Sediment Accumulation Rates Research Articles

Discrepant mass accumulation rates of sediments in the South Pacific Ocean from 230Th and 3He measurements

A common technique for determining the mass accumulation rates of marine sediments is through measurements of constant flux proxies. These proxies, like unsupported 230Th and extraterrestrial 3He, are buried at a known rate at the seafloor, and thus their concentration in sediments is inversely proportional to the vertical mass accumulation rate of ambient sediments. These two proxies have varied assumptions regarding their behavior that have been difficult to test, particularly in regions of very low sedimentation. We present new measurements of helium and thorium isotopes in coretop sediments from the South Pacific Gyre. Our main finding is that 230Th- and 3He-derived mass accumulation rates of these sediments differ by a factor of 2–10, with 230Th-based mass accumulation rates systematically higher than those derived from 3He. While the final cause of the discrepancy is difficult to elucidate, we suggest that up to a factor of 2 worth of the sedimentary 230Th deficit can be explained by lateral transport of 230Th, while the remainder must be explained by other processes, such as ancient coretops undercorrected for post-depositional 230Th decay. Regardless of the mechanism, our findings have critical implications for the application of constant flux proxies in the South Pacific Gyre, with one example being the calibration of dust deposition models in this region. Ultimately, additional testing is required to determine the accuracy of the 3He and 230Th techniques for estimating sediment accumulation rates in regions of the open ocean with extremely low sedimentation rates.

Declining nutrient availability and metal pollution in the Red Sea

Reconstructing sediment accumulation rates reveals historical environmental shifts. We analyzed 15 element concentrations and accumulation rates in two Red Sea sediment cores over 500 years. Post-1870s, the South Red Sea experienced a significant drop in element accumulation rates, with a noticeable decline in nutrients like magnesium (−8.52%), organic carbon (−14.9%), nitrogen (−14.0%), phosphorus (−16.4%), sulfur (−17.2%), and calcium (−17.8%). This suggests a potential reduction in nutrient inflow from the Indian Ocean, possibly due to warming-induced ocean stratification. Conversely, the North Red Sea saw an increase in all element accumulation rates after the 1870s, highlighting a rise in trace elements such as iron (4.56%), cadmium (8.69%), vanadium (12.6%), zinc (13.8%), copper (14.4%), chromium (17.6%), and nickel (19.5%), indicative of increased anthropogenic coastal activities. We introduce the term “Cai-Agusti Marine Crisis Conflux” to encapsulate the escalating thermal stress, nutrient depletion, and elemental pollution in the Red Sea, underscoring potential risks to its ecosystems and global implications.

Cross-basin Mo and U analysis of the Upper Mississippian Bowland Shale, UK

Abstract The Bowland sub-basin is a target for hydrocarbon exploration, but to a large extent it remains unexplored. To determine the economic potential of the Bowland sub-basin, it is important to identify the oceanographic processes involved in the deposition of the Bowland Shale Formation in the Late Mississippian ( c. 330 Ma). Palaeoceanographic processes are known to be a major control on the development of hydrocarbon source rocks. This study investigates core (Preese Hall-1 and Becconsall-1Z) materials from the Upper Bowland Shale, and makes a comparison with previously published data (outcrop Hind Clough), all from the Bowland sub-basin, Lancashire, UK. The sedimentology and geochemistry of this formation were determined via a multi-technique approach including X-ray fluorescence, sedimentology, gamma-ray spectra, X-ray diffraction and Rock-Eval pyrolysis. Key trace metal abundances and enrichment factors were used to assess sediment provenance and to determine the bottom-water redox conditions during the deposition of the Upper Bowland Shale. Our results support interpretations of contemporaneous anoxia developing in bottom waters in at least three sites in the Bowland sub-basin. In a comparison with the Fort Worth Basin (Barnett Shale, USA), the Bowland sub-basin was apparently less restricted and deposited under a much higher mean sediment accumulation rate. Knowledge from this study will improve future resource estimates of the Bowland Shale Formation, and challenge the early assumptions that the Barnett Shale is an analogue of the Bowland Shale.

Fire, volcanism and climate change: the main factors controlling mercury (Hg) accumulation rates in Tropical Lake Lantoa, Sulawesi, Indonesia (∼16,500–540 cal yr BP)

The effects of climate change on long-term mercury (Hg) cycling are still not well understood, as climate changes are usually gradual and can only be assessed using high-resolution archives. Our study site (a small, lowland tectonic lake in Sulawesi, Indonesia) provides a unique opportunity to further understanding of Hg cycling in the Southeast Asian (SEA) tropics during the transition from the Pleistocene to the Holocene, a period of significant climate variability. We present a high-resolution record of Late Glacial and Holocene Hg deposition within the sediments of tropical Lake Lantoa, Sulawesi. Using a multi-proxy framework (including pollen, charcoal, carbon:nitrogen ratio and high-resolution geochemistry records) we investigate the response of Hg accumulation rates (HgAR) in sediments to shifts in climate between ∼16,488 and 538 cal BP. This period encompasses the Bølling-Allerød (BA) warming, Younger Dryas (YD) cooling and Holocene warming events, providing new insights into the effects of global climatic transitions on HgAR in SEA sediments. The Pleistocene Termination had the highest HgAR and substantial variability (µ = 11.32, 5.38–33.91 μg m−2 yr−1), when drier conditions and high charcoal accumulation rates suggest that fire activity was the main source of Hg to the lake. The Holocene Transition was marked by a decrease in HgAR (µ = 8, 3.50–18.84 μg m−2 yr−1) as humid conditions precluded forest burning, followed by high HgAR (µ = 11.35, 3.30–158.32 μg m−2 yr−1) in the Early Holocene. Mercury accumulation rate in the Late Holocene (µ = 3.80, 1,67–43.65 μg m−2 yr−1) was the lowest in the Lake Lantoa record, marked by the lowest fire events and a stable catchment. An increase in carbon:nitrogen ratios during the Late Holocene, coupled with a decrease in HgAR, suggests that the establishment of lowland forest resulted in suppressed Hg erosion/leaching. Our results demonstrate that forest fires, vegetation change and volcanism are important drivers of Hg inputs to Lake Lantoa, a relationship which is strongly mediated by climate and lake-catchment dynamics.

210Pb-dating of recent sediments with the χ-mapping CF and CSAR models. On the attractors

Conventional 210Pb-dating models use assumptions on sedimentary conditions that allow for analytical formulations. The novel χ-mapping models use numerical methods to generate and test a large number (∼106) of potential solvers. Empirical data (excess 210Pb vs. mass depth profile) serve to attract the solver that minimizes the χ function (the attractor), and it has been assumed that it also defines the most likely chronology. This work aims to test this assumption in a deep way. In synthetic and varved sediments, the performance of each solver can be quantified through a parameter ξa accounting for the deviation of the model and the true ages. This work studies the complex relationships between χ and ξa using the constant flux (χ-CF) and the constant sediment accumulation rate (CSAR) models, which operate in a parametric 3D space. The full mapping of the 3D χ function serves to find the absolute minimum, for the graphical representation of the complex topology of the attractors, which is model-specific, and for plotting clouds of chronological lines from solvers with varying χ values. The minimum value of ξa (the best chronology) is achieved for a wide range of χ values, including the region of the absolute minimum. In complex cases, tiny changes in χ can result in quite different chronologies. Alternative attractors that include a reference date and an objective function are studied. The results provide guidelines for strengthening the 210Pb-based chronologies.

Marine oligotrophication due to fine sediments and nutrient starvation caused by anthropogenic sediment and water retention in large rivers: the Nile damming case

In the last two centuries, human activities have radically reduced the transport of suspended sediment and water to marine systems, mainly in the northern hemisphere, while complete sediment retention has been reported for the Nile River after the construction of the Aswan High Dam (AHD). Here, we focused on changes in the inner-shelf sediments most exposed to the pre-AHD flood plume in the distal part of its littoral cell as a predictor of the ecological response to large river fragmentation. Substantial reductions in fine (15-40%) and increases in coarse (~8 fold) sediment accumulation rates, increases in CaCO3 (~50%), decreases in autochthonous and total organic carbon (OC), and changes in the benthic foraminiferal assemblage toward more OC-sensitive species suggest an enhanced oligotrophication trend. The reduced nutrient fluxes and OC accumulation, and the coarsening of the shelf sediments inhibit the retention of “blue” carbon. Combined with fast climate warming and salinization, river fragmentation may have essential implications for the Eastern Mediterranean ecosystem via benthic oligotrophication processes.

Accumulation and contamination of gully pot sediments from varied land-use types: metal loads, concentrations and speciation

Urban stormwater typically enters sewer networks through gully pots, which allow a primary sedimentation of solids upstream of the piped network. The regular removal and disposal of retained sediment are necessary, costly and can involve environmental risks due to the contamination of sediments with substances from the urban environment such as metals. The concentrations and speciation of Cd, Cr, Cu, Ni, Pb and Zn were analysed in sediments from 26 gully pots located in different land use areas in Stockholm, Sweden. In addition, accumulation rates of both sediment and metal masses were evaluated, providing a basis for optimising maintenance practices and better understanding of impacts of characteristic urban land use types. Metal concentrations varied by at most a factor of eight between samples and were always below Swedish polluted site guidelines for less sensitive land use, with only eight samples exceeding the guideline values for Cu and Zn for sensitive land use. Sequential extraction showed Pb and Zn to be the most mobile metals. Sediment accumulation rates varied from 0.003 to 0.197 kg/m2 impermeable surface/year. Metal accumulation rates were much more variable than metal concentrations, with a factor of up to 172 between the highest and lowest rates and the highest metal accumulation rates corresponding to the lower range of mass loads in road runoff. Differences in metal concentrations, sediment or metal mass accumulations could not be solely attributed to either traffic or catchment land use. In contrast, traction grit used for winter road maintenance, which has low (but detectable) metal concentrations, is identified as a major component of gully pot sediments, with a combined effect of both moderating metal concentrations and contributing to total mass.

Carbon Stocks and Recent Rates of Carbon Sequestration in Nutrient‐Rich Freshwater Wetlands From Lake Simcoe Watershed (Southern Canada)

AbstractWe examined soil properties and accumulation rates over the last ca. 100 years in four swamps and four marshes in southern Canada where these wetlands are common but under increasing anthropogenic pressure. One 50‐cm long core was collected from each wetland and analyzed to determine bulk density (BD) and organic matter (OM). Lead‐210 and cesium‐137 dating were used to estimate sediment accumulation rates. In the datable portion of each core, we determined the organic carbon (Corg), nitrogen (N), Corg/OM, Corg/N, Corg density, Corg stocks, and Corg accumulation rates. All parameters but one—Corg accumulation rates—were significantly different in swamps compared to marshes and between seasonally wet soils and those regularly flooded. Since 1950, Corg stocks varied from 6 to 13.6 kg m−2 with ≈23% more Corg in swamps than in marshes. When hydrology and deeper soils where considered, Corg stocks in regularly flooded wetlands were 60% higher than those of seasonally wet systems, emphasizing the role of hydrology in building up C stocks long‐term. Our measurements are within the wide range reported for similar systems in North America. The average rate of Corg accumulation in the studied wetlands (112 ± 87 g m−2 yr−1) is ≈50% higher than that of oligotrophic/ombrotrophic peatlands, but ≈47% lower than in tidal marshes from eastern Canada. Our study lends support to the case for wetland restoration through re‐wetting as an important nature‐based climate solution for mitigation of GHG emissions in areas where they were drained for agriculture and other purposes.

How to quantify blue carbon sequestration rates in seagrass meadow sediment: geochemical method and troubleshooting

Seagrasses take up carbon dioxide and transform it into organic carbon, some of which is buried in meadow sediments. Very high carbon burial rates have been claimed for seagrass meadows globally, and international protocols have been developed with a view to awarding carbon offset credits. However, recent geochemical work has shown that a misunderstanding of how marine sediment buries and processes organic carbon has led to overestimates of at least an order of magnitude. Common blue carbon methodology does not adequately account for bioturbation or remineralization in surface sediment, and there is often a conflation of standing stock with ongoing burial. To determine accurate seagrass carbon burial rates requires the following steps: (1) Determine the sediment accumulation rate below the surface mixed layer, using 210Pb and porosity; (2) Determine the burial concentration of organic carbon; (3) Multiply the sediment accumulation rate by the buried % organic carbon; (4) If excluding allochthonous carbon burial, use biomarkers to determine the proportion of seagrass-derived organic carbon; and (5) Account for the offset due to the burial of carbonate formed inside the meadow. Seagrass meadows provide valuable habitat and protect coastlines from erosion. They can also play a role in short-term carbon sequestration. However, if carbon credits are awarded based on inflated estimates and used to offset emissions elsewhere, the net effect could be an increase in carbon dioxide emissions to the atmosphere.

A novel subsurface sediment plate method for quantifying sediment accumulation and erosion in seagrass meadows

Sediment dynamics in seagrass meadows are key determinants of carbon sequestration and storage, surface elevation, and resilience and recovery from disturbance. However, current methods for measuring sediment accumulation are limited. For example, 210Pb dating, the most popular tool for quantifying sediment accretion rates over decadal timescales, relies on assumptions often at odds with seagrass meadows. Here, we have developed a novel subsurface sediment plate method to detect changes in sediment accumulation and erosion in real time that: 1) is affordable and simple to implement, 2) can quantify short-term (weeks to months) sediment dynamics of accumulation and erosion, 3) is non-destructive and minimizes impacts to surface-level processes, and 4) can quantify long-term (years) net sediment accumulation rates. We deployed subsurface sediment plates at two sites within a 20 km2 seagrass meadow in the Virginia Coast Reserve Long-Term Ecological Research site, USA. Here, we discuss spatial and temporal trends in sediment dynamics over a 25-month period, the sediment accretion rates estimated using the subsurface sediment plate method compared to previous estimates based on 210Pb dating, the precision of the method, and our recommendations for implementing the method for measuring surface sediment dynamics in other seagrass settings. We recommend the application of this method for quantifying short- and long-term changes in seagrass surface sediments across various spatial scales to improve our understanding of disturbance, recovery, restoration, carbon cycling, sediment budgets, and the response of seagrasses to rising sea levels.

New insights on black carbon in pelagic Atlantic sediments

Black carbon (BC) is ubiquitous in pelagic sediments and presumed to have an older radiocarbon age due to long ocean residence times and pre-aging in terrestrial soils. Here, we analyzed sediments from five regions in the subtropical Atlantic Ocean to quantify the black carbon fraction of the total organic carbon pool. Black carbon, derived from the chemothermal oxidation method, comprised between 17 ± 6% of the sedimentary organic carbon in the Northwest Argentina Basin and 65 ± 18% in the Amazon Delta. Black carbon sediment accumulation rates were six times greater in the Sierra Leone Rise (8.4 ± 4.1 mg cm−2 kyr−1) compared to the remote Northwest Argentina Basin (1.3 ± 0.4 mg cm−2 kyr−1), possibly due to enhanced regional atmospheric deposition from annual African grassland fires. The radiocarbon age for BC from subtropical Atlantic sediments were more modern compared to the bulk total organic carbon, and BC source was apportioned as biomass burning byproducts from their stable carbon isotopic signatures and characteristic ratios of polycyclic aromatic hydrocarbons. This study demonstrated that subtropical Atlantic Ocean sediments serve as an important sink for young BC.

Comparison of spatiotemporal burial and contamination of heavy metals in core sediments of two plateau lakes with contrasting environments: implication for anthropogenic-driven processes.

Investigating the impacts of climatic factors and human activities on sedimentary records of heavy metal (HM) contamination in lakes is essential for decision-making in global environmental monitoring and assessment. Spatiotemporal distributions of grain size (GS) and HM (Al, Cr, Mn, Ni, Cu, Zn, As, and Pb) concentrations have been conducted in core sediments that are collected from two adjacent plateau fault-bound lakes in southwest China with contrasting environments, i.e., deep oligotrophic Lake Fuxian (FX) and shallow hypertrophic Lake Xingyun (XY). Results showed that the average value of d50 in FX (4.61 μm) was lower than that in XY (8.35 μm), but the average concentrations of HMs (except Cr and Mn) in XY were higher than those in FX. Heavy metal burial rates (HMBR) were mainly controlled by sediment accumulation rates (SARs) rather than HM concentrations. The correlation coefficients between GS and HM concentrations became strong as the increasing water depths were associated with a stable sedimentary environment. Time-integrated enrichment factors (EF) and source identification of HMs between FX and XY represented that Cr, Ni, and Cu originated from natural sources but Mn, Zn, As, and Pb from anthropogenic sources, respectively. Regardless of FX and XY, the transition times of HMs from natural to anthropogenic sources occurred in the mid-1960s. Comparison of qualification impacts of climatic factors and human-induced factors on increased anthropogenic HMBR by the partial least squares path modeling (PLS-PM) implied that socio-economic activities, such as population density (PD) and gross domestic product (GDP), provided higher contributors to increased anthropogenic HMBR in XY (0.23/0.71) than FX (0.11/0.18). The comparative results of this study provided new insights into environmental monitoring and management of HM contamination for adjacent lakes with contrasting environments.

A case study on how astronomical cycles affect the organic carbon accumulation

The paleoclimate change impacts the sedimentary environment and process, which in turn control the accumulation of organic carbon. Numerous studies have shown that the paleoclimate is controlled by astronomical cycles. Hence, understanding how these cycles impact the accumulation of organic carbon is a critical question that requires in-depth discussion. Previous studies have shown that Milankovitch cycle can be revealed from the sediments of the 7th Oil Member (Chang 7 Member for short) of the Triassic Yanchang Formation in the southern Ordos Basin, suggesting that the deposition was controlled by astronomically-forced climate changes. Building on previous research, this study collected natural gamma (GR) data of Chang 7 Member from the N36 Well to further analyze astronomical cycles, combined with X-ray fluorescence (XRF) analysis and total organic carbon (TOC) tests, to reconstruct the paleoenvironment and analyze the organic matter enrichment characteristics. The results of this contribution show that, paleoclimate, paleo-redox conditions, paleo-water level, paleo-productivity and sediment accumulation rate (SAR) collectively controlled the enrichment of organic matter. Notably, this study identified the presence of eccentricity, obliquity, precession, and the 1.2 Myr long obliquity cycle in the Chang 7 Member. These cycles controlled the paleoenvironmental changes at different timescales and influenced the enrichment of organic matter, which has implications for subsequent energy exploration.

Multi-annual and multi-decadal evolution of sediment accretion in a saltmarsh of the French Atlantic coast: Implications for carbon sequestration

Coastal marshes offer natural solutions for adapting to and mitigating the effects of climate change and sea level rise. However, the resilience of the marsh physical system and, with it, the ecosystem services that it provides, is largely site specific. This calls for the increase in the spatial cover of coastal marsh studies in order to assess the controlling factors of marsh evolution, and their long-term carbon storage capacities. Here, we study the spatio-temporal variations in sedimentation rates and organic carbon (OC) sequestration capacity of the macrotidal minerogenic saltmarshes in Aiguillon Bay, belonging to one of the largest French coastal marshes. Supported by aerial photographs and satellite image analysis, we first show that saltmarshes of the Aiguillon Bay have prograded at very high rates, up to 14 m yr−1 since 1950. Sediment accumulation rates (SAR) were estimated at both multi-annual to multi-decadal scales based on two approaches: (i) LiDAR-based digital elevation models from multiple acquisition dates (2010–2021); and (ii) depth profiles of 210Pb in excess and 137Cs in sediment cores collected along cross-shore transects in the saltmarshes. Long-term SAR range from 0.8 to 2.2 cm yr−1 and are among the highest reported worldwide for equivalent systems. The positive accretion balance (accretion rate minus local sea-level rise rate) provides important clues on marsh resilience suggesting that the Aiguillon Bay is currently able to adapt to rising sea level. Despite relatively low organic carbon content (1.3–6.0%), high SAR leads to high carbon sequestration rates (99–345 gC m−2 yr−1; or a mean value of 2.5 Mg C ha−1 yr−1). The isotopic signature of sediment OC reveals a significant and rapid decomposition of organic material in surface cores, while allochthonous sediment of marine origin dominates the signature of chemically-stable OC of marsh sediments. This implies that the carbon sequestration capacity of minerogenic saltmarshes, such as those of the Pertuis Charentais, also depends upon the wealth of adjacent coastal environments through high sediment supply and primary productivity.

Environmental Consequences of Intensive Aquaculture Practices at Moyna Purba Medinipur West Bengal India with Special Reference to Carbon Footprint and Carbon Sequestration.

Moyna of Purba Medinipur district is widely known as an aquaculture hub of West Bengal, India. Though very good production is achievable from this fish culture system, management practices are inappropriate, which could create the sustainability problem of this culture system. The present study was thus undertaken for the estimation of plankton population, water quality, carbon footprint and carbon sequestration of this intensive aquaculture practices. Information on spawn to fry, fry to fingerlings and grow-out culture were collected through the structured questionnaire from the fish farmers. The plankton density, primary productivity, carbon footprint and carbon sequestration were analyzed using standard procedures. The phytoplankton, zooplankton and primary productivity were maximum at the stocking period and minimum during the middle of culture period. The lowest feed conversion ratio (FCR) was noticed with the minimum amount of feed applied in the pond. The CO2-e emission ranged from 0.56 to 4.89kg CO2-e/kg fish (av. 2.13) for the production levels of 5.0 to 10.7 t/ha/yr. The pond water developed salinity and ammonium-N increased from 0.01 to 0.50mg/l. The ponds with high feed loading (28 to 32 t/ha/yr) had the highest average sediment accumulation rate (11.0 ± 3.0cm/yr) and carbon sequestration (704 ± 30g C/m2/yr).

Sediment accumulation rates and carbonate fluxes of deep-sea sediments in the southern Gulf of Mexico

Here we present the mass and carbonate annual fluxes, collected by two sediment traps at 1000 m depth, located on the western and southern deep-water region of the Gulf of Mexico (GM), and compare them with the total mass and carbonate accumulation rates (CAR) from 46 sediment cores retrieved from continental slopes and the abyssal plain of the southern Gulf of Mexico (sGM). CaCO3 fluxes in the sediment traps located close to 1000 m water depth, range between 15.1 and 22.4 g m−2 yr−1, these values fall on the high-end range of the mean fluxes reported for the global ocean (9–22 g m−2 yr−1). The carbonate fluxes from the water column are remarkably close to the CAR in the lower slope and abyssal sediments of the southern GM, implying that dissolution processes of biogenic carbonate in the sediments below 1000 m are negligible in the sGM. The spatial patterns of CARs in the sediments are mainly linked with surface productivity of calcareous organisms and export to depth over the continental slope and abyssal plain regions, with mean values of 15.7 ± 5.7 g m−2 yr−1 (0.15 ± 0.06 mol m−2 yr−1). However, there are some large areas over the abyssal plain to the north of the Campeche escarpment showing enhanced CAR values most likely as a result from two processes, lateral input from the Yucatan carbonate shelf region and massive collapse events originating at the Campeche escarpment and deposited to the north of the Yucatan Platform. These processes can account for an additional increase in carbonate mass accumulation by approximately 8 g m−2 yr−1 in this area, showing a decreasing gradient towards the N of the escarpment. Lateral transport by turbidity currents of carbonate platform sediments along submarine canyons and probably episodic gravity flows further aid to explain the localized higher carbonate mass accumulation (> 20 g m−2 yr−1) observed at the foot of the continental slopes to the west and south of the southern GM. We estimate total carbonate accumulation estimates for the entire Gulf of Mexico, from the upper slope to the abyssal plain (1000–3750 m), considering the northern deep-water region reported by Giering et al., 2018, of 0.09 to 0.12 Tmol/yr accounts for 0.8 to 1.8% of all carbonate sedimentation in the ocean below 1000 m. Taking into considerations its small areal extent of <0.3% of the global ocean the GM carbonate accumulation accounts for a factor of 3 to 6 its areal importance, implying that changes in the production and export of carbonate in the GM due to surface ocean warming and acidification processes in this inland sea will have a sensible effect in the global carbon cycle.

East Asian summer monsoon variations across the Miocene−Pliocene boundary recorded by sediments from the Guide Basin, northeastern Tibetan Plateau

Records of atmospheric carbon dioxide concentration, sea-surface temperature, and global vegetation show that Earth’s climate and environment changed significantly during the late Miocene−early Pliocene. Understanding the environmental response to insolation forcing during this transitional period may provide insights into future environmental variations resulting from the perturbation of the global carbon cycle caused by fossil fuel combustion. However, terrestrial paleoclimate records capable of resolving orbital time-scale environmental variations are mostly from Europe, especially from the region around the Mediterranean Sea. Here, we present high-resolution records of grain size, black carbon, and geochemistry from a sedimentary sequence from the northeastern margin of the Tibetan Plateau, where precipitation is mainly via the East Asian summer monsoon. We observed increases in sediment accumulation rate and black carbon mass accumulation rate at ca. 5.3 Ma, which we interpret as the result of intensified seasonal precipitation associated with the strengthening of the East Asian summer monsoon; concurrently, precessional and obliquity cycles became more prominent during the early Pliocene. Our results suggest that, in response to current and future high atmospheric carbon dioxide concentrations, changes in the East Asian summer monsoon are likely to result in increased precipitation and seasonality within its region of influence.

Dating pelagic sediments from the northwestern Pacific Ocean by integration of Multi-geochronologic approaches

As the largest promising rare earth elements and yttrium (termed as REY) resource in the world, pelagic sediments enriched in REY (REY-rich sediments) have gained extensive attention. However, the mechanism responsible for the enrichment of REY in pelagic sediments remains unknown, primarily due to the challenge of obtaining robust geochronology. Despite previous attempts, integration of multi-geochronologic approaches seems better suited to determine robust geochronology for pelagic sediments. Here, we present a continuous chronostratigraphic framework for a pelagic sediment core collected from the northwestern Pacific Ocean, integrating authigenic 10Be/9Be dating, 230Thex dating, and magnetostratigraphy. Our results indicate that the REY-rich sediments deposited prior to ∼ 2.5 Ma, and a highly REY-rich sediment layer deposited at ∼ 11.5–9.5 Ma in the study area. We suggest that a low sedimentation accumulation rate (SAR) was necessary for REY enrichment in pelagic sediment, while the deposition of highly REY-rich sediments should be attributed to the additional contribution from active bottom currents. Our study proposes that the enrichment of bioapatite fossils and micronodules related to enhanced bottom currents under a low SAR sedimentary environment could promote the widespread highly REY-rich sediments in the study region.

Mammalian bioturbation amplifies rates of both hillslope sediment erosion and accumulation along the Chilean climate gradient

Abstract. Animal burrowing activity affects soil texture, bulk density, soil water content, and redistribution of nutrients. All of these parameters in turn influence sediment redistribution, which shapes the earth's surface. Hence it is important to include bioturbation into hillslope sediment transport models. However, the inclusion of burrowing animals into hillslope-wide models has thus far been limited and has largely omitted vertebrate bioturbators, which can be major agents of bioturbation, especially in drier areas. Here, we included vertebrate bioturbator burrows into a semi-empirical Morgan–Morgan–Finney soil erosion model to allow a general approach to the assessment of the impacts of bioturbation on sediment redistribution within four sites along the Chilean climate gradient. For this, we predicted the distribution of burrows by applying machine learning techniques in combination with remotely sensed data in the hillslope catchment. Then, we adjusted the spatial model parameters at predicted burrow locations based on field and laboratory measurements. We validated the model using field sediment fences. We estimated the impact of bioturbator burrows on surface processes. Lastly, we analyzed how the impact of bioturbation on sediment redistribution depends on the burrow structure, climate, topography, and adjacent vegetation. Including bioturbation greatly increased model performance and demonstrates the overall importance of vertebrate bioturbators in enhancing both sediment erosion and accumulation along hillslopes, though this impact is clearly staggered according to climatic conditions. Burrowing vertebrates increased sediment accumulation by 137.8 % ± 16.4 % in the arid zone (3.53 kg ha−1 yr−1 vs. 48.79 kg ha−1 yr−1), sediment erosion by 6.5 % ± 0.7 % in the semi-arid zone (129.16 kg ha−1 yr−1 vs. 122.05 kg ha−1 yr−1), and sediment erosion by 15.6 % ± 0.3 % in the Mediterranean zone (4602.69 kg ha−1 yr−1 vs. 3980.96 kg ha−1 yr−1). Bioturbating animals seem to play only a negligible role in the humid zone. Within all climate zones, bioturbation did not uniformly increase erosion or accumulation within the whole hillslope catchment. This depended on adjusting environmental parameters. Bioturbation increased erosion with increasing slope, sink connectivity, and topography ruggedness and decreasing vegetation cover and soil wetness. Bioturbation increased sediment accumulation with increasing surface roughness, soil wetness, and vegetation cover.

Sequence stratigraphy and reservoir quality of the Gulf of Suez syn-rift deposits of the Nukhul formation: Implications of rift initiation and the impact of eustacy and tectonic on deposition

The Nukhul Formation represents the sediments deposited during the earliest phase of the syn-rift period in the Gulf of Suez rift. It is the primary hydrocarbon reservoir for fifteen fields in the region. However, the timing of rifting needs to be better constrained, and the influence of local tectonics and global eustatic sea-level fluctuations on reservoir quality and deposition is still being determined. This research aims to establish a stratigraphic sequence framework, determine the age of the Suez Rift commencement, use changes in paleobathymetry, and assess reservoir quality. The methods employed involve the analysis of four boreholes in the Abu Rudeis-Sidri field, incorporating biostratigraphy, well-logs, and 3D seismic data. The integrated paleo-structure and biostratigraphic analyses indicate that the beginning of rifting in the Gulf of Suez occurred at 23.53 Ma at the first common occurrence (FCO) of Trilobatus primordius. The paleobathymetric analysis of the Nukhul Formation reveals deeper paleo-water depths during certain intervals, indicating deposition during a phase of high subsidence and rift-climax. The Nukhul stratigraphic sequence reflects sea-level changes leading to shifts in accommodation, and facies changes, erosion, and sequence formation during the late Chattian and early Burdigalian stages. However, the reservoir characterization of the Nukhul Formation is significantly affected by various factors, including cementation, pore system properties, sediment sorting, rift system geometry, and relative sea-level fluctuations. These factors must be carefully considered in any regional exploration or development efforts. The study also reveals that tectonic activity played a role in forming fault-bounded basins, and eustatic sea-level changes influenced the rate and timing of sediment accumulation. These findings can aid in predicting the distribution of the Nukhul sedimentary deposits and improve the ability to explore and develop their resources.