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The sediment mixed layer (SML) in the deep ocean is an important interface with a rich diversity of benthic organisms. With increasing ocean mineral exploration, and eventual mining, the effect of sediment mixing on deep ocean ecosystems has raised considerable concern. We evaluate the distribution patterns and driving factors of SML depth in deep ocean nodule fields using naturally occurring 210Pb–226Ra isotopes. Results show that average SML depth has increased in Mn‐nodule fields since the end of the last century. SML processes are associated with significant desorption of 226Ra from sediments, resulting in a departure from radioactive equilibrium. By estimating possible driving factors, we conclude that anthropogenic exploration activities, rather than natural physical and/or biological drivers, are the most likely mechanism for intensified sediment mixing. 210Pb–226Ra disequilibria may be a potential tracer for quantifying the impact of human exploration on deep‐ocean sediment mixing and associated biological and geochemical effects. Plain Language Summary: The surface sediment mixed layer (SML) in the deep ocean is essential to benthic community structure and the biogeochemical cycling of many elements. The typical depth of mixed layers in the global deep ocean is <15 cm, which is mainly driven by natural biological and/or physical forces. By mapping sediment excess 210Pb profiles throughout the ocean, we found the depth of the SML in manganese nodule fields has increased significantly since the end of the twentieth century (reaching to >40 cm). The determine that the deepened mixed sediment layer is related to human exploration activities rather than other previously recognized natural drivers like bioturbation, internal solitary waves, and submarine storms. Keen attentions should be paid to the deepening and associated effects of sediment mixing in the deep ocean as human demand for critical materials continues to increase in the Anthropocene. Exploration approaches that involve low or negligible disturbance to deep‐ocean sediment should be encouraged. Key Points: Human exploration is the main reason for deepening of the sediment mixed layer in the manganese nodule areaSediment mixed processes are associated with significant desorption of 226Ra from sediments210Pb–226Ra disequilibria is a potential tracer for quantifying the impact of human drivers on deep‐ocean sediment mixing [ABSTRACT FROM AUTHOR]

Microorganisms in sediments are critical to marine ecosystems. The microbial communities in marine sediments of the Bohai Sea (BS) and Yellow Sea (YS), the eastern Chinese marginal seas, were uncovered in employing the metagenomic approach. In addition, the taxonomic and functional compositions of microbes were compared among various sediment core depths. Results showing the compositions, diversities, and functions of the microbial communities showed no significant variations with sea areas, and significant seasonal variations was observed in station 3500–7 only on functions of the microbial communities. Moreover, the compositions, diversities, and functions of the microbial communities changed noticeably in different sediment depths in close correlation with physical and chemical properties of sediments. However, the large fraction of the variation in functional communities remained unexplained. From bioinformatic analysis of the metagenomic data, the carbon-metabolism-related genes such as glycosyl transferase (GT), glycoside hydrolase (GH), and carbohydrate esterase (CE) genes were rich in the microbial community, especially in the top sediment depth. Additionally, in this N-polluted habitat, nitrification and anaerobic ammonia oxidation (anammox) were dominant in the top sediment depth, whereas dissimilatory nitrate reduction to ammonium (DNRA) and denitrification were dominant in the middle and bottom depth, respectively. Further identification of possible biogeochemical links suggested that Gammaproteobacteria, Alphaproteobacteria, Nitrospirae, Nitrospinae, Chloroflexi, and Methanomicrobia might promote effective circulation of carbon and nitrogen cycling. This study expanded our knowledge about the structure and functional potential of microbial communities associated with different sediment depth, and provided further comprehensive information on element cycles in marine environments. [ABSTRACT FROM AUTHOR]

Illumina sequencing and quantitative PCR (qPCR) based on the 16S ribosomal RNA (rRNA) gene were conducted to characterize the vertical distribution of bacterial and archaeal communities in the sediments of two sites from the South Yellow Sea. Both bacterial and archaeal communities showed a clear stratified distribution with sediment depth. The microbial communities in the upper layers were distinct from those in the deeper layers; the relative abundances of sequences of Thaumarchaeota, Gammaproteobacteria, and Actinobacteria were higher in the upper than in the deeper sediments, whereas the sequences of Bathyarchaeia, Lokiarchaeota, Euryarchaeota, Chloroflexi, and Deltaproteobacteria were relatively more abundant in the deeper sediments. Sediment depth and total organic carbon (TOC) can significantly influence both the bacterial and archaeal communities. Furthermore, bacterial and archaeal groups potentially involved in nitrogen, sulfur, and methane metabolism were detected in both sites. In our study, both ammonia-oxidizing bacteria (Nitrospira) and ammonia-oxidizing archaea (Candidatus Nitrosopumilus) were responsible for ammonia oxidization. Additionally, sulfur-reducing bacteria SEEP-SRB1 forming consortia with anaerobic methane-oxidizing archaea ANME-2a-2b were capable of anaerobic methane oxidation (AOM) in the 3400-02 sediment samples. [ABSTRACT FROM AUTHOR]

In this study, bacterial and archaeal communities in sediments from the adjacent waters of Rushan Bay were studied based on 16S ribosomal RNA (rRNA) gene. Illumina sequencing and quantitative PCR (qPCR) analyses were used to analyze the bacterial and archaeal community characteristics. The ecological analyses of sequences revealed that the diversity of bacterial communities was higher than that of archaeal communities. The abundance of bacterial 16S rRNA genes was observed to be greater than that of archaeal 16S rRNA genes. Proteobacteria and Piscirickettsiaceae were the most abundant bacterial phylum and family; Thaumarchaeota dominated the archaeal communities, and MGI in Thaumarchaeota and Halobacteria in Euryarchaeota were prevalent and the predominant archaeal class in this study. Temperature and ammonium concentration were related to the bacterial communities, whereas the nitrite concentration and ammonium concentration had a correlation with the archaeal communities; meanwhile, a complex combination of environmental factors might shape the bacterial and archaeal communities in this dynamic environment. Functional Annotation of Prokaryotic Taxa (FAPROTAX) analysis showed that most bacterial sequences were involved in chemoheterotrophy, sulfate respiration, respiration of sulfur compounds, aerobic nitrite oxidation and nitrification; for the archaeal communities, the essential ecological functions were chemoheterotrophy, other ecological functions such as aerobic ammonia oxidation and methanogenesis, were also predicted to be present in this study. The comparison of bacterial and archaeal communities in different environments suggest that similar conditions are hypothesized to give rise to similar microbial communities, and environmental conditions may contribute significantly to the bacterial and archaeal community structure. [ABSTRACT FROM AUTHOR]

Ammonia oxidation plays a significant role in the nitrogen cycle in marine sediments. Ammonia-oxidizing archaea (AOA) and bacteria (AOB) are the key contributors to ammonia oxidation, and their relative contribution to this process is one of the most important issues related to the nitrogen cycle in the ocean. In this study, the differential contributions of AOA and AOB to ammonia oxidation in surface sediments from adjacent waters of Rushan Bay were studied based on the ammonia monooxygenase (amoA) gene. Molecular biology techniques were used to analyze ammonia oxidizers' community characteristics, and potential nitrification incubation was applied to understand the ammonia oxidizers' community activity. The objective was to determine the community structure and activity of AOA and AOB in surface sediments from adjacent waters of Rushan Bay and to discuss the different contributions of AOA and AOB to ammonia oxidation during summer and winter seasons in the studied area. Pyrosequencing analysis revealed that the diversity of AOA was higher than that of AOB. The majority of AOA and AOB clustered into Nitrosopumilus and Nitrosospira, respectively, indicating that the Nitrosopumilus group and Nitrosospira groups may be more adaptable in studied sediments. The AOA community was closely correlated to temperature, salinity and ammonium concentration, whereas the AOB community showed a stronger correlation with temperature, chlorophyll-a content (chla) and nitrite concentration. qPCR results showed that both the abundance and the transcript abundance of AOA was consistently greater than that of AOB. AOA and AOB differentially contributed to ammonia oxidation in different seasons. AOB occupied the dominant position in mediating ammonia oxidation during summer, while AOA might play a dominant role in ammonia oxidation during winter. [ABSTRACT FROM AUTHOR]

N 2 O is among the most potent greenhouse gases. In this study, we investigated one of the important N 2 O production hotspots, the continental margins. We looked at N 2 O spatiotemporal distributions in situ as well as the potential contributions of nitrification and denitrification to N 2 O production in sediment cores from the Bohai and South Yellow Seas. Real-time PCR and shotgun metagenomics sequencing were used to analyze the microbial communities related to N 2 O production. The results showed that N 2 O concentrations roughly decreased with depth—a trend that was consistent throughout the year and showed no significant seasonal variations. When all the research stations along the continental margin were considered, the estuary exhibited the lowest average N 2 O concentration. Moreover, nitrification was identified as the main process responsible for N 2 O production in estuary areas. This study demonstrates that spatial, as opposed to temporal, heterogeneity is the primary factor influencing N 2 O concentration differences in sediments. [Display omitted] • N 2 O concentrations roughly decreased with depth and showed no significant seasonal variations. • The estuary depicted the lowest average N 2 O concentration along the continental margin areas. • Nitrification was the main process responsible for N 2 O production in estuary. • TOC content was the most important environmental factor influencing N 2 O concentration. [ABSTRACT FROM AUTHOR]

Suspended particulate matter (SPM) samples were collected along a salinity gradient in the Changjiang Estuary in June 2011. A custom-built water elutriation apparatus was used to separate the suspended sediments into five size fractions. The results indicated that Cr and Pb originated from natural weathering processes, whereas Cu, Zn, and Cd originated from other sources. The distribution of most trace metals in different particle sizes increased with decreasing particle size. The contents of Fe/Mn and organic matter were confirmed to play an important role in increasing the level of heavy metal contents. The Cu, Pb, Zn, and Cd contents varied significantly with increasing salinity in the medium–low salinity region, thus indicating the release of Cu, Pb, Zn, and Cd particles. Thus, the transfer of polluted fine particles into the open sea is probably accompanied by release of pollutants into the dissolved compartment, thereby amplifying the potential harmful effects to marine organisms. [ABSTRACT FROM AUTHOR]

Dissolved nutrient concentration in the Huanghe (Yellow) River at Lijin was monitored during a water-sediment regulation period and a subsequent rainstorm from 14 June to 19 July, 2005. This study provides detailed information on nutrient concentrations in the Huanghe River during the water-sediment regulation and rainstorm periods, and is of significance for the downstream area of the Huanghe River and the Bohai Sea. The average concentrations of nitrate, nitrite and ammonia were 304.7 μmol/L, 0.19 μmol/L, and 1.10 μmol/L, respectively, while the average concentrations of dissolved inorganic phosphorus (DIP) and dissolved silicate (DSi) were 0.23 μmol/L and 122.9 μmol/L, respectively. Nutrient concentrations during the water-sediment regulation period were mainly influenced by the dilution effect, floodplain effect and sediment resuspension while dilution and erosion effects were the main factors during the rainstorm. The fluxes of dissolved inorganic nitrogen (DIN), DIP and DSi during the water-sediment regulation and rainstorm periods accounted for 20.4%, 19.5%, 16.7% and 4.97%, 6.45%, 5.47% of the annual nutrient fluxes, respectively. Discharge was the main factor influencing the fluxes of nutrients during both the water-sediment regulation and the rainstorm periods. [ABSTRACT FROM AUTHOR]

The Huanghe River (Yellow River) had been the second largest river in the world in terms of sediment load to the sea; however, the river water discharge and sediment flux to the sea and their seasonal variability have been significantly altered by the dam activities and recent water–sediment regulation. These changes are believed to have important impacts on the flux of phosphorus that is generally transported in particulate form. In this article, the samples of suspended particulate matter (SPM) were collected at the Lijin Station during two high-discharge events in 2005 and were separated by particle size. Sequential extractions were applied to determine the forms of P in different particle size fractions and to assess the potential bio-availability of particulate phosphorus (PP). Based on the in-laboratory measurement, the impacts of different hydrological regimes on the source of PP and its bio-availability were also analyzed. The results indicate that exchangeable, organic, authigenic, and refractory P were preferentially associated with clay, very fine, and fine silt fractions. Detrital P was mainly associated with the medium and coarse silt fractions. Detrital P and authigenic P (two forms of calcium bound phosphorus) were the dominant fractions in all samples. Thus, the potential bio-available PP (exchangeable P and organic P) was mainly associated with the finer particles, such as clay. Higher content of exchangeable, organic, authigenic, and residual P and lower content of detrital P were found during the period of rainstorm compared to that of WSR. P forms and partitioning of P forms among different particle size fractions were assumed to depend on the sources of SPM. It is likely that the pathways and fates of PP forms were controlled by damming and by the related changes of hydrological regime. Therefore, anthropogenic changes of hydrological regime and particle size dominanted the amount and distribution pattern of bio-available P transportation to the estuary and the adjacent sea, which will have profound impacts on the marine ecosystems at the Huanghe River Estuary and even the Bohai Sea. [ABSTRACT FROM AUTHOR]

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are ubiquitous in marine environments. Nevertheless, it is unclear whether these brGDGTs are derived from terrestrial soils or produced in situ. Recently, it was proposed that the weighted average number of cyclopentane moieties of tetramethylated brGDGTs, #Rings tetra , could be used to identify sources of sedimentary brGDGTs in marine environments. However, little is known about #Rings tetra in seawater. In this study, we report #Rings tetra data in suspended particulate materials (SPM) in the surface shelf waters of the East China Sea (ECS) and coastal South China Sea (SCS), as well as in core-top sediments of the deep SCS. According to a two-end member model, #Rings tetra values in SPM increase offshore from 0.48 to 0.86 in the ECS and from 0.39 to 0.83 in the SCS, suggesting increasing marine-produced brGDGTs. An offshore increasing trend of #Rings tetra is also observed in the shelf surface sediments of the ECS and SCS, suggesting increased contributions of marine-produced brGDGTs. However, the offshore increasing trend in core-top sediments of the SCS ceases at a water depth ca. 100 m, with constantly low #Rings tetra values (0.3 ± 0.1) at sites deeper than 780 m and a transition value of 0.58 at 329 m. Instead of interpreting the low #Rings tetra values in deep-sea sediments as the result of increased contributions of terrestrial-derived brGDGTs, we propose that brGDGTs in deep-sea sediments are produced in situ. The lower pH in the deep-sea bottom water and sediment porewater than in the seawater column could be the reason for the low #Rings tetra values. We further propose that pH reconstructions of deep-sea sediment cores (e.g., >1000 m water depth) with the least terrestrial influence should reflect pH changes in marine bottom environments. • BrGDGTs data in SPM and sediments in China Seas; • #Rings tetra increases with water depth in shelf areas due to more marine brGDGT production; • Low #Rings tetra values in deep sea sediments are not soil signal but due to low pH in situ. • BrGDGTs in deep sea sediments with little terrestrial source have the potential to reconstruct bottom water pH. [ABSTRACT FROM AUTHOR]

Abstract: The speciation, potential bioavailability and preservation of phosphorus (P) in surface sediments of the Changjiang (Yangtze River) Estuary and adjacent East China Sea (ECS) inner shelf were investigated through the analyses of P fractions and sediment bulk properties. A sequential extraction method (SEDEX) was used to separate and quantify the following six sedimentary P reservoirs: exchangeable P (Ex–P), authigenic P (Au–P), detrital P (De–P), organic P (Or–P), refractory P (Re–P) and Fe-bound P (Fe–P). Total P (TP) in surface sediments ranged from 15.0 to 21.4 μmol g−1 and was highest near the Changjiang river mouth. The average contribution of each form of P to TP was 55.6% (De–P), 17.8% (Re–P), 16.1% (Or–P), 5.5% (Au–P), 2.5% (Ex–P) and 2.5% (Fe–P), respectively. De–P showed relatively higher concentrations in the river mouth and the ECS shelf region, off the Changjiang Estuary. High concentrations of Or–P were found mainly in mud areas showing a similar distribution pattern with silt, sediment surface area (SSA), and total organic carbon (TOC). Re–P was mainly distributed near the estuarine area and the Zhe–Min coast. Bioavailable P (BAP), accounted for 9.5–32.0% of TP (with a mean of 21.2%) and showed a similar distribution pattern to that of Or–P. De–P/SSA and TOC/SSA loadings both decreased with increasing of SSA, while Or–P/SSA loadings varied little with SSA, indicating that Or–P may have reached an adsorption–desorption equilibrium on mineral surfaces. TOC to total organic P (TOP; sum of Re–P and Or–P) ratios less than the Redfield ratio (84 in average) may have indicated efficient remineralization of organic matter in mobile muds of the Changjiang Estuary and adjacent ECS inner shelf. Furthermore, the relatively high TOC/Or–P ratios (72–422 with a mean of 188) likely suggest a higher degree of preferential regeneration of labile Or–P over TOC in sediments. [Copyright &y& Elsevier]

The phylum Bathyarchaeota, which has high species and functional diversity, is abundant and widespread in marine sediments. In this study, the abundance and communities of Bathyarchaeota in surface sediment samples from the southern Yellow Sea (SYS) and northern East China Sea were investigated. The high numbers of Bathyarchaeota 16S rRNA gene copies indicated that Bathyarchaeota plays an important role in the biogeochemical cycles in these surface sediments. In total, 16 subgroups of Bathyarchaeota were detected, with Bathy-8 having the highest relative abundance in nearshore surface sediment samples. Redundancy analysis showed that the water depth, temperature and salinity were the most influential factors determining the Bathyarchaeota community spatial distribution. In addition, the diversity index and Chao1 estimator values were negatively correlated with the temperature and water depth, respectively (P < 0.05). Our results improve the understanding of the Bathyarchaeota diversity and the environmental conditions influencing the Bathyarchaeota distribution in surface sediment samples. • The high numbers of Bathyarchaeota 16S rRNA gene copies were detected in the surface sediments from the SYS and NECS. • Bathy-8 having the highest relative abundance in nearshore surface sediment samples of the SYS and NECS. • Water depth, temperature and salinity can significantly influence the Bathyarchaeota community in surface sediments. [ABSTRACT FROM AUTHOR]

Sulfate- and sulfite-reducing prokaryotes (SSRP) communities play a vital role in both sulfur and carbon cycles. Community composition and abundance of SSRP were investigated using dissimilatory sulfite reductase β subunit ( dsrB ) gene sequencing in sediments from the Changjiang estuary and its adjacent area in the East China Sea (ECS). Clone libraries were constructed and real-time fluorescence quantitative polymerase chain reaction (qPCR) was applied to understand the community information of SSRP. In addition to sequences affiliated to sulfate-reducing prokaryotes (SRP), those affiliated with sulfite-reducing prokaryotes (SiRP) were also observed. Four phylotypes of SRP in this study showed genetic similarity to Desulfobulbaceae, Syntrophobacteraceae, Desulfobacteraceae and Peptococcaceae, and an unknown group that could not be clearly affiliated with known lineages was found. Salinity, temperature and contents of total organic carbon (TOC) were most closely correlated with the SSRP communities by canonical correspondence analysis (CCA). 210 Pb activities demonstrated the sedimentary environment at S33 was more stable than that at S31. Intense resuspension and reconstruction of sediments made the vertical abundance profile of SSRP fluctuate violently. For surface sediments, the dsrB gene copy numbers near the Changjiang estuary were higher than those in the mouth of Hangzhou Bay and the mud deposits along the Zhejiang coast, and contents of TOC were positively related to the copy numbers of dsrB gene. Our data provided valuable information to achieve a better understanding of the potential role of SSRP in sediments from the Changjiang estuary and adjacent East China Sea. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports on the spatial distribution patterns and investigates the controlling mechanisms of phytoplankton biomarkers (brassicasterol for diatoms, alkenones for haptophytes, dinosterol for dinoflagellates) and terrestrial biomarkers (odd C number long-chain (C27 +C29 +C31) n-alkanes) in surface sediments from the southern Yellow Sea (SYS). The contents of the phytoplankton biomarkers in the SYS surface sediments reveals a clear spatial pattern, with low values near the coasts and increased values seaward, caused by higher phytoplankton primary productivity and low sedimentation rates in the basin. The contents of terrestrial biomarkers show high values in the northern part of the study areas off the Shandong Peninsula and Jiangsu coast, caused by inputs of materials from the modern Huanghe River and the old Huanghe delta, respectively. The results also indicate that biomarker ratios offer the best approach for reconstructing marginal sea C cycles, as these proxies can be used to estimate the contributions of both terrestrial and marine organic matter and to reconstruct paleoproductivity and paleoecological changes in the SYS. [Copyright &y& Elsevier]