Hayes John M, Waldbauer Jacob R
Woods Hole Oceanographic Institution, Department of Geology and Geophysics, Woods Hole, MA 02543, USA.
Philos Trans R Soc Lond B Biol Sci. 2006 Jun 29;361(1470):931-50. doi: 10.1098/rstb.2006.1840.
Earth's biogeochemical cycle of carbon delivers both limestones and organic materials to the crust. In numerous, biologically catalysed redox reactions, hydrogen, sulphur, iron, and oxygen serve prominently as electron donors and acceptors. The progress of these reactions can be reconstructed from records of variations in the abundance of 13C in sedimentary carbonate minerals and organic materials. Because the crust is always receiving new CO2 from the mantle and a portion of it is being reduced by photoautotrophs, the carbon cycle has continuously released oxidizing power. Most of it is represented by Fe3+ that has accumulated in the crust or been returned to the mantle via subduction. Less than 3% of the estimated, integrated production of oxidizing power since 3.8 Gyr ago is represented by O2 in the atmosphere and dissolved in seawater. The balance is represented by sulphate. The accumulation of oxidizing power can be estimated from budgets summarizing inputs of mantle carbon and rates of organic-carbon burial, but levels of O2 are only weakly and indirectly coupled to those phenomena and thus to carbon-isotopic records. Elevated abundances of 13C in carbonate minerals ca 2.3 Gyr old, in particular, are here interpreted as indicating the importance of methanogenic bacteria in sediments rather than increased burial of organic carbon.
地球的碳生物地球化学循环将石灰岩和有机物质输送到地壳。在众多生物催化的氧化还原反应中，氢、硫、铁和氧作为主要的电子供体和受体。这些反应的进程可以从沉积碳酸盐矿物和有机物质中碳-13丰度变化的记录中重建。由于地壳不断从地幔接收新的二氧化碳，并且其中一部分被光合自养生物还原，碳循环不断释放出氧化能力。其中大部分以在地壳中积累或通过俯冲返回地幔的三价铁表示。自38亿年前以来估计的氧化能力综合产量中，不到3%以大气中以及溶解在海水中的氧气表示。其余部分以硫酸盐表示。氧化能力的积累可以通过总结地幔碳输入和有机碳埋藏速率的预算来估计，但氧气水平与这些现象以及碳同位素记录的关联较弱且间接。特别是约23亿年前的碳酸盐矿物中碳-13丰度升高，在此被解释为表明产甲烷细菌在沉积物中的重要性而非有机碳埋藏增加。
