Purpose

We investigated the magnetic properties (abundance, grain size, and mineralogy) of iron oxides present in Lake L-55 sediments, Schirmacher Oasis, East Antarctica, with an aim to understand their spatial distribution and the underlying mechanisms that control their formation and distribution.

Methods

Twenty-five surficial sediments retrieved from different parts of Lake L-55 were subjected to the entire range of environmental magnetic (magnetic susceptibility, anhysteretic remanent magnetization (ARM), isothermal remanent magnetization (IRM)) measurements (at different field strengths). Inter-parametric ratios (χ_ARM/SIRM, χ_ARM/χ_lf, χ_ARM/χ_fd, IRM_{20 mT}/SIRM, IRM_{20 mT}/ARM, S-ratio, L-ratio) provided insights into the magnetic properties (abundance, grain size, and mineralogy of iron oxides). Scanning electron microscopic-energy dispersive X-ray spectroscopic (SEM-EDS) analysis was performed on magnetic extracts from a few sediments. Besides, organic matter (%) was also calculated for the sediment samples. Principal component analysis was performed to gain information on the presence of different components and their relative dominance.

Results

The iron oxides are strongly magnetic (high values of concentration-dependent parameters). The principal iron oxide is magnetite (S-ratio > 0.90) which is coarse-grained (multi-domain (MD) and stable single-domain (SSD) grains), and there is no influence of authigenic greigite, bacterial magnetite, and anthropogenic magnetite. The mineralogy is confirmed by SEM-EDS data. The iron oxides are of different grain sizes, and their contribution is in the order of MD > SSD > SP as shown by the principal component analysis. Pedogenic iron oxide minerals seem to be present in the samples whose formation is due to the oxidation of magnetite into hematite. However, they are of SSD size and not SP, suggesting that the intensity of pedogenesis is not sufficient to form SP grains.

Conclusion

The iron oxide minerals are mainly terrigenous, and the biogenic activity within the lake is not sufficient to modify the ferrimagnetic minerals. Spatial distribution patterns suggest the non-uniform distribution of magnetite/titanomagnetite of varying sizes in the lake basin which is transported by both melt water streams and winds.

中文翻译：

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南极东部席尔马赫绿洲表层沉积物的磁性：空间分布和控制因素

目的

我们调查了南极东部Schirmacher Oasis L-55湖沉积物中存在的铁氧化物的磁性（丰度，晶粒度和矿物学），旨在了解其空间分布以及控制其形成和分布的潜在机制。

方法

对从L-55湖不同部分取回的25个表层沉积物进行了整个范围的环境磁测量（磁化率，滞回剩磁（ARM），等温剩磁（IRM））（在不同的场强下）。间参数比（χ _ARM / SIRM，χ _ARM / χ _LF，χ _ARM / χ _FD，IRM _20mT下/ SIRM，IRM _20mT下/ ARM，s ^ -ratio，大号-比率）提供了对磁性（丰度，晶粒大小和氧化铁矿物学）的了解。扫描电子显微镜-能量色散X射线光谱（SEM-EDS）分析是对一些沉积物的磁性提取物进行的。此外，还计算了沉积物样品的有机物含量（％）。进行主成分分析以获取有关不同成分的存在及其相对优势的信息。

结果

氧化铁具有强磁性（浓度依赖参数值较高）。主要的氧化铁是磁铁矿（S比率> 0.90），它是粗晶粒（多畴（MD）和稳定的单畴（SSD）晶粒），并且没有自生的钙铁矿，细菌性磁铁矿和人为的影响磁铁矿。通过SEM-EDS数据证实了矿物学。如主成分分析所示，氧化铁具有不同的晶粒尺寸，其贡献顺序为MD> SSD> SP。样品中似乎存在成矿作用的氧化铁矿物，其形成是由于磁铁矿氧化成赤铁矿所致。然而，它们是SSD大小SP的，而不是，这表明成土的强度是不充分的，以形成SP晶粒。

结论

氧化铁矿物主要是陆源性的，湖中的生物活动不足以修饰亚铁磁性矿物。空间分布格局表明，湖盆中大小不一的磁铁矿/钛磁铁矿的不均匀分布，由融化的水流和风共同输送。