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Microplastics are ubiquitous in the environment, eventually becoming part of the geological record as 'technofossils'. However, research on the chronological characteristics of microplastics remains limited. This study reviewed dating methods, microplastic abundance, and microplastic polymer type in sedimentary cores globally. Furthermore, the 'evolution' of plastic types was compiled in sequence, and a microplastic chronological sequence in the sedimentary record was established. This microplastics chronological sequence was applied to 39 published cores with microplastic polymer analysis. The sediment age ranges determined by microplastic type were found to correspond to the published ages, indicating that microplastics could be useful for dating sedimentary cores on a centennial scale. Furthermore, good preservation and limited mobility of microplastics in burial records make microplastic dating an effective supplementary dating method for determining ages of Anthropocene sediments. [ABSTRACT FROM AUTHOR]

Pollution status and ecological risks associated with sediment heavy metals (Cu, Pb, Zn, Cd, and Cr) were investigated around Xincun Bay, assessing their spatial variations and relationship with sediment physiochemical factors. Higher concentrations and associated risks were observed in the central region, where mariculture activities were concentrated, compared to non-maricultured areas. Despite with overall low concentrations, Cd had a higher ecological risk. Correlation and principal component analyses revealed similar sources for all metals in Xincun Bay. Heavy metal concentrations varied with expansion of mariculture operations in terms of quantity and scale, confirming the influence of mariculture activities. Sediments around mariculture had higher contents of clay, silt, and total organic carbon (TOC), and finer particle sizes. Quantitative analyses through correlation and linear regression indicated that TOC significantly regulated heavy metal concentration and distribution (p < 0.05). Considering its significant association with TOC, the influence of mean grain size should not be overlooked. [Display omitted] • Increased heavy metal pollution is observed near the mariculture area. • At lowest heavy metal contents, cadmium has the highest contamination risk. • TOC may control abundance and distribution of sediment heavy metal pollution. • Heavy metals of lagoon sediments have similar sources. • Mariculture is the primary source of heavy metal pollution in Xincun Bay. [ABSTRACT FROM AUTHOR]

The grain size characteristics and aging of beach sediments from six islands of the Yongle Atoll, South China Sea, were measured to examine the taphonomic degradation of coral clasts in sediment reservoirs of reef environments. Seventy-one beach sediment samples were collected from 22 transects on 6 islands for sediment characteristic analyses, and 16 bulk sand samples and 28 coral samples were selected for 230Th dating. The mean grain size and ages of coral clasts showed a significant negative correlation (F 25 = −0.721, p = 0.01). A grain size age model was established to explain the taphonomic degradation mechanism of coral clasts over time, and an empirical relationship between the mean grain size and 230Th ages was obtained from the Yongle Atoll. The mismatch of the taphonomic clock by grain size data was analyzed, and it was mainly caused by the influence of sorting processes and the intrinsic morphology of coral skeletons that occurred at the early stage of the breakdown process. The application of the model to a nearby atoll island showed that for coral sediments with homogeneous taphonomic conditions, the predicted age was well matched with the measured age. This work presents a general framework for understanding coral clast degradation trajectories with time in taphonomic environments, and it provides a feasible method to predict the coral age independent of other dating methods. • A significant negative correlation was found between the grain size and 230Th of coral clasts. • A grain size age model was established to find the mechanism of the bioclastic degradation. • The grain size model was proved to be a good predictor of the coral sand age. • This study provides a convenient method to determine coral age. [ABSTRACT FROM AUTHOR]

The water discharge and sediment load of rivers are changing substantially under the impacts of climate change and human activities, becoming a hot issue in hydro-environmental research. In this study, the water discharge and sediment load in the mainstream and seven tributaries of the Yangtze River were investigated by using long-term hydro-meteorological data from 1953 to 2013. The non-parametric Mann-Kendall test and double mass curve (DMC) were used to detect trends and abrupt change-points in water discharge and sediment load and to quantify the effects of climate change and human activities on water discharge and sediment load. The results are as follows: (1) the water discharge showed a non-significant decreasing trend at most stations except Hukou station. Among these, water discharge at Dongting Lake and the Min River basin shows a significant decreasing trend with average rates of − 13.93 × 10 8 m 3 /year and − 1.8 × 10 8 m 3 /year ( P < 0.05), respectively. However, the sediment load exhibited a significant decreasing trend in all tributaries of the Yangtze River. (2) No significant abrupt change-points were detected in the time series of water discharge for all hydrological stations. In contrast, significant abrupt change-points were detected in sediment load, most of these changes appeared in the late 1980s. (3) The water discharge was mainly influenced by precipitation in the Yangtze River basin, whereas sediment load was mainly affected by climate change and human activities; the relative contribution ratios of human activities were above 70% for the Yangtze River. (4) The decrease of sediment load has directly impacted the lower Yangtze River and the delta region. These results will provide a reference for better resource management in the Yangtze River Basin. [ABSTRACT FROM AUTHOR]

Marine microplastic pollution has become a major global concern in recent years and the fate of microplastics in the ocean is a hot issue of research. We investigated microplastic pollution in surface sediments in the northern South China Sea to explore its distribution characteristics and influencing factors across the continental shelf, continental slope, and deep-sea environments. It was found that the microplastic abundance of surface sediments was 130.56 ± 40.48 items/kg. The average abundance of microplastics in all three topographic areas gradually decreased with increasing distance offshore. However, the differences in microplastic diversity indices between the three areas were not significant and were higher than those in other seas of the world, indicating that the waters of the northern South China Sea are rich in microplastics from complex sources, with more pollution input channels. In the continental shelf, fibrous and low density microplastics accounted for the largest amount, with a low degree of microplastic aging, and were mostly transported by suspended-load. These microplastics were mainly influenced by human activities. In the deep sea, microplastics with higher density were the most abundant and the number of fibrous microplastics was fewer, while the average size was larger, mainly influenced by the bottom currents. These microplastics underwent long-term bedload transport. In the continental slope, the main factors affecting the distribution of microplastics were more complex. In addition to pollution by human activities, the slope also receives microplastic materials carried by bottom currents; therefore, the composition of microplastics in the slope combines those characteristics of microplastics in both the continental shelf and deep-sea areas. The findings of this study indicate that the South China Sea is affected by complex pollution sources under the dual effects of human activities and natural conditions; in particular, the pollution situation in the deep-sea area needs extensive attention. [Display omitted] • Distribution of microplastic and characteristics from the northern SCS are reported. • MPs distribution is mainly affected by human activities and bottom currents. • Continental shelf has higher abundance than continental slope and deep-sea areas. • Deep-sea areas potentially pool large amounts of microplastics. • Prominent MDI in northern SCS reflects the diversity of pollution input channels. [ABSTRACT FROM AUTHOR]

Based on data from the Datong hydrological station and 147 meteorological stations, the influences of climate change and human activities on temporal changes in water discharge and sediment load were examined in the Yangtze River basin from 1953 to 2010. The Mann–Kendall test, abrupt change test (Mann–Kendall and cumulative anomaly test), and Morlet wavelet method were employed to analyze the water discharge and sediment load data measured at the Datong hydrological station. The results indicated that the annual mean precipitation and water discharge exhibited decreasing trends of − 0.0064 mm/10 yr and − 1.41 × 10 8 m 3 /yr, respectively, and that the water sediment load showed a significant decreasing trend of − 46.5 × 10 6 t/yr. Meanwhile, an abrupt change in the water discharge occurred in 2003. The sediment load also exhibited an abrupt change in 1985. From 1970 to 2010, the climate change and human activities contributed 72% and 28%, respectively, to the water discharge reduction. The human-induced decrease in the sediment load was 914.03 × 10 6 t/yr during the 1970s and 3301.79 × 10 6 t/yr during the 2000s. The contribution from human activities also increased from 71% to 92%, especially in the 1990s, when the value increased to 92%. Climate change and human activities contributed 14% and 86%, respectively, to the sediment load reduction. Inter-annual variations in water discharge and sediment load were affected by climate oscillations and human activities. The effect of human activities on the sediment load was considerably greater than those on water discharge in the Yangtze River basin. [ABSTRACT FROM AUTHOR]

The main objective of ecosystem health management is to preserve the capacity of ecosystems to respond to disturbances and future changes. We proposed a set of ecological indicators for coastal ecosystem health assessment using physical stressors such as total suspended matter, chemical stressors including nutrients and heavy metal pollutants, community structure metrics including species richness, diversity and evenness, and ecosystem level eco-exergy indicators. The results of our case study indicate that the health status of the Jiangsu coastal ecosystem is limited by environmental stressors and factors that affect the community species diversity. The health status of nektonic and benthic communities is reflected by water quality and sediment physicochemical properties, respectively. The results of our case study demonstrate that the integrated ecological health indicator system can provide a comprehensive assessment that corresponds with the current health of coastal ecosystems and a reliable theoretical basis for regional coastal management. [ABSTRACT FROM AUTHOR]

This study investigated the distribution and characteristics of microplastics in surface sediments of the Gulf of Thailand (GoT), and discussed the correlation between sediment grain size and microplastic content. The results indicate the abundance of microplastics is 150.4 ± 86.2 pieces/kg dry weight, representing a medium microplastic pollution level compared to other sea areas. Small microplastics (0.5–1 mm) take up >70% of total microplastic numbers. Fibrous microplastics are the dominant component of microplastics. According to micro-Fourier transform infrared spectroscopy, rayon (37%) and polyester (PES: 16%) are the most typical polymer types found in sediments. The results imply that secondary microplastics are the dominant pollutant, while fibrous microplastics are mainly from municipal sewage discharge. We also find that inconspicuous correlation between grain size and microplastics, which is caused by the multi-sources and different flow field. This study deepens our understanding of the environmental risks posed by microplastics to marine ecosystems in the GoT. • Gulf of Thailand has medium plastic pollution level compared to surrounding areas. • Small microplastics (0.5–1 mm) dominate the microplastic share. • Fibrous microplastics are the dominant component in sediments. • Rayon and polyester are most common polymers found in sediments. [ABSTRACT FROM AUTHOR]

• The 230Th ages of beach sediments of Yongle Atoll fall with a ca. 5000-yr time span. • Tropical cyclone–generated waves and winnowing by tides are the main factors that influenced the grain size characteristics. • The ages of coral clasts on a single island indicated that the coral sands provided within a relatively close time period. • The atoll islands have different coral sediment supply rates. Low-lying reef islands constructed from unconsolidated sediments are of growing interest due to concerns over the future stability of island landforms in response to climatic change and sea-level rise. Sediment characteristics, combined with the constituents and physical processes, are fundamental to understand the links between sediment production and their supply to an island's beach reservoir. The grain size, constituents, and 230Th age of beach sediments from five islands at Yongle Atoll in the South China Sea were analyzed. Data reveal that coral grains are the dominant constituents of the beach sediments, followed by mollusks, coralline algae, foraminifera, Halimeda , and bryozoans. The mean grain sizes of the beach sediment were within a range of 226–4215 μm, and the coarsest sands were located near the passages in the atoll rim. Transportation by tropical cyclone–generated waves and winnowing by tides are potentially the main factors that influenced the grain-size characteristics. Calibrated 230Th age dates for bulk sand samples date the beach sediment between 424 yr BP and 5953 yr BP. Dating of coral sand samples from the beach sediment provides ages of 686–5780 yr BP; the coral sands from a vertical section (1.2 m depth) located on the beach at Jinqing Island were dated at 1154–3824 yr BP. The age reversal on the vertical section, with similar ages of beach sediment on any single island and different age ranges on different islands in an atoll, indicates that the coral sediment supply processes occurred within a relatively close time period and that different islands had different sediment supply rates. The temporal link between the coral-dominated sediment production and the beach reservoir provides an important insight into understanding the sediments supply mechanism of atoll islands in the northwestern Pacific Ocean. [ABSTRACT FROM AUTHOR]

Abstract: The origin of a large field of sand ridges offshore from the north Jiangsu coast in the South Yellow Sea has been investigated on the basis of bathymetry, seabed samples, high-resolution seismic profiles and 31 to 71m deep boreholes. Sediment composition including heavy minerals and clay minerals sampled from surface sediments shows that most of the sand was derived from the Changjiang (Yangtze) River, but in the northern part of the field particularly the clay came from the Huanghe (Yellow) River. Seismic profiles show late Pleistocene distributary channels of the ancient Changjiang River underlying much of the southern part of the sand ridge field. The Holocene transgression cut a widespread ravinement surface reworking abundant late Pleistocene sandy sediment. The available sand was reworked by tidal currents into large ridges. The location of the ridges is strongly influenced by relict channels in the southern part of the field and by tidal currents in the northern, and especially the northeastern part of the field, resulting in a radiating ridge pattern. These ridges provide an example of the evolution of a large scale geomorphic feature resulting from river–sea interaction, in which climatic and sea level changes played an important role. [Copyright &y& Elsevier]

High emissions of synthetic compounds are damaging the marine environment and threatening human health. This study represents the first extensive and comprehensive analysis of three typical persistent organic pollutants (POPs), i.e., organochlorine pesticides (n = 228), perfluoroalkyl substances (n = 202), and short-chain chlorinated paraffins (n = 162), using a highly resolved spatial dataset. The results revealed the complex distribution of POPs in the Eastern China Marginal Seas (ECMSs). POPs in the surface sediments of the ECMSs showed spatial heterogeneity, with high levels observed mainly in areas with fine-grained sediments (e.g., the Yellow River and Changjiang River estuaries and the central south Yellow Sea). Strong positive correlations were identified between POP concentration and sediment grain size/components/longitude/latitude in the ECMSs, suggesting that POP distribution was significantly influenced by river input and regional hydrodynamics. The annual deposition fluxes of POPs in the ECMSs were also calculated and high values were recorded in the Yellow River Estuary and East China Sea. Human-induced changes in the catchments could affect the fate of POPs in the ECMSs and other river-dominated marginal seas worldwide. Our findings highlight concerns regarding local aquaculture and provide a basis for government decision-making. We also suggest the need for increased attention to be paid to the effects of marine organic pollution on aquaculture on a global scale. ga1 • The distribution of POPs in the ECMSs have obvious spatial heterogeneity. • Terrestrial input and stable sedimentary environment determined high POPs level. • The influence of pollution center on aquaculture needs to be paid enough attention. • Costal oceans in the worldwide will undergo similar drastic threat. [ABSTRACT FROM AUTHOR]