Search

The source and processes controlling the deposition of the sand fraction of muddy seafloor sediments remain poorly understood. Surficial seafloor sediments were collected offshore of the Eastern Shandong Peninsula and were analyzed regarding their detrital heavy mineral constituents and grain size distributions to determine their spatial distribution patterns, sand fraction provenance, and transport pathways. Five sediment types were identified in the study area: clayey silt, silt, sandy silt, silty sand, and sand. Each of these sediment types displayed distinct grain size parameters of their corresponding sand fractions. Moreover, three statistical clusters of sand grains were identified, suggesting variations in provenances and sedimentary processes from one cluster to the next. Twenty-five species of detrital heavy minerals in the sand fraction were identified and then assigned to four categories based on their mineral stability (i.e., ultrastable, stable, moderately stable, and unstable). The sandy sediments were enriched in ultrastable and stable heavy minerals, indicating that these sand grains mostly originated from coastal erosion of granitic and/or metamorphic rocks. In contrast, the muddy sediments were characterized by unstable heavy minerals dominated by hornblende and epidote. The results of principal component analysis further suggested that these sand grains are similar in terms of their provenance (coastal erosion) but have undergone complex sedimentary processes. Relative sea level changes during the late Quaternary caused shifts in the sediment sources and supplies, which were the primary factors controlling the grain sizes of the sand fractions and heavy mineral assemblages in the surficial sediments of the study area. [ABSTRACT FROM AUTHOR]

The heavy metals in surface sediments of the continental shelf of the South Yellow Sea (SYS) and the East China Sea (ECS) collected in 2016 were analyzed to assess the heavy metal distributions, contamination status, and likely sources. The metal concentrations generally met the China Marine Sediment Quality criteria. However, the enrichment factor and geoaccumulation index values clearly showed elevated Cd and Pb concentrations in the region. Cd and Pb contamination occurred mostly to the southwest of the Changjiang River mouth and to the east of the Shandong Peninsula because of rapid economic and industrial development. The results are likely to be useful for authorities responsible for sustainable coastal zone management. [ABSTRACT FROM AUTHOR]

One sediment core spanning approximately 138 years was taken from the muddy deposits along the Zhejiang coast of the East China Sea, which is located in a hypoxic zone south of the Yangtze River estuary. When the sources of the trace metals in the core were analyzed, the three geochemical sources were identified as lithogenic, anthropogenic, and reductive deposits based on both principal component analysis and the ratios of terrigenous elements. The temporal distribution of the enrichment factor of copper in the sediment core matches the timeline of economic development and national policy in China. The rapid increase in human activity and economic development in the Yangtze River catchment accounts for the enrichment of copper in the sediment core. Based on the vertical distribution of arsenic concentration, the hypoxic zone south of the Yangtze River estuary may have not only existed, but worsened since 1875.