Giant magnetofossils and hyperthermal events
Giant magnetofossils and hyperthermal events
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DOI：
10.1016/j.epsl.2012.07.031
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发表时间：
2012-10-15
影响因子：
5.3
通讯作者：
Muxworthy, Adrian R.
中科院分区：
文献类型：
--
作者：
Chang, Liao;Roberts, Andrew P.;Muxworthy, Adrian R.
趋磁细菌生物矿化磁性矿物精确控制的大小，形态和化学计量。这些世界性细菌在水生环境中广泛观察到。如果在埋葬后被保存下来，趋磁细菌的无机遗骸就像记录古代地磁场变化的磁化石。它们还具有提供古环境信息的潜力。与传统的磁化石不同，巨磁化石（最有可能是由真核生物产生的）以前只在新泽西沿海平原的古新世-始新世热盛期（PETM; 55.8 Ma）沉积物中报道过一次。在这里，使用透射电子显微镜观察，我们提出了丰富的巨磁化石的证据，包括以前报道的细长棱柱和纺锤体，和新的巨大的子弹形磁铁矿晶体，在南极洲附近的南大洋，不仅在PETM，但也不久之前和之后的PETM。此外，我们还在中始新世气候适宜期（近似40 Ma）从赤道印度洋发现了巨大的子弹形磁铁矿晶体。我们的研究结果表明，一个更广泛的地理，环境和时间分布的巨型磁化石的地质记录与“超高温”事件。高温时全球风化作用的增强，以及亚氧成岩环境的扩大，可能提供了更多的生物有效铁，使巨磁化石的生物矿化。我们的微磁性模型表明存在磁性多畴（即，对于导航不理想）和单域（即，理想的导航）结构的巨大磁铁矿颗粒取决于它们的大小，形态和空间排列。不同的巨磁铁矿晶体形态似乎具有不同的生物功能，包括趋磁性和其他非航行目的。我们的观察表明，高温为巨型磁化石提供了理想的条件，并且这些生物体分布在全球。需要做更多的工作来了解磁化石形态，气候，养分供应和环境变化之间的相互作用。(C)2012爱思唯尔有限公司版权所有。
Magnetotactic bacteria biomineralize magnetic minerals with precisely controlled size, morphology, and stoichiometry. These cosmopolitan bacteria are widely observed in aquatic environments. If preserved after burial, the inorganic remains of magnetotactic bacteria act as magnetofossils that record ancient geomagnetic field variations. They also have potential to provide paleoenvironmental information. In contrast to conventional magnetofossils, giant magnetofossils (most likely produced by eukaryotic organisms) have only been reported once before from Paleocene-Eocene Thermal Maximum (PETM; 55.8 Ma) sediments on the New Jersey coastal plain. Here, using transmission electron microscopic observations, we present evidence for abundant giant magnetofossils, including previously reported elongated prisms and spindles, and new giant bullet-shaped magnetite crystals, in the Southern Ocean near Antarctica, not only during the PETM, but also shortly before and after the PETM. Moreover, we have discovered giant bullet-shaped magnetite crystals from the equatorial Indian Ocean during the Mid-Eocene Climatic Optimum (similar to 40 Ma). Our results indicate a more widespread geographic, environmental, and temporal distribution of giant magnetofossils in the geological record with a link to "hyperthermal" events. Enhanced global weathering during hyperthermals, and expanded suboxic diagenetic environments, probably provided more bioavailable iron that enabled biomineralization of giant magnetofossils. Our micromagnetic modelling indicates the presence of magnetic multi-domain (i.e., not ideal for navigation) and single domain (i.e., ideal for navigation) structures in the giant magnetite particles depending on their size, morphology and spatial arrangement. Different giant magnetite crystal morphologies appear to have had different biological functions, including magnetotaxis and other non-navigational purposes. Our observations suggest that hyperthermals provided ideal conditions for giant magnetofossils, and that these organisms were globally distributed. Much more work is needed to understand the interplay between magnetofossil morphology, climate, nutrient availability, and environmental variability. (C) 2012 Elsevier B.V. All rights reserved.