Magnetotactic bacterial response to Antarctic dust supply during the Palaeocene-Eocene thermal maximum
Magnetotactic bacterial response to Antarctic dust supply during the Palaeocene-Eocene thermal maximum
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DOI：
10.1016/j.epsl.2012.04.003
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发表时间：
2012-06-01
影响因子：
5.3
通讯作者：
Zachos, James C.
中科院分区：
文献类型：
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作者：
Larrasoana, Juan C.;Roberts, Andrew P.;Zachos, James C.
记录古新世-始新世热最大值（PETM）的海洋沉积物的独特磁性被认为是由于细菌磁化石信号，该信号与古新世-始新世热最大值（PETM）期间增强的风化条件有关。研究结果表明，克尔格伦高原南部（海洋钻探计划738C孔，南大洋）深海沉积物中细菌磁铁矿的优势不仅存在于PETM时期，而且存在于热事件前后。贯穿始新世纪的磁化石的出现表明细菌磁小体的出现不是由于保存作用。相反，我们认为这是由于持续温和的铁还原条件，溶解了最不稳定的风成铁，这有利于持续的趋磁细菌活性，而没有强大到足以溶解活性较低的磁铁矿和赤铁矿。第三纪始新世早期风成赤铁矿丰度的增强表明当时邻近的南极大陆较为干燥。我们的研究结果提供了证据表明，除了在始新世（PETM）开始和结束的两个短暂的快速变化的古环境条件外，风沙的铁营养是制约克格伦高原南部深海趋磁细菌增殖的主要限制因素。风成尘增加的铁供应，提高了海洋初级生产力和随后向海底输送的有机碳，以及温和的铁还原成岩条件，似乎是为趋磁细菌提供磁铁矿生物矿化所需的铁所必需的，从而驱动了在研究的克格伦高原南部的PETM记录中磁铁矿丰度的显著增加。我们对Blake Nose（大西洋）1051B洞深海PETM记录的分析未能识别出磁化石，尽管有证据表明可能起源于风成的磁铁矿和赤铁矿的存在。这些PETM剖面的磁性特征对比表明，需要进一步了解古环境和成岩因素，它们的相互作用导致深海沉积物中磁性化石的产生和保存。(C) 2012 Elsevier B.V.版权所有
Distinct magnetic properties of marine sediments that record the Palaeocene-Eocene thermal maximum (PETM) have been suggested to be due to a bacterial magnetofossil signal that is linked to enhanced weathering conditions during the PETM. We document the dominance of bacterial magnetite in deep-sea sediments from southern Kerguelen Plateau (Ocean Drilling Program Hole 738C, southern Ocean) not only during the PETM, but also before and after the thermal event. This occurrence of magnetofossils throughout the PETM indicates that the occurrence of bacterial magnetosomes is not due to a preservation effect. Instead, we suggest that it is due to sustained mild iron-reducing conditions that dissolved the most labile aeolian-derived iron, which favoured continued magnetotactic bacterial activity without being strong enough to dissolve the less reactive magnetite and haematite. Enhanced aeolian haematite abundances at the beginning of the PETM indicate drier conditions on the neighbouring Antarctic continent at those times. Our results provide evidence that iron fertilisation by aeolian dust was the main limiting factor that conditioned proliferation of magnetotactic bacteria in the deep sea at the southern Kerguelen Plateau, with the exception of two short periods of rapidly changing palaeoenvironmental conditions at the onset and termination of the PETM. Increased iron supply from aeolian dust, that enhanced oceanic primary productivity and subsequent delivery of organic carbon to the seafloor, along with mild iron-reducing diagenetic conditions, seem to have been necessary to provide the iron needed for magnetite biomineralization by magnetotactic bacteria to drive their marked increase in abundance in the studied PETM record from southern Kerguelen Plateau. Our analyses of a deep-sea PETM record from Hole 1051B at Blake Nose (Atlantic Ocean) failed to identify magnetofossils despite evidence for the occurrence of magnetite and haematite of probable aeolian origin. Contrasting magnetic properties at these PETM sections indicate that further work is needed to understand the palaeoenvironmental and diagenetic factors whose interactions lead to production and preservation of magnetofossils in deep-sea sediments. (C) 2012 Elsevier B.V. All rights reserved.