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The archaeal phylum Bathyarchaeota, which is composed of a large number of diverse lineages, is widespread and abundant in marine sediments. Environmental factors that control the distribution, abundance and evolution of this largely diversified archaeal phylum are currently unclear. In this study, a new pair of specific primers that target the major marine subgroups of bathyarchaeotal 16S rRNA genes was designed and evaluated to investigate the distribution and abundance of Bathyarchaeota in marine sediments. The abundance of Bathyarchaeota along two sediment cores from the deep-sea sediments of South China Sea (SCS, each from the Dongsha and Shenhu area) was determined. A strong correlation was found between the bathyarchaeotal abundance and the content of total organic carbon (TOC), suggesting an important role of Bathyarchaeota in organic matter remineralisation in the sediments of SCS. Furthermore, diversity analysis revealed that subgroups Bathy-2, Bathy-8 and Bathy-10 were dominant bathyarchaeotal members of the deep-sea sediments in the SCS. Bathy-8 was found predominantly within the reducing and deeper sediment layers, while Bathy-10 occurred preferentially in the oxidizing and shallower sediment layers. Our study lays a foundation for the further understanding of the ecological functions and niche differentiation of the important but not well-understood sedimentary archaeal group. [ABSTRACT FROM AUTHOR]

The article presents a study which aims to determine the decomposition temperature of cold seep carbonate through delta carbonate method. The result shows that the carbon dioxide content yielded from all the eight samples increase gradually with time and pyrolysis temperature. Carbon isotopic composition of carbon dioxide reveals distinct isotopic-change tend of two groups with time increase and temperatures.

With the exploration, development, and research of deep‐sea resources, there is an urgent need for long‐term and continuous observation data of the deep‐sea seabed boundary layer. The traditional method of deep‐sea seabed survey and sampling based on scientific research vessels has the discontinuity of observation data in space and time scales. There are some problems in the seabed in situ observation method based on the seabed observation network for low mobility and high operation and maintenance costs, restricting the in‐depth understanding of the dynamic change process of the deep‐sea floor. To solve the above problems, an open and modular data acquisition control system was designed based on an embedded system and signal processing technology. In terms of the physical, chemical, geological, and ecosystem characteristics of the seafloor or near the seafloor boundary layer, various functional sensors and instrumentation were matched to form an independent underwater integrated measurement or experimental device, eventually realizing in situ multiparameter and long‐time series observations of the seafloor. The system data acquisition and control test were completed through laboratory experiments, which verified the feasibility of the system design. The research showed important theoretical and technical reference significance for the exploration and development of resources in the submarine boundary layer and the promotion of deep‐sea scientific research. [ABSTRACT FROM AUTHOR]

Deep‐sea environments are the largest ecosystem of the global biosphere and constitute a crucial role in global biogeochemical cycles. We integrated biogeochemical and molecular ecological approaches to investigate microbial activity and diversity, with the goal of elucidating pathways and regulations of methane cycling and low molecular weight (LMW) compounds metabolism in different deep‐sea sediments of the South China Sea. We found that methanogenesis, anaerobic oxidation of methane, and sulfate reduction occurred concurrently with low rates in surface sediments of the Haima area (~ 50 cm push cores) and in subsurface sediments of the Shenhu area (~ 8 m piston core). In the presence of sulfate, methanogenesis was fueled by methylotrophic substrates, in agreement with thermodynamic calculations as well as the detection of the methylotrophic methanogenic genus Methanococcoides. Higher oxidation rates of LMW compounds than methanogenesis rates, suggested acetate, and to a lesser extent, methanol and methylamine, were predominantly utilized as an energy source by nonmethanogenic microorganisms (e.g., sulfate‐reducing bacteria). Diverse methanotrophic archaea (e.g., ANME‐1a/b and ANME‐2a/b) and sulfate‐reducing bacteria (e.g., Desulfarculaceae and Desulfobacteraceae) were observed and the abundance of mcrA and dsrA genes varied over depth and between sites. Dominant archaeal groups, such as Bathyarchaeota, Thermoplasmatale, Woesearchaeota, Lokiarchaeota, were consistently detected at both areas. Multivariate statistical analysis demonstrated sulfate was the most relevant environmental variable that correlated with the archaeal community composition. These results suggested that the presence of sulfate controlled methane cycling and LMW carbon metabolism pathways, and also affected the composition of the microbial community. [ABSTRACT FROM AUTHOR]

The accumulation of authigenic carbonate in marine sediments has been regarded as a significant contributor to the carbon cycle over Earth's history. However, accurate quantification of the extent of authigenic carbonate formation in both modern and ancient oceans has been challenging due to limited approaches. Here, we analyzed calcium, magnesium, dissolved inorganic carbon, and alkalinity pore‐water profiles of 153 sites influenced by methane diffusion from the northern South China Sea. By combining these data with published data of diffusive sulfate flux, we found a significant positive correlation between carbonate precipitation rate and sulfate flux in the subseafloor. This correlation can be used to quantify the regional extent of authigenic carbonate formation, representing an advantage over a spatial interpolation approach. We therefore propose that the observed correlation can serve as a new approach for quantifying authigenic carbonate formation in shallow sediments along continental margins for both modern and ancient oceans. Plain Language Summary: Carbonate mineral precipitation through removing seawater dissolved inorganic carbon—the marine carbonate factory—plays a critical role in shaping marine carbon cycling and global climate. The formation of authigenic carbonate from pore‐water of marine sediments represents a variable share of the marine carbonate factory throughout geological history. However, it is challenging to quantify the extent of such authigenic carbonate formation. By analyzing pore‐water parameters from 153 sites influenced by methane diffusion of the northern South China Sea, we found a significant positive correlation between the rate of carbonate precipitation and the diffusive flux of sulfate into shallow sediments. Given the existence of estimates on the sizes of the seawater sulfate pool and diffusive fluxes of sulfate into sediments over Earth's history, we propose that the observed correlation can be used for quantifying authigenic carbonate formation in shallow sediments along continental margins through time, which will greatly advance our understanding for past carbon cycling and its relation to climate. Key Points: Porewater parameters from 153 sites of the northern South China Sea were evaluated to quantify the extent of authigenic carbonate formationRate of carbonate formation strongly correlates with diffusive flux of sulfate into sediments affected by methane diffusionA correlation of carbonate formation rate with sulfate flux is used to quantify most of authigenic carbonate formation in shallow sediments [ABSTRACT FROM AUTHOR]

Summary: Methane is a potent greenhouse gas; methane production and consumption within seafloor sediments has generated intense interest. Anaerobic oxidation of methane (AOM) and methanogenesis (MOG) primarily occur at the depth of the sulfate–methane transition zone or underlying sediment respectively. Methanogenesis can also occur in the sulfate‐reducing sediments through the utilization of non‐competitive methylated compounds; however, the occurrence and importance of this process are not fully understood. Here, we combined a variety of data, including geochemical measurements, rate measurements and molecular analyses to demonstrate the presence of a cryptic methane cycle in sulfate‐reducing sediments from the continental shelf of the northern South China Sea. The abundance of methanogenic substrates as well as the high MOG rates from methylated compounds indicated that methylotrophic methanogenesis was the dominant methanogenic pathway; this conclusion was further supported by the presence of the methylotrophic genus Methanococcoides. High potential rates of AOM were observed in the sediments, indicating that methane produced in situ could be oxidized simultaneously by AOM, presumably by ANME‐2a/b as indicated by 16S rRNA gene analysis. A significant correlation between the relative abundance of methanogens and methanotrophs was observed over sediment depth, indicating that methylotrophic methanogenesis could potentially fuel AOM in this environment. In addition, higher potential rates of AOM than sulfate reduction rates at in situ methane conditions were observed, making alternative electron acceptors important to support AOM in sulfate‐reducing sediment. AOM rates were stimulated by the addition of Fe/Mn oxides, suggesting AOM could be partially coupled to metal oxide reduction. These results suggest that methyl‐compounds driven methane production drives a cryptic methane cycling and fuels AOM coupled to the reduction of sulfate and other electron acceptors. [ABSTRACT FROM AUTHOR]