Reductive dissolution of magnetite is known to occur below the Fe-redox boundary in sediments. In this study, detailed processes associated with biogenic magnetite dissolution are documented. A sediment core from the Japan Sea was used for this purpose, in which reductive dissolution of magnetic minerals is known to start at depths of about 1.15 m and is mostly complete within a depth interval of about 0.35 m. Using first-order reversal curve diagrams, preferential dissolution of biogenic magnetite within this interval is estimated from the observation that a narrow peak that extends along the coercivity axis (central ridge), which is indicative of biogenic magnetite, diminishes downcore. Transmission electron microscopy is used to demonstrate that the sediments contain three magnetofossil morpho-types: octahedra, hexagonal prisms, and bullet-shaped forms. Within the reductive dissolution zone, partially etched crystals are commonly observed. With progressive dissolution, the proportion of bullet-shaped magnetofossils decreases, whereas hexagonal prisms become more dominant. This observation can be explained by the differences in resistance to dissolution among crystal planes of magnetite and the differences in surface area to volume ratios. Magnetofossil morphology may reflect the preference of magnetotactic bacterial lineages for inhabiting specific chemical environments in sediments. However, it could also reflect alteration of the original morphological compositions during reductive diagenesis, which should be considered when using magnetofossil morphology as a paleoenvironmental proxy.

中文翻译：

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生物磁铁矿的还原溶解

已知磁铁矿的还原溶解发生在沉积物中的 Fe-氧化还原边界以下。在这项研究中，记录了与生物磁铁矿溶解相关的详细过程。为此，使用了日本海的沉积岩心，其中磁性矿物的还原溶解已知开始于约 1.15 m 的深度，并在约 0.35 m 的深度间隔内完成。使用一阶反转曲线图，根据观察到沿矫顽力轴（中央脊）延伸的窄峰（指示生物磁铁矿）减少了铁芯，估计了该区间内生物磁铁矿的优先溶解。透射电子显微镜用于证明沉积物包含三种磁化石形态类型：八面体、六棱柱、和子弹形状。在还原溶解区内，通常会观察到部分蚀刻的晶体。随着逐渐溶解，子弹形磁体化石的比例减少，而六边形棱柱则占主导地位。这一观察结果可以通过磁铁矿晶面之间抗溶解性的差异和表面积与体积比的差异来解释。磁化石形态可能反映了趋磁细菌谱系在沉积物中栖息特定化学环境的偏好。然而，它也可以反映还原成岩过程中原始形态成分的改变，在使用磁化石形态作为古环境代理时应该考虑这一点。通常观察到部分蚀刻的晶体。随着逐渐溶解，子弹形磁体化石的比例减少，而六边形棱柱变得更加突出。这一观察结果可以通过磁铁矿晶面之间抗溶解性的差异和表面积与体积比的差异来解释。磁化石形态可能反映了趋磁细菌谱系在沉积物中栖息特定化学环境的偏好。然而，它也可以反映还原成岩过程中原始形态成分的改变，在使用磁化石形态作为古环境代理时应该考虑这一点。通常观察到部分蚀刻的晶体。随着逐渐溶解，子弹形磁体化石的比例减少，而六边形棱柱则占主导地位。这一观察结果可以通过磁铁矿晶面之间抗溶解性的差异和表面积与体积比的差异来解释。磁化石形态可能反映了趋磁细菌谱系在沉积物中栖息特定化学环境的偏好。然而，它也可以反映还原成岩过程中原始形态成分的改变，在使用磁化石形态作为古环境代理时应该考虑这一点。这一观察结果可以通过磁铁矿晶面之间抗溶解性的差异和表面积与体积比的差异来解释。磁化石形态可能反映了趋磁细菌谱系在沉积物中栖息特定化学环境的偏好。然而，它也可以反映还原成岩过程中原始形态成分的改变，在使用磁化石形态作为古环境代理时应该考虑这一点。这一观察结果可以通过磁铁矿晶面之间抗溶解性的差异和表面积与体积比的差异来解释。磁化石形态可能反映了趋磁细菌谱系在沉积物中栖息特定化学环境的偏好。然而，它也可以反映还原成岩过程中原始形态成分的改变，在使用磁化石形态作为古环境代理时应该考虑这一点。