Recycled Archean sulfur in the mantle wedge of the Mariana Forearc and microbial sulfate reduction within an extremely alkaline serpentine seamount
Recycled Archean sulfur in the mantle wedge of the Mariana Forearc and microbial sulfate reduction within an extremely alkaline serpentine seamount
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马里亚纳前弧地幔楔中回收的太古代硫和极碱性蛇纹石海山内的微生物硫酸盐还原
DOI：
10.1016/j.epsl.2018.03.002
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发表时间：
2018
影响因子：
5.3
通讯作者：
Takai Ken
中科院分区：
文献类型：
--
作者：
Aoyama Shinnosuke;Nishizawa Manabu;Miyazaki Junichi;Shibuya Takazo;Ueno Yuichiro;Takai Ken
极端条件下微生物活动的识别对于确定陆地和外星生物形式的可居住和不可居住区域的潜在边界非常重要。马里亚纳前弧蛇纹岩海隆的海底以下区域是地球上生命最极端的环境之一，因为普遍存在pH值大于12的强碱性流体。根据孔隙水中硫酸盐的减少和溶解硫化物的富集，在南查莫罗蛇纹岩海山内存在着硫酸盐还原微生物的潜在活动。然而，硫酸盐还原微生物的垂直分布和硫酸盐的来源仍然不确定。为了解决这些问题，我们分析了S顶部沉积序列上部56 m中硫化物矿物和孔隙水硫酸盐的四重硫同位素。查莫罗海山和上升流流体中的溶解硫酸盐在同一海山山顶附近的一个套管井中收集，深度达202 mbsf（海底以下米）。硫化物矿物和孔隙水硫酸盐的浓度、δ 34 S和Δ 33 S′值的深度剖面表明微生物硫酸盐还原深度达30 mbsf。硫酸盐还原过程中的表观同位素分馏（ε 34）和质量相关指数（λ 33）分别为62±14‰和0.512±0.002。涌升流体显示出氯相对于海水的贫化和氨的负δ 15 N值（− 4‰）。虽然这些特征表明俯冲洋板块的脱水作用，但硫酸盐的负Δ 33 S′值（− 0.16‰至− 0.26‰，分析误差为±0.01‰）不太可能来自周围的现代地壳。相反，上升流流体中的硫酸盐可能具有非质量依赖（NMD）硫。由于NMD硫主要是在太古代大气中产生的，我们的研究结果表明，存在的回收太古代地壳，可以通过俯冲太古代洋壳或从NMD轴承OIB海山位于太平洋板块南缘的上地幔。
The identification of microbial activity under extreme conditions is important to define potential boundaries of the habitable and uninhabitable zones of terrestrial and extraterrestrial living forms. The subseafloor regimes of serpentinite seamounts in the Mariana Forearc are among the most extreme environments for life on earth owing to the widespread presence of highly alkaline fluids with pH values greater than 12. The potential activity of sulfate-reducing microorganisms has been suggested within the South Chamorro serpentinite seamounts on the basis of depletion of sulfate and enrichment of dissolved sulfide in pore water. However, the vertical distribution of sulfate-reducing microorganisms and the origin of sulfate are still uncertain. To address these issues, we analyzed quadruple sulfur isotopes of sulfide minerals and pore water sulfate in the upper 56 m of sedimentary sequences at the summit of the S. Chamorro Seamount and those of dissolved sulfate in upwelling fluids collected as deep as 202 mbsf (meters below the seafloor) in a cased hole near the summit of the same seamount. The depth profiles of the concentrations and the δ 34 S and Δ 33 S′ values of sulfide minerals and pore water sulfate indicate microbial sulfate reduction as deep as 30 mbsf. Further, apparent isotopic fractionations (ε 34) and exponents of mass dependent relationships (λ 33) during sulfate reduction are estimated to be 62±14‰ and 0.512±0.002, respectively. The upwelling fluids show both the chlorine depletion relative to seawater and the negative δ 15 N values of ammonia (− 4‰). Although these signatures point to dehydration of the subducting oceanic plate, the negative Δ 33 S′ values of sulfate (− 0.16‰ to− 0.26‰ with analytical errors of±0.01‰) are unlikely to originate from surrounding modern crusts. Instead, sulfate in the upwelling fluid likely possess non-mass-dependent (NMD) sulfur. Because NMD sulfur was produced primarily in the Archean atmosphere, our results suggest that the presence of recycled Archean crust that could be incorporated into the upper mantle through subduction of Archean oceanic crusts or from the NMD-bearing OIB seamounts located in the southern margin of the Pacific Plate.