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      Data report: grain size distribution of unconsolidated sands offshore Shimokita Peninsula, Japan (IODP Site C0020): Expedition 337

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      Proceedings of the IODP

      Integrated Ocean Drilling Program

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          Abstract

          We report particle size analyses measured from 28 unconsolidated sand samples recovered during Integrated Ocean Drilling Program Expedition 337 from Hole C0020A. These samples span from 1277 to 2002 meters below seafloor (mbsf) across two lithostratigraphic units that record a transition from a nearshore estuarine/intertidal to an offshore hemipelagic paleoenvironment. Most recovered lithologies, including coarse-grained lithologies, are semiconsolidated to consolidated; however, some intervals of sand are unconsolidated and suitable for particle size analysis. Bulk sand samples were measured using a laser diffraction particle size analyzer. All samples fall within the range of sand to silty sand, with silty sand more abundant deeper than 1925 mbsf. Samples contain 49%–97% sand, 3%–42% silt, and 0%–13% clay. Median grain diameter ranges from 55 to 405 µm. Clay and silt content in these sands reach a minimum at ~1500 mbsf and then increase below 1925 mbsf in a coal-bearing unit containing shale, siltstone, sandstone, and unconsolidated sand.

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          DEEP BIOSPHERE. Exploring deep microbial life in coal-bearing sediment down to ~2.5 km below the ocean floor.

          Microbial life inhabits deeply buried marine sediments, but the extent of this vast ecosystem remains poorly constrained. Here we provide evidence for the existence of microbial communities in ~40° to 60°C sediment associated with lignite coal beds at ~1.5 to 2.5 km below the seafloor in the Pacific Ocean off Japan. Microbial methanogenesis was indicated by the isotopic compositions of methane and carbon dioxide, biomarkers, cultivation data, and gas compositions. Concentrations of indigenous microbial cells below 1.5 km ranged from <10 to ~10(4) cells cm(-3). Peak concentrations occurred in lignite layers, where communities differed markedly from shallower subseafloor communities and instead resembled organotrophic communities in forest soils. This suggests that terrigenous sediments retain indigenous community members tens of millions of years after burial in the seabed.
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            Microbial population structures in soil particle size fractions of a long-term fertilizer field experiment.

            Soil structure depends on the association between mineral soil particles (sand, silt, and clay) and organic matter, in which aggregates of different size and stability are formed. Although the chemistry of organic materials, total microbial biomass, and different enzyme activities in different soil particle size fractions have been well studied, little information is available on the structure of microbial populations in microhabitats. In this study, topsoil samples of different fertilizer treatments of a long-term field experiment were analyzed. Size fractions of 200 to 63 microm (fine sand fraction), 63 to 2 microm (silt fraction), and 2 to 0.1 microm (clay fraction) were obtained by a combination of low-energy sonication, wet sieving, and repeated centrifugation. Terminal restriction fragment length polymorphism analysis and cloning and sequencing of 16S rRNA genes were used to compare bacterial community structures in different particle size fractions. The microbial community structure was significantly affected by particle size, yielding higher diversity of microbes in small size fractions than in coarse size fractions. The higher biomass previously found in silt and clay fractions could be attributed to higher diversity rather than to better colonization of particular species. Low nutrient availability, protozoan grazing, and competition with fungal organisms may have been responsible for reduced diversities in larger size fractions. Furthermore, larger particle sizes were dominated by alpha-Proteobacteria, whereas high abundance and diversity of bacteria belonging to the Holophaga/Acidobacterium division were found in smaller size fractions. Although very contrasting organic amendments (green manure, animal manure, sewage sludge, and peat) were examined, our results demonstrated that the bacterial community structure was affected to a greater extent by the particle size fraction than by the kind of fertilizer applied. Therefore, our results demonstrate specific microbe-particle associations that are affected to only a small extent by external factors.
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              A Scale of Grade and Class Terms for Clastic Sediments

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                Author and article information

                Journal
                10.2204/iodp.proc.337.2013
                Proceedings of the IODP
                Integrated Ocean Drilling Program
                1930-1014
                11 December 2017
                Article
                10.2204/iodp.proc.337.203.2017
                10c58522-cd4b-4c56-bd4a-1ed3c549a39e

                This work is licensed under a Creative Commons Attribution 4.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/

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                Self URI (journal page): http://publications.iodp.org/

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