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Cryoconite granules are naturally occurring microbial structures on glacier surfaces worldwide. They play a key role in carbon and nitrogen cycling in glacier ecosystems and can accelerate the melting of snow and ice. However, detailed mechanism of nitrogen cycling in cryoconite granules remains unclear. Here, we demonstrate that redox stratification affects the spatial distribution of N cycling processes in cryoconite granules. Based on microsensor measurements for O2, NH4+, NO2– and NO3–, we identified the presence of fine-scale redox stratification within cryoconite granules. Cyanobacteria at the surface layer of the granules created oxic conditions, whereas the inner core of the granules was anoxic. Metatranscriptomic analyses indicated the active occurrences of nitrification in the inner core, whereas denitrification actively occurred both in the inner core and the surface layer of the granules. Cyanobacteria in the inner core of the granules were inactive, and likely dead and being degraded, providing carbon and nitrogen to support nitrifiers and denitrifiers. Quantities of nitrification genes/transcripts were greater in large cryoconite granules than small ones, most likely because nitrogen substrates were more abundantly present in the inner core of large granules due to distinct redox stratification. Our results suggest that the development of a granular structure of cryoconite granules can largely affect carbon and nitrogen cycling on glaciers. [ABSTRACT FROM AUTHOR]

We recorded P and S waves traveling through the oceanic lithosphere-asthenosphere system (LAS) using broadband ocean-bottom seismometers in the northwest Pacific, and we quantitatively separated the intrinsic (anelastic) and extrinsic (scattering) attenuation effects on seismic wave propagation to directly infer the thermomechanical properties of the oceanic LAS.The strong intrinsic attenuation in the asthenosphere obtained at higher frequency (~3 hertz) is comparable to that constrained at lower frequency (~100 seconds) by surface waves and suggests frequency-independent anelasticity, whereas the intrinsic attenuation in the lithosphere is frequency dependent.This difference in frequency dependence indicates that the strong and broad peak dissipation recently observed in the laboratory exists only in the asthenosphere and provides new insight into what distinguishes the asthenosphere from the lithosphere. [ABSTRACT FROM AUTHOR]

This study presents an approach to better characterize the P‐wave and S‐wave velocity structure of the seafloor sediment layer using ocean bottom seismometers. The presence of low‐velocity seafloor sediment layers influences the observed seismic record at the seafloor over a broad frequency range, such that detailed knowledge of this sediment structure is essential to predict its effect on teleseismic records. We use the radial component of teleseismic P waves and autocorrelation functions of the radial, vertical, and pressure components of teleseismic P and S waves to obtain sediment layer models using the Markov chain Monte Carlo approach with parallel tempering. Synthetic tests show that the body waves constrain the P‐ and S‐wave impedances and travel times and the P‐ to S‐wave velocity ratio of the sediment layers. The proposed method resolves thin layers at a high resolution, including the uppermost thin (∼50 m to a few hundred meters) low S‐wave velocity layer. Real data applications at sites across the Pacific Ocean that are coincident with previous in situ studies demonstrate the effectiveness of this method in characterizing the seafloor sediment unit. The sediment models characterized by this new approach will allow us to more accurately predict and correct the effects of sediment layers in generating P‐ and S‐wave reverberations. Plain Language Summary: Ocean bottom seismometers are powerful tools for investigating the detailed structure of the oceanic mantle. However, most ocean bottom seismometers are placed above the low‐velocity water‐saturated sediment layer, such that their seismic records are inevitably affected by this seafloor sediment layer. Detailed constraints on the structure of the seafloor sediment layer allow us to accurately predict its effects on the observed seismic records. The seafloor sediment layer may consist of multiple discontinuities and vary regionally. This study proposes a new approach for characterizing the seismic properties of the seafloor sediment layer using teleseismic body waves recorded at ocean bottom seismometers. Synthetic tests show that the method can resolve thin sublayers within the sediment layer, such as a very thin low shear‐wave velocity layer and sharp seismic velocity jumps. Real data applications show that the sediment models obtained using this approach are in good agreement with those obtained from direct measurements and previous body‐wave analyses. Our proposed method will enable more detailed prediction and correction of the influence of the sediment layer on ocean bottom seismometer records, thereby providing more accurate constraints on deeper Earth structures. Key Points: The seismic properties of the seafloor sediment layer are characterized using ocean bottom seismometer teleseismic body‐wave recordsThe P‐ and S‐wave impedances and travel times and the VP/VS values of each sublayer within the sediment layer are resolvedIn situ seafloor sediment structure constraints will enable accurate correction and prediction of shallow structure effects [ABSTRACT FROM AUTHOR]

Determination of a response of the sea water column to teleseismic plane wave is important to suppress adverse effects of water reverberations in calculating receiver functions (RFs) using ocean-bottom seismometer (OBS) records. We present a novel non-linear waveform analysis method using the simulated annealing algorithm to determine such a water-layer response recorded by an OBS array. We then demonstrate its usefulness for the RF estimation through its application to synthetic and observed data. Synthetic experiments suggest that the water-layer response constrained in this way has a potential to improve RFs of OBS records drastically even in the high-frequency range (to 4 Hz). By applying it to data observed by the OBS array around the Kii Peninsula, southwestern Japan, we identified a low-velocity zone at the top of the subducting Philippine Sea plate. This zone may represent the incoming fluid-rich sediment layer that has been reported by active-source seismic survey. [ABSTRACT FROM AUTHOR]

Cryoconite granules are aggregations of microorganisms with mineral particles that form on glacier surfaces. To understand the processes by which the granules develop, this study focused on the altitudinal distribution of the granules and photosynthetic microorganisms on the glacier, bacterial community variation with granules size and environmental factors affecting the growth of the granules. Size-sorted cryoconite granules collected from five different sites on Qaanaaq Glacier were analyzed. C and N contents were significantly higher in large (diameter greater than 250 µm) granules than in smaller (diameter 30-249 µm) granules. Bacterial community structures, based on 16S rRNA gene amplicon sequencing, were different between the smaller and larger granules. The filamentous cyanobacterium Phormidesmis priestleyi was the dominant bacterial species in larger granules. Multivariate analysis suggests that the abundance of mineral particles on the glacier surface is the main factor controlling growth of these cyanobacteria. These results show that the supply of mineral particles on the glacier enhances granule development, that P. priestleyi is likely the key species for primary production and the formation of the granules and that the bacterial community in the granules changes over the course of the granule development. [ABSTRACT FROM AUTHOR]

The glacier ice worm, Mesenchytraeus solifugus, is a unique annelid, inhabiting only snow and ice in North American glaciers. Here, we analyzed the taxonomic composition of bacteria associated with M. solifugus based on the 16S rRNA gene. We analyzed four fixed-on-site and 10 starved ice worm individuals, along with glacier surface samples. In total, 1341 clones of 16S rRNA genes were analyzed for the ice worm samples, from which 65 bacterial phylotypes (99.0% cut-off) were identified. Of these, 35 phylotypes were closely related to sequences obtained from their habitat glacier and/or other components of cryosphere; whereas three dominant phylotypes were affiliated with animal-associated lineages of the class Mollicutes. Among the three, phylotype Ms-13 shared less than 89% similarity with database sequences and was closest to a gut symbiont of a terrestrial earthworm. Using fluorescence in situ hybridization, Ms-13 was located on the gut wall surface of the ice worms. We propose a novel genus and species, 'Candidatus Vermiplasma glacialis', for this bacterium. Our results raise the possibility that the ice worm has exploited indigenous glacier bacteria, while several symbiotic bacterial lineages have maintained their association with the ice worm during the course of adaptive evolution to the permanently cold environment. [ABSTRACT FROM AUTHOR]