A global transition to ferruginous conditions in the early Neoproterozoic oceans
A global transition to ferruginous conditions in the early Neoproterozoic oceans
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DOI：
10.1038/ngeo2434
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发表时间：
2015-06-01
影响因子：
18.3
通讯作者：
Shields-Zhou, Graham A.
中科院分区：
文献类型：
--
作者：
Guilbaud, Romain;Poulton, Simon W.;Shields-Zhou, Graham A.
真核生物在25亿至5.42亿年前的元古宙（1）期间扩张，其背景是海洋化学的波动（2-4）。大约18亿年前之后，全球海洋的特征被认为是表层含氧沃茨，沿着生产性大陆边缘的中层深度为缺氧和硫化物沃茨，较深的沃茨为缺氧和含铁（含铁）海水（5-7）。硫化物沃茨的空间范围可能随时间而变化（5、6），但这种从表层到深层的氧化还原结构一直持续到大约7.17亿年前的第一次新元古代冰川作用（8-11）。在这里，我们报告的海洋氧化还原条件的分析，整个元古代使用新的和现有的铁形态和硫同位素数据从多个核心和露头。我们发现一个全球性的过渡，从硫化物到含铁的中深度沃茨在最早的新元古代，在低纬度的超大陆Rodinia的合并。我们认为，含铁的条件是由高活性铁相对于硫酸盐的海洋流入量的增加，在风化制度的变化和广泛的大陆上Rodinia的硫酸盐的吸收驱动。我们认为，这一过渡基本上解毒海洋边缘设置，允许扩大的机会，真核生物多样化后，一个长期的进化停滞在10亿年前。
Eukaryotic life expanded during the Proterozoic eon(1), 2.5 to 0.542 billion years ago, against a background of fluctuating ocean chemistry(2-4). After about 1.8 billion years ago, the global ocean is thought to have been characterized by oxygenated surface waters, with anoxic and sulphidic waters in middle depths along productive continental margins and anoxic and iron-containing (ferruginous) deeper waters(5-7). The spatial extent of sulphidic waters probably varied through time(5,6), but this surface-to-deep redox structure is suggested to have persisted until the first Neoproterozoic glaciation about 717 million years ago(8-11). Here we report an analysis of ocean redox conditions throughout the Proterozoic using new and existing iron speciation and sulphur isotope data from multiple cores and outcrops. We find a global transition from sulphidic to ferruginous mid-depth waters in the earliest Neoproterozoic, coincident with the amalgamation of the supercontinent Rodinia at low latitudes. We suggest that ferruginous conditions were initiated by an increase in the oceanic influx of highly reactive iron relative to sulphate, driven by a change in weathering regime and the uptake of sulphate by extensive continental evaporites on Rodinia. We propose that this transition essentially detoxified ocean margin settings, allowing for expanded opportunities for eukaryote diversification following a prolonged evolutionary stasis before one billion years ago.