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      Data report: water activity of the deep coal-bearing basin off Shimokita from IODP Expedition 337

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          Abstract

          Water activity (Aw) is one of the physicochemical properties that may influence microbial activity in deep subseafloor environments; however, Aw for subseafloor sediments has never been examined, even at shallow depths. This study investigated Aw data obtained from core samples collected during Integrated Ocean Drilling Program Expedition 337 in the deep-water coal-bearing basin off Shimokita, Japan. Aw did not show any depth dependence and was relatively low in coal-bearing layers. Aw at depths of 0–2466 meters below seafloor ranged from 0.95 to 0.98, which is quite high and well suited to sustaining microorganisms. Aw for sedimentary rocks was less affected by lithology and porosity than it was by the NaCl concentration and degree of fluid saturation. In addition, the Aw measurements performed in this study yielded results that corresponded closely with values estimated using Raoult’s law and interstitial water chemistry. It therefore appears that Aw for deep-marine sediments is strongly affected by pore water chemistry. The low Aw anomaly in the coalbed unit is considered to be due to contamination by drilling mud and fluid into core samples.

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          Global distribution of microbial abundance and biomass in subseafloor sediment.

          The global geographic distribution of subseafloor sedimentary microbes and the cause(s) of that distribution are largely unexplored. Here, we show that total microbial cell abundance in subseafloor sediment varies between sites by ca. five orders of magnitude. This variation is strongly correlated with mean sedimentation rate and distance from land. Based on these correlations, we estimate global subseafloor sedimentary microbial abundance to be 2.9⋅10(29) cells [corresponding to 4.1 petagram (Pg) C and ∼0.6% of Earth's total living biomass]. This estimate of subseafloor sedimentary microbial abundance is roughly equal to previous estimates of total microbial abundance in seawater and total microbial abundance in soil. It is much lower than previous estimates of subseafloor sedimentary microbial abundance. In consequence, we estimate Earth's total number of microbes and total living biomass to be, respectively, 50-78% and 10-45% lower than previous estimates.
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            Thermodynamics of hydrothermal systems at elevated temperatures and pressures

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              Equations for the soil-water characteristic curve

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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
                22 March 2018
                Article
                10.2204/iodp.proc.337.204.2018
                300428d6-34ae-4c69-b97a-c4102b03fb14

                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/

                History

                Earth & Environmental sciences,Oceanography & Hydrology,Geophysics,Chemistry,Geosciences

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