Coarse Sediment Grains Research Articles

Reconstruction of coastal flooding processes and human response at the end of the Liangzhu Culture, East China

Understanding coastal flooding processes in response to centennial-scale sea-level rise is essential in preparing for the challenge of present-day global warming. Mid-Holocene sea-level rise induced widespread coastal flooding along the East China coast and precipitated the collapse of the Neolithic Liangzhu Culture, the earliest known prehistoric state in East Asia. This paper presents multi-proxy analyses of sedimentology, grain size, total organic carbon (TOC), and alkaline-earth metals extracted by acetic acid (HAc) of a dated sediment core, ZK07, collected from Liangzhu City, with the aim of revealing the detailed progression of coastal flooding phases and the response of prehistoric people at the end of the associated Liangzhu Culture. A three-step succession of coastal flooding processes between ca. 4.6–4.3 cal kyr BP, brought about by relative sea-level rise, is evident in core ZK07. Initially, an increase in the local water level in response to the first phase of sea-level rise is indicated by a gradual increase in TOC at ca. 4630 cal yr BP. Subsequently, at ca. 4520 cal yr BP, a second phase of increased local water-level, consistent with further sea-level rise and salinity intrusion, is suggested by higher Sr concentrations accompanied by a sharp increase in TOC. Thirdly, at ca. 4480–4315 cal yr BP, low TOC content, high - but strongly fluctuating - Sr and Ba concentrations and coarser sediment grain size are all indicative of coastal inundation caused by both storm surges and river flooding associated with typhoon events that correspond with a concurrent phase of accelerated sea-level rise. Considering the evidence of cultural deposits preserved at Liangzhu City, it appears that the Liangzhu people were forced to respond rapidly to the inundation by abandoning the city at ca. 4480 cal yr BP. We suggest that relative sea-level rise and coastal flooding at the terminal stage of the Liangzhu Culture was the regional response to global climate warming and eustatic sea-level rise at that time. Given evidence that a contemporaneous cultural transition took place in the lower Yellow River basin, we further propose that global climate change around 4.5 cal kyr BP had a widespread impact on Neolithic cultural evolution in East China. Furthermore, the rise in local water levels and associated salinity intrusions may be considered as an early warning signal in monitoring future coastal flooding risk.

Inertial drag and lift forces for coarse grains on rough alluvial beds measured using in-grain accelerometers

Abstract. Quantifying the force regime that controls the movement of a single grain during fluvial transport has historically proven to be difficult. Inertial micro-electromechanical system (MEMS) sensors (sensor assemblies that mainly comprise micro-accelerometers and gyroscopes) can used to address this problem using a “smart pebble”: a mobile inertial measurement unit (IMU) enclosed in a stone-like assembly that can measure directly the forces on a particle during sediment transport. Previous research has demonstrated that measurements using MEMS sensors can be used to calculate the dynamics of single grains over short time periods, despite limitations in the accuracy of the MEMS sensors that have been used to date. This paper develops a theoretical framework for calculating drag and lift forces on grains based on IMU measurements. IMUs were embedded a spherical and an ellipsoidal grain and used in flume experiments in which flow was increased until the grain moved. Acceleration measurements along three orthogonal directions were then processed to calculate the threshold force for entrainment, resulting in a statistical approximation of inertial impulse thresholds for both the lift and drag components of grain inertial dynamics. The ellipsoid IMU was also deployed in a series of experiments in a steep stream (Erlenbach, Switzerland). The inertial dynamics from both sets of experiments provide direct measurement of the resultant forces on sediment particles during transport, which quantifies (a) the effect of grain shape and (b) the effect of varied-intensity hydraulic forcing on the motion of coarse sediment grains during bedload transport. Lift impulses exert a significant control on the motion of the ellipsoid across hydraulic regimes, despite the occurrence of higher-magnitude and longer-duration drag impulses. The first-order statistical generalisation of the results suggests that the kinetics of the ellipsoid are characterised by low- or no-mobility states and that the majority of mobility states are controlled by lift impulses.

The characteristics of the surface sediments in Co To island

552 grain size samples and 33 mineral quality defined samples have been collected in the Co To island, Tonkin Bay of Vietnam, to study the distribution and the sediment provenance. The field investigation method, the grain analysis, and the detrital composition examination method have been used to study the characteristics of the surface sediments in Co To island. The obtained results show that the surface sediments in the area consist of ten different fields, namely: sandy gravel, gravelly sand, sand, gravelly muddy sand, sand mixed gravel, muddy sand, gravelly mud mixed sand, silty sand, muddy sandy gravel, and sandy mud. The mineral component method shows that quartz is the main contain of the surface sediment (72,0÷90,6%), less rock detritus, felspat, mica, and very few of the shells. It is to confirm that the continent is the main primary material source of the study area. The distribution of the sediment is complicated. As the East-Southeast side of the research area, the sediment distribution following gravity way, coarse grain near the shore (gravel, sandy gravel,…), finer grain far off the shore (gravelly muddy sand, silty sand,…), choice level is very low. Which This is saying that the movement of sediment in the area is dominant, ; the flow energy is governed by the topography near the island and seafloor. In tMhe meanwhile, the west-northwest side, the topography of seafloor is the complicated, coarse sediment grains (gravel, sand), ); the roundness is bad, which is saying that the hydrodynamic flow there plays an important role in the sediment distribution.

Reconstructing the historical pollution levels and ecological risks over the past sixty years in sediments of the Beijiang River, South China

Three sediment cores were collected from the Beijiang River to investigate the effects of human activities on the geochemical fractions of trace metals (Ni, Cr, Cu, Zn, Cd, Pb and Fe) and to reconstruct the ecological risks for the period 1951–2015. Cd had the highest concentration in exchangeable and carbonate fractions and was probably contributed by smelting wastewater. High Cu, Zn and Pb contents were observed in the iron oxide fraction (mean values of 32.2%, 38.2% and 43.9%, respectively), reflecting the influence of mining activities. Flood events led to coarser sediment grain sizes and higher trace metal residual fractions at upstream sites (S1 and S2). Similar to the mining history of the basin, the excess metal fluxes of Cu, Zn, Pb, and Fe in the 210Pb-dating core (S3) increased slowly from 1951 to 1987, increased rapidly from 1988 to 1998 and decreased gradually after 1999 because of government intervention. However, the excess Cd flux decreased continuously from 1951 to 1961, increased from 1961 to 2005, and declined by approximately 78.2% from 2005 to 2014. The excess Ni and Cr fluxes increased noticeably after 1996 because of the increasing sedimentation rate after the construction of the Feilai Gorge Dam. The enrichment factor (EF) and ratio of secondary and primary phases (RSP) indicated that sediments (S3) were moderately to strongly polluted by Cu, Zn and Pb from 1961 to 2007 and extremely polluted by Cd from 1951 to 2011. Human activities increased the bioavailable metal concentrations and resulted in a high risk of toxicity to benthic organisms, especially during intense mining activity (1990s) and Cd pollution incidents (2005). Cd and Pb were primarily responsible for the sediment toxicity in the Beijiang River. The integrated pollution and risk assessment methods provided a clearer understanding of the aquatic environmental quality.

Meiofauna abundance and community patterns along a transatlantic transect in the Vema Fracture Zone and in the hadal zone of the Puerto Rico trench

Despite the increasing sampling effort that occurred in the deep-sea environment during the last decades, knowledge about meiofauna ecology in trenches and Fracture Zones is still scarce. Based on the lack of this information, a longitudinal transect across the Vema Fracture Zone in the North Atlantic was sampled to test whether meiofauna abundances differ between Northeast and Northwest Atlantic basins, separated by the Mid-Atlantic Ridge. Also, for examination of meiofauna depth pattern, the Puerto Rico trench floor, its upper trench slope and the Western North Atlantic abyssal were investigated.In this study, meiofauna communities were dominated by Nematoda (93%) and Copepoda (4%). The highest total abundance of meiofauna was found in the Puerto Rico trench and the lowest in the Western basin. We found significant differences between the Eastern and Western Atlantic basins, which were potentially caused by differences in current regimes. Stronger currents observed in the Western basin possibly led to the coarser sediment grain size observed in this region, and consequently to the lower abundances of the major groups found there. Besides grain size, the total abundance of meiofauna was significantly correlated with total nitrogen, total organic carbon, and water depth. Moreover, our study reveals a trend of increasing abundance of total meiofauna with increasing water depth in the Puerto Rico trench. Also, significant differences between the Western abyssal and the Puerto Rico trench were discovered. Generally, the meiofauna abundance in the investigated area decreased from East to West but increased with increasing water depth in the Puerto Rico trench. Due to funnelling of organic sediments increased food availability towards deeper regions in trenches could occur and promote higher abundance.

An experimental investigation of wave‐induced sediment responses in a natural silty seabed: New insights into seabed stratification

AbstractThe widely recognized global phenomenon of wave–seabed interactions and the resulting secondary stratification processes are complex and poorly understood. To better understand the mechanisms by which the differentiation between fine‐grained and coarse‐grained materials occurs and how new sedimentary sequences form, laboratory flume experiments were performed under varying wave conditions using natural silty sediment samples collected from the Yellow River Delta (China). Detailed observations led to the description of variations in the grain‐size composition and texture of sediment under waves of progressively increasing height and the recognition of the typical, secondarily formed seabed stratification that forms during processes of increasing pore pressure and subsequent liquefaction. The development of a stratified seabed, which is characterized by a superficial fluid mud layer, a subsurface that alternates between coarse and fine sediment banding, and an internal liquefied layer from top to bottom, is closely related to wave‐driven pore‐water flow through the sediment. Localized fluidization and the onset of piping leads to progressive changes in the grain composition with initial particle dislocation, the development of macro‐voids and micro‐conduits and, finally, pipe formation. Internal liquefaction occurs in the presence of a critical value of excess pore pressure, during which most fine particles can be scoured by the pore‐water flow along the sliding surface while the coarse sediment grains settle, leading to a more compact, homogeneous seabed. These elements are combined to produce the first model of wave‐induced stratification initiation and evolution in an originally uniform silty seabed. In addition, the implications of this model for future studies are explored.

Habitat use and selection of black scoters in southern New England and siting of offshore wind energy facilities

ABSTRACTThe southern New England continental shelf is an important region for black scoters (Melanitta americana) during winter and migratory staging periods and a priority area for developing offshore wind energy facilities. However, little is known about the migration phenology and habitat use of black scoters in this portion of their range and this information is necessary to assess potential risks to black scoters during the marine spatial planning process. In this regional black scoter study over 2 winters, we used satellite telemetry and spatial modeling techniques to estimate migratory timing and length of stay, quantify winter home range size and site fidelity between winters, examine key habitat characteristics associated with core‐use areas, and map relative probabilities of use across a 3,800‐km2 marine spatial planning area for 2 proposed offshore renewable energy facilities. Black scoters spent nearly 5 months in southern New England, with wide variation among individuals in the size of winter utilization distributions (range 16–12,367 km2). Approximately 50% of the tagged birds returned to southern New England during the subsequent winter and had variable fidelity to core‐use areas occupied the previous winter. During both winters, black scoter core‐use areas were located closer to shore, at shallower water depths, with coarser sediment grain size and higher probability of hard‐bottom occurrence relative to available areas. Resource selection functions classified the majority of a nearshore 5‐turbine, 34‐km2 renewable energy zone off Block Island as high probability of use by black scoters, whereas an offshore 200‐turbine, 667‐km2 federal lease block zone was classified as low to medium‐low probability of selection. Wind energy facilities, such as the Block Island site, constructed in relatively shallow (<20 m deep), nearshore habitats (<5 km) over hard‐bottomed or coarse‐sand substrate could displace some foraging black scoters wintering in this region, whereas the larger federal lease block zone located farther offshore is more likely to affect scoters dispersing among core‐use areas and during migration between wintering and breeding grounds. © 2014 The Wildlife Society.

Turbidite deposition in the southern South China Sea during the last glacial: Evidence from grain-size and major elements records

High-resolution grain size and major element geochemical measurements were performed on the marine sediments of Core MD05-2895 to help understand the formation of turbidite sequences. Grain-size results show that these turbidite sediments contain more coarse sediment grains than normal marls. The coarse sediment grains are mostly derived from relict sediments on the Sunda Shelf. Relict sediments are composed mainly of quartz, feldspar, tephra and a few titaniferous or ferruginous heavy minerals. Corresponding to the concentration of these minerals, increases in Si/Al, K/Al, Ti/Al and Fe/Al ratios are observed in the turbidite layers. As all the observed turbidite sequences were deposited during the last glacial, the occurrence of these turbidity events is implied to be closely related to instabilities in sea-level-induced sediment supply. We suggest that deposition of sediment particles from a single turbidity current is usually controlled by a counterbalance between gravity and buoyancy, with the interaction of individual grains being of minor importance.

Temporal trends of aliphatic and polyaromatic hydrocarbons in the Bohai Sea, China: Evidence from the sedimentary record

This work reports the historical trends and sources of aliphatic hydrocarbons (AHs) and polycyclic aromatic hydrocarbons (PAHs) in two 210Pb dated sediment cores extracted from the central mud areas of Bohai Sea (Bohai). The TOC/TN ratio of the bulk organic matter (OM) and the composition of the n-alkanes suggest that the sedimentary organic matter was of mixed marine and terrigenous sources. The coarser sediment grain size and decreasing C/N ratios since ∼1976 could be attributed to the relocation of the Yellow River mouth causing a decreased influence of Yellow River derived sediments and associated OM into the central Bohai. The concentration of total 16 PAHs in the two cores ranged from 34.2–202 ng/g (mean, 91.5) for BC1, and from 53.3–186 ng/g (mean, 103) for BC2, with a high abundance of 2–3 ring PAHs. Perylene in the two cores mainly originated from terrigenous sources via riverine discharge and thus could be potentially related to changes in the sediment load from the Yellow River into the Bohai over time. Petroleum inputs could be revealed by ratios of methylphenanthrenes to phenanthrene (MP/P) and the patterns of more stable geochemical biomarkers (hopanes and steranes) along the two cores, in addition to the presence of unresolved complex mixtures (UCM) in the surface layers. Source diagnostic ratios of PAHs indicated a pyrogenic origin from biomass and coal combustion with a minor petroleum contribution. Downcore trends of compositional PAHs profiles were in agreement with the socio-economic development in China in the past decades. This temporal variation of sedimentary PAHs can also reflect a different evolution stage of energy structure in China as compared with those of the western developed countries.

Role of instantaneous force magnitude and duration on particle entrainment

A new criterion for the onset of entrainment of coarse sediment grains is presented here. It is hypothesized that not only the magnitude, but also the duration of energetic near bed turbulent events is relevant in predicting grain removal from the bed surface. It is therefore proposed that the product of force and its duration, or impulse, is a more appropriate and universal criterion for identifying conditions for particle dislodgement. This conjecture is investigated utilizing two theoretical models, representative of two modes of entrainment: saltation and rolling. In these models, instantaneous, highly fluctuating turbulent forces are simulated as short‐lived pulses of characteristic magnitude and duration, which transfer adequate fluid momentum to the particle, to trigger its entrainment. The analytical solution of the respective equations of motion is employed in deriving representations of threshold conditions in terms of the impulse characteristics. It is shown that hydrodynamic forces of sufficiently high magnitude are capable of entraining a particle only when they last long enough so that their impulse exceeds a critical value. To illustrate further the validity of the critical impulse concept, as well as extend and generalize its application to different entrainment levels of an individual grain, a novel experimental setup is utilized. This setup facilitates observations of angular displacement of a steel mobile particle in air due to electromagnetic pulses of different magnitude and duration. The experimentally obtained conditions for partial or complete entrainment support the concept of a critical impulse.

Combining multivariate analysis and geochemical approaches for assessing heavy metal level in sediments from Sudanese harbors along the Red Sea coast

Multivariate statistical analysis and geochemical approaches were exploited for the assessment of the level of some heavy metals (Mn, Fe, Ni, Cu, Zn and Pb) in sediments from Sudanese harbors along the Red Sea coast. Principal component analysis, as a multivariate statistical analysis approach, was applied to identify contribution sources by heavy metals in sediments. While a single source (crustal) was recorded in the bulk sediments and coarse sediment grains (grain-size 1000–500 µm), two sources (crustal and anthropogenic) were recorded in fine sediment grains (grain-size < 500 µm). Furthermore, enrichment factor (EF), as a geochemical approach, appointed polluted sites by heavy metals in the study area. Based upon a previous study addressed the interpretation of EF values, minor to moderate anthropogenic enrichment were recorded in sediments from some sites in the study area. The main anthropogenic activities that believed to be the major sources of pollution by heavy metals in the study area are discharges from oil refinery, industry, shipping activity and domestic waste. Hierarchical cluster analysis (HCA), as another multivariate statistical analysis approach, was applied for the concentrations of heavy metals in bulk sediments to group sediments according to their mineralogical composition. The output of HCA is that sediments from the Port-Sudan harbor can be divided mainly into three areas — east, west and south. For the Sawakin harbor, no apparent trend for the spatial distribution of heavy metals in sediments was recorded.

Biological and physical processes structuring deep-sea surface sediments in the Scotia and Weddell Seas, Antarctica

Abstract Five deep-sea transects were sampled in the Scotia Sea and Weddell Sea from the Drake Passage to the South Sandwich Islands, Antarctica, with depths ranging from 767 to 6333 m. A combination of sediment surface and sediment profile imaging was used to characterize the physical and biological processes structuring the benthic boundary layer and surface sediments from the sediment–water interface (SWI) to as much as 17 cm below the SWI. The factors structuring surface sediments were related to distance from Antarctic landmasses, which are the main source of sediment, and deposition of water-column or sea-ice primary productivity. Stations near the continental shelf and slope tended to have coarse (granule to cobble) sediments derived from melting sea-ice. Input of fine sediments was estimated to be low at these stations because many of the coarse sediment grains appeared to be manganese coated. At the deepest stations in the Ona Basin, South Shetland Trench, and South Sandwich Trench, sediment appeared to be primarily hemipelagite silt-clay but were varved with as many as four distinct color laminations. These layers varied in thickness fom 0.6 to 10.6 cm and may have been related to turbidite flows. While geology and physical processes that deliver sediment to the bottom were the primary factors dictating substratum characteristics, biological processes were, to varying degrees, important in structuring the SWI and sediment fabric. Biological processes, primarily in the form of bioturbation, were most prominent at fine-grained stations but were also obvious even on rock substratum on top of the Shackleton Fracture Zone. There were gradients between the degree of bioturbation and type of biogenic structure present with depth. At depths 75% of the sediment bioturbated) the structure of surficial sediments at 5 of 13 stations. At depths >2000 m, biological processes were overall less diverse but dominated at 8 of 11 stations.

Effects of bioturbation in controlling turtlegrass ( Thalassia testudinum Banks ex König) abundance: evidence from field enclosures and observations in the Northern Gulf of Mexico

Bioturbation by stingrays and sand dollars can limit the distribution of temperate zone seagrass (eelgrass, Zostera marina Lamarck) meadows through the disruption of the root-rhizome matrix. The effects of bioturbation by these organisms on tropical or subtropical seagrass (turtlegrass, Thalassia testudinum Banks ex König) meadows are less well known. Stingray enclosure studes in St. Joseph Bay, Florida (29°N, 85.5°W) found that rays were unable to create unvegetated patches within continuous turtlegrass and that only large (disc width ≥0.9 m) rays ( Dasyatis americana Hildebrand & Schroeder) can damage rhizomes at the turtlegrass/sand flat interface habitats. Field surveys found large rays to be abundant in turtlegrass habitats only during July–August. These data indicate that stingrays are not responsible for the widespread occurrence of unvegetated patches within St. Joseph Bay. Additional exclosure experiments found that sand dollars ( Mellitta quinquiesperforata Leske) did not affect turtlegrass colonization of unvegetated sand flats. Comparisons of sand flat perimeters enclosing sand dollars at ambient densities (5–15 individuals/m 2) and those from which sand dollars were removed showed no inhibition of turtlegrass colonization of unvegetated sand patches after a 2-yr period. However, stone crab ( Menippe spp.) burrow construction at the seaward edge of turtlegrass habitats was found to cause significant, previously unreported, losses of turtlegrass habitat (average seagrass recession > 1 m/7 months). We conclude that bioturbation has less impact on turtlegrass than eelgrass habitats due to thicker, deeper turtlegrass rhizomes, and coarser sediment grain size.