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In Lake Matano, Indonesia, the world's largest known ferruginous basin, more than 50% of authigenic organic matter is degraded through methanogenesis, despite high abundances of Fe (hydr)oxides in the lake sediments. Biogenic CH₄ accumulates to high concentrations (up to 1.4 mmol L⁻¹) in the anoxic bottom waters, which contain a total of 7.4 × 10⁵ tons of CH₄. Profiles of dissolved inorganic carbon (ΣCO₂) and carbon isotopes (δ¹³C) show that CH₄ is oxidized in the vicinity of the persistent pycnocline and that some of this CH₄ is likely oxidized anaerobically. The dearth of NO₃⁻ and SO₄²⁻ in Lake Matano waters suggests that anaerobic methane oxidation may be coupled to the reduction of Fe (and/or Mn) (hydr)oxides. Thermodynamic considerations reveal that CH₄ oxidation coupled to Fe(III) or Mn(III/IV) reduction would yield sufficient free energy to support microbial growth at the substrate levels present in Lake Matano. Flux calculations imply that Fe and Mn must be recycled several times directly within the water column to balance the upward flux of CH₄. 16S gene cloning identified methanogens in the anoxic water column, and these methanogens belong to groups capable of both acetoclastic and hydrogenotrophic methanogenesis. We find that methane is important in C cycling, even in this very Fe-rich environment. Such Fe-rich environments are rare on Earth today, but they are analogous to conditions in the ferruginous oceans thought to prevail during much of the Archean Eon. By analogy, methanogens and methanotrophs could have formed an important part of the Archean Ocean ecosystem.

We apply a recently developed measurement technique for methane (CH 4 ) isotopologues * (isotopic variants of CH 4 - 13 CH 4 , 12 CH 3 D, 13 CH 3 D, and 12 CH 2 D 2 ) to identify contributions to the atmospheric burden from fossil fuel and microbial sources. The aim of this study is to constrain factors that ultimately control the concentration of this potent greenhouse gas on global, regional, and local levels. While predictions of atmospheric methane isotopologues have been modeled, we present direct measurements that point to a different atmospheric methane composition and to a microbial flux with less clumping (greater deficits relative to stochastic) in both 13 CH 3 D and 12 CH 2 D 2 than had been previously assigned. These differences make atmospheric isotopologue data sufficiently sensitive to variations in microbial to fossil fuel fluxes to distinguish between emissions scenarios such as those generated by different versions of EDGAR (the Emissions Database for Global Atmospheric Research), even when existing constraints on the atmospheric CH 4 concentration profile as well as traditional isotopes are kept constant.

Author(s): S. Farokhipoor [1]; C. Magen (corresponding author) [2, 3]; S. Venkatesan [4]; J. Iniguez [5]; C. J. M. Daumont [1]; D. Rubi [1]; E. Snoeck [3, 6]; M. Mostovoy [...]

A large volume of freshwater is incorporated in the relatively fresh (salinity ~32-33) Pacific Ocean waters that are transported north through the Bering Strait relative to deep Atlantic salinity in the Arctic Ocean (salinity ~34.8). These freshened waters help maintain the halocline that separates cold Arctic surface waters from warmer Arctic Ocean waters at depth. The stable oxygen isotope composition of the Bering Sea contribution to the upper Arctic Ocean halocline was established as early as the late 1980's as having a δ18OV-SMOW value of approximately -1.1‰. More recent data indicates a shift to an isotopic composition that is more depleted in 18O (mean δ18O value ~-1.5‰). This shift is supported by a data synthesis of >1400 water samples (salinity from 32.5 to 33.5) from the northern Bering and Chukchi seas, from the years 1987-2020, which show significant year-to-year, seasonal and regional variability. This change in the oxygen isotope composition of water in the upper halocline is consistent with observations of added freshwater in the Canada Basin, and mooring-based estimates of increased freshwater inflows through Bering Strait. Here, we use this isotopic time-series as an independent means of estimating freshwater flux changes through the Bering Strait. We employed a simple end-member mixing model that requires that the volume of freshwater (including runoff and other meteoric water, but not sea ice melt) flowing through Bering Strait has increased by ~40% over the past two decades to account for a change in the isotopic composition of the 33.1 salinity water from a δ18O value of approximately -1.1‰ to a mean of -1.5‰. This freshwater flux change is comparable with independent published measurements made from mooring arrays in the Bering Strait (freshwater fluxes rising from 2000-2500 km3 in 2001 to 3000-3500 km3 in 2011)., Competing Interests: The first author (Cooper) is a section editor for PLOS One. This does not alter our adherence to PLOS ONE policies on sharing data and materials.

Structural and chemical properties of InAs/AlSb interfaces have been studied by transmission electron microscopy. InAs/AlSb multilayers were grown by molecular beam epitaxy with different growth sequences at interfaces. The out-of-plane strain, determined using high resolution microscopy and geometrical phase analysis, has been related to the chemical composition of the interfaces analyzed by high angle annular dark field imaging. Considering the local strain and chemistry, we estimated the interface composition and discussed the mechanisms of interface formation for the different growth sequences. In particular, we found that the formation of the tensile AlAs-type interface is spontaneously favored due to its high thermal stability compared to the InSb-type interface. We also showed that the interface composition could be tuned using an appropriate growth sequence. [ABSTRACT FROM AUTHOR]

In this work we report the growth and structural and magnetic characterization of heteroepitaxial [Fe.sub.3][O.sub.4]/MgO/Fe junctions. All three layers have been deposited by pulsed laser deposition. Combining High Resolution Transmission Electron Microscopy and X-ray results, we have obtained for the heterostructure the epitaxy relation MgO(001) [100]//[Fe.sub.3][O.sub.4] (001)[100]/MgO(001)[100]/Fe(001)[110]. All interfaces appear very sharp with relatively small root-mean square (rms) roughness, ~ 0.2 nm. The magnetic coupling between [Fe.sub.3][O.sub.4] and Fe electrodes is also very small, J ~ 0.03 mJ/[m.sup.2] (MgO barrier thickness of 2 nm). Microfabrication of Magnetic Tunnel Junctions from these heterostructures is in progress. Index Terms--Epitaxial layers, pulsed laser deposition, spintronics, thin films.

We have investigated the magnetic properties of Ni nanoaggregates produced by ion implantation in ZnO single crystals. Several deviations from classical models usually adopted to describe the magnetic properties of nanoparticle systems were found. The strain between host and Ni nanoaggregates induces a magnetic anisotropy with a preferred direction. We show that these anisotropy effects can be misinterpreted as a ferromagnetic or antiferromagnetic coupling among the nanoaggregates similar to that of an oriented, interacting nanocrystal ensemble. [ABSTRACT FROM AUTHOR]

Carbon dioxide (CO 2 ) and methane (CH 4 ) are natural and anthropogenic products that play a central role in the global carbon cycle and regulating Earth's climate. Applications utilizing laser absorption spectroscopy, which continuously measure concentrations and stable isotope ratios of these greenhouse gases, are routinely employed to measure the source and magnitude of atmospheric inputs. We developed a discrete sample introduction module (DSIM) to enable measurements of methane and CO 2 concentrations and δ 13 C values from limited volume (5-100 mL) gas samples when interfaced with a commercially available cavity ring-down spectroscopy (CRDS) analyzer. The analysis has a dynamic range that spans six orders of magnitude from 100% analyte to the lower limit of instrument detection (2 ppm). We demonstrate system performance for methane by comparing concentrations and δ 13 C results from the DSIM-CRDS system and traditional methods for a variety of sample types, including low concentration (nanomolar CH 4 ) seawater and high concentration (>90% CH 4 ) natural gas. The expansive concentration range of the field-portable DSIM-CRDS system can measure enhances analytical performance for investigating methane and CO 2 dynamics and, potentially, other gases measured by laser absorption spectroscopy.

The expected reduction of ice algae with declining sea ice may prove to be detrimental to the Pacific Arctic ecosystem. Benthic organisms that rely on sea ice organic carbon (iPOC) sustain benthic predators such as the Pacific walrus (Odobenus rosmarus divergens). The ability to track the trophic transfer of iPOC is critical to understanding its value in the food web, but prior methods have lacked the required source specificity. We analyzed the H-Print index, based on biomarkers of ice algae versus phytoplankton contributions to organic carbon in marine predators, in Pacific walrus livers collected in 2012, 2014 and 2016 from the Northern Bering Sea (NBS) and Chukchi Sea. We paired these measurements with stable nitrogen isotopes (δ15N) to estimate trophic position. We observed differences in the contribution of iPOC in Pacific walrus diet between regions, sexes, and age classes. Specifically, the contribution of iPOC to the diet of Pacific walruses was higher in the Chukchi Sea (52%) compared to the NBS (30%). This regional difference is consistent with longer annual sea ice persistence in the Chukchi Sea. Within the NBS, the contribution of iPOC to walrus spring diet was higher in females (~45%) compared to males (~30%) for each year (p < 0.001), likely due to specific foraging behavior of females to support energetic demands associated with pregnancy and lactation. Within the Chukchi Sea, the iPOC contribution was similar between males and females, yet higher in juveniles than in adults. Despite differences in the origin of organic carbon fueling the system (sea ice versus pelagic derived carbon), the trophic position of adult female Pacific walruses was similar between the NBS and Chukchi Sea (3.2 and 3.5, respectively), supporting similar diets (i.e. clams). Given the higher quality of organic carbon from ice algae, the retreat of seasonal sea ice in recent decades may create an additional vulnerability for female and juvenile Pacific walruses and should be considered in management of the species., Competing Interests: The authors have declared that no competing interests exist.

We report a strong variation of the magnetic properties and of the antiphase boundaries (APBs) density of Fe3O4(001) epitaxial thin films grown on thin Fe(001) and Cr(001) buffer layers on a MgO(001) substrate in comparison with similar magnetite films grown directly on MgO(001). The magnetization of the Fe/Fe3O4 and Cr/Fe3O4 bilayers presents a more squared hysteresis loop and reach saturation at much lower magnetic field (∼10–15 kOe) than the Fe3O4 thin films of same thickness, which hardly saturate at 70 kOe. The magnetization of the magnetite layers has been estimated on both the Fe- and Cr-based samples and a value close to that of the bulk Fe3O4 has been obtained, which points to the magnetic saturation of the Fe3O4 layer induced by the metallic buffers. Transmission electron microscopy has been used to investigate the possible structural origin of this phenomenon studying the APB network of Fe3O4 in the three types of samples. The calculation of the average domain size reveals that the APB density in the bilayers is substantially reduced in comparison with their counterparts without buffer. The domain sizes obtained in Fe and Cr samples are similar, which points to a structural origin probably due to the strain caused by the lattice misfit between the buffers and the magnetite. A lower APB density statistically reduces the influence of the antiferromagnetic interactions existing across some of the boundaries, achieving the saturation of the Fe3O4 layer at much lower magnetic fields. [ABSTRACT FROM AUTHOR]

We report a strong variation of the magnetic properties and of the antiphase boundaries (APBs) density of Fe3O4(001) epitaxial thin films grown on thin Fe(001) and Cr(001) buffer layers on a MgO(001) substrate in comparison with similar magnetite films grown directly on MgO(001). The magnetization of the Fe/Fe3O4 and Cr/Fe3O4 bilayers presents a more squared hysteresis loop and reach saturation at much lower magnetic field (∼10–15 kOe) than the Fe3O4 thin films of same thickness, which hardly saturate at 70 kOe. The magnetization of the magnetite layers has been estimated on both the Fe- and Cr-based samples and a value close to that of the bulk Fe3O4 has been obtained, which points to the magnetic saturation of the Fe3O4 layer induced by the metallic buffers. Transmission electron microscopy has been used to investigate the possible structural origin of this phenomenon studying the APB network of Fe3O4 in the three types of samples. The calculation of the average domain size reveals that the APB density in the bilayers is substantially reduced in comparison with their counterparts without buffer. The domain sizes obtained in Fe and Cr samples are similar, which points to a structural origin probably due to the strain caused by the lattice misfit between the buffers and the magnetite. A lower APB density statistically reduces the influence of the antiferromagnetic interactions existing across some of the boundaries, achieving the saturation of the Fe3O4 layer at much lower magnetic fields. [ABSTRACT FROM AUTHOR]

The high resolution and scanning transmission electron microscopy techniques are employed to explain the preparation, morphology and the magnetic properties of the various W-capped Co nanoparticles. A increase in the nominal thickness of the W capping layer is shown to lead to a reduction in the formation of the Co-E alloys.

The transport and magnetotransport properties in Fe/MgO multilayers around the Fe percolation threshold are explored as a function of the temperature and the nominal thickness of iron layer (t). The samples with Fe thickness below percolation threshold are explained by considering spin-polarized electron tunneling between nanometer-sized, superparamagnetic Fe grains.