Coastal ocean alkalinity enhancement (OAE) is a promising ocean-based carbon dioxide removal (CDR) approach for mitigating climate change and counteracting ocean acidification. However, uncertainties persist regarding the efficacy and environmental safety of alkaline materials under realistic coastal conditions. This study comparatively investigated the CO2 sequestration potential, geochemical processes, and environmental impacts of four alkaline materials-natural silicates (olivine, basalt) and industrial byproducts (fly ash, steel slag)-through laboratory incubations with natural seawater (filtered and unfiltered) and in situ deployments off the East China Sea. Over 31-day incubations, basalt induced negligible alkalinity release, while olivine showed limited alkalinity enhancement (12 μmol/kg/day) compared to theoretical estimation, projecting a CO2 sequestration rate of 0.57 ± 0.06 Tg/month for a hypothetical coastal deployment in China. Notably, fly ash exhibited faster alkalinity release (30 μmol/kg/day) and the highest projected CO2 uptake (1.24 ± 0.05 Tg/month). In contrast, steel slag caused rapid pH increase and alkalinity consumption via secondary carbonate precipitation, representing a distinct carbon sequestration pathway. Heavy metal pollution index (HPI) assessments indicated low overall contamination risks of the materials, particularly in unfiltered seawater that better resembles natural conditions, though Ni release from olivine remains a concern. Streamlined life cycle analysis (S-LCA) highlighted fly ash's advantages due to the avoidance of upstream carbon emissions (as a byproduct) and waste valorization potential, resulting in superior net CO2 removal efficiency. This work provides critical insights into material-specific trade-offs, suggesting fly ash as a promising candidate for short-term coastal OAE deployment that balances CO2 sequestration efficiency, manageable environmental risks, scalability, and affordability.

This study investigates whether cadmium (Cd) isotope compositions obtained from carbonate leachates of unlithified deep-sea sediments can reliably record primary productivity. Carbonate leachates obtained from Quaternary sediments of core MD05-2901 in the western South China Sea were analysed for rare earth element (REE + Y), redox-sensitive trace elements, bioavailable trace elements and stable Cd isotopes. Shale-normalised rare earth element (REE + Y) patterns display enrichments of medium REE, weak positive Y and absence of negative Ce anomalies, reflecting reducing porewater rather than ambient bottom seawater. Nevertheless, ΣREE concentrations archive glacial-interglacial cycles. Cd isotopic compositions of weak acetic acid carbonate leachates (δ114Cdcarb = -0.79 ∼ -0.31 ‰) are significantly lighter than modern deep water values. We suggest that the δ114Cdcarb signals in these unlithified deep water sediments are dominated by organic matter remineralisation in pore water. This study highlights that Cd isotopes from carbonate leachates of unlithified, deep-water, mixed-lithological sediments do not reliably preserve primary productivity signals as they have undergone organic matter remineralisation in exchange with pore waters.

Glacial-interglacial cycles are marked by large fluctuations in atmospheric CO2, with the oceanic biological pump playing a critical role in regulating these changes. The South China Sea (SCS), a low-latitude marginal sea characterized by oligotrophic conditions and high sedimentation rates, provides a unique setting to investigate past variations in the biological pump on continental margins. In this study, we present the first record of 230Th-normalized biogenic fluxes (total organic carbon, opal, CaCO3) in the SCS over the past 120 kyr. We examine the potential controlling factors of organic carbon burial to infer the evolution of the biological pump over this period. The record reveals that sediment focusing was persistent, but varied, highlighting the need to correct for lateral transport. Total organic carbon (TOC) flux increased across the marine isotope stage (MIS) 5a-4 transition, potentially reflecting enhanced surface-to-deep transfer efficiency, which may be linked to cooler ocean conditions and associated changes in remineralization dynamics. Between late MIS 3 and MIS 2, TOC flux peaked, likely reflecting both increased transfer efficiency and enhanced preservation under high sedimentation rates. These changes are consistent with a strengthened biological pump in glacial periods that may have facilitated CO2 drawdown. Moreover, reduced CaCO3 fluxes indicate a weakened carbonate pump during the MIS 4 and MIS 2, further reinforcing CO2 sequestration. The temporal alignment between elevated TOC fluxes and major phases of atmospheric CO2 decline suggests the potential role of the biological pump on continental margins in amplifying glacial CO2 drawdown. These findings provide a framework for integrating continental margin processes into global carbon cycle reconstructions.

The continental shelf, as a transitional zone between land and ocean, is one of the most active regions for material and energy exchange within the Earth system and plays a crucial role in regulating global climate and the carbon cycle. However, the response of silicate weathering on continental shelves to paleoclimate changes on glacial-interglacial timescales, as well as its impact on the global carbon cycle, remains unclear. In particular, there is a notable lack of long-term geological records from mid-latitude continental shelf regions, which are sensitive to temperature and sea-level changes. In this study, we conducts high-resolution clay mineral analyses on sediments from Site CSDP-1 in the South Yellow Sea continental shelf, aiming to reconstruct the history of sediment provenance and weathering evolution since the middle Pleistocene and identifying their controlling factors. Comprehensive analyses indicate that over the past 600,000 yr, fine-grained sediments in the study area were primarily derived from the Yellow River. Weathering indicators, including clay mineral ratios and major element geochemistry, suggest that enhanced chemical weathering occurred predominantly during glacial periods. This is likely due to the exposure of unconsolidated shelf sediments during glacial sealevel lowstands, making them susceptible to subaerial re-weathering. Our estimates indicate that the intensified silicate weathering of exposed sediments on the Yellow and East China Sea continental shelf during glacial periods contributed approximately 0.3

The pronounced spatial heterogeneity in the severity of the end-Permian mass extinction is suggested as the result of changes in oceanic connectivity, which regulate the buffering capacity of marine environments against global perturbations. However, direct geochemical constraints remain limited. Magnesium isotopes (delta 26Mg) of seawater serve as a sensitive tracer for oceanic restriction. Here, we present reconstructed seawater delta 26Mg records from the Neo-Tethys and Panthalassa oceans and compare them with existing data from the Paleo-Tethys. Our results reveal a fundamental divergence: seawater delta 26Mg remained stable (-0.4%o to -0.3%o) in the NeoTethys and Panthalassa across the Permian-Triassic transition, whereas it increased by more than 0.5%o in the Paleo-Tethys. This contrast suggests that the Neo-Tethys was effectively connected to the vast, well-buffered Panthalassa Ocean, while the Paleo-Tethys was a more restricted basin. Mass balance modeling suggests that the open Panthalassa/Neo-Tethys system maintained a significantly larger Mg reservoir and greater capacity to buffer external changes, thereby supporting relatively stable environmental conditions. However, the restricted Paleo-Tethys is more sensitive to chemical disturbances, potentially leading to more pronounced environmental stress. Our Mg isotope data provide geochemical constraints on ocean connectivity and suggest that differences in buffering capacity may have played an important role in shaping the spatial heterogeneity of biotic catastrophe during the end-Permian mass extinction. The degree of restriction and inter-basin exchange in deep-water areas warrant further investigation.

Continental weathering plays a crucial role in maintaining the equilibrium of the carbon cycle and Earth's habitability. Interpreting weathering records registered in marginal sea sediments is a key approach to understanding the mechanisms of continental weathering. However, these weathering indices are often influenced by factors such as catchment lithology, mineral sorting during river transport, and diagenetic modifications during deposition. Thus, accurately interpreting the geological significance of these weathering indices remains a challenge in continental weathering research. In this study, we compiled a series of published sediment archives (<100 ka) from the continental margin of Asia. By comparing Chemical Index of Alteration (CIA) values and other common chemical weathering indices in these records, we attempted to identify the patterns of weathering records and their controlling factors along the Asian continental margin. The weathering indices in Asian continent marginal seas sediments are primarily influenced by two factors: Temperature and Sea Level. Comprehensive comparison of chemical weathering indices from multiple sediment cores, spanning from tropical to Arctic regions, revealed stronger weathering in tropical areas and weaker weathering in polar regions. The impact of sea level on weathering indices can be further attributed to changes in sediment provenance or variations in the weathering area, e.g., the exposure of the continental shelf. In low-latitude marginal seas (Arabian Sea, Bay of Bengal, Andaman Sea, and northern South China Sea), chemical weathering intensity is associated with temperature, consistent with glacial-interglacial cycles. In mid-latitude marginal seas (Okinawa Trough and Sea of Japan), sediment weathering intensity is dominated by sediment provenance changes driven by sea level fluctuations. In high-latitude marginal seas (Sea of Okhotsk, Bering Sea, Chukchi Sea, and East Siberian Sea) and the southern South China Sea, chemical weathering intensity is stronger during glacial periods and weaker during interglacial periods. This pattern is attributed to enhanced weathering of unconsolidated shelf sediments exposed during glacial sea level lowstands and the increased fracturing of rocks and sediments due to glacial erosion in polar regions. This study provides a novel perspective for deciphering silicate chemical weathering signals registered in the Asian continent marginal seas in the late Quaternary, and helps us explore the factors influencing continental weathering in sedimentary records in continental margins.

Silicate weathering plays a fundamental role in regulating Earth's climate and carbon cycle. Despite numerous studies on silicate weathering in large river basins, its response to millennial-scale climate variability and anthropogenic activities remains poorly constrained, largely due to prolonged sediment residence times and complex source-to-sink processes within large catchments. Here, we present high-resolution Holocene records of geochemical and mineralogical compositions from Core TY sediments in the Changjiang (Yangtze River) Delta, aiming to reconstruct temporal variations in silicate weathering over the past 7.0 kyr. By integrating other borehole data and paleoclimate archives, we identify two stages of weathering evolution in the Changjiang Basin during the mid-to late Holocene. In Stage 1 (7.0-1.0 ka), the core sediments were moderately weathered with relatively stable compositions, primarily attributed to steady sediment supply from the mid-lower basin. The weathering proxies did not respond promptly to the weakening Asian Summer Monsoon after the Holocene Climatic Optimum, likely due to the weak climate-weathering dependency and strong buffering of weathering signals within the large alluvial plains. Stage 2 (since 1.0 ka) recorded a marked enhancement in weathering proxies of deltaic sediments, accompanied by increasing sediment contributions from the upper basin. This shift coincides with strengthened monsoon rainfall and intensified human activities upstream. We infer that largescale population migrations have accelerated deforestation and land reclamation in Southwest China, likely promoting the erosion and remobilization of older weathered soils transported to the delta. Overall, our findings indicate that on millennial timescales, both climatic and anthropogenic forcings jointly modified sediment source-to-sink pathways in the Changjiang Basin, thereby modulating the transmission and preservation of weathering signals in deltaic sediments. This study provides new insights into the complex interplay among chemical weathering, climate change, and human activities in the large river systems worldwide.

The South China Sea (SCS) constitutes a vital archive for investigating paleoenvironmental and climatic dynamics, with its sedimentary record predominantly derived from adjacent river systems. Traditionally, the Mekong River is regarded as the principal sediment source for the southern SCS (sSCS). However, this perspective is increasingly contested by evidence suggesting that ocean currents may facilitate sediment transport from the northern SCS. This study examines marine sediment core 18252-3, retrieved from the continental slope off southeastern Vietnam near the Sunda Shelf. This sedimentary archive spans the last 40 ka, capturing the critical transition from the Late Glacial to the Holocene. Through Sr-Nd-U isotopic analyses, we identify significant shifts in sediment provenance and transport dynamics within the sediment core, primarily driven by sea level oscillations and oceanographic transformations. The Sr-Nd mixing models suggest that during the last glacial period (Unit 1, ca. 28-40 ka), the Mekong River accounted for approximately 61 f 9 % of sediment input. The shift observed in Unit 2 (ca. 16-28 ka) is marked by a progressive rise in South China Rivers (SCRs) contributions, notably the Pearl and Red Rivers, to approximately 74 f 6 % by the end of the unit, while the Mekong input declined to 26 f 6 %. In the Holocene (Unit 3, ca. 0-16 ka), contributions from the SCRs surged to an average of 82 f 6 %. Furthermore, the application of the comminution age technique, leveraging uranium isotopic ratios, reveals a significant extension in integrated sediment residence duration-from 148 f 13 kyr in the glacial period to 215 f 22 kyr in the postglacial period-reflecting a transition from proximal to distal sources in the SCS at the core site. This shift may correspond to the postglacial incursion of the South China Sea western boundary current (SCSwbc) onto the Sunda Shelf, potentially establishing a hydrodynamic barrier that curtailed Mekong sediment dispersal during the Holocene. These findings from the southwestern SCS slope underscore the importance of sea level and ocean current interactions in controlling sediment provenance at this location, and suggest that SCRs' contributions to the sSCS have been underestimated in some previous reconstructions.

The South China Sea is the largest marginal sea in the Western Pacific. Understanding the geochemical composition of its detrital sediments is crucial for deciphering terrestrial weathering processes on the surrounding landmasses and the evolution of the East Asian Monsoon. However, the South China Sea is bordered by numerous islands and rivers, making the accurate identification of sediment provenance a prerequisite for interpreting these sedimentary records. The Sunda Shelf, located in the southwestern South China Sea, is the world's largest non-polar continental shelf. Late Quaternary sea-level changes have caused the shelf to be subaerially exposed during glacial periods, forming new land, which significantly influenced sediment provenance and flux to the southern South China Sea. This study presents grain size and Sr-Nd-U isotopic analyses of the fine-grained detrital fraction from Core 17964-3 in the southern South China Sea. The results reveal a three-stage evolution in the Sr-Nd isotopic composition of the sediments since 23 ka. Stage I (23.0-19.0 ka) shows stable Sr-87/Sr-86 ratios (similar to 0.723627) and epsilon(Nd) values (similar to - 9.78). In Stage II (19.0-11.8 ka), Sr-87/Sr-86 ratios rose to similar to 0.726669, while epsilon(Nd) values declined to similar to - 10.17. During Stage III (11.8 ka to present), Sr-87/Sr-86 ratios fluctuated near 0.726670, and epsilon(Nd) values stabilized around -10.82. A comparison between the Sr-Nd isotopes and sediment grain size revealed no significant grain-size effect on these two isotopes, leading the conclusion that these isotopic variations primarily reflect changes in sediment provenance. During the glacial lowstand, the sediments in Core 17964-3 were primarily derived from the Mekong River. However, due to the lower sea level, which positioned the paleo-coastline closer to the core site, contributions from southern islands (e.g. Borneo) and the exposed shelf were also identified. During the highstand period, although the Mekong River remained the dominant contributor, the intensification of the East Asian Summer Monsoon increased precipitation and erosion over the Indochina Peninsula, thereby enhancing the sediment flux from the northern Indochina Peninsula. These northern materials were then transported southward to the core location by the Vietnam Coastal Current. Concurrently, rising sea levels caused coastlines to retreat toward the islands, making it increasingly difficult for materials from the southern islands to reach the core site, trapping them instead on the shallow shelf. Furthermore, U isotopic compositions were employed to assess the relative "age" or weathering history of the sediments. The lower (U-234/U-238) ratios during the lowstand indicate "older" sediments, supporting the inference of reworked older material from the exposed shelf. In contrast, the higher (U-234/U-238) ratios (closer to 1) during the highstand reflect "younger", fresher weathering products. By utilizing a multi-isotope (Sr-Nd-U) approach, this study reconstructs provenance changes in sediments from the core 17964-3 near the Sunda Shelf in the southern South China Sea. It investigates the relationship between sediment sources, sea-level change, and East Asian Monsoon evolution from geochemical, sedimentological, and paleoenvironmental perspectives. The findings highlight the complexity of source-to-sink processes in marginal seas and provide a novel methodology and conceptual framework for future reconstructions of sedimentary environments and studies of land-sea interactions.

The impact of climate on continental denudation is most pronounced in high mountain ranges, which generate a disproportionally large amount of sediment for their area. However, there currently are limited tools to accurately reconstruct past denudation. We present a record of basin-scale paleo-denudation rates since the last glacial period in the low-latitude, rapidly eroding Taiwan orogen. We measured 10Be(meteoric)/9Be ratios in dated coastal sediments and converted them into paleo-denudation rates. Our results reveal large variations in denudation rates (0.1-3.0 mm/yr). These variations do not mirror large-scale climate trends recorded by marine benthic delta 18O. Instead, denudation rates are primarily influenced by the intensity of the East Asian monsoon. This observation is complementary to previous paleo-10Be studies in mid-latitude regions, where basin-scale denudation is mainly driven by glacial or periglacial processes. Climatic cycles appear to exert a primary control over denudation, where the relative importance of specific climatic factors likely varies across latitudinal zones.

The comminution age method estimates the time elapsed since the physical weathering of bedrock into detrital sediment, offering a promising tool for quantifying the timescale of earth surface processes, e.g. catchment weathering and erosion. This method is now extensively used in sediment source-to-sink investigations across various environments, including fluvial, marine, aeolian, and glacial sediment systems. The fundamental principle of this method relies on quantifying the time-dependent 234U depletion caused by alpha-recoil effects in sediment grains. Nevertheless, significant uncertainty persists regarding the model's key parameter, the 234U recoil loss factor (f alpha). This study utilized a suite of well-characterized typical East Asian sediment samples with precisely constrained f alpha values, including ancient deposits from the Changjiang (Yangtze) River Delta, Chinese loess, and the South China Sea (SCS), to evaluate the applicability of various methods for estimating f alpha. Our results show that f alpha is significantly affected by the specific surface area of sediment particles. Compared to other models hindered by the limitations of specific surface area measurements or overly simplified grain morphologies, the weighted geometric model (Model 2) is expected to be a more robust approach for calculating f alpha. However, this model is heavily restricted by the empirical values assigned to maximum surface roughness (lambda max) and maximum aspect ratio (beta max). In this study, Monte Carlo simulations were employed to objectively constrain the values of lambda max and beta max. The results revealed that valid solutions for lambda max can reach up to 317 and beta max up to 7.1, which differ significantly from the empirical constants used in previous studies. Applying the simulated outputs to modern Changjiang sediments yielded a comminution age of 720 kyr (95% CI: 580-963 kyr), substantially older than previous estimates of 400-600 kyr. Furthermore, based on the simulation results, the comminution ages calculated for Changjiang sediments deposited during the Last Glacial Maximum (LGM) ranged from 354 to 593 kyr, which also deviates significantly from the 141-310 kyr estimated by previous studies. This study not only provides a more reliable timescale for the source-to-sink processes of East Asian sediments but also offers a new methodological reference for the application of the weighted geometric model and the comminution age method.

The role of river-disconnected submarine canyons, which comprise roughly 98% of the global total, remains poorly understood in organic carbon (OC) transport and burial. We investigate the 750-km-long Toyama Deep-sea Channel (TDSC) system with its large river-disconnected canyon in the Japan Sea to quantify OC sources, clarify controlling processes, and evaluate burial potential. Surface sediments and sinking particles are collected for analysis of the stable carbon isotope, grain-size, elemental composition, and Nd isotopes analysis, as well as multivariate statistics. The results reveal terrigenous OC contributions of up to 64%, sourced largely from the region's major Class A rivers, Japan's largest nationally managed rivers, despite the absence of any direct river connection. This transport is mainly driven mainly by turbidity currents likely triggered by slope failures. In the TDSC slope, OC loading is higher than at the TDSC bottom, with hydrodynamic conditions controlling preservation efficiency through the formation of iron and manganese minerals. River-disconnected canyons exhibit terrigenous OC loads that are up to three times greater than non-canyon marginal systems, underscoring their overlooked significance in long-term carbon sequestration. Our findings highlight the underestimated role of river-disconnected systems in carbon cycling, thus emphasizing the need to reassess OC burial efficiency and to incorporate these pathways into deep-sea carbon cycle models. Moreover, our results suggest that further global-scale investigations of river-disconnected canyons are urgently needed to assess their cumulative role in long-term carbon storage and climate regulation.

Abstract Estuarine sediments are critical zones for element cycling between land and ocean, where redox oscillation driven by unsteady sedimentation amplifies the role of iron (Fe) as a reversible regulator for the benthic cycling of trace elements. Yet, key uncertainties persist regarding the quantitative partitioning and the mineralogical mechanisms of microbially mediated Fe(III) reduction, especially the distribution of newly formed Fe(II) between solid phase and porewater. Here, surficial sediments from the Changjiang Estuary were incubated with the Fe‐reducing bacterium Ferrimonas balearica, with or without additional molybdate amendment and subjected to reoxygenation experiments. Based on sequential extractions and Flow‐Through Time‐Resolved Analyses (FT‐TRA), we found that microbial Fe(III) reduction promoted the formation of authigenic Fe(II) minerals, potentially Fe carbonate, which preceded the release of Fe 2+ into porewater. Inhibition of sulfate reduction significantly facilitated Fe(II) accumulation in the solid phase and reduced the release of Fe 2+ and P, suggesting a crucial role of sulfide‐mediated chemical reduction of Fe(III) in Fe 2+ and P liberation. Multiple trace metals (e.g., Cr, Co) exhibited strong correlations with Fe 2+ release ( p < 0.01), and FT‐TRA revealed the enhanced lability of these trace elements in solid phase after microbial incubation. During reoxidation, Fe 2+ was rapidly oxidized and precipitated. Subsequently, dissolved P was retained by newly formed Fe(III) oxyhydroxides, highlighting the reversible nature of labile Fe and its high efficiency in elemental mobilization during redox oscillation. These results provide quantitative evidence of microbially mediated labile Fe transformation processes in dynamic estuarine environments.

As a vital component of the big river systems on the Tibetan Plateau,the Yarlung Tsangpo River(YTR)receives a large volume of weathered and eroded materials from various geological units including the Lhasa Block,Yarlung Tsangpo Suture Zone,and Tethyan Himalayas.The enrichment of rare earth elements(REEs)in its sediments is of significance for deciphering source to sink processes of plateau-derived river sediments and exploring REEs resources.In this study,the floodplain sediment and suspended particulate matter were collected from the middle reaches of the YTR mainstem and its main tributaries(Lhasa River,Nyang River,and Parlung Tsangpo River)in the north,and the REEs compositions of the detrital components of these sediments were systematically analyzed.The results show that the total content of REEs in the YTR sediments is generally higher than that of major rivers in the world,and exceptionally high in some tributaries.These river sediments exhibit pronounced negative Eu anomalies but no significant Ce anomalies,mainly inheriting the provenance characteristics of bedrocks such as the granite in the Lhasa Block,which has high content of REEs and obvious Eu anomalies.Furthermore,the significant correlation between contents of total REEs(ΣREEs)and elements such as U,Zr,Th,P indicates that heavy minerals basically control the REE composition of detrital sediment.Combined with regional heavy mineral investigations,we infer that the heavy minerals such as apatite,zircon,and garnet are the main reasons for the abnormally high REE contents observed in these river sediments.

Dissolved black carbon (DBC) is recognized as the most abundant molecularly identified refractory dissolved organic carbon pool in the ocean. However, its dynamics within major river-estuary systems remain poorly constrained, hindering a more robust assessment of negative carbon cycle-climate feedback. Through multiseason sampling in the Changjiang River Estuary (CRE), we elucidated the spatiotemporal patterns and drivers of DBC and estimated its annual export under contrasting hydrological regimes. We found that, across all sampling seasons and layers, water mixing was strongly associated with the spatiotemporal variations of DBC, as indicated by the significant positive correlations between DBC concentrations and salinity. Annual DBC export from Changjiang showed an approximately twofold variation, ranging from 28.02 +/- 3.62 Gg-C in a dry year (2023) to 65.51 +/- 12.94 Gg-C in a wet year (2020). Summer with abundant freshwater discharges consistently contributed the largest share (>43%) despite considerable interannual variability. These findings highlighted hydrological controls upon DBC dynamics in major river-estuary systems. Nevertheless, large uncertainties persist, calling for higher resolution sampling and molecular characterization of multiple DBC pools in landocean interfaces under a changing climate.

Dust significantly impacts the Earth's climate system, and loess, as dust deposit, holds valuable clues for understanding past climate and environment changes. However, the complex interplay of erosion, transport, and deposition processes may result in different grain size fractions originating from distinct sources, potentially complicating paleoclimate reconstructions. The Danube loess as one of Europe's best-preserved deposits, has a basal age exceeding 1 Ma, while its origin remains unresolved. In this study, we integrated the first systematic grain-size-specific Sr-Nd isotopic compositions of the Stari Slankamen (Serbia) loess across different loess and paleosol layers with modeled paleo-atmospheric circulations to determine the provenance and evaluate the potential Saharan dust contribution. Our results show that the Sr-87/Sr-86 ratios are highly grain-size dependent, while Nd-143/Nd-144 ratios are less affected and more relevant for provenance. We further identified, for the first time, anomalous isotopic patterns in the clay fraction (<2 mu m) of loess deposits, indicating the preferential contribution of surrounding volcanic materials and contrasting clearly with the isotopic fingerprint of Saharan dust. Comparison with potential sources suggests that the Danube fluvial sediment was the dominant provenance since the Middle Pleistocene, and atmospheric modeling shows prevalent westerly winds from near-surface to upper level restrain dust intrusions from the Sahara. These findings underscore the necessity of grain-size-specific provenance investigations and highlight the persistent supply of fluvial sediments to regional loess deposits.

Late Quaternary sediments in semi-enclosed bays serve as valuable archives of sea-level fluctuations and shifts in depositional environments. Thus, these regions are ideal for investigating the last glacial-interglacial transition. In this study, we focus on borehole HSZK04B retrieved from the semi-enclosed Kaozhouyang Bay (KZYB), located in the northern coastal region of the South China Sea (SCS). Analyses were conducted based on the lithological and grain size characteristics, chronostratigraphy and microfossil stratigraphy. By comparing its stratigraphic sequence with those of adjacent boreholes, we reconstructed the late Quaternary sedimentary and environmental evolution of KZYB. The results showed that borehole HSZK04B can be divided into seven distinct sedimentary units (U7-U1), corresponding to the Old Red Sand deposits of early MIS 4 (U7), mottled clay deposits from late MIS 4 to early MIS 3 (U6), fluvial deposits of early MIS 3 (U5), marsh deposits from late MIS 3 to early MIS 2 (U4), lacustrine deposits during the last deglaciation period (U3), neritic deposits of the early Holocene (U2), and coastal bay deposits of the late Holocene (U1), respectively. Comprehensive stratigraphic analysis of boreholes in the northern SCS coast revealed that the MIS4 strata were the basal boundary of the Quaternary sequences. Variations in sea level and sedimentation accommodation space governed the development of diverse sedimentary facies within semi-enclosed bays. During the lowstand sea-level phase of the Last Glacial Maximum (LGM), continental deposits were formed. In the subsequent deglacial period, drowned valleys or freshwater lakes emerged, followed by neritic deposits during the early Holocene, and coastal progradational deposits during the late Holocene. This scenario highlights the dominant control of global sea-level fluctuations on sedimentary processes and environmental evolution in semi-enclosed coastal settings, thereby enhancing our understanding of the late Quaternary sedimentation mechanism in such bay environments.

Understanding the ecological risks of heavy metals is critical for effective environmental management. Yet, the combined influence of tidal processes and tropical storms on heavy-metal dynamics in rivers remains poorly understood. This study examines the variations of heavy metals in sediments from a typical mountainous river in Southeast China, aiming to assess the combined influence of tides and typhoons on metal enrichment and ecological risks. The results show that from 2016 to 2019, there were no significant temporal changes in the ecological risks of heavy metals. Nevertheless, a distinct spatial pattern was observed, with higher levels in the tidal reach than in the non-tidal reach. This spatial variation is due to changes in sediment composition, such as shifts in source areas and grain size, which are driven by tidal processes. The clay fraction had significantly higher concentrations of heavy metals, enrichment, and ecological risks because metals are preferentially adsorbed onto fine-grained particles. Under normal conditions, tidal activity and anthropogenic inputs mainly affect the distribution of heavy metals. However, during typhoons, sediment mobilization intensifies, leading to a 2-4-fold increase in heavy metal concentrations and a higher risk of environmental contamination. The results of this study suggest that effective management of heavy-metal contamination in dynamic river systems requires a holistic approach that considers sediment composition, hydrodynamic conditions, and anthropogenic activities.

Abstract Evaporation exerts a dominant influence on groundwater‐lake interactions in arid environments, yet its coupling with redox dynamics and trace element mobilization remains poorly understood. Here, we combine stable isotope (δ2H, δ18O) and trace element concentration analyses of manganese (Mn), arsenic (As), and barium (Ba) to quantify evaporation intensity and evaluate its geochemical effects in the Badain Jaran Desert, China. These trace elements were selected because they are commonly enriched in arid regions and highly sensitive to both evaporative concentration and redox transformations, posing potential risks to human health. High‐resolution sampling along two groundwater transects at South Sumujaran Lake reveals distinct isotopic and geochemical patterns. Deuterium excess (d‐excess) and evaporation coefficients jointly indicate that evaporative fractionation is stronger in the oxidation‐dominated eastern transect, where evaporation drives Mn and Ba accumulation, whereas in the reduction‐dominated western transect, redox‐controlled mobilization and desorption lead to As and Ba enrichment. At the regional scale, Bayesian isotope modeling of lakes across the Badain Jaran Desert indicates that pre‐evaporation δ18O decreases and the evaporation coefficient increases from southeast to northwest, reflecting regional gradients in precipitation, continentality, and aridity. The lakes are sustained primarily by local and mountain‐block groundwater recharge, with about 91% occurring under reducing conditions that enhance trace element mobility. These findings provide a process‐based understanding of how coupled evaporative and redox processes regulate isotopic evolution and solute dynamics in desert aquifers and highlight the growing vulnerability of groundwater quality in arid regions under intensified evaporative stress.

The riverine particulate flux is a major vector for trace metal delivery to the ocean, yet the processes controlling copper (Cu) isotopic composition in suspended particulate matter (SPM) of large, human-impacted rivers remain poorly understood. Here, we present the first catchment-scale delta Cu-65 dataset for SPM in the Changjiang (Yangtze River) Basin, a system characterized by high sediment yield, diverse lithology, strong anthropogenic pressure, and monsoon-driven hydrology. The results show that the Changjiang SPM exhibits delta Cu-65 signature ranging from -0.31 parts per thousand to +0.46 parts per thousand, averaging +0.08 parts per thousand (n = 59), which are consistently lighter than those of the dissolved load. Enrichment Factor (0.7-2.2) and Geoaccumulation indices (<1.8) indicate minimal anthropogenic Cu enrichment, with weathering processes dominating the particulate Cu budget. We propose that delta Cu-65(SPM) is controlled by inorganic isotopic partitioning during weathering and transport. Preferential retention of heavy Cu in the dissolved pool via organic complexation leaves residual SPM enriched in the lighter isotopes. Subsequent sorption onto clays and Fe-Mn oxides during transport generates an efficient basin-wide sorting effect that regulates the SPM pool and determines the particulate Cu flux in this large river. Temporal data from the Datong Hydrological Station reveal that monsoon floods act as a hydrological switch, introducing isotopically lighter material and perturbing this Cu isotopic signal. Our findings redefine the controls on Cu isotopes in large river systems, highlighting the dominance of inorganic partitioning over source signals in governing the particulate Cu flux to the ocean.