Measured hysteresis parameters shown on a Day plot. Red diamonds (gray circles) indicate data points for samples from floor surface (−20-cm level). The red (gray) square represents the averaged parameter for samples from floor surface (−20-cm level) with their one standard deviation. Threshold values for single domain (SD), pseudo-single domain (PSD), and multi-domain (MD) regions are adopted from Dunlop (2002). Dotted curves are theoretical mixing curves for SD-MD and SD-SP (super paramagnetic) magnetite grains adapted also from Dunlop (2002).