Interpretation of Anhysteretic Remanent Magnetization Carriers in Magnetofossil‐Rich Marine Sediments

• Published in: Journal of geophysical research. Solid earth Vol. 127; no. 11
• Main Authors: Zhang, Qiang, Roberts, Andrew P., Ge, Shulan, Liu, Yanguang, Liu, Jianxing, Liu, Shuangchi, Tang, Xu, Wang, Haosen, Wang, Dunfan, Li, Jinhua, Liu, Qingsong
• Format: Journal Article
• Language: English
• Published: 01.11.2022
• Subjects: first‐order reversal curve; magnetic minerals; rock magnetism
• DOI: 10.1029/2022JB024432
• ISSN: 2169-9313

The anhysteretic remanent magnetization (ARM) is an important magnetic parameter for quantifying the concentration of “fine”, mostly sub‐micron ferrimagnetic particles in rocks and sediments. A sound understanding of ARM carriers is needed to interpret magnetic and environmental information in sedimentary archives. This is often not achieved for marine sediments, which routinely contain several magnetic mineral components. Here, we analyze marine sediment records over different timescales for four sediment cores from the Eastern Pacific Ocean (Hole 1218A), the Antarctic margin (core P4‐1), the Arctic Ocean (core ARC5‐ICE4), and the South China Sea (core L07), using coercivity spectra analyses of ARM, first‐order reversal curve principal component analysis (FORC‐PCA), transmission electron microscopy (TEM), and unmixing of isothermal remanent magnetization (IRM) curves. By combining rock magnetic and TEM results, we find that the ARM is mainly carried by non‐interacting single domain (SD) biogenic magnetite (magnetofossils) in the studied sediments over all timescales. Low‐coercivity magnetic particles (detrital and fine‐grained extracellular magnetite) also contribute to the bulk ARM. Variable magnetofossil chain structures are detected and have a significant influence on ARM data interpretation. Quantitative FORC‐PCA endmember analyses based on quantile contours and coercivity distributions provide valuable information on the nature of endmembers and improve ARM data interpretation. We provide an integrated strategy to help reduce interpretational ambiguities related to ARM in future studies. Plain Language Summary The anhysteretic remanent magnetization (ARM) is an important parameter that is used to assess information about Earth's magnetic field variations and environmental changes. To interpret ARM signals robustly, we must understand the sedimentary magnetic minerals that control ARM changes. However, the origin of ARM changes in marine sediments is not well understood. Here, we analyze marine sediment records from the Eastern Pacific Ocean, the Antarctic margin, the Arctic Ocean, and the South China Sea to identify the carriers of ARM in the respective sediments. Our results indicate that all of the sediments contain abundant remains of magnetotactic bacteria (known as magnetofossils). Magnetofossil abundance variations dominate ARM on both 10,000 to million‐year timescales. Part of the bulk ARM is also contributed by other low‐coercivity magnetite particles. Furthermore, ARM is influenced significantly by magnetofossil chain structure variations. Our results have important implications for future studies involving use of ARM in magnetofossil‐rich sediments. Key Points Integrated component analyses are presented for four sediment cores to identify magnetic particle sources Magnetofossils are the predominant anhysteretic remanent magnetization (ARM) carrier with detrital and extracellular magnetite also contributing to the ARM Quantitative analyses provide valuable insights into the nature of components to improve ARM data interpretation of marine sediments