % of bream and carp remaining. Hence, the package of cohesive measures that was based on a thorough diagnosis resulted in rapidly, strongly and enduringly improved water quality. This case provides evidence for the power of combining measures in restoring eutrophic lakes.

Ditch cleaning in boreal catchments: Impacts on water chemistry and dissolved greenhouse gases in runoff

Ditch cleaning (DC) is a forestry practice commonly conducted in boreal regions that aim to lower groundwater tables (GWT) in waterlogged soils, thereby maintaining or improving forest growth. However, there is limited information on the impact of DC on water chemistry and dissolved greenhouse gases (GHG) in draining ditch networks. Based on a repeated synoptic sampling of a paired catchment design we here evaluated water chemistry and GHG data in ditch waters from 25 cleaned sites (being cleaned 1–4 years prior to sampling) and 25 non-cleaned reference sites (REF). The sampled sites were further selected to test whether there were any differences in the DC effect if the operations were conducted in forested or clear-cut areas. Across all sites, we found that DC sites exhibited higher pH, sulfate and calcium concentrations than REF sites. Also, lower dissolved carbon dioxide and higher nitrous oxide concentrations were observed in DC sites. In forested areas, DC sites exhibited significantly higher calcium and potassium concentrations, along with reduced levels of methylmercury and carbon dioxide. In clear-cuts, sulfate concentrations were significantly elevated in the DC sites. We suggest that the observed differences in water chemistry and GHG´s between DC and REF sites were induced by the DC and largely driven by lower GWT following DC, resulting in deeper groundwater flow paths through more mineral-rich soil layers, and altered redox conditions. Also, the removal of organic rich sediments and vegetation from the ditches themselves may affect water chemistry and GHG´s e.g. by decreasing the formation of methylmercury and carbon dioxide.

Water extractable carbon and nitrogen across vegetated and non-vegetated coastal habitats

Many coastal ecosystems have a high carbon (C) and nitrogen (N) accumulation capacity. Extractable C and N have been shown to be useful indicators to assess changes in soil C and N in terrestrial systems but have not been widely used in coastal habitats. Here, we quantified cold and hot water extractable organic C (cweC, hweC) and N (cweN, hweN) and determined specific ultraviolet absorbance (SUVA254) to evaluate how water extractable C and N concentration and chemistry change along the transition from mangrove (vegetated) to tidal flat (non-vegetated) and with sediment depth. Sediment cores (20 cm depth) were collected along transects in a muddy (29–46 % clay + silt, Snells Beach) and sandy (8–11% clay + silt, Hobson Bay) estuary in the Auckland region, New Zealand. Cold water exactable C and N concentrations were similar in the muddy and sandy estuary (7–173 μg C g−1 soil; 1–32 μg N g−1 soil). However, cweC and cweN made up a larger proportion of sediment C and N concentration at the sandy estuary. The hweC and hweN concentrations were significantly higher in the muddy (240–2440 μg C g−1 soil; 25–244 μg N g−1 soil) than sandy estuary (50–960 μg C g−1 soil; 6–119 μg N g−1 soil) suggesting a higher release of C and N from the muddy estuary with organic matter rich sediments. Habitat had a strong effect at both sites with extractable C and N concentrations being higher in mangroves compared to tidal flat. The C:N ratios and SUVA254 values of cweC tended to be lower than hweC across all habitats in both estuaries, suggesting a higher proportion of algal-derived organic matter and a lower proportion of aromatic molecules. Our findings demonstrate that water extractable C and N provide valuable insights into the quality and drivers of C and N in coastal habitats.

Petroleum potential from Permian-Triassic strata of the Maniamba Basin, Mozambique: A preliminary characterisation

Abstract In order to further our understanding regarding the petroleum potential of the Maniamba Basin, Mozambique, organic rich sediments from four outcrops were investigated. Organic-rich shales, claystones, sandstones and siltstones were sampled for geochemical organic analyses that included Total Organic Carbon (TOC), and Rock Eval Pyrolysis. The pyrolysis analysis showed that the TOC ranges from good to excellent, thus indicating a potential for hydrocarbon generation. Based on the hydrogen index (HI) versus oxygen index (OI) diagram, most samples were classified as kerogen type III or IV, however, a mixed type II and III was also observed. These data suggest that the Organic Matter (OM) is of terrigenous origin with the occurrence of organofacies C, CD and D. The majority of the studied samples are found to be at mature to overmature stages. The overmaturation of the OM may be associated with tectonic events during the process of basin subsidence, and close proximity to igneous intrusions. Further, an indigenous nature of the hydrocarbon has been identified. Similar organic matter properties of the studied sections are correlatable with those from Moatize Minjova, Sanangoé-Mefidezi (Mozambique), Ruhuhu (Tanzania) and the Main Karoo Basin in South Africa. Overall, the results of this study suggest a good potential for gas.

Aragonite crystallization in a sulfate-rich hypersaline wetland under dry Mediterranean climate (Laguna Honda, eastern Guadalquivir basin, S Spain)

This research investigates the influence of water composition, the presence of seasonal algal mats, detrital inputs and the activity of microorganisms on the crystallization of aragonite in the sediments deposited in the hypersaline Laguna Honda wetland (S of Spain). The high alkaline and hypersaline waters (pH > 9.2 and C.E. > 70 mS/cm) of the wetland lake are rich in SO42− (>24,000 mg/l), Cl− (>21,000 mg/l), Na+ (>11,000 mg/l) Mg2+ (>8400 mg/l) and Ca2+ (>1000 mg/l), and are supersaturated for dolomite, calcite and aragonite. Sediments have lower pH values than column waters, oscillating from 8.54 in the low Eh (up to −80.9 mV) central deep sediments and 6.33 in the shallower higher Eh (around −13.6 mV) shore sediments. Erosion of the surrounding olive groves soils produced detrital silicates rich sediments with concretions of carbonate or sulfate. Aragonite (up to 19 %) and pyrite (up to 13 %) are mainly concentrated in the organic matter rich samples from the upper part of the sediment cores, whereas gypsum is preferably concentrated in low organic matter content samples. Mineral crusts containing a MgAl silicate phase, epsomite, halite and gypsum are precipitated on the floating algal mats covering the wetland waters. Floating algal mats deposit increased the organic matter content of the upper sediments which promoted the presence of fermentative microorganisms, sulfate-reducing bacteria (SRB) and sulfur-oxidizing bacteria (SOB) communities and variations of Eh that influence the authigenesis of carbonate and S-bearing minerals. Replacement of poorly crystalline MgSi phases infilling algal cells by aragonite was favored in the organic matter rich sediments with low Eh values and important SRB communities that promoted sulfate bioreduction processes to form pyrite. Aragonite precipitation was favored by the increase of carbonate and bicarbonate concentration produced by the SRB oxidation of organic matter, the CO2 degassing by high summer temperatures and the CO2 uptake by photosynthesis of the algal mats.

Diverse Lophoctenium burrows from the Upper Devonian (Famennian V and VI) of Algeria

Three ichnospecies of Lophoctenium (L. comosum, L. richteri and L. cf. haudimmineri) are reported from the Upper Devonian Argiles de Marhouma Formation (southwestern Algeria) for the first time. This formation contains a diverse assemblage of trace fossils belonging to the Nereites ichnofacies. We describe three ichnospecies of Lophoctenium that correspond to three different feeding strategies among the diverse ichnofauna of the Argiles de Marhouma Formation. The strategy of L. comosum evidences food-rich sediments as it maximises the amount of collected food per foraged distance. The strategy of L. richteri is probably most efficient for feeding in slightly less nutrient rich sediment, but gives the opportunity to discover more prolific feeding sites by moving on longer distances. The strategy with a straight central burrow and probes on both sides of the main burrow with long interspaces (L. cf. haudimmineri) was presumably used in the least food rich sediment. It seems that the Lophoctenium was widespread in the Devonian, but restricted to seas surrounding Gondwana.

The Holocene silicon biogeochemistry of Yellowstone Lake, USA

Silicon (Si) is an essential macronutrient for diatoms, an important component of lacustrine primary productivity that represents a link between the carbon and silicon cycles. Reconstructions of lake silicon cycling thus provide an underexploited window onto lake and catchment biogeochemistry. Silicon isotope geochemistry has potential to provide these reconstructions, given the competing source and process controls can be deconvolved. The silica-rich volcanic and hydrothermal systems in Yellowstone National Park are a great source of dissolved silicon into Yellowstone Lake, a system with high silicon, and thus carbon, export rates and the formation of diatom–rich sediment. Yellowstone Lake sediments should be an archive of past silicon biogeochemistry, although the effect of sublacustrine hydrothermal activity or hydrothermal explosion events is unclear.Here, we analysed lake water, tributaries, and hydrothermal vent fluids from Yellowstone Lake for their dissolved Si concentrations, isotope composition (δ30Si) and Ge/Si ratios to evaluate the sources of variability in the lake's Si cycle. Bulk elemental composition and biogenic SiO2 (bSiO2) content, together with δ30Si and Ge/Si ratios from a single diatom species, Stephanodiscus yellowstonensis, were analysed in two sediment cores spanning the last 9880 cal. yr BP. We investigate these datasets to identify long term Holocene changes in hydrothermal activity and effects of large and short-term events i.e., hydrothermal and a volcanic eruption.Combinations of bSiO2, δ30Si and Ge/Si with XRF and lithology data revealed that Yellowstone Lake has a resilient biogeochemical system: hydrothermal explosions are visible in the lithology but have no identifiable impact on bSiO2 accumulation or on the δ30Si signature. Both cores show similarities that suggest a stable and homogeneous dSi source across the entire lake. A narrow range of δ30Si and Ge/Si values suggests that the productive layer of the lake was well mixed and biogeochemically stable, with consistently high hydrothermal inputs of Si throughout the Holocene to buffer against the disturbance events. Variation in bSiO2 concentration through time is weakly correlated with an increase towards younger sediment in the δ30Si fossil diatom record in both cores. This increase mirrors that seen in ocean records, and follows changes known in summer insolation, summer temperatures and lake water-column mixing since the deglaciation. This suggests that climate forcing, and soil formation ultimately govern the silicon isotope record, which we suggest is via a combination of changes in weathering stoichiometry, diatom production, and relative proportion of dSi sources.

Movement dynamics, sediment turnover and sheltering behaviours of the nocturnal coral reef sea cucumber, Stichopus cf. monotuberculatus

Animal movement and feeding studies shed light on ecological roles and can inform management strategies for fished species. However, the feeding and movement of nocturnal sea cucumbers have been rarely studied. We determined the movement dynamics, feeding ecology and sheltering behaviour of the nocturnal Stichopus cf. monotuberculatus (dragonfish) at One Tree Reef and Heron Island Reef on the southern Great Barrier Reef. The short-term movement of individual sea cucumbers were tracked, and sediment defecation rates were measured. Displacement rates averaged 3–33 cm h−1 across the four sites, with the sea cucumbers moving more slowly approaching sunrise and within patches of organically rich sediment. The movement paths were moderately tortuous, with larger sea cucumbers moving along straighter paths. Rates of sediment turnover averaged 7.8 g h−1 and were greatest for larger individuals. The faecal casts were organically richer and composed of finer grains than the ambient surface sediments, implying that S. cf. monotuberculatus avoids consuming coarse sediments and feeds on nutritionally rich particles. The sea cucumbers sheltered under hard reef substrata and moved non-directionally on the seascape, with a few individuals homing back to their original refuges. The affinity to reef substrata and short nightly net displacements of S. cf. monotuberculatus have implications for the spatial management of this and other similar species. Larger individuals occupied deeper refuges, implying that projected declines in substratum rugosity on coral reefs due to climate change could impact the size structure of sea cucumber populations, with implications for fisheries.

Controls of Tellurium enrichment in the rare earth elements and yttrium (REY) rich deep-sea sediments from the Central Indian Ocean Basin (CIOB)

As a potential Te reservoir for the global budget, the occurrence, material sources, migration and enrichment mechanism of Te in deep-sea sediments remain unclear. Based on the major and trace elements measurements of bulk sediments, this study proposed a procedure to quantify the contribution of Te by main host minerals, combining with TIMA and LA-ICP-MS in two cores (GC04 and GC11) from the Central Indian Ocean Basin (CIOB) and a core from east of the 90°E Ridge (GC03). Te shows the highest enrichment coefficient of 650 referred to UCC (Upper Continental Crust) in the REY (Rare Earth Elements and Yittrium) rich sediments in GC04, GC11 and GC02 (a core at the south of GC04 and GC11). Clinoptilolite-K and osumilite are indicated as the main host minerals, which correlates Te sources with volcanogenic materials and weathering products of terrigenous rocks. The inter elements correlation, cluster analysis and factors analysis further indicate distinct hydrothermal genetic Te. So, we put forward a hypothesis that Te is mainly sourced from the submarine volcanogenic hydrothermal activities, which are closely associated with local intraplate volcanism episodes from late Miocene with spatial and temporal differences. This study is the first attempt to quantify Te from different minerals and to reveal its geochemical behavior in the deep sea sediments, which will be benefit to the understanding of Te reservoir and cycle in deep sea and the comprehensive utilization of REY-rich deep-sea sediments. However, for the abundant presence of undetectable nanoscale minerals in these sediments, the contribution of Fe-Mn (oxyhydr) oxides and clay minerals of Te need more investigation.

Linking Sediment Gas Storage to the Methane Dynamics in a Shallow Freshwater Reservoir

AbstractFreshwater reservoirs are globally relevant sources of the greenhouse gas methane. Organic matter rich sediments are hot spots of methane production and can store large amounts of methane dissolved in porewater and as free gas. Yet, in situ data on the gas storage as free gas (bubbles) in freshwater sediments are scarce. Here, an acoustic approach was tested and used to map the gas content in the sediment of a shallow temperate reservoir. The sediment gas storage was linked to the methane budget obtained from almost 2 years of in situ monitoring. The emission fluxes were dominated by ebullition and degassing at the reservoir outlet, which combined accounted for 93% of the total methane emissions. 66% of the ebullition variability was explained by a combination of environmental parameters. Mappings of sediment gas content using echo sounder surveys revealed the accumulation of free gas in regions of elevated sediment deposition. Temporally, the gas storage in the sediment was related to methane emissions, in which a period of intensified emissions resulted in a reduction of sediment gas storage. The sediment could store an equivalent of 4 to 13 days of accumulated potential methane production, which could supply the mean ebullition flux for more than 2 months. We suggest that sediment gas storage plays an important role in buffering and modulating methane emissions in aquatic systems and need to be accounted for in process‐based models.

Geo-environmental factors controlling groundwater hydrogeochemistry, salinization and quality in El Qaa plain coastal aquifer, Southwest Sinai, Egypt

AbstractEl Qaa plain is one of the promising areas for agriculture projects, owing to its soil and groundwater resources. So, 14 groundwater samples were collected, chemically analyzed, hydrochemical (ratios, models and plots) and GIS techniques were applied, to evaluate the factors governing this water chemistry and suitability for irrigation. The results indicated the expansion of the agricultural area 8 times in the last 2 decades. The water can be divided into two groups; (A) freshwater (TDS ≤ 1000) in the eastern part of the study area within the clastic weathered basement rocks part of the aquifer, and (B) saline water (TDS > 1000) in the western part within the carbonates and evaporites rich sediments and close to the Gulf of Suez. The deduced factors controlling groundwater chemistry were precipitation, evaporites dissolution, seawater intrusion and ion exchange process. The calculated sodium absorption ratio (SAR) was < 10 indicating the good quality of this water for irrigation without sodicity hazard. Water of Group (A) (electric conductivity < 2250µS/cm) can be used safely for irrigation without any impact of salinity on all types of soil and plants. Group (B) water (electric conductivity > 2250µS/cm) has salinity hazard and can be used for irrigation on well-permeable soils and salt-tolerant plants. The concentrations of the studied potentially toxic elements (PTEs) were within the permissible limit for irrigation. Expansion in agricultural activities has adverse impact on groundwater quality. So, eco-friendly fertilizers should be applied in this promising area with the application of hydrologic pumping advises to safe aquifer quality from the degradation.

Bacterial Diversity in Heavy Metal Poluted Soil Explored via 16S rRNA Gene Molecular-Genetic Analysis

Bacterial diversity in a xenobiotic polluted soil sample called KCM B was investigated using the 16S rRNA gene approach. The sample was collected from the vicinity of a Pb-Zn (KCM) smelter and pesticides manufacturing plant AGRIA both situated in short distance to each other near the town of Plovdiv, South Bulgaria. MS-ICP analysis showed the sample was moderately contaminated. Only Pb exceeded the EU Maximum Permission Levels (MPL). One clone library was constructed consisting of 150 clones. Our results demonstrated that in the investigated soil bacterial community was dominated by representatives of phylum Proteobacteria (α (28), β (2), γ (40) and δ (2) or in total 72%. Among them the most abundant were γ -Proteobacteria - 40%. Phyla Actinobacteria, Holophaga/Acidobacteria (AHA) and members of AD1 division were detected in an equal amount of 7% each. Bacteria belonging to phyla Cytophaga/Flavobacterium/Bacteroides (CFB) represented 5% of the bacterial community. 2% of the studied clones were affiliated to novel bacteria. In the clone library were detected many unique bacterial fingerprints respectively 16S rDNA sequences. Most of the identified bacterial groups were closely related to bacteria inhabiting other extreme- or xenobiotics polluted environments as uranium mill tailings, metal rich sediments, mine drainages, hydrocarbon contaminated environments, rocks at 300 m under the Ocean floor, deserts and waste water treatment facilities. Great number of recovered sequences in the sample were affiliated to not-yet-cultured bacteria with unknown physiology, morphology or metabolism. Once successfully cultivated these bacteria might be promising for biotransformation of heavy metals and biotechnological application.

Spatiotemporal diversity and community structure of cyanobacteria and associated bacteria in the large shallow subtropical Lake Okeechobee (Florida, United States).

Lake Okeechobee is a large eutrophic, shallow, subtropical lake in south Florida, United States. Due to decades of nutrient loading and phosphorus rich sediments, the lake is eutrophic and frequently experiences cyanobacterial harmful algal blooms (cyanoHABs). In the past, surveys of the phytoplankton community structure in the lake have been conducted by morphological studies, whereas molecular based studies have been seldom employed. With increased frequency of cyanoHABs in Lake Okeechobee (e.g., 2016 and 2018 Microcystis-dominated blooms), it is imperative to determine the diversity of cyanobacterial taxa that exist within the lake and the limnological parameters that drive bloom-forming genera. A spatiotemporal study of the lake was conducted over the course of 1 year to characterize the (cyano)bacterial community structure, using 16S rRNA metabarcoding, with coincident collection of limnological parameters (e.g., nutrients, water temperature, major ions), and cyanotoxins. The objectives of this study were to elucidate spatiotemporal trends of community structure, identify drivers of community structure, and examine cyanobacteria-bacterial relationships within the lake. Results indicated that cyanobacterial communities within the lake were significantly different between the wet and dry season, but not between periods of nitrogen limitation and co-nutrient limitation. Throughout the year, the lake was primarily dominated by the picocyanobacterium Cyanobium. The bloom-forming genera Cuspidothrix, Dolichospermum, Microcystis, and Raphidiopsis were highly abundant throughout the lake and had disparate nutrient requirements and niches within the lake. Anatoxin-a, microcystins, and nodularins were detected throughout the lake across both seasons. There were no correlated (cyano)bacteria shared between the common bloom-forming cyanobacteria Dolichospermum, Microcystis, and Raphidiopsis. This study is the first of its kind to use molecular based methods to assess the cyanobacterial community structure within the lake. These data greatly improve our understanding of the cyanobacterial community structure within the lake and the physiochemical parameters which may drive the bloom-forming taxa within Lake Okeechobee.

In situ Strontium isotope stratigraphy of fish teeth in deep-sea sediments from the western Clarion-Clipperton Fracture Zone, eastern Pacific Ocean

The geochronology of deep-sea sediments beneath the carbonate compensation depth (CCD) presents a challenge due to the calcareous microfossils dissolution, low sedimentation rates, sedimentary hiatus, and redeposition. Fish teeth, commonly found in deep-sea sediments, have been utilized for Sr isotope stratigraphic dating. However, continuous Sr isotope exchange with pore water limits the utility of fish teeth in this context.In this study, we employed laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICPMS), scanning electron microscopy (SEM), and laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) to obtain accurate stratigraphic chronology results from rare earth element and yttrium (REY)-rich sediments in the Clarion-Clipperton Fracture Zone (CCFZ) of the Pacific Ocean.Our analysis indicated that a fish tooth characterized by a dense structure and low La content exhibited a relatively initial 87Sr/86Sr ratio. Additionally, La contents at the same depth displayed a strong positive correlation with 87Sr/86Sr ratios, suggesting that Sr isotopes exchange with pore water during early diagenesis when La and other elements entered the fish teeth. However, certain fish teeth were able to resist early diagenesis alteration due to their dense structure.Based on in situ Sr-isotope stratigraphy results, we estimated the REY-rich layer age in core GC1901 to be 24–32 Ma, consistent with the REY-rich layers of DSDP/ODP in the CCFZ. Our study thus provides a new method for in situ Sr isotope analysis of fish teeth, which improves the accuracy of Sr isotope stratigraphy of pelagic sediments and could be widely used in deep-sea exploration.

Do beaver ponds increase methane emissions along Arctic tundra streams?

Beaver engineering in the Arctic tundra induces hydrologic and geomorphic changes that are favorable to methane (CH4) production. Beaver-mediated methane emissions are driven by inundation of existing vegetation, conversion from lotic to lentic systems, accumulation of organic rich sediments, elevated water tables, anaerobic conditions, and thawing permafrost. Ground-based measurements of CH4 emissions from beaver ponds in permafrost landscapes are scarce, but hyperspectral remote sensing data (AVIRIS-NG) permit mapping of ‘hotspots’ thought to represent locations of high CH4 emission. We surveyed a 429.5 km2 area in Northwestern Alaska using hyperspectral airborne imaging spectroscopy at ∼5 m pixel resolution (14.7 million observations) to examine spatial relationships between CH4 hotspots and 118 beaver ponds. AVIRIS-NG CH4 hotspots covered 0.539% (2.3 km2) of the study area, and were concentrated within 30 m of waterbodies. Comparing beaver ponds to all non-beaver waterbodies (including waterbodies >450 m from beaver-affected water), we found significantly greater CH4 hotspot occurrences around beaver ponds, extending to a distance of 60 m. We found a 51% greater CH4 hotspot occurrence ratio around beaver ponds relative to nearby non-beaver waterbodies. Dammed lake outlets showed no significant differences in CH4 hotspot ratios compared to non-beaver lakes, likely due to little change in inundation extent. The enhancement in AVIRIS-NG CH4 hotspots adjacent to beaver ponds is an example of a new disturbance regime, wrought by an ecosystem engineer, accelerating the effects of climate change in the Arctic. As beavers continue to expand into the Arctic and reshape lowland ecosystems, we expect continued wetland creation, permafrost thaw and alteration of the Arctic carbon cycle, as well as myriad physical and biological changes.

Capping fiberbank sediments to reduce persistent organic pollutants (POPs) fluxes: A large-scale laboratory column experiment

Deposits of contaminated wood fiber waste (fiberbanks), originating from sawmills and pulp and paper industries, have been found in the aquatic environment in boreal countries. In-situ isolation capping has been proposed as a remediation solution because it has the potential to prevent dispersal of persistent organic pollutants (POPs) from this type of sediment. However, knowledge about the performance of such caps when placed on very soft (unconsolidated), gaseous organic rich sediment is scarce. We investigated the effectiveness of conventional in-situ capping to limit POPs fluxes to the water column from contaminated fibrous sediments that produce gas. A controlled, large-scale laboratory column (40 cm diameter, 2 m height) experiment was performed over 8 months to study changes in sediment-to-water fluxes of POPs and particle resuspension before and after capping the sediment with crushed stones (≥4 mm grain size). Two different cap thicknesses were tested (20 and 45 cm) on two types of fiberbank sediment with different fiber type composition. Results showed that capping fiberbank sediment with a 45 cm gravel cap reduced the sediment-to-water flux by 91–95% for p,p’-DDD, o,p’-DDD, by 39–82% for CB-101, CB-118, CB-138, CB-153, CB-180 and by 12–18% for HCB, whereas for less hydrophobic PCBs, capping was largely ineffective (i.e. CB-28 and CB-52). Although cap application caused particle resuspension, the long-term effect of the cap was reduced particle resuspension. On the other hand, substantial sediment consolidation released large volumes of contaminated pore water into the overlying water body. Importantly, both sediment types produced large amount of gas, observed as gas voids forming inside the sediment and gas ebullition events, which increased pore water advection and affected the structural integrity of the cap. This may limit the practical applicability of this method on fiberbank sediments.

Paleoenvironmental reconstruction preceding and during the early Aptian Oceanic Anoxic Event 1a in southern Tibet, eastern Tethys

The early Aptian Oceanic Anoxic Event (OAE 1a, ∼120 Ma) represents an episode of severe paleoenvironmental disturbance during the Cretaceous, marked by the widespread deposition of organic matter (OM)-rich sediments. The OAE 1a has been extensively studied in the Pacific, Boreal, and western and southern Tethyan regions. However, limited studies of the OAE 1a were conducted in the eastern Tethys (especially in southern Tibet). Here, high-resolution organic and inorganic geochemical data are used to reconstruct paleoenvironmental and paleoclimatic conditions during the OAE 1a in the Gucuo area of southern Tibet, eastern Tethys. Enrichment factors of redox-sensitive Mo and U elements and the Th/U ratio revealed oxic-to-suboxic bottom water oscillations preceding and at the base of OAE 1a. A shift from oxic to suboxic condition occurred prior to the OAE 1a, followed by a change from suboxic to oxic at the base of OAE 1a. Based on multiple geochemical proxy indicators and plots, a warm-humid climate in response to global warming was prevalent during the early Aptian. The ratios of B/Ga, Sr/Ba, Rb/K, and CaO/(CaO + Fe) revealed freshwater-dominated salinity conditions prior to and at the base of the OAE 1a. Low salinity conditions during the deposition suggested that massive freshwater runoff took place into the ocean due to a warm-humid climate and related hydrological cycles at this time. OM production was controlled by a high surface water bioproductivity driven by enhanced freshwater input that promoted fluvial delivery of micronutrients and accelerated hydrological cycles. However, oxic-suboxic redox conditions played a negative role in oxidizing and decomposing available labile OM in the water column, which led to moderate organic carbon burial at this time.

Radiogenic Nd in bioapatite from rare earth elements rich deep sea sediments from Central Indian Oceanic Basin and its implication in material sources

Rare Earth Element and Yttrium (REY)-rich deep sea sediments have been estimated to be a highly important potential resource. However, the main material sources that supply the huge amount of REY resources, as well as geochemical procedure determines the distinct REY patterns of these sediments, remain unclear. To fill this research gap, in this study, three sediment cores (GC02, GC04, and GC11) collected from the Central Indian Ocean Basin (CIOB) and a core (GC03) from eastern of the 90° E Ridge (NER) were sampled for mineral identification and elemental (major, trace, and rare earth elements) analyses. Fish teeth and detrital minerals were isolated from the sediments, and their 87Sr/86Sr and 143Nd/144Nd ratios were measured. Accumulation of REY is revealed in three cores of GC02, GC04, and GC11 from CIOB with mean value of 511.93 μg/g, 614.79 μg/g, and 1036.14 μg/g, respectively. Most REY rich sediment exhibit obvious to slight negative Ce abnormal, slight positive Eu and Y abnormal. The detrital fraction of the REY rich sediments exhibit less radioactive εNd values of − 8.36295 and more radioactive 87Sr/86Sr of of 0.71651. On the contrary, the fish teeth exhibit less radiogenic 87Sr/86Sr ratio of 0.70915 but more radiogenic εNd values of − 5.13511 than those of the sea water of the Indian Ocean. The results reveal that the REY-rich sediments in the CIOB are characterized by multiple material sources including weathering continental products, alteration of volcanogenic glasses, hydrothermal and marine authigenic materials. Distinct volcanogenic materials input are obvious in the CIOB evidenced with radiogenic 143Nd/144Nd ratios of the fish teeth, the wide occurrence of clinoptilolite and high Te contents contained. The volcanogenic related hydrothermal materials are then indicated to provide most part of REY for the fish teeth, which contribute the most amount of REY of the sediments. However, the terrestrial input of REY cannot be neglected, which indicates the REY-rich deep sediments were formed under multi-source supply system. The study indicated that continuous exchange of Sr between fish teeth and ambient pore water after deposition, and ambient pore water was concluded to contain an abundance of released radiogenic terrestrial Sr. However, the exchange of Nd between fish teeth and bottom sea water ceased after buried in depth. Nd ratios on the fish teeth recorded the more radioactive hydrothermal material carried by bottom seawater at the early stage of precipitation.