Fluid mixing and the deep biosphere of a fossil Lost City-type hydrothermal system at the Iberia Margin
Fluid mixing and the deep biosphere of a fossil Lost City-type hydrothermal system at the Iberia Margin
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DOI：
10.1073/pnas.1504674112
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发表时间：
2015-09-29
影响因子：
11.1
通讯作者：
Orsi, William D.
中科院分区：
文献类型：
--
作者：
Klein, Frieder;Humphris, Susan E.;Orsi, William D.
海底下还原热液流体与海水的混合被认为提供了支持水合海洋地幔中深部化能自养生命所需的能量和基质（即，蛇纹岩）。然而，在蛇纹岩托管的海底下混合区的地圈-生物圈相互作用仍然没有受到很好的约束。在这里，我们研究化石微生物群落和流体混合过程中的海底下的白垩纪失落的城市型热液系统在岩浆贫乏的被动伊比利亚边缘（大洋钻探计划腿149，孔897 D）。水镁石-方解石矿物组合从混合流体中沉淀出来。白垩纪古海底下65米，温度为31.7 +/- 4.3摄氏度，风化、富含碳酸盐的蛇纹岩角砾岩和蛇纹岩之间存在陡峭的化学梯度。在中等温度下，氧化海水和强还原热液流体的混合创造了能够支持微生物活动的条件。致密的微生物菌落在强烈富集有机碳（高达0.5重量%）的水镁石-方解石脉中结晶总碳量），但C-13贫化（Δ C-13（TOC）=-19.4ppm）。我们检测到的细菌二醚脂质生物标志物，古菌和古菌四醚的组合类似于在活跃的迷城热液场的碳酸盐烟囱中发现的。在泛古陆解体期间，地幔岩石暴露于海水中，可能在海底扩张开始之前，为伊比利亚边缘的化能自养微生物群落提供了燃料。失落之城型蛇纹岩化系统已被发现在南极海脊、俯冲带的弧前环境和大陆边缘。看来，无论它们出现在哪里，它们都可以支持微生物的生命，即使是在深海海底环境中。
Subseafloor mixing of reduced hydrothermal fluids with seawater is believed to provide the energy and substrates needed to support deep chemolithoautotrophic life in the hydrated oceanic mantle (i.e., serpentinite). However, geosphere-biosphere interactions in serpentinite-hosted subseafloor mixing zones remain poorly constrained. Here we examine fossil microbial communities and fluid mixing processes in the subseafloor of a Cretaceous Lost City-type hydrothermal system at the magma-poor passive Iberia Margin (Ocean Drilling Program Leg 149, Hole 897D). Brucite-calcite mineral assemblages precipitated from mixed fluids ca. 65 m below the Cretaceous paleo-seafloor at temperatures of 31.7 +/- 4.3 degrees C within steep chemical gradients between weathered, carbonate-rich serpentinite breccia and serpentinite. Mixing of oxidized seawater and strongly reducing hydrothermal fluid at moderate temperatures created conditions capable of supporting microbial activity. Dense microbial colonies are fossilized in brucite-calcite veins that are strongly enriched in organic carbon (up to 0.5 wt.% of the total carbon) but depleted in C-13 (delta C-13(TOC) = -19.4 parts per thousand). We detected a combination of bacterial diether lipid biomarkers, archaeol, and archaeal tetraethers analogous to those found in carbonate chimneys at the active Lost City hydrothermal field. The exposure of mantle rocks to seawater during the breakup of Pangaea fueled chemolithoautotrophic microbial communities at the Iberia Margin, possibly before the onset of seafloor spreading. Lost City-type serpentinization systems have been discovered at midocean ridges, in forearc settings of subduction zones, and at continental margins. It appears that, wherever they occur, they can support microbial life, even in deep subseafloor environments.