PNAS：热液系统与地球的地幔微生物

摘要 : 美国Woods Hole海洋学研究所一项研究提出，在洋底的热液流与海水的混合提供了支持微生物所需的化学能量。

美国Woods Hole海洋学研究所一项研究提出，在洋底的热液流与海水的混合提供了支持微生物所需的化学能量。在地球的大部分历史中，构造板块的运动让来自地幔的火成岩暴露在海水中，制造出了能量丰富的热液系统，这可能支持了地球上的生命的出现。Frieder Klein及其同事使用分析化学和显微镜技术研究了在葡萄牙沿海附近伊比利亚边缘的海底下面提取的热液改变的地幔岩芯。在这些海洋环境中发现了诸如细菌、古生菌和蚌类等生物，但是人们对在海底之下发生的这些生物过程的了解仍然很少。地质学岩石记录和热力学约束条件提示，这个热液系统的能量情况是有利于需氧和厌氧反应的。此外，这组作者发现，在岩石样本中化石化的密集的微生物群落强烈地富含有机碳。除了蛋白质和氨基酸，这些群落含有的脂类可能被归结于减少硫酸盐的细菌和制造甲烷的古生菌。这组作者说，热液系统在地质学时间尺度上可能提供支持海底之下的一个独特的微生物群落所需的化学能量。

原文链接：

Fluid mixing and the deep biosphere of a fossil Lost City-type hydrothermal system at the Iberia Margin

原文摘要：

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 °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 13C (δ13CTOC = −19.4‰). 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.

doi: 10.1073/PNAS.1504674112

作者：Frieder Klein

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