Fig. 3. Methods for identifying magnetofossils in samples from core MD01-2444 at 26.74 m depth.

a Low-temperature magnetic measurements (blue and red curves: normalized zero-field cooled (ZFC) and field cooled (FC) curves, respectively; black curve: normalized first derivative of the FC curve; peaks with arrows (~100 K and ~115 K) are indicative of biogenic and detrital magnetite, respectively). b Coercivity distribution from IRM acquisition curve unmixing (gray dots: IRM acquisition data; orange curve: spline fit based on measured data; purple and red curves: biogenic soft and biogenic hard components, respectively; shaded areas for each curve are 95% confidence intervals). c, f TEM images of magnetic extracts from the same sample. Scale bars: c = 200 nm, f = 100 nm. The main magnetofossil morphotypes are prisms, octahedra and bullets. d FORC diagram with a central ridge signature that is indicative of non-interacting single-domain magnetic particles. e Ferromagnetic resonance (FMR) and FMR absorption spectra (black curve: measured FMR spectrum; red curve: fitted FMR spectrum; black humped curve: normalized FMR absorption spectrum). Definition of commonly used magnetofossil-indicative parameters are shown in (e)¹²³.