Surface Sediment Distribution Research Articles

Dinoflagellate cyst distribution in surface sediments from the South China Sea in relation to hydrographic conditions and primary productivity

The geographical distribution of dinoflagellate cysts was investigated in palynologically treated surface sediments from the South China Sea (SCS) to understand the driving environmental factors associated with specific taxa. The western SCS generally has higher total cyst concentrations (>300 cysts g−1) than the eastern region (<200 cysts g−1). The highest concentrations (>1000 cysts g−1) occur off southern Vietnam, whereas the lowest cyst concentrations are off Luzon. The ratio of heterotrophic to autotrophic taxa has inverse distributional patterns to total cyst concentrations, and is likely to be related to an increase in relative abundances of autotrophic taxa when nutrient inputs increase. Brigantedinium spp., Selenopemphix nephroides, and Stelladinium reidii have their highest relative abundances and concentrations off Borneo. Their concentrations are significantly positively correlated with January sea-surface temperature (SST-Jan). In contrast, concentrations of Selenopemphix undulata, Spiniferites hyperacanthus, Dapsilidinium pastielsii and Operculodinium?longispinigerum are negatively correlated with SST-Jan. Lejeunecysta sabrina, cysts of Protoperidinium spp., Votadinium spp., Quinquecuspis concreta and Selenopemphix quanta are positively correlated with chlorophyll-a (chl-a) concentrations and are found in the high primary productivity regions of the SCS. Total Impagidinium, Impagidinium aculeatum, Impagidinium paradoxum, Impagidinium patulum, Nematosphaeropsis labyrinthus, and Polysphaeridium zoharyi are positively correlated with water depth. Their highest abundances are recorded in the northern slope-deep basin that is influenced by the Kuroshio Current, and this cyst assemblage indicates an open-ocean environment.

Distribution of Diatoms and Dinocysts in Surface Sediments from the East Siberian and Chukchi Seas

Surface sediment samples from the East Siberian and Chukchi seas have been analyzed for the quantitative distribution, taxonomic composition, and ecological structure of diatom and dinoflagellate cyst assemblages. According to the results, the diatom and dinocyst distribution in surface sediments indicates the distribution of different water masses in the region.

Reconstructing spring sea ice concentration in the Chukchi Sea over recent centuries: insights into the application of the PIP25 index

In this study, we aimed to reconstruct spring (April–June) sea ice changes in the western Arctic Ocean over recent centuries (ca. the last 250 years) by measuring biomarker distributions in a multicore (ARA01B-03MUC) retrieved from the Chukchi Shelf region and to evaluate outcomes against known or modelled estimates of sea ice conditions. Specifically, we analyzed for the Arctic sea ice proxy IP25 and assessed the suitability of a further highly branched isoprenoid (HBI) lipid (HBI III), epi-brassicasterol, and dinosterol as complementary biomarkers for use with the so-called phytoplankton marker-IP25 index (PIP25; PIIIIP25, PBIP25, and PDIP25, respectively). The presence of IP25 throughout core ARA01B-03MUC confirms the occurrence of seasonal sea ice at the study site over recent centuries. From a semi-quantitative perspective, all three PIP25 indices gave different trends, with some dependence on the balance factor c, a term used in the calculation of the PIP25 index. PIIIIP25-derived spring sea ice concentration (SpSIC) estimates using a c value of 0.63, determined previously from analysis of Barents Sea surface sediments, were likely most reliable, since SpSIC values were high throughout the record (SpSIC > 78%), consistent with the modern context for the Chukchi Sea and the mean SpSIC record of the 41 CMIP5 climate models over recent centuries. PBIP25-based SpSIC estimates were also high (SpSIC 108%−127%), albeit somewhat over-estimated, when using a c value of 0.023 obtained from a pan-Arctic distribution of surface sediments. In contrast, PDIP25 values using a pan-Arctic c value of 0.11, and PIP25 data based on the mean biomarker concentrations from ARA01B-03MUC, largely underestimated sea ice conditions (SpSIC as low as 13%), and exhibited poor agreement with instrumental records or model outputs. On the other hand, PBIP25 values using a c factor based on mean IP25 and epi-brassicasterol concentrations exhibited a decline towards the core top, which resembled recent decreasing changes in summer sea ice conditions for the Chukchi Sea; however, further work is needed to test the broader spatial generality of this observation.

Microplastics: Sources and distribution in surface waters and sediments of Todos Santos Bay, Mexico

Microplastics (MPs) are ubiquitous and a threat to marine and freshwater environments. Effluent waters from secondary wastewater treatment plants (WWTPs) into Todos Santos Bay (TSB) were investigated as sources of MPs. MPs were detected in all analyzed matrices and presented variable morphologies. MPs from surface water samples (n = 18) varied from 0.01 to 0.70 plastic particles/m3 (pp/m3). Fragments (47 ± 23%) and fibers (47 ± 23%) were the most abundant particles found in the surface water samples. In sediment samples (n = 11), MPs varied from 85 to 2494 pp/0.1 m2. Sediment samples showed fragments of 70 ± 19%, fibers 28 ± 18% in mean. The range of MP values from WWTP effluents (n = 24) was 81 to 1556 pp/m3, and fibers (65 ± 28%) were the most abundant MP particles. Several synthetic polymers (polypropylene, polyethylene, polyethylene-propylene, polyvinyl chloride, cellophane), and natural fibers (cotton and wood) were identified. The surface currents and the parameters that modulate them, are the main factors that dominate the distribution of MPs in surface waters. While in the sediments the parameters such as bathymetry and grain size distribution have more influence on their distribution in the marine environment, where the effluent waters from WWTPs only contributes MPs to the TSB.

Large-scale pollen distribution in marine surface sediments from the Bohai Sea, China: Insights into pollen provenance, transport, deposition, and coastal-shelf paleoenvironment

To elucidate the mechanisms responsible for pollen and spore transportation and deposition in the Bohai Sea, fully covered seafloor-surface sediment samples were collected for palynological and grain size analysis. The results reveal that the pollen and spore concentrations were higher in the head of Liaodong Bay and in the muddy area of the Bohai Sea. The Yellow River was the main source of pollen and spores in the Bohai Sea. The sediments with relatively high pollen concentrations consisted mainly of clay and fine silt, whereas sediment with lower pollen concentrations was mostly fine sand. In addition, the percentages of Pinus pollen and pteridophyte spores increased with increasing sea water depth, while other arboreal (excluding Pinus) and herbaceous pollen generally decreased with increasing distance from the shore. The relationship between the pollen taxa and the water depth of the sampling points shows that the fluvial water plays a predominant role in pollen transmission within 20 m of water depth, while the wind is the main driving force for pollen transmission when the water depth exceeds 20 m. Although Pinus pollen and pteridophyte spores were over-represented, there was good correlation between marine pollen signals and terrestrial vegetation. Apart from the influence of rivers and wind on pollen and spore deposition, the tidal currents and circulation were also main force responsible for transporting sediment and determining the differentiation of pollen and spores in the Bohai Sea. The comparison of pollen and spore percentages between surface sediment and fossil records from sedimentary cores made it possible to identify changes in pollen sources and transport mechanisms. Meanwhile, the percentage fluctuations of fossil Pinus and herbaceous pollen revealed concomitant changes of the sea level and climate. These findings are of paramount importance to the interpretation of Quaternary marine pollen data from the Bohai Sea, China.

Ruditapes philippinarum Habitat Mapping Potential Using SVM and Naïve Bayes

Oh, H.-J.; Syifa, M.; Lee, C.-W., and Lee, S., 2019. Ruditapes philippinarum habitat mapping potential using SVM and Naïve Bayes. In: Jung, H.-S.; Lee, S.; Ryu, J.-H., and Cui, T. (eds.), Advances in Remote Sensing and Geoscience Information Systems of Coastal Environments. Journal of Coastal Research, Special Issue No. 90, pp. 41-48. Coconut Creek (Florida), ISSN 0749-0208.The aim of this study was to compare the performance of Support Vector Machine (SVM) and Naïve Bayes (NB) models for potential R. philippinarum habitat mapping in the Geunso Bay, Korea. R. philippinarum samples were collected during field observation. Remote sensing data were used to identify the factors controlling the distribution of R. philippinarum. Habitat potential maps were constructed and eight controlling factors were generated from satellite imagery, namely elevation of intertidal zone, aspect, exposure time, slope, density of tidal channel, distance from tidal channel, surface-sediment distribution, and near-infrared reflectance (NIR). Validation of the maps was conducted by comparison with surveyed habitat locations. Performance of the SVM model (AUC=0.777) is better compared with NB model (0.733). The GIS-based SVM and NB models combined with remote sensing techniques are efficient tools for mapping potential R. philippinarum habitat in tidal flats.

Development of a Marine Environmental Information System (MEIS) using data on Land–Sea Interactions in the Nakdong River Estuary, South Korea

Lee, J.-H., Choi, J.U., Jung, H.-S., Kwon, J.-I., and Woo, H.J., 2019. Development of a Marine Environmental Information System (MEIS) using data on Land–Sea interactions in the Nakdong River Estuary, South Korea. In: Lee, J.L.; Yoon, J.-S.; Cho, W.C.; Muin, M., and Lee, J. (eds.), The 3rd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 91, pp. 191-195. Coconut Creek (Florida), ISSN 0749-0208.The Nakdong River in South Korea is about 510 km long and is subject to natural erosion and sedimentation and various potential sources of human pollution, such as urban dumping and input from industrial complexes and many cities. This study developed a marine environmental information system (MEIS) to understand the land–sea interactions and provide data on the characteristics of the brackish water zone around the barrier islands. The MEIS was run in real time (1-s intervals) and made periodic marine observations (one to four times a year). The real-time data were largely obtained from a closed-circuit television and automatic weather stations using long-term evolution communication at two stations in March 2016. Since May 2015, the data have included periodic observations of surface sediment distributions (n = 90), the characteristics of suspended sediments in inlets and channel (n = 4), the brackish water zone environment during spring tide ebb and flood (n = 14, three lines), the seasonal variation in sedimentation along tidal flats (n = 29, three lines), and landscape classifications of the sub-environment (n = 30) in the barrier islands. The collected information includes real-time and a huge heterogeneous dataset characterized by multi-dimensional, multivariate, and spatiotemporal distribution variability. The system enables data management, and open access is necessary. The MEIS will enable effective estuary management and contribute to reducing the damage caused by natural disasters. Real-time prediction information has been integrated with environmental sensitivity index maps, which are provided using a geographic information system to enable a response strategy.

Microplastics in Tampa Bay, Florida: Abundance and variability in estuarine waters and sediments.

This study provides the first measurement of microplastic abundance and distribution in surface waters and sediments in Tampa Bay, FL. Microplastic concentrations in discrete water samples ranged from 0.25 to 7.0 particles/L with an average of 0.94 (±0.52) particles/L. Samples taken with a 330 μm plankton net had 1.2-18.1 particles/m3 with an average of 4.5 (±2.3) particles/m3. Discrete samples were 200 times higher than net samples, suggesting substantial losses or undersampling with the net. For both discrete and plankton tow samples, there were no significant differences in concentrations between stations or regions. Intense rainfall events in the summer always preceded samples with substantially higher counts. Most (>75%) microplastics were fibers. Using an average value of 1 particle/L, Tampa Bay contains ~4 billion microplastic particles. Surface sediments had an average of 280 (±290) particles/kg, ranging from 30 to 790 particles/kg. Highest concentrations of microplastics were found in sediments close to industrial sources; lowest values in Middle and Lower Tampa Bay are consistent with shorter residence times.

Geochemical characteristics of microelement distribution in surface sediments of Ust-Ilimsk Reservoir

This research examines the characteristics of spatial distribution of As, Pb, Hg, Cd, Zn, Ni, Co, Cu, Cr in bottom sediments of Ust-Ilimsk reservoir. Two zones of the reservoir with elevated accumulation levels of potentially toxic elements have been determined: Vihorevsky bay (inflow from anthropogenic sources) and the reservoir area near the dam (inflow from natural and anthropogenic sources). Mobility of studied trace elements and the probability of the secondary contamination has been assessed based on the determined speciation of trace elements in bottom sediments.

Lipid biomarkers in paleoreconstruction of lake sedimentogenesis

Lakes are important paleoenvironmental archives retaining abundant information due to their typical high sedimentation rates and susceptibility to environmental changes. Lipid biomarkers distributions in surface sediments were determined using gas chromatography (GC) and GC-mass-spectrometry in order to investigate the lipid biomarkers signature in sediments of four lakes of the Baikal region. They are linked to autochthonous and/or allochthonous sources, which can lead to distinct lipid molecular distributions. Lipid biomarkers of terrestrial origin (i.e. high-molecular weight n-alkanoic acids, n-alkanols, dicarboxylic acids, β-sitosterol) and aquatic source (i.e. short chain fatty acids, hydroxy fatty acids, etc.) were detected in all lakes in different ratios. The results of this study show the compatibility of different lipid biomarkers in assessing the origin of organic matter. Therefore, lipid molecular proxies in combination with molecular distribution of n-alkanes, dD or D/H ratios, palynological studies, etc. can be applied as paleoclimate and paleoenvironment proxies.

A novel biomarker-based proxy for the spring phytoplankton bloom in Arctic and sub-arctic settings – HBI T25

The spring phytoplankton bloom is a characteristic feature of mid-high latitudes in modern times, but can be challenging to identify in palaeo records. In the current study, we investigated the absolute and relative distributions of two diatom-derived tri-unsaturated highly branched isoprenoid (HBI) lipids, at least one of which has previously been suggested to be a possible proxy for the productive region of the marginal ice zone (MIZ) in the Polar Regions. Based on a comparison of their distributions in surface sediments from the Barents Sea and neighbouring regions with a range of oceanographic parameters, we identify, via principal component analysis, a strong association between the relative proportion of the two HBIs and satellite-derived spring chlorophyll a (chl a) concentration. Further, based on agglomerative hierarchical clustering, we identify two clusters of HBI biomarker ratios and spring chl a together with a potential threshold biomarker ratio (termed HBI TR25) for the spring phytoplankton bloom. A modified version of HBI TR25 (i.e. HBI T25) provides a potentially more straightforward binary measure of the spring phytoplankton bloom. Analysis of HBI TR25 and HBI T25 values in a series of short (spanning recent centuries) and long (Holocene) sediment cores from the region provides an initial evaluation of the applicability of this novel proxy in the palaeo record. Outcomes are mainly consistent with the findings from the surface sediments and with other proxy-based reconstructions, including estimates of past sea ice cover, which is well-known to influence primary production in the region. Indeed, we suggest that the new HBI T25 phytoplankton bloom proxy may also represent an important new tool for characterising the MIZ in palaeo records, especially when used alongside well-established sea ice proxies, such as IP25 and PIP25. Despite the largely empirical nature of the study, we also provide a possible explanation for the observed biomarker ratio-chl a relationship. Thus, a previous laboratory investigation showed that the distributions of the same two HBIs analysed herein in their likely source (viz. Rhizosolenia setigera) was strongly influenced by culture temperature and growth rate. Confirmation of the generality of our findings and of the causal relationship between HBI T25 and the spring phytoplankton bloom will, however, require further laboratory- and field-based studies in the future.

Distribution and dispersal of surface sediments on the continental margins of India

Abstract The vast area, varying climate regimes, diverse source terrain lithology of the mainland India generate complex weathering and erosional patterns and leads to diverse sediment distribution and dispersal on the surrounding continental margins of India. Thus, to delineate the sources, distribution and sediment dispersal pathways around India, 254 sediment cores from the eastern and western continental margins of India were investigated for physical properties using non-destructive, whole core logging technique combined with grain-size analyses. The distribution of magnetic susceptibility, gamma ray density and grain-size traces the sources in the Indian landmass which contribute sediments to the margins and demarcates their extent of influence. The results from the magnetic susceptibility distribution indicate that the dominant influx of modern high susceptibility sediment into the margins of India originates from the weathering of Deccan Basalts and its subsequent transportation by Narmada and Tapti Rivers in the west coast and Krishna and Godavari Rivers in the east coast. Though the Himalayan sources are the second largest supplier of magnetic minerals to the shelf, their contribution, when compared to the Deccan sediments is not significant. The lack of present-day sedimentation in the outer shelf regions of margins of India is evident from the gamma ray density distribution and is confirmed by the discrete sample grain-size analysis. Gamma ray density variations in the margins follow the same pattern as the grain size variations and demarcate the boundary between inner shelf modern clayey sediments and the outer shelf relict carbonate sands. Regional distribution maps of physical properties and grain-size for both the margins of India are presented and geographical limits of each provenance are defined, thus providing a comprehensive picture of sediment distribution and dispersal patterns in the area and highlights the use of magnetic susceptibility as a powerful tool in deciphering the source to sink pathways of sediments.

Surface sediment composition and distribution of hydrothermal derived elements at the Duanqiao-1 hydrothermal field, Southwest Indian Ridge

The study of the hydrothermal component in oceanic sediments provides key data for locating active and inactive hydrothermal systems. In this work, we report the geochemistry of surface sediments collected in the newly discovered basaltic-hosted Duanqiao-1 hydrothermal field (DHF) on the Southwest Indian Ridge (SWIR). The sediments are mainly composed of a pelagic fraction (carbonate ooze) with minor clay contents, basaltic debris, FeMn oxyhydroxides, and hydrothermal components. Hydrothermal elements in the DHF exhibit a precipitation sequence of Cu ≈ Co > Zn ≈ Pb > Fe > Mn ≈ Ni ≈ As. Proximal sediments to the hydrothermal discharge area are characterized by high Cu, Pb, Zn, and Co concentrations and higher Cu/Fe and Zn/Fe ratios, decreasing abruptly within the first kilometer. After this proximal area, an evident increase of Mn concentrations and Mn/Fe ratios was observed, denoting higher oxidizing conditions of the hydrothermal plume. Hydrothermal derived Pb and Co precipitated together with the sulfide phases, whereas at the distal sediments Pb, Co, Ni, and As seem to be scavenged from seawater by oxyhydroxides. This was corroborated by increased REE/Fe ratios with distance to the discharge zone. The geochemistry of DHF sediments is consistent with an effective separation of metals during gradual cooling, and concomitant Eh and pH modifications, of the hydrothermal plume when in contact with seawater. This promotes the precipitation of Cu sulfides first, closest to the discharge area, followed by CuZn and Fe sulfides and FeMn oxyhydroxides, in more distal areas. A comparison of the DHF sediments with those from Dragon Horn, another hydrothermal site at the SWIR, suggests that the hydrothermal fluids responsible for mineral precipitation at DHF are less reduced, favoring the formation of sulfides and oxyhydroxides at shorter distances from the discharge zone. These findings are particularly valuable to the understanding of the variation in hydrothermal anomalies detected in sediments from proximal and distal areas of discharge zones, contributing to the development of tools for the discovery of hydrothermal fields.

Microplastic distribution in surface sediments along the Spanish Mediterranean continental shelf

Microplastics (MPs) are widely recognised as a contaminant of emerging concern in the marine environment. This work provides original data of the presence of MPs in coastal sediments along the Spanish Mediterranean continental shelf. Ten surface sediment samples were collected in order to document baseline microplastic distribution from Algeciras to Barcelona. Microplastics were extracted from bulk sediments by density separation. The number of microplastics per kilogramme of dry weight ranged from 45.9 ± 23.9 MPs/kg d.w. observed at Palma de Mallorca to 280.3 ± 164.9 MPs/kg d.w. noted at Málaga, with an average value of 113.2 ± 88.9 MPs/kg d.w. The lower limit is defined by the pore filter size used (1.2μm). For all analysed locations, the dominant microplastic type was fibres (82.9%), followed by fragments, and the main colours were transparent and blue. Microplastic size distribution was presented; in the case of fragments, 85% was lower than 0.5mm, and in the case of fibres, the three studied intervals (0.5-1, 1-2, 2-5mm) had similar distribution (35, 34 and 31%, respectively). Attending to all available data, no statistically significant relationship (Spearman's correlation) was found between microplastic average size and distance to the coast, the depth, density population and sediment grain size. Neither relationship was observed between these variables and microplastic concentration using the non-parametric Kruskal-Wallis H test. This study has confirmed the widespread distribution of MPs in surface sediments from the Spanish Mediterranean continental shelf, and these data are useful to define baselines for MPs in the Western Mediterranean region.

Generation of a Large-Scale Surface Sediment Classification Map Using Unmanned Aerial Vehicle (UAV) Data: A Case Study at the Hwang-do Tidal Flat, Korea

Tidal flats are associated with complicated depositional and ecological environments, and have changed considerably as a result of the erosion and sedimentation caused by tidal energy; consequently, the surface sediment distribution in tidal flats must be constantly monitored and mapped. Although several studies have been conducted with the aim of classifying intertidal surface sediments using various remote sensing methods combined with field survey, most of these studies were unable to consider various sediment types, due to the low spatial resolution of remotely sensed data. Therefore, previous studies were unable to efficiently describe precise surface sediment distribution maps. In the present study, unmanned aerial vehicle (UAV) red, green, blue (RGB) orthoimagery was used in combination with a field survey (232 samples) to produce a large-scale classification map for surface sediment distribution, in accordance with sedimentology standards, using an object-based method. The object-based method is an effective technique that can classify surface sediment distribution by analyzing its correlations with spectral reflectance, grain size, and tidal channels. Therefore, we distinguished six sediment types based on their spectral reflectance and sediment properties, such as grain composition and statistical parameters. The accuracy assessment of the surface sediment classification based on these six types indicated an overall accuracy of 72.8%, with a kappa coefficient of 0.62 and 5-m error range related to the Global Positioning System (GPS) device. We found that 11 samples were misclassified due to the effects of sun glint and cloud caused by the UAV system and shellfish beds, while 14 misclassified samples were influenced by surface water related to the elevation, tidal channels, and sediment properties. These results indicate that large-scale classification of surface sediment with high accuracy is possible using UAV RGB orthoimagery.

Characterization of phosphorus forms in a Eutrophic Lake, China

In this study, molecular compositions of cyanobacteria, suspended matter, and surface sediments in the Dianchi Lake, a highly eutrophic lake, were investigated by solution and solid-state 31P nuclear magnetic resonance (NMR) spectroscopy. A solution-state 31P NMR spectral analysis of NaOH-EDTA-extracted samples revealed the presence of orthophosphate (ortho-P, 48.5%–91.2% of the total extracted phosphate), orthophosphate monoester (mono-P, 7.3%–43.9%), orthophosphate diester (diester-P, 0.9%–3.9%), and pyrophosphate (pyro-P, 0.7%–5.5%). The organic phosphorus (Po) distribution in suspended matters and cyanobacteria was relatively similar but different from surface sediments. The inorganic phosphorus (Pi) distribution in suspended matters and surface sediments was slightly similar. Results of the solid-state 31P NMR spectral analysis of non-extractable residue showed that cyanobacteria and suspended matter contain a large proportion of Po and poly-P. For surface sediment, only metal-bonded pyro-P and a high proportion of ortho-P were detected. The solid-state 31P NMR spectra results of extracted residual indicated that several of the pyro-P bound to metals and other Pi or Po compounds associated with mineral phases in suspended matter and surface sediment are non-extractable. This result revealed that a high proportion of biogenic phosphorus is bioavailable. These results verify the process of biogenic poly-P regeneration in the Dianchi Lake given that Po, poly-P, and pyro-P are predominant in cyanobacteria and can be released into lake water through chemical and biological degradation, thus further worsening eutrophication.

Black Carbon Content and Distribution in Surface Sediments From Temperate-zone Reservoirs (Poland)

Black Carbon Content and Distribution in Surface Sediments From Temperate-zone Reservoirs (Poland)

The impact of biotic and abiotic factors on the distribution of surface sediment dinoflagellate cyst assemblages on the Nanji Island in the East China Sea

The dinoflagellate cyst assemblages on the Nanji Island in the East China Sea, are documented at the first time to construct a quantitative overview of the cyst bank from 2014 to 2015. Thirty-four morphotypes from six groups are identified and quantified at eight sampling sites around the island, including a high proportion of potentially toxigenic species (14%). Autotrophic dinocysts constitute 74% of the total cyst counts, which is relatively low (two to thirty-three per millilitre sediment) compared with previous studies in adjacent areas. Scrippsiella trochoidea and Protoperidinium avellana are the most abundant autotrophic and heterotrophic species, respectively. A multivariate analysis is performed to assess associations between dinocysts and abiotic or biotic variables. Differentiation among seasons is evident in the detrended correspondence analysis (DCA) ordination plot, while a spatial pattern is not clearly revealed despite heterogeneity of the hydrodynamic conditions between sampling sites. Soluble reactive phosphate, the ratio of nitrogen to phosphorus concentrations and Karenia mikimotoi bloom are the three factors significantly (P<0.05) related to surface sediment cyst assemblage defined by the canonical correspondence analysis (CCA), highlighting the importance of nutrient regime to a dinocyst distribution in this area. Although attempts to address the origin of HAB events in recent years using seed banks have failed, knowledge can be valuable for further investigation of dinocyst dynamics and potential toxin threats on the Nanji Island.

Grain-size distribution of surface sediments of climbing and falling dunes in the Zedang valley of the Yarlung Zangbo River, southern Tibetan plateau

Climbing and falling dunes are widespread in the wide valleys of the middle reaches of the Yarlung Zangbo River. Along a sampling transect running from northeast to southwest through 10 climbing dunes and two falling dunes in the Langsailing area, the surface sediments were sampled to analyse the grain-size characteristics, to clarify the transport pattern of particles with different grain sizes, and to discuss the effects of terrain factors including dune slope, mountain slope, elevation and transport distance to sand transport. Sand dunes on both sides of the ridge are mainly transverse dunes. Fine and medium sands were the main particles, with few very fine and coarse particles in the surface sediments. Particles \({>}4.00\varPhi \) were blown upslope by suspension, particles \(1.00{-}4.00\varPhi \) were mainly transported upslope by saltation with opposite change tendency, and particles \({<}1.00\varPhi \) mainly moved by creep were found almost exclusively at the bottom of the slopes. As terrain factors, elevation and transport distance were more important factors influencing the distribution of grain size and particle fraction on dunes. Local winds observation might be helpful for the transport mechanism study of particles on climbing and falling dunes, while the wind data from nearby weather station was hardly helpful.

Distinct bacterial and archaeal diversities and spatial distributions in surface sediments of the Arctic Ocean

Environmental changes in the polar oceans are more pronounced than in other regions. The lack of knowledge regarding the microbial diversity, distribution and succession in the polar oceans has hampered our understanding about the effects of environmental changes on microbial ecosystems. This study investigated bacterial and archaeal diversities and spatial distributions in surface sediments of the Bering Sea and the Chukchi Sea. The results showed that bacterial α-diversity was higher than archaea, and these differences were due to compositional changes. β-diversities were not significantly different for bacterial and archaeal communities. Proteobacteria and Bacteroidetes were the dominant bacterial phyla, and the subdivisions of Proteobacteria changed obviously when compared with previous results. However, different assemblages dominated archaeal communities in different regions. Bacterial and archaeal communities were mainly determined by metallic ions, and geochemical properties were the major contributors to community dissimilarities. Interactions between geographical and geochemical properties had more pronounced impacts on archaeal communities.