The subseafloor marine biosphere may be one of the largest reservoirs of microbial biomass on Earth and has recently been the subject of debate in terms of the composition of its microbial ...inhabitants, particularly on sediments from the Peru Margin. A metagenomic analysis was made by using whole-genome amplification and pyrosequencing of sediments from Ocean Drilling Program Site 1229 on the Peru Margin to further explore the microbial diversity and overall community composition within this environment. A total of 61.9 Mb of genetic material was sequenced from sediments at horizons 1, 16, 32, and 50 m below the seafloor. These depths include sediments from both primarily sulfate-reducing methane-generating regions of the sediment column. Many genes of the annotated genes, including those encoding ribosomal proteins, corresponded to those from the Chloroflexi and Euryarchaeota. However, analysis of the 16S small-subunit ribosomal genes suggests that Crenarchaeota are the abundant microbial member. Quantitative PCR confirms that uncultivated Crenarchaeota are indeed a major microbial group in these subsurface samples. These findings show that the marine subsurface is a distinct microbial habitat and is different from environments studied by metagenomics, especially because of the predominance of uncultivated archaeal groups.
A fourth of the global seabed sediment volume is buried at depths where temperatures exceed 80 °C, a previously proposed thermal barrier for life in the subsurface. Here, we demonstrate, utilizing an ...extensive suite of radiotracer experiments, the prevalence of active methanogenic and sulfate-reducing populations in deeply buried marine sediment from the Nankai Trough subduction zone, heated to extreme temperature (up to ~120 °C). The small microbial community subsisted with high potential cell-specific rates of energy metabolism, which approach the rates of active surface sediments and laboratory cultures. Our discovery is in stark contrast to the extremely low metabolic rates otherwise observed in the deep subseafloor. As cells appear to invest most of their energy to repair thermal cell damage in the hot sediment, they are forced to balance delicately between subsistence near the upper temperature limit for life and a rich supply of substrates and energy from thermally driven reactions of the sedimentary organic matter.
Microplastics (MPs) form the most investigated plastic category since their size (1 μm- 5 mm) enables them to accumulate in various environmental compartments and to be ingested by biota. Beach sand ...and sediment can be indicators of the MP contamination levels of the coastal and marine ecosystem and, thus, they are widely analyzed. With the increasing number of publications in recent years, there is a need for constant updates on the variety of extraction and analysis procedures developed. Thus, this review aims to evaluate the sample preparation techniques for MPs and provide a critical discussion on their determination in sand and sediment based on studies published in the last 5 years. We also report the conditions imposed by the MPs identification and quantification techniques on sample preparation and MPs isolation as well as the materials used in the procedures. Finally, we address the expectations and new challenges related to instrumental innovations.
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•Novelties in the MP analysis in sand and sediment are explored.•Compatibility between extraction and determination is analyzed.•There is a need for protocols optimization in MP analysis.•Challenges and future aspects focus on instrumental innovations.
Polycyclic Aromatic Hydrocarbons (PAHs) are among the main persistent organic pollutants in the Arcticwhich enter the polar region from lower latitudes by air transport and ocean currents and ...accumulate in marine sediments. This work represents the first study in 25 years of the least studied and hard-to-reach areas of Siberian arctic seas. Sixteen priority PAHs as well as 1- and 2-methylnaphthalenes were analyzed by gas chromatography – tandem mass spectrometry in the twenty-four sediment samples taken from Kara, Laptev and East Siberian Seas in October 2020. The obtained sum concentrations ranged from 31 to 223 ng/ g with the greatest contribution of phenanthrene, benzobfluoranthene, benzokfluoranthene, as well as naphthalene and its methyl derivatives while the greatest PAH levels were observed in Laptev Sea. No correlations between sum PAH concentration, total organic carbon and black carbon contents were found. The toxic equivalent in benzoapyrene units was from 2.2–18.2 ng/ g that shows the general safe environmental situation in the region. The overall PAH level is comparable with the data obtained in 1990s which indicates a long-term persistence of pollution despite an overall decline in global PAH emissions. The main sources of PAHs involve mainly coal/biomass and liquid fuel combustion with weaker contribution of petroleum sources.
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•Priority PAHs and methylnaphthalenes from Kara, Laptev and East Siberian Seas in 2020.•No correlation between PAHs and total organic carbon•The origin of PAHs in arctic marine sediments
Dansgaard‐Oeschger (D‐O) cycles are the most dramatic, frequent, and wide‐reaching abrupt climate changes in the geologic record. On Greenland, D‐O cycles are characterized by an abrupt warming of 10 ...± 5°C from a cold stadial to a warm interstadial phase, followed by gradual cooling before a rapid return to stadial conditions. The mechanisms responsible for these millennial cycles are not fully understood but are widely thought to involve abrupt changes in Atlantic Meridional Overturning Circulation due to freshwater perturbations. Here we present a new, high‐resolution multiproxy marine sediment core monitoring changes in the warm Atlantic inflow to the Nordic seas as well as in local sea ice cover and influx of ice‐rafted debris. In contrast to previous studies, the freshwater input is found to be coincident with warm interstadials on Greenland and has a Fennoscandian rather than Laurentide source. Furthermore, the data suggest a different thermohaline structure for the Nordic seas during cold stadials in which relatively warm Atlantic water circulates beneath a fresh surface layer and the presence of sea ice is inferred from benthic oxygen isotopes. This implies a delicate balance between the warm subsurface Atlantic water and fresh surface layer, with the possibility of abrupt changes in sea ice cover, and suggests a novel mechanism for the abrupt D‐O events observed in Greenland ice cores.
Key Points
High‐resolution Nordic Seas core showing DO‐events synchronous to Greenland
Abrupt changes in Nordic Seas sea ice related to warm subsurface Atlantic water
A novel mechanism explaining DO‐cycles without ad‐hoc freshwater forcing
Iron (Fe) fluxes from reducing sediments and subglacial environments are potential sources of bioavailable Fe into the Southern Ocean. Stable Fe isotopes (δ56Fe) are considered a proxy for Fe sources ...and reaction pathways, but respective data are scarce and Fe cycling in complex natural environments is not understood sufficiently to constrain respective δ56Fe “endmembers” for different types of sediments, environmental conditions, and biogeochemical processes.
We present δ56Fe data from pore waters and sequentially extracted sedimentary Fe phases of two contrasting sites in Potter Cove (King George Island, Antarctic Peninsula), a bay that is affected by fast glacier retreat. Sediments close to the glacier front contain more easily reducible Fe oxides and pyrite and show a broader ferruginous zone, compared to sediments close to the ice-free coast, where surficial oxic meltwater streams discharge into the bay. Pyrite in sediments close to the glacier front predominantly derives from eroded bedrock. For the high amount of easily reducible Fe oxides proximal to the glacier we suggest mainly subglacial sources, where Fe liberation from comminuted material beneath the glacier is coupled to biogeochemical weathering processes (likely pyrite oxidation or dissimilatory iron reduction, DIR). Our strongest argument for a subglacial source of the highly reactive Fe pool in sediments close to the glacier front is its predominantly negative δ56Fe signature that remains constant over the whole ferruginous zone. This implies in-situ DIR does not significantly alter the stable Fe isotope composition of the accumulated Fe oxides. The nonetheless overall light δ56Fe signature of easily reducible Fe oxides suggests pre-depositional microbial cycling as it occurs in potentially anoxic subglacial environments. The strongest 56Fe-depletion in pore water and most reactive Fe oxides was observed in sediments influenced by oxic meltwater discharge. The respective site showed a condensed redox zonation and a pore water δ56Fe profile typical for in-situ Fe cycling.
We demonstrate that the potential of pore water δ56Fe as a proxy for benthic Fe fluxes is not straight-forward due to its large variability in marine shelf sediments at small spatial scales (−2.4‰ at the site proximal to oxic meltwater discharge vs. −0.9‰ at the site proximal to the marine glacier terminus, both at 2 cm sediment depth). The controlling factors are multifold and include the amount and reactivity of reducible Fe oxides and organic matter, the isotopic composition of the primary and secondary ferric substrates, sedimentation rates, and physical reworking (bioturbation, ice scraping). The application of δ56Fe geochemistry may prove valuable in investigating biogeochemical weathering and Fe cycling in subglacial environments. This requires, however (similarly to the use of δ56Fe for the quantification of benthic fluxes), that the spatial and temporal variability of the isotopic endmember is known and accounted for. Since geochemical data from subglacial environments are very limited, further studies are needed in order to sufficiently assess Fe cycling and fractionation at glacier beds and the composition of discharges from those areas.
Benthic bacteria and archaea can be considered biogeochemical engineers as they play a major role in organic matter (OM) degradation and nutrient cycling. As such, prokaryotic community structure, ...yielded from 16S rRNA amplicon sequencing, can reflect environmental conditions such as OM composition and quantity, nutrient availability, redox conditions, and natural/anthropogenic contaminants (e.g. petroleum hydrocarbons). To assess prokaryotic community structure, we sequenced marine sediments in the upper 10-cm layer on the northern Bering and southern Chukchi Sea shelves, a high-latitude region undergoing rapid environmental change. We then explored broader spatial patterns in community structure for surface sediments (upper 1 cm), incorporating samples from the Northeast Chukchi and Beaufort Seas in relation to environmental variables. Three assemblages were characterized at distinct depth horizons in the upper 10-cm sediment layer from the Northern Bering and Southern Chukchi benthos. One assemblage was exclusively found in sediments at greater than 1 cm sediment depth and contained a relatively higher proportion of anaerobic taxa (e.g. Anaerolineaceae, Desulfobulbaceae, and Desulfosarcinaceae). Overall, community distribution in the upper 10-cm reflected sediment grain size, OM quantity and composition, and possibly the influence of bioturbation. Two assemblages were characterized in surface sediments (upper 1 cm) across the broader Northern Bering and Chukchi Sea study area. A relatively high abundance of anaerobic taxa (e.g. SEEP-SRB4, Subgroup 23, and R76-B128) in one assemblage suggested comparatively suboxic sediments, and the other suggested allochthonous input of phytodetritus based on high abundance of diatom/particle associated microbes (e.g. Polaribacter, Dokdonia, and Ulvibacter), combined with high sediment Chl-a concentration. This latter assemblage may reflect depositional areas influenced by hydrographic patterns. Prokaryotic community structure across the North American Arctic highlights regional differences in environmental controls, with food-supply regimes influencing structure on the Bering-Chukchi inflow shelves, in contrast to the Beaufort interior shelves where nearshore heterogeneity (riverine input and terrigenous material) are major drivers of sediment prokaryote communities.
Dinoflagellate resting cysts with rare exception produce the only discrete link between the biology of extant dinoflagellate species and their fossil record. The geological preservability of such ...cysts allows them to be used for quantitative paleoecological reconstructions, especially in the Quaternary, and for biostratigraphy and the calibration of molecular clocks with the geological record. This contribution reviews and updates the taxonomy of 27 uncommon dinoflagellate cyst species and morphotypes belonging to the orders Gonyaulacales and Suessiales with occurrences in upper Quaternary marine sediments of the Northern Hemisphere. Comparative descriptions and illustrations are provided along with the biological affinity of each taxon where known and lowest stratigraphic occurrence.
•25 rare or endemic extant dinoflagellate cyst species and two morphotypes are briefly described and illustrated.•23 belong to the Gonyaulacales and 4 to the Suessiales.•Their stratigraphic ranges are provided.
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.
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•CH4/CO2 replacement behaviors in natural marine sediments are investigated.•CO2 diffusion is weakened by clayey sediment during replacement process.•NGH reservoir with moderate water ...content has excellent potential for replacement.•Optimized P-T conditions are crucial to improve CH4 recovery from hydrates.
The use of CH4/CO2 replacement from hydrate bearing sediments for CH4 recovery and CO2 storage is an alternative option to mitigate energy shortage and global warming. Fine marine sediments are highly attractive for abundant gas hydrate reserves and tremendous CO2 sequestration potential. However, the CH4/CO2 replacement regularity previously obtained from coarse sands may not be suitable for fine marine sediments because of their distinct differences in physical properties. In this study, fine natural marine sediments obtained from the South China Sea were used as porous media to investigate the CH4/CO2 replacement characteristics. The results indicated that the pressure and the temperature were the main controlling factors affecting the replacement efficiency. The content of initial methane hydrate and water in reservoir had a more significant effect on CO2 storage than CH4 recovery. The gas exchange kinetics in hydrates presented in fine marine sediments were significantly different from those in coarse grained sediments. CH4/CO2 replacement in fine marine sediment seemed to be inhibited by weak CO2 diffusion as peculiarities of the sediment including fine grain size, clay swelling and high proportion of bound water. According to the observed experimental results, the pressure and temperature conditions should be comprehensively optimized to enhance the mass transfer effect and improve economic benefits. This work provided greater insights into future marine NGH exploitation and contributed to carbon sequestration with applying CH4/CO2 replacement method.
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