Department of Geosciences, University of Bremen, Klagenfurter Straße, 28359 Bremen, Germany.
Geochem Trans. 2012 Jan 27;13:2. doi: 10.1186/1467-4866-13-2.
The East Pacific Rise (EPR) at 9°50'N hosts a hydrothermal vent field (Bio9) where the change in fluid chemistry is believed to have caused the demise of a tubeworm colony. We test this hypothesis and expand on it by providing a thermodynamic perspective in calculating free energies for a range of catabolic reactions from published compositional data. The energy calculations show that there was excess H2S in the fluids and that oxygen was the limiting reactant from 1991 to 1997. Energy levels are generally high, although they declined in that time span. In 1997, sulfide availability decreased substantially and H2S was the limiting reactant. Energy availability dropped by a factor of 10 to 20 from what it had been between 1991 and 1995. The perishing of the tubeworm colonies began in 1995 and coincided with the timing of energy decrease for sulfide oxidizers. In the same time interval, energy availability for iron oxidizers increased by a factor of 6 to 8, and, in 1997, there was 25 times more energy per transferred electron in iron oxidation than in sulfide oxidation. This change coincides with a massive spread of red staining (putative colonization by Fe-oxidizing bacteria) between 1995 and 1997.For a different cluster of vents from the EPR 9°50'N area (Tube Worm Pillar), thermodynamic modeling is used to examine changes in subseafloor catabolic metabolism between 1992 and 2000. These reactions are deduced from deviations in diffuse fluid compositions from conservative behavior of redox-sensitive species. We show that hydrogen is significantly reduced relative to values expected from conservative mixing. While H2 concentrations of the hydrothermal endmember fluids were constant between 1992 and 1995, the affinities for hydrogenotrophic reactions in the diffuse fluids decreased by a factor of 15 and then remained constant between 1995 and 2000. Previously, these fluids have been shown to support subseafloor methanogenesis. Our calculation results corroborate these findings and indicate that the 1992-1995 period was one of active growth of hydrogenotrophic communities, while the system was more or less at steady state between 1995 and 2000.
东太平洋海隆 9°50'N 处拥有一个热液喷口场（Bio9），据信这里的流体化学变化导致了管蠕虫殖民地的消亡。我们通过提供一个热力学视角，根据已发表的成分数据计算一系列分解代谢反应的自由能，来检验这一假说并加以扩展。能量计算表明，流体中存在过量的 H2S，而氧气是 1991 年至 1997 年的限制反应物。尽管在此期间能量水平普遍较高，但它们有所下降。1997 年，硫化物的可用性大幅减少，H2S 成为限制反应物。与 1991 年至 1995 年相比，能量可用性下降了 10 到 20 倍。管蠕虫殖民地的消亡始于 1995 年，与硫化物氧化剂能量减少的时间一致。在同一时间间隔内，铁氧化剂的能量可用性增加了 6 到 8 倍，而在 1997 年，铁氧化过程中每传递一个电子的能量是硫化物氧化过程的 25 倍。这种变化与 1995 年至 1997 年之间大量出现的红色染色（假定为铁氧化细菌的定植）相吻合。对于东太平洋海隆 9°50'N 地区的另一个喷口群（管状蠕虫柱），使用热力学模型来研究 1992 年至 2000 年间海底分解代谢代谢的变化。这些反应是根据扩散流体成分偏离氧化还原敏感物质保守行为推断出来的。我们表明，与保守混合预期相比，氢的含量显著降低。虽然 1992 年至 1995 年期间热液端元流体中的 H2 浓度保持不变，但扩散流体中氢营养型反应的亲和力下降了 15 倍，然后在 1995 年至 2000 年期间保持不变。此前，这些流体已被证明支持海底甲烷生成。我们的计算结果证实了这些发现，并表明 1992-1995 年是氢营养型群落活跃生长的时期，而 1995 年至 2000 年期间，该系统或多或少处于稳定状态。
