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Data report: carbon content and isotopic composition of basalts and sediments in North Pond, Expedition 336

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Proceedings of the IODP

Integrated Ocean Drilling Program

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      Abstract

      The uppermost about 500 m of basaltic ocean crust is permeable, and fluid flow is focused in specific areas at the contacts of lava flows or in brecciated zones. In these areas, seawater oxidizes young basaltic crust (younger than 10 Ma), and this interaction affects the microbial ecosystems. Iron cycling, both oxidation and reduction of iron, supports metabolic activity in basalts; however, the microorganisms responsible for Fe oxidation of basalts are not clear. In this study, carbon isotopic analyses of basalts and sediments at North Pond, the western flank of the mid-Atlantic Ridge, were conducted to understand the origin and formation of carbon compounds in relation to possible microbial activity in basaltic crust. Total carbon (TC) contents range approximately from 6 to 11 wt% for whole-sediment samples. Depth profiles of the carbon isotopic compositions (δ1C-TC) for sediments (approximately -0.04 to +1.93 ) are similar to those of TC. TC (approximately 0.01-0.37 wt%) and total organic carbon (TOC) (approximately 0.01-0.03 wt%) contents for basalts are almost constant with depth, whereas sediment breccias and carbonates contain more carbon than basalts (approximately 3.56-11.9 wt%). The value of δ13C-TC for basalts ranges approximately from -21.8 to +2.69. Sediment breccias and carbonates have larger δ13C-TC values, approximately from -18.6 to +2.82. The value of δ13C-TOC for hard rocks is lower at greater depths. The value of δ13C-kerogen is slightly smaller than that of δ13C-TOC.

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      Most cited references 12

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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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          Microbial ecology of the dark ocean above, at, and below the seafloor.

          The majority of life on Earth--notably, microbial life--occurs in places that do not receive sunlight, with the habitats of the oceans being the largest of these reservoirs. Sunlight penetrates only a few tens to hundreds of meters into the ocean, resulting in large-scale microbial ecosystems that function in the dark. Our knowledge of microbial processes in the dark ocean-the aphotic pelagic ocean, sediments, oceanic crust, hydrothermal vents, etc.-has increased substantially in recent decades. Studies that try to decipher the activity of microorganisms in the dark ocean, where we cannot easily observe them, are yielding paradigm-shifting discoveries that are fundamentally changing our understanding of the role of the dark ocean in the global Earth system and its biogeochemical cycles. New generations of researchers and experimental tools have emerged, in the last decade in particular, owing to dedicated research programs to explore the dark ocean biosphere. This review focuses on our current understanding of microbiology in the dark ocean, outlining salient features of various habitats and discussing known and still unexplored types of microbial metabolism and their consequences in global biogeochemical cycling. We also focus on patterns of microbial diversity in the dark ocean and on processes and communities that are characteristic of the different habitats.
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            Author and article information

            Journal
            10.2204/iodp.proc.336.2012
            Proceedings of the IODP
            Integrated Ocean Drilling Program
            1930-1014
            21 September 2015
            10.2204/iodp.proc.336.203.2015

            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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