Influence of Magnetofossils on Paleointensity Estimations Inferred From Principal Component Analyses of First‐Order Reversal Curve Diagrams for Sediments From the Western Equatorial Pacific
Influence of Magnetofossils on Paleointensity Estimations Inferred From Principal Component Analyses of First‐Order Reversal Curve Diagrams for Sediments From the Western Equatorial Pacific
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DOI：
10.1029/2021gc010081
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发表时间：
2021-10
期刊：
影响因子：
3.7
通讯作者：
Kosuke Inoue;T. Yamazaki;Y. Usui
中科院分区：
文献类型：
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作者：
Kosuke Inoue;T. Yamazaki;Y. Usui
沉积物中趋磁细菌(磁性化石)来源的磁铁矿的相对丰度可能会影响地磁场的相对古强度(RPI)的估算，因为一些研究报道了RPI与滞后剩磁磁化率与饱和等温剩磁的比率(KARM/SIRM)之间的负相关，KARM/SIRM代表了生物与陆源磁性矿物的比例以及磁性颗粒的大小。这项研究旨在更有选择性地使用一阶逆转曲线(FORC)图来评估磁化石对RPI估计的影响。我们研究了赤道西太平洋的三个岩芯(KR0515-PC4、MD982187和MR1402-PC1)，其中ARM和KARM/SIRM归一化的平均天然剩余磁化强度存在较大差异。利用主成分分析方法对三个岩心的块状样品和MD982187岩心提取的硅酸盐磁性包裹体进行了主成分分析，发现了三个端元(EM)(EM1：硅酸盐磁性包裹体，EM2：其他陆源磁性包裹体，EM3：生物成因)。EM3的比例在三个核心之间差别很大。平均RPI随着EM3比例的增加而减小，这可能是由于小的静磁相互作用提高了磁化石的ARM捕获效率所致。EM3比例与KARM/SIRM相关，证实了KARM/SIRM代表了生物磁性成分与陆源磁性成分的比例。核心MR1402-PC1的EM3比例最高，其核心内变异较小。从FORC-PCA单独应用于该岩心，我们推断生物成因磁铁矿链的构型，如弯曲和坍塌，也可能影响KARM/SIRM和RPI估计。
Relative abundance of magnetite originated from magnetotactic bacteria (magnetofossils) in sediments may influence relative paleointensity (RPI) estimations of the geomagnetic field, as some studies reported an inverse correlation between RPI and the ratio of anhysteretic remanent magnetization susceptibility to saturation isothermal remanent magnetization (kARM/SIRM), a proxy of the proportion of biogenic to terrigenous magnetic minerals as well as magnetic grain size. This study aims to evaluate the influence of magnetofossils on RPI estimations more selectively using first‐order reversal curve (FORC) diagrams. We studied three cores (KR0515‐PC4, MD982187, and MR1402‐PC1) from the western equatorial Pacific, among which large differences exist in the average natural remanent magnetization intensity normalized by ARM and kARM/SIRM. Principal component analyses (PCAs) were applied to FORC diagrams measured on bulk specimens from the three cores and silicate‐hosted magnetic inclusions extracted from Core MD982187, and three endmembers (EMs) were revealed (EM1: silicate‐hosted magnetic inclusions, EM2: other terrigenous, EM3: biogenic). EM3 proportions vary widely among the three cores. The average RPI decreases with increasing EM3 proportion, which is probably caused by higher ARM acquisition efficiency of magnetofossils due to small magnetostatic interactions. EM3 proportion correlates with kARM/SIRM, which confirms that kARM/SIRM represents the proportion of biogenic to terrigenous magnetic components. Core MR1402‐PC1 has the highest EM3 proportion, and its within‐core variation is small. From FORC‐PCA applied solely to this core, we infer that the configurations of biogenic magnetite chains such as bending and collapse may also influence kARM/SIRM and RPI estimations.