129I released from the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident has been observed in the atmospheric, terrestrial and oceanic environments, and it also entered the marine sediments via ...dispersion by sea water movement and deposition around Japan. However, there have been few studies of marine sediment cores in contrast to the large number of studies on seawater. In this work, a sediment core collected near FDNPP was analyzed for 129I. It is observed that the 129I/127I atomic ratios in this sediment core are comparable to those in the seawater and sediments collected from offshore Fukushima after the accident, but 2 orders of magnitude higher than those in seawater in this region before the accident, suggesting the significant amount of 129I has been transferred and incorporated to the offshore shallow sediments. The difference in environmental behavior between 129I and 137Cs is discussed based on their depth distributions in the sediment core in comparison with the grain size distribution of sediments. The peak concentrations of iodine isotopes were found in a relatively deeper layer than radiocesium. Radiocesium follows the distribution of fine grains in the sediment core, implying its high association to fine grains.
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•Fukushima accident caused elevated 129I/127I ratio up to 10−9 in offshore sediment.•129I/137Cs activity ratios were found to be higher than the Fukushima effluent.•129I peaks in a deeper layer than 137Cs does.•Cs was concentrated in layers high in fine particles while iodine was not.•Different affinity to particles between I and Cs leads to different environmental record.
Dissolved sulfide, iron (Fe), and phosphorus (P) concentrations in sediments of the East China Sea were simultaneously measured in situ by diffusive gradients in thin films (DGT) technique. The ...results, by combination with solid-phase Fe speciation, were used to characterize the interplays of Fe, S and P. Diverse distributions of dissolved sulfide among the sites are attributable to highly dynamic diagenetic regimes and varying availability of labile organic carbon (OC). The DGT technique provided high-resolution evidence for coexistence of microbial iron reduction (MIR) and sulfate reduction in localized zones, and for Fe-coupled P mobilization. Measured Fe2+/P ratios suggest that Fe2+ reoxidatiion at the oxic zones can serve as an efficient scavenger of P. Empirical estimation indicates that MIR plays an important role in anaerobic OC mineralization in the sediments, which is a combined result of low availability of labile OC, high reactive Fe content, and unsteady diagenetic regimes.
•Dissolved sulfide, iron(II), and phosphorus (P) were measured by DGT technique.•P mobilization is coupled to reductive dissolution of iron oxides in the sediments.•Coexistence of microbial iron reduction (MIR) and sulfate reduction was inferred.•MIR plays an important role in anaerobic organic matter mineralization.
New proxy records from deep‐sea sediment cores from the northwestern continental margin of Western Australian reveal a 5.3 million year (Ma) history of aridity and tropical monsoon activity in ...northwestern Australia. Following the warm and dry early Pliocene (~5.3 Ma), the northwestern Australian continent experienced a gradual increase in humidity peaking at about 3.8 Ma with higher than present‐day rainfall. Between 3.8 and about 2.8 Ma, climate became progressively more arid with more rainfall variability. Coinciding with the onset of the Northern Hemisphere glaciations and the intensification of the Northern Hemisphere monsoon, aridity continued to increase overall from 2.8 Ma until today, with greater variance in precipitation and an increased frequency of large rainfall events. We associate the observed large‐scale fluctuations in Australian aridity with variations in Indian Ocean sea surface temperatures, which largely control the monsoonal precipitation in northwestern Australia.
Plain Language Summary
Australia is the driest inhabited continent on the planet, with its moisture mostly sourced from the tropical monsoon in the north and the southern westerlies in the south. The continent has experienced large climate fluctuations in the geologic past, but long continuous records of paleoenvironmental changes are lacking, particularly prior to ~0.55 Ma. Here, we address this paucity by presenting a continuous and fluctuating record of continental aridity and monsoonal activity in northwestern Australia since the Pliocene (5.3 Ma). These records are based on bulk‐chemical X‐Ray Fluorescence scans and particle‐size distributions of the terrigenous fraction in two marine sediment cores from the NW Western Australian continental margin. A comparison with present‐day sources of windblown and fluvial sediments taken near the NW Western Australian coast corroborates our interpretation of the terrigenous fraction in the marine sediment cores. We show how the northwestern part of the Australian continent has experienced large climate fluctuations since 5.3 Ma, expressed by large aridity contrasts and great changes in monsoonal precipitation that are driven by Indian Ocean sea‐surface temperatures.
Key Points
Continental margin sediments off northwestern Australia record large continental aridity shifts at 5.3, 3.8, 2.8, and 1.4 Ma
Grain size and chemistry of the terrigenous fraction of seafloor sediments and source areas on land allow a characterization of river mud
Monsoonal activity responds to changes in Indian‐Ocean SSTs and drives river runoff in northwestern Australia
Blue carbon, the carbon fixed by vegetated coastal ecosystems including seagrasses, is reported to have a large potential to sequester atmospheric carbon dioxide. Planting, expanding or protecting ...seagrass meadows has, accordingly, been proposed as a form of geoengineering. Seagrasses are reported to account for up to 18% of the carbon burial in the world's oceans, which is on the same order of magnitude as other proposed geoengineering techniques, including iron fertilization. International protocols have been developed to quantify carbon sequestration in seagrass meadows, with a view to awarding carbon credits under the Verified Carbon Standard. Unfortunately, because these protocols do not adequately account for post-depositional processes in marine sediment, they significantly overestimate carbon capture by seagrass beds and give an incorrect view of its distribution. Specifically, neglecting biomixing and remineralization of carbon in surface sediments biases burial rates high, while using sediment carbon inventory (soil carbon stock) over the top 1 m as a proxy for burial rate incorrectly identifies areas of high carbon burial. Seagrass beds likely provide a limited setting for geoengineering, because they generally comprise slowly-accumulating, fine to medium sand, which captures organic carbon less efficiently than fine-grained sediments or rapidly-accumulating delta deposits. While there is no question that seagrass meadows provide valuable habitat, nor that they are disappearing rapidly, their contribution to the global burial of carbon has not yet been established. The danger of geoengineering with seagrasses before reliable assessment methods have been established is that overestimated carbon offsets could lead to a net increase in emissions of carbon dioxide to the atmosphere.
A novel methylotrophic methanogen
sp. nov. was isolated from East China Sea sediment. Type strain LMO-1
of
sp. nov. was irregular 1-2 µm cocci without flagella. Strain LMO-1
could utilize a variety ...of methylated compounds including methanol, methylamine, dimethylamine and trimethylamine for growth and methanogenesis, while H
/CO
or acetate could not be used for growth or methanogenesis. Optimum growth temperature was 30-35 °C, optimum pH range for growth was 7.0-7.5, while the optimum salinity spectrum for growth was 1.0%-5.0% NaCl. Based on 16S rRNA gene similarity, strain LMO-1
belongs to
, with the highest sequence similarity to
DSM 2657
(99.8 %),
SLH33
(99.4 %), followed by
AK-5
(98.1 %),
DSM 6242
(98.0 %). Digital DNA-DNA hybridization also showed highest similarity with
DSM 2657
, with the value of 58.4 %. The average nucleotide identity between strain LMO-1
and
DSM 2657
was 94.06 %. In summary, LMO-1
represents a novel species of the genus
, for which the name
sp. nov. is proposed. The type strain is LMO-1
(=MCCC 4K00106
=JCM 39195
).
•Branched GDGTs of sediment cores from the Chukchi Sea were analyzed.•BrGDGTs in the investigated core had a mainly marine origin.•Distributions of 5- and 6-methyl IIIa brGDGTs differ in the marine ...sediment core.•Relative abundances of 5- and 7-methyl IIIa brGDGTs are correlated with temperature.
Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are thought to be produced by as yet unknown bacteria on land, and their distribution in soils, peats, and lake sediments has been shown to correlate with mean annual air temperature (MAAT). Recently, an increasing number of studies have shown that in situ production of brGDGT in marine environments is likely. However, the influence of environmental factors on marine-derived brGDGT distributions is still unknown. In this study, we assessed the sources of brGDGTs preserved in a sediment core from the Chukchi Sea shelf using multiple brGDGT-based indices, including the branched and isoprenoid tetraethers (BIT) index, the ratio of IIIa/IIa, cyclization degree of branched tetraethers (CBT), and #rings indices, and discuss the influence of seawater temperature changes over the last 70 years on the distribution of brGDGT isomers. The low BIT and CBT values, high IIIa/IIa ratios, and significant correlations between different #rings indices suggest that these brGDGTs primarily have a marine source. With increasing sea surface temperatures (SSTs), the fractional abundances of 5-Me IIIa (IIIa5) showed an increased trend, while there was no obvious trend in 6-methyl IIIa (IIIa6). This finding indicates different behaviors of 5-Me and 6-Me isomers in marine-derived brGDGTs, similar to what has been observed in soils, peats and lakes. In addition, we found a significant correlation between IIIa5 and IIIa7 (a novel isomer of IIIa), indicating that they might share the same bacterial source and/or are controlled by the same environmental factors (e.g., temperature). Finally, the fractional abundances of IIIa5 and IIIa7 are significantly correlated with SST (r2 = 0.64 and 0.49, respectively), which suggests that marine-derived brGDGTs have the potential to reconstruct seawater temperature.
We investigated the colonization dynamics of different microplastic (MP) pellets, namely, polyethylene (PE), polyethylene terephthalate (PET), polystyrene (PS), polypropylene (PP) and polyvinyl ...chloride (PVC), either pristine or contaminated with polychlorinated biphenyls (PCBs), by an organohalide respiring marine microbial community and its biotransformation activity towards PCBs sorbed on MPs, in anaerobic laboratory microcosms of a marine sediment.
All MPs were rapidly colonized by the microbial community within 2 weeks of incubation, when approximately 1010 16S rRNA gene copies cm−2 were detected on PVC, 109 copies cm−2 on PE, and 108 copies cm−2 on PET, PP and PS. A greater biofilm growth on PVC pellets than other MPs was confirmed by quantification of the reducing sugars of the EPS and biofilm staining with crystal violet. Illumina sequencing of the 16S rRNA genes and Principal Coordinate Analysis (PCoA) revealed that the biofilm community on MPs significantly differed from the sediment community, being enriched of chemoorganotrophic fermenting species, and was significantly affected by the type of polymer. The presence of sorbed PCBs did not significantly affect the overall community composition, and mainly resulted in the enrichment of Dehalococcoidia, i.e., of the organohalide respiring members of the community.
Reductive dechlorination of PCBs sorbed to MPs was observed after 2 weeks of incubation, when the average number of chlorines per biphenyl molecule was reduced from 5.2 to 4.8–4.3, and was faster (35.2 ± 1.9 to 61.2 ± 5.8 μmol of Cl removed kgMP−1 week−1) than that of sediment-sorbed ones (33.9 ± 9.1 μmol of Cl removed kgsediment−1 week−1), which started only after 10 weeks of incubation. These data suggest that microbial colonization of contaminated MPs might change the composition of sorbed PCB mixtures and therefore the toxicity associated to PCB-polluted MPs.
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•Marine bacterial biofilm composition changes on different MP types.•MP-associated bacterial communities differ from the surrounding sediment ones.•MP-sorbed PCBs do not significantly affect the MP-biofilm composition.•PCBs sorbed on MPs can be rapidly dehalogenated by anaerobic marine biofilms.
A facultative anaerobic, Gram-strain-negative, rod-shaped bacterium (strain NBU2970
T
) was isolated by using modified ichip
in situ
cultivation from a marine sediment sample collected from Meishan ...Island in the East China Sea. Strain NBU2970
T
grew optimally at 37 °C, with a NaCl concentration of 2.0 % (w/v) and at pH 7.0. The 16S rRNA gene sequence analyses revealed that strain NBU2970
T
represents a novel species with the genus
Muricauda
, sharing highest sequence identities with
Muricauda beolgyonensis
BB-My12
T
(96.1 %),
Muricauda alvinocaridis
SCR12
T
(96.0 %),
Muricauda taeanensis
105
T
(96.0 %) and
Muricauda ruestringensis
B1
T
(95.6 %). Phylogenetic analyses also indicated that strain NBU2970
T
clustered with the genus
Muricauda
and was closely related to
M. beolgyonensis
BB-My12
T
and
M. ruestringensis
B1
T
. The draft genome sequence of strain NBU2970
T
was composed of six contigs with a size of 3.2 Mbp, containing 3045 protein-coding genes and 38 RNA genes. The DNA G+C content was 43.8 mol%. The average nucleotide identity and digital DNA–DNA hybridization values between strain NBU2970
T
and related species of the genus
Muricauda
were well below the threshold limit for prokaryotic species delineation. The major cellular fatty acids were iso-C
15 : 0
, iso-C
15 : 1
G and iso-C
17 : 0
3-OH. The only respiratory quinone was MK-6. The major polar lipid was phosphatidylethanolamine. Based on its phenotypic, chemotaxonomic and genotypic data, strain NBU2970
T
is considered to be a representative of a novel species in the genus
Muricauda
, for which the name
Muricauda meishanensis
sp. nov. is proposed. The type strain is NBU2970
T
(=KCTC 82915
T
=MCCC 1K06394
T
).
An international sampling campaign was carried out to comprehensively investigate the occurrence of polycyclic aromatic hydrocarbons (PAHs) in the marine sediments from the European Baltic and North ...Seas, Chinese Bohai and Yellow Seas. The concentrations of ∑18PAHs in the samples from these four seas were in the range of 0.91–5361 ng/g dry weight (dw), 0.46–227 ng/g dw, 25.0–308 ng/g dw and 4.3–659 ng/g dw, respectively. 4-rings PAHs, e.g., fluoranthene, pyrene and benzo(b)fluoranthene, were commonly the dominant compounds in all the samples. The PAH sources were identified via composition patterns, diagnostic ratios, principal component analysis (PCA) and positive matrix factorization (PMF). Coal combustion, vehicular emission, coke plant and petroleum residue were apportioned as the main sources in these marine sediments. However, through PMF modeling, different contributions of these sources were quantified to the deposited PAHs in the seas, suggesting distinct anthropogenic impacts on the adjacent marine system. It is note-worthy that biomass combustion may not be the main source of PAHs in the majority of sediments from these seas. This was evidenced by the ratios of naphthalene against its methylated derivatives (i.e. 1-,2-methylnaphthalenes) other than the composition pattern in the samples, of which the approach is in prospect of developing in future studies.
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•Relatively higher level of PAHs was observed in the Baltic Sea.•PAHs in the European seas revealed the effect of proximity from source.•Spatial distribution in the Chinese seas closely related to the hydrodynamic effect.•Ratio of naphthalene against its methylated derivatives may indicate PAH sources.
The ubiquity of microplastics (MPs) has now been demonstrated throughout Earth's geographic areas in both terrestrial and marine environments. Marine ecosystems are the end point of the plastic waste ...cycle, and marine sediments are increasingly considered to be a sink for plastic debris, with possible deleterious effects on seafloor ecosystems. However, the low concentration of MPs in a complex matrix such as marine sediment makes their reliable analysis difficult. MP concentration in marine sediments is usually determined by various extraction procedures followed by optical, spectroscopy or mass spectrometry techniques, and are therefore hard to compare. Therefore, reliable determination of MPs in sediment is a challenging task. Here we present a short review on studies dealing with analytical determination protocols and MP detection in marine sediments and discuss the advantages of the different techniques used. This analysis of the literature reveals that most of the 70 studies were carried out in European and Asian coastal environments. The use of NaCl saturated solution, hydrogen peroxide (H2O2) and Fourier transform infrared spectroscopy (FTIR) are by far the most-used techniques for the different steps of separation, digestion and identification, respectively. Based on this body of literature, we present recommendations and suggestions for future research in order to increase the reliability of results and to facilitate inter-comparison. The use of NaCl saturated and H2O2 solution is strongly recommended for the separation and digestion steps, respectively, whereas during the filtration step it is necessary to choose filter type based on the identification technique. More thorough investigation is needed to establish a systematic protocol for MP identification. A combination of techniques would permit to identify all items, and personal bias could be avoided if automatic identification was implemented. Nanoplastics (NP) occurrence in marine sediments is also discussed, although no data are available to date.
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•MPs in marine sediments have been published in at least 70 articles, at a total of 813 locations on all continents.•Areas studied are mainly in coastal environments, and the number of locations examined per study ranges from 1 to 72.•We recommend the use of a NaCl solution for the separation step.•A digestion step using an H2O2 solution and automatic identification are recommended
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