Sediment Grain Size Research Articles

Operating Effects of the Three Gorges Reservoir on the Riverbed Stability in the Wuhan Reach of the Yangtze River

Reservoir construction may modify the downstream flow and sediment transport, and correspondingly result in adjustments in morphodynamics of a river, especially riverbed instability. Based on hydrological datasets from 2003 to 2019 during the post-dam period using the topographic data of 57 fixed cross-sections in the Wuhan reach of the Yangtze River, we calculated the indexes representing the channel stability. Moreover, considering the effects of flow, sediment concentration, grain size of sediment, and water depth, we propose a method for calculating the equilibrium values of cumulative erosion and the lateral migrate intensity of thalweg in this paper, and the method combines with the delayed response model (DRM) to comprehensively analyze the variations in the longitudinal and lateral stabilities of the riverbed. The results revealed that the channel has been obviously eroded in the downstream reach, resulting in a 76% decrease in sediment discharge after the impoundment of the Three Gorges Reservoir (TGR). Specifically, in the past 17 years, the cumulative erosion in the Wuhan reach of the Yangtze River reached 1.72 m, while the bankfull depth increased by 1.87 m. The lateral migrate intensity of thalweg increased in response to Coriolis force, with an increase of 22.3%. Taken together, the results show that the proposed formula can effectively simulate the variation process of channel stability, and it also quantifies the extent of the influence weight of interannual flow and sediment regimes. The morphodynamics adjustments in the channel stability of our studied reach were closely related to the previous five-year flow and sediment regimes, implying that channel evolution may lag behind the changes in flow and sediment discharges.

Grain-size characteristics in lake Fuxian sediments: Implication for dry-humid transformation of Indian summer monsoon over the past 150 years

Polymodal distributions and end-member modeling of grain-size in lacustrine sediments can reveal the changes in sedimentary processes, transportation mechanisms, and climatic changes. The temporal and spatial variation characteristics of grain-size were investigated in six sediment cores of the plateau deep-lake Fuxian, in southwest China, where the climate was driven by Indian Summer Monsoon (ISM). Results indicated that the size of the dominant grain-size exponentially decreased with the declining hydrodynamic condition towards the deep-water zones, with an exception of the maximum grain-size near the outlet of the lake. Measured grain-size distributions were classified into four end-members (EMs) with a basic end-member model algorithm (BasEMMA), of which could be linked to a distinct transport mechanism and source: EM1 (long-term suspended load from atmospheric dust) with the modal size of 0.3–11.2 µm, EM2 (off-shore suspended load from fine riverine input) with 7.9–14.2 µm, EM3 ((near-shore suspended load from coarse riverine input) with 15.9–31.7 µm, and EM4 (near-shore riverbed load from extremely coarse riverine input) with 35.6–70.9 µm, respectively. Temporal variation of EM2 + EM3 components of grain-size in Core F5 are responses to the changes in instrumentally recorded precipitation in Chengjiang (1961–2008) and ISM (1860–2006), which indicates that changes in river flow in response to changes in precipitation is the primary driver of clastic sediment deposition especially in the narrow section of the lake. Our findings indicate grain-size distribution and sediment compositions are significant tools for improving the understanding of the spatiotemporal heterogeneity in dry-humid transformation of ISM over the past 150 years.

Accumulation and distribution of microplastics in coastal sediments from the inner Oslofjord, Norway

Microplastic presence in benthic marine systems is a widely discussed topic. The influence of the natural matrix on microplastic distribution within the sedimentary matrix is often overlooked. Marine sediments from the western inner Oslofjord, Norway, were investigated for temporal trends, with a particular focus on the relationship between sediment grain-sizes and microplastic distribution. Density separation, optical microscopy and chemical validation were used to categorize microplastics. Microplastic concentrations ranged from 0.02 to 1.71 MPs g −1 dry weight (dw). Fibres were the most common (76%), followed by fragments and films (18%, 6%). Common polymers were polyesters (50%), polypropylene (18%), polymethylmethacrylate (9%), rayon and viscose (5%) and elastane (4%). Microplastics appear to accumulate preferentially according to their morphology and polymer type in certain sediment grain-sizes. Microplastics inputs to the Oslofjord appear to derive from a wastewater treatment plant in the vicinity. Although, the redistribution of microplastics within the fjord needs further investigation.

Hydrodynamic‐Driven Changes in the Source and Composition of Sedimentary Organic Matter via Grain Size Distribution in Shallow Lakes

AbstractSediment organic matter (SOM) differs in composition and function in different size fractions in relation to material and energy flows. The hydrodynamic effects on a lake's autochthonous (terrestrial plants) and allochthonous (microalgae, aquatic plants, and bacteria) inputs and transformation, and the components of SOM are still far from clear. To elucidate the SOM composition as driven by the hydrodynamic conditions associated with sedimentary grain size, we performed an ecosystem‐level investigation in the shallow lake Izunuma, Japan, measuring source‐specific fatty acids and the current velocity. High organic matter concentrations occurred in the finer fractions. Bacteria were dominant in the <32 μm fraction, microalgae were mainly present in the <32 and 63–125 μm fractions, aquatic plants appeared to be evenly distributed in all size fractions, and terrestrial plants mainly comprised the >125 μm fraction. Although the linear correlation between current velocity and sedimentary total organic carbon (TOC) was not statistically significant, the relationship between current velocity frequency and sedimentary TOC was significant. The highest Pearson coefficient occurred at a current velocity of 6 cm/s in sand. The relationship between allochthonous inputs and current velocity frequency was similar to that of TOC. Autochthonous organics had the greatest coefficient with two peaks at 4.5 and 8 cm/s. The threshold for sand resuspension varied with organic sources, while this phenomenon was absent in cohesive mud. Hydrodynamic forces affected the grain size of sediments and drove the gradient distribution of the SOM sources, which should be considered when managing freshwater lakes in light of future climate change.

Experimental study of fan delta evolution: Autogenic cycles of fully confined channelized flow and small secondary channelized flows

Fan deltas grow largely through repeated cycles of lobe construction and channel erosion during the period of channelized flow. Although previous studies suggest that variable flood discharge may play a key role in strong erosion and related fully confined main channel formation in fan deltas, analog experiments with constant discharge and sediment supply showed that strong erosional events were cyclic. Understanding erosion cycles is important for land management and flood hazard mitigation. Here, we present flume experiments to investigate the mechanism and controlling factors of fully confined main channel-related erosion under constant discharge conditions. The results reveal that: (1) fully confined main channel-related erosion is triggered by turbulence within stratified fluid in hydraulic jump process. When the topography difference of the fan delta is sufficiently small, the flow direction changed from steeper flanks to the centerline. The flow velocity along centerline increase due to weak viscosity and steep slope of fan delta, changing the subcritical flow to supercritical flow. Supercritical flow transports sediment to the shoreline and is resisted by the standing body of water in the basin, causing the decrease of flow velocity accompanied by hydraulic jump. The turbulence formed in hydraulic jump process triggers the formation of scour hole which erodes the fan delta. (2) Input conditions control the range of the critical slope and frequency of erosion cycles. The critical slope is inversely related to the slope of the discharge and grain size of sediments, whereas it is directly related to the sediment/water ratio. The frequency of erosion cycles is directly related to the slope of substrate layer, discharge and sediment/water ratio. (3) The fan delta evolves under the interaction between the deposition process and topography. Moreover, dynamic equilibrium of experiments including main channel-related erosions and autogenic slope adjustments can be found in natural fan deltas.

Sediment Coarsening in Tidal Flats and Stable Coastline of the Abandoned Southern Yellow River Sub-Delta in Response to Fluvial Sediment Flux Decrease During the Past Decades

Due to remarkable reduction of sediment supply, the vulnerability of Yellow River deltaic system increased and ecological impacts occurred to some extent. To have a comprehensive and quantitative understanding of the morphological evolution of deltas, surficial sediments of tidal flat along the abandoned southern Yellow River sub-delta and two adjacent coastal units were systematically collected and evaluated by grain-size analysis in the study. The results reveal that surficial sediments of the abandoned southern Yellow River sub-delta have been coarsening significantly since the 1980s, as characterized by a decrease in both the mud content and the clay/mud ratio. In particular, the transition from cohesive to non-cohesive sediment was completed between 2007 and 2013. With a sharp decrease in sediment flux from the Yellow River estuary, the flood currents from the submarine coastal slope carry few fine particles into the tidal zone, whereas the ebb currents with reverse direction remove some fine particles from the tidal flat. This is a major cause of sediment coarsening in the tidal flat. As sediment coarsening, the coastline of the abandoned southern Yellow River sub-delta has remained stable. The significant change in the grain size of the tidal flat surficial sediments may have a profound impact on the future coastal geomorphic evolution.

Evidence of the Early Holocene eruptive activity of Volcán de Colima and the 8.2 kyr global climatic event in lacustrine sediments from a debris avalanche-dammed lake

Abstract Volcán de Colima, one of the most active volcanoes in Mexico, experienced at least nine flank failures during the last 30 000 years, with catastrophic effects on the environment that implies the formation of temporary dams where lacustrine sediments accumulated for hundreds of years. These lacustrine sequences preserve an exceptional record from which to reconstruct the effect of subsequent volcanic eruptions and, eventually, contemporary environmental and climatic conditions. Here we analyse an Early Holocene lacustrine sequence, named ‘Gypsum King’, which accumulated in a short-lived temporary lake, likely formed by emplacement of the 10 755–11 230 cal years BP Mesa-Yerbabuena debris avalanche. Through detailed analysis of the 1.8 m thick lacustrine sequence ( 14 C ages, sulfur content, grain size), it was possible to identify the 8.2 kyr global climate event and better constrain the Early Holocene main sub-plinian to plinian eruptions of Volcán de Colima. The results presented here highlight the potential to explore sulfur content and abrupt change in grain size in lacustrine sediments as additional proxies to better constrain eruptive phases in volcanic environments. Finally, the Gypsum King sequence provides the first evidence of the 8.2 kyr global climate event along the Eastern tropical Pacific Coast.

Dropping the microbead: Source and sink related microplastic distribution in the Black Sea and Caspian Sea basins

Microplastic pollution is a growing, yet poorly understood problem. Here, we assessed the relationship between microplastic concentration and distance to rivers, shorelines, cities, sediment grain size or water depth in sediments of the world's largest (semi-)enclosed aquatic basins. Microplastic was extracted from sediment using density separation, elutriation and hydrophobic adhesion. Fibers and transparent or white microplastic particles were the most abundant shape and color. The microplastic concentration in sediments of the Black Sea was about twice as high compared to that in the Caspian Sea. Fragment concentrations decreased with depth, while fiber concentrations were independent of depth. Overall, no relationship with distance to shores, rivers and cities or with grain size was observed. However, within some depth classes concentrations were related to the distance from rivers, shores and cities.

Quantitative geochemistry as a provenance indicator for surface sediments in the north Jiangsu radial sand ridges (NJRSR) in the South Yellow Sea, East China

The North Jiangsu radial sand ridges (NJRSR) are typical sedimentary bodies distributed along the continental margin of China. Historically, the Yellow and Changjiang Rivers transported terrigenous sediments into the sea, depositing them in the study area. However, the provenance of the sediments in the NJRSR is not conclusively understood. In this study, the grain sizes and major elemental geochemistry of 33 surface sediment samples were investigated to discern the provenance of the sediments in the NJRSR. The results indicate that the sedimentary components are primarily silt (53.60%), sand (35.60%), and clay (10.80%). The grain size (Mz) of the NJRSR coastal surface sediments was 2.5–8.5 Φ, with an average of 5.1 Φ, and had high SiO2 and Al2O3 contents (on average, SiO2 and Al2O3 accounted for >68%). The statistical results of the geochemical analyses were reflected in the control on sediment elemental components by riverine transport in the study area, which were then used to divide the study area into three sedimentary provinces. Elemental ratios (Mg/Al, Fe/Al, K/Al) were used to discern the provenance of the NJRSR surface sediments, indicating that the inputs from the Yellow and Yangtze rivers are the dominant sediment sources in the study area. Using the inverse model, a quantitative estimation revealed that average sediment contributions of the Abandoned Yellow and Yangtze rivers were 67.4% and 32.6%, respectively. In addition, modern current systems play an important role in controlling sediment transport from the Abandoned Yellow and Yangtze rivers to the NJRSR. This study demonstrates the importance of geochemistry for quantitatively determining the provenance of the NJRSR, which is especially useful for quantitatively investigating Earth surface processes in global shelf-marginal seas.

Changes in the distribution of surface sediment in Pearl River Estuary, 1975–2017, largely due to human activity

In recent decades, the surface sediments in the Pearl River Estuary (PRE), China, have been intensely disturbed by human activities. Data from 1975 to 2017 show that the mean surface sediment grain size in PRE is distributed between 5 and 8 ϕ, while the sorting coefficient of the sediments vary between 0.39 and 4.53, and the skewness is between −0.31 and 0.55. From 1975 to 1994, sandy sediment was mainly distributed near the outlets. However, sandy sediments have been present in the south of the West Shoal and Middle Shoal, and north of Lantau Island, and have had a patchy distribution since the 2000s. From 1975 to 2017, the average total grain size of the surface sediments in PRE changed from 6.4 to 5.3 ϕ, indicating a coarsening trend. This was mainly caused by the sharp reduction in upstream sediment load since the 1980s, as well as channel dredging and sand mining in PRE. On the one hand, the decrease in the sediment load caused an increase in the erosion area, which caused a large amount of fine-grained sediment to be eroded and transported to the open sea. On the other hand, channel dredging and sand mining resulted in coarse-grained sediments in the paleo-sedimentary layer being stirred to the surface, thus making a significant contribution to the coarsening of the average grain size. Channel dredging and sand mining are also the main reasons for the patchy distribution of sediments in PRE. In the future, with further reductions in the sediment load and the persistence of reclamation, channel dredging, and sand mining, the grain size of surface sediments in PRE will continue to show a coarsening trend.

Theory of delayed response in river morphodynamics: Applicability and limitations

The delayed response of fluvial rivers to external disturbances has been described by many researchers. To simulate such behavior, the rate law model (or the delayed response model) was developed by previous researchers, and has been applied to a series of river morphological problems. However, to date, the applicability of the rate law model has not been fully understood. In the current paper, a physically-based analysis of the rate law model is presented to assess the responses of bed elevation and the grain size of surface sediment, using the response of the Shi-ting River, China, after the 2008 Wenchuan Earthquake as an example. First, a physically-based river morphodynamic model is implemented to reproduce the post-earthquake adjustments of the Shi-ting River. Next, the mathematical properties of the Hirano–Exner equation, which describes the dynamics of both bed elevation and surface texture, are analyzed. It is shown that the dynamics of bed elevation are dominated by a diffusion process and the analytical solution for bed elevation has a similar mathematical formulation to that of the rate law model. Thus, the rate law and morphodynamic models similarly predict the adjustment of bed elevations. In contrast, the dynamics of bed surface texture are controlled by both advection and diffusion processes. The advection and diffusion processes dominate adjustments over the short (annual to decadal scale) and long (century to millenial scale) terms, respectively. These physics produce the multi-scale and non-monotonic character of the adjustment of bed surface texture. As a result, the rate law model is incapable of describing the adjustment of bed surface texture. These findings highlight the applicability and limitations of the rate law model in simulating river morphodynamic processes.

Sediment Transport and Water Flow Resistance in Alluvial River Channels: Modified Model of Transport of Non-Uniform Grain-Size Sediments

The paper presents recommendations for using the results obtained in sediment transport simulation and modeling of channel deformations in rivers. This work relates to the issues of empirical modeling of the water flow characteristics in natural riverbeds with a movable bottom (alluvial channels) which are extremely complex. The study shows that in the simulation of sediment transport and calculation of channel deformations in the rivers, it is expedient to use the calculation dependences of Chézy’s coefficient for assessing the roughness of the bottom sediment mixture, or the dependences of the form based on the field investigation data. Three models are most commonly used and based on the original formulas of Meyer-Peter and Müller (1948), Einstein (1950) and van Rijn (1984). This work deals with assessing the hydraulic resistance of the channel and improving the river sediment transport model in a simulation of riverbed transformation on the basis of previous research to verify it based on 296 field measurements on the Central-East European lowland rivers. The performed test calculations show that the modified van Rijn formula gives the best results from all the considered variants.

Spatial distribution patterns of sandfish juveniles released in a sea ranch area in Maliwaliw Island, Philippines

Biophysical characteristics that affect the distribution of sandfish in the sea ranch were investigated to determine indicators for a suitable habitat for sandfish sea ranching. These include sediment grain size, organic matter (OM), chlorophyll a, pheophytin, penetrability, depth and seagrass cover. A total of 5864 hatchery-produced sandfish juveniles were released in seven batches in a 5-ha ranching site in Maliwaliw Island over a period of three years. The 5-ha ranch was divided into three zones, with Zone A (50 × 50 m) being the juvenile release site. Survey of the released sandfish was done quarterly from February 2016 until May 2017 and sediment collection done twice. A total of 750 sandfish weighing 10–600 g were recorded; 23% were <150 g, 59% were 151–350 g, 17% were 351–550 g, and 2% were >550 g. Distribution of substrate parameters between the different sea ranch zones showed no significant differences (p > 0.05). Visualized sediment grain-size data showed multiple cohorts of sandfish with varying sizes in different zones with predominantly medium and fine grains with relatively higher total OM and labile OM. Sandfish >351 g were found in deeper waters (>70 cm at low tide) with lower concentrations of labile OM and chlorophyll a, and higher pheophytin. Sandfish <350 g were found in areas with higher labile OM, higher chlorophyll a and lower pheophytin. Results of this study indicate the need for a sandfish sea ranch site with water depth >30 cm at low tide, and varying sediment particle size and composition to support the different stages of growth and development of sandfish.

Organic Matter Compositions and Loadings in River Sediments From Humid Tropical Volcanic Luzon Island of the Philippines

AbstractTropical rivers deliver ∼60% of particulate organic carbon to the world ocean. However, compositions and loadings of sedimentary organic matter (OM) from tropical small mountainous rivers are largely unknown. Here, we provide an initial constrain on sources of sedimentary OM from 28 fluvial systems across Luzon in the Philippines by measuring total organic carbon (TOC), total nitrogen (TN), stable carbon isotope (δ13C) and radiocarbon activity of TOC (expressed as fraction modern—Fm), as well as grain size and mineral surface area (SA) of sediments. Results indicate that sediments in Luzon rivers contain both contemporary and 14C‐depleted OM (Fm: 0.71–1.06, mean 0.97 ± 0.07) with a wide range of δ13C values (−28.3‰ to −17.7‰, −24.9 ± 2.2‰). This is attributed to the OM sources originated from modern surface soil and 14C‐depleted subsoil and deep soil vegetated by C3 and C4 plants, with mean fraction of C3 plant at 80% ± 11%. Minor input from bedrock may also contribute to the 14C‐depleted OM in sediments, accounting for 6% ± 6%. Sediments in most rivers are featured by low OC loadings (OC/SA ratio &lt; 0.4 mg C m−2), owing either to a less OM input or intensive OM degradation. The estimated yields of particulate OC from Luzon vary between 3.2 and 3.7 t km−2 yr−1, which is higher than most tropical large rivers.

Mapping of Sediment on the Waters Around Panjang Island, Banten Bay, Indonesia

This study was conducted to map the surface sediment conditions in the waters around Panjang Island, Banten Bay. The survey method was conducted in February 2015 by taking sediment samples using a grab sampler at 15 stations. Sediment analysis was conducted to determine the grain size using the granulometry method which was then processed using the KUMMOD-SEL software to obtain the composition and texture of the sediment. The results of processing sediment samples at each station obtained that the grain size of sediments in the waters around Panjang Island ranged from -0.7 to 2.6 in the phi (φ) scale. Sediment composition consists of sand and gravel, with sand dominance of 89.1 %. Sediment textural classification consists of only 4 categories i.e. very coarse sand, coarse sand, medium sand, and fine sand. In general, the pattern of sediment distribution follows the pattern of water depth, where fine sand occupies deeper areas. Meanwhile, medium sand dominates surface sediment distribution in the study area.

Evaluation of the Tidal-flat Ecosystem Restoration Effect on the Construction of Hwangdo Bridge in Taean

In 2011, a bridge was installed in Hwangdo, located in Taean-gun, Chungcheongnam-do, where seawater circulation was blocked for 30 years due to an inland dike. In this study, changes in the ecosystem of tidal-flats around the bridge were analyzed after the opening of the bridge(2011). To analyze the restoration effect, a survey of the marine environment around Hwangdo bridge was conducted and compared with the historical data before the restoration of Hwangdo bridge. After the construction of the bridge, the ecosystem of benthic community was changing due to the improvement of the tidal-flat environment around the bridge. The effect is manifested as a change of surface sediment grain-size in mudflat. The ratio of sand in the southern tidal-flats of Hwangdo bridge, which accounted for about 10 percent of the sand, has continued to increase since the sea-water circulation by the bridge. Due to the improvement of the tidal-flat environment, the number of species, habitat density, and biomass of the macrobenthos on the tidal-flat in Hwangdo is gradually increasing. The production of Manila clam(Ruditapes philippinarum) in the Hwangdo tidal-flat is also showing a steady increase. As the mudflat deposition environment, which had deteriorated due to the cutoff of sea-water circulation, has improved, more and more tourists are experiencing fishing activities such as manila clam digging. This shows that the effect of mudflat restoration due to seawater circulation continues. It is expected that the Hwangdo tidal-flat restoration project will be used as a success story in promoting similar tidal-flats restoration projects as sea-water circulation in the future. Keywords: Hwangdo tidal-flat restoration, Sea-water circulation, Benthic community, Effect analysis, Hwangdo Bridge

An environmental magnetic record of heavy metal pollution in Vembanad lagoon, southwest coast of India

Magnetic signature of the iron-bearing minerals archived in sediments is sensitive to change in environment and therefore, studied to reconstruct the signals linked with environmental processes. In the present work, we have analyzed 11 sediment cores from Vembanad lagoon, southwest coast of India, to estimate the magnetic fluctuations associated with environmental processes. Down-core variation in magnetic susceptibility and anhysteretic, isothermal and saturation isothermal remnant magnetization and S and H-ratios have been interpreted to map the degree and spatial distribution of anthropogenic pollution in and around the lagoon. Downcore variation of magnetic susceptibility of Vembanad lagoon sediments varies from 10 to 100 × 10−8 m3/ kg. The top layers of sediment samples from river mouth regions (Periyar and Muvattupuzha rivers) show higher susceptibility values and incidentally these samples are of coarse sized. The subtle variations in SIRM/χlf ratios suggest that there are magnetic grain size differences in the samples. The SIRM and χlf relation suggests that dominant magnetic grain size in sediments. The low ARM/χlf ratios suggest a relatively higher ferrimagnetic contribution and coarser magnetite grain size. Rock magnetism data reveal that the coarse magnetic grain size is affecting the pollution of Vembanad lagoon. We also analyzed downcore variability of metal concentrations such as Fe, Mn, Cu, Zn, Ni and Cr, and all these metals exhibit higher concentrations in the top layers of the cores. Our study suggests that higher values of magnetic parameters and metal concentrations are due to various anthropogenic sources.

Riverbed dune morphology of the Lowermost Mississippi River – Implications of leeside slope, flow resistance and bedload transport in a large alluvial river

Dunes are critical for understanding riverine sediment transport, deposition, flow resistance and channel flow processes. Although previous studies have examined the riverbed micromorphology of the Lower Mississippi River in the USA, our knowledge of detailed quantification of dune morphology in this and other large alluvial rivers is still limited. It is also not well understood how dunes in a straight channel reach and a meander bend differ in their characteristics, as well as how dune morphology may have been affected by human activities (i.e., river engineering). In this study, we utilized multi-beam bathymetric measurements over four 1.6–8.0 km long reaches in the Lowermost Mississippi River (LmMR) to analyze riverbed micromorphologic features. Three of the four reaches were located in the upper part of the LmMR between river kilometers (RK) 474–477, 483.6–485.2 and 491.7–493.3, and the other reach was located in the lower part, between RK 120 and RK 128. We analyzed a total of 3258 dunes in these river reaches and found that large dunes were dominant in the LmMR. These dunes were characterized by low mean leeside slope angle (10.8°), indicating that flow resistance caused by dunes should be relatively small. When compared with dunes in the straight reaches, dunes in the meander bends were much larger (1.06 m vs. 0.81 m) and had a higher bed roughness (0.91 vs. 0.68), which may be related to the varied flow velocity. Dune size increased with increasing water depth across the river channel of a straight reach, while it decreased with increasing water depth across the river channel of a meander bend. When compared with the dunes in the lower-river reach, the dunes in the upper-river reach were significantly higher in height and shorter in wavelength, and showed much higher bed roughness (1 vs. 0.68), which may be closely related to the greater riverbed slope and grain size of bed sediment occurred in the upper-river reach, as well as a combined effect of the Old River Control Structure (RK 500) and backwater. These findings indicate the strong impact of turbulent flow, slope and sand source on dune formation and riverbed deposition.

Inversion of the physical properties of seafloor surface sediments based on AUV sub-bottom profile data in the northern slope of the South China Sea

Based on the seafloor reflection coefficient obtained from autonomous underwater vehicle (AUV) sub-bottom profile survey data of the northern slope of the South China Sea, combined with the sample test data of seafloor surface sediments, we use the Biot–Stoll model to establish the equations relating the seafloor reflection coefficient to the porosity, density, and mean grain size of the sediments at the dominant frequency of 5 kHz (the dominant frequency of the AUV sub-bottom profiler). The physical property parameters such as the porosity, density, and mean grain size of seafloor surface sediments are further inverted. Comparison of inversion results with measured results shows that the overall deviation ratios of the inverted mean grain size, porosity, and density of the surface sediments are in the ranges of − 13.56 to 14.44%, − 6.15 to 8.06%, and − 10.85 to 0.46%, respectively. Among them, the mean grain size directly reflects the size of seafloor sediment particles, and the particles are finer in deeper water. Overall, the inversion results are basically consistent with the measured values and thus can well reflect the variation characteristics of the physical properties of seafloor surface sediments.

Magnetic properties of cave sediments at Gran Dolina site in Sierra de Atapuerca (Burgos, Spain)

We report new rock magnetic results from a cave in the “Sierra de Atapuerca” (Burgos, North of Spain), that is one of the most important archaeological and palaeontological sites of Lower to Middle Pleistocene in Europe. Our samples are taken in cave sediments of Gran Dolina Cave. Rock magnetic analyses allowed us to determine changes in grain size, composition, and concentration in both cave-entrance and cave-interior sediments. Generally, the cave-entrance sediments are characterized by a high concentration of magnetic minerals while the cave-interior presents a more variable concentration. Because rock magnetic properties, in particular the iron oxides, are affected by environmental factors (such as the intensity of physical and chemical weathering) they offer an important reconstruction proxy for better understanding the paleoenvironmental conditions at the time the earliest hominins began to migrate into Europe. The main goal of this study is to identify magnetic proxies that help to better reconstruct the environmental conditions of this archaeological and palaeontological site.