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Analyses of gene expression of subsurface bacteria and archaea provide insights into their physiological adaptations to in situ subsurface conditions. We examined patterns of expressed genes in hydrothermally heated subseafloor sediments with distinct geochemical and thermal regimes in Guaymas Basin, Gulf of California, Mexico. RNA recovery and cell counts declined with sediment depth, however, we obtained metatranscriptomes from eight sites at depths spanning between 0.8 and 101.9 m below seafloor. We describe the metabolic potential of sediment microorganisms, and discuss expressed genes involved in tRNA, mRNA, and rRNA modifications that enable physiological flexibility of bacteria and archaea in the hydrothermal subsurface. Microbial taxa in hydrothermally influenced settings like Guaymas Basin may particularly depend on these catalytic RNA functions since they modulate the activity of cells under elevated temperatures and steep geochemical gradients. Expressed genes for DNA repair, protein maintenance and circadian rhythm were also identified. The concerted interaction of many of these genes may be crucial for microorganisms to survive and to thrive in the Guaymas Basin subsurface biosphere.

 

The solid inner core grows through crystallization of the liquid metallic outer core. This process releases latent heat as well as light elements, providing thermal and chemical buoyancy forces to drive the Earth’s geodynamo. Here we investigate temporal changes in the liquid outer core by measuring travel times of core-penetrating SKS waves produced by pairs of large earthquakes at close hypocenters. While the majority of the measurements do not require a change in the outer core, we observe SKS waves that propagate through the upper half of the outer core in the low latitude Pacific travel about one second faster at the time when the second earthquake occurred, about 20 years after the first earthquake. This observation can be explained by 2–3% of density deficit, possibly associated with high-concentration light elements in localized transient flows in the outer core, with a flow speed in the order of 40 km/year.

 

The seismic quality factor (Q) of the Earth’s mantle is of great importance for the understanding of the physical and chemical properties that control mantle anelasticity. The radial structure of the Earth’s Q is less well resolved compared to its wave speed structure, and large discrepancies exist among global 1-D Q models. In this study, we build a global data set of amplitude measurements of S, SS, SSS and SSSS waves using earthquakes that occurred between 2009 and 2017 with moment magnitudes ranging from 6.5 to 8.0. Synthetic seismograms for those events are computed in a 1-D reference model PREM, and amplitude ratios between observed and synthetic seismograms are calculated in the frequency domain by spectra division, with measurement windows determined based on visual inspection of seismograms. We simulate wave propagation in a global velocity model S40RTS based on SPECFEM3D and show that the average amplitude ratio as a function of epicentral distance is not sensitive to 3-D focusing and defocusing for the source–receiver configuration of the data set. This data set includes about 5500 S and SS measurements that are not affected by mantle transition zone triplications (multiple ray paths), and those measurements are applied in linear inversions to obtain a preliminary 1-D Q model QMSI. This model reveals a high Q region in the uppermost lower mantle. While model QMSI improves the overall datafit of the entire data set, it does not fully explain SS amplitudes at short epicentral distances or the amplitudes of the SSS and SSSS waves. Using forward modelling, we modify the 1-D model QMSI iteratively to reduce the overall amplitude misfit of the entire data set. The final Q model QMSF requires a stronger and thicker high Q region at depths between 600 and 900 km. This anelastic structure indicates possible viscosity layering in the mid mantle.

 

Multifunctional coatings with simultaneous antibacterial and anticorrosive properties are essential for marine environments, oil and gas industry, medical settings, and domestic/public appliances to preserve integrity and functionality of pipes, instruments, and surfaces. In this work, we developed a simple and effective method to prepare graphene oxide (GO)-hybridized waterborne epoxy (GOWE) coating to simultaneously improve anticorrosive and antibacterial properties . The effects of different GO filler ratios (0.05, 0.1, and 0.5, 1 wt%) on the electrochemical and antibacterial behaviors of the waterborne epoxy coating were investigated over short- and long-term periods. The electrochemical behavior was analyzed with salt solution for 64 days. The antibacterial effect of GOWE coating was evaluated with Shewanella oneidensis (MR-1), which is a microorganism that can be involved in corrosion. Our results revealed that concentrations as low as 0.1 wt% of the GO was effective performance than the waterborne epoxy coating without graphene oxide. This result is due to the high hydrophilicity of the graphene oxide fillers, which allowed great dispersion in the waterborne epoxy coating matrix. Furthermore, this study used a corrosion relevant bacterium as a model organism, that is, Shewanella oneidensis (MR-1), which is more relevant for real-word applications. This as-prepared GO-hybridized waterborne polymeric hybrid film provides new insight into the application of 2D nanomaterial polymer composites for simultaneous anticorrosive and antibacterial applications.