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

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.

Automated summary

The anhysteretic remanent magnetization (ARM) is an important parameter for quantifying the concentration of fine ferrimagnetic particles in rocks and sediments. However, the understanding of ARM carriers in marine sediments is often limited. In this study, sediment cores from different regions were analyzed using various techniques, and it was found that the ARM is mainly carried by non-interacting single domain biogenic magnetite. Low-coercivity magnetic particles also contribute to the ARM. The study provides insights into the interpretation of ARM data in sedimentary archives.