Magnetization of Sediments and the Environment - Paleomagnetism of Sedimentary Rocks: Process and Interpretation - page 110

Fig. 8.11 IRM acquisition modeling (Kruiver et al. 2001) showing two coercivity components, possibly Egli's (2004) BH and
BS magnetosomes in Lake Ely sediments. (See Colour Plate 19)

magnetosome coercivity components which he detected
in other lake sediments and refers to as BH (biogenic
hard) and BS (biogenic soft). However, the resolution
of the IRM acquisition curves in the coercivity range
<100 mT is poor. Taking the fi rst derivative makes the
data even noisier. The primary reason for this is that
most laboratories use an impulse magnetizer, that dis-
charges a capacitor through a coil surrounding the
sample, to magnetize a sample for IRM acquisition
experiments. The set-up is perfect for higher fi elds,
but harder to control the fi eld strength for magnetic
fi elds <100 mT. The Lake Ely samples were therefore
given partial ARMs with the DC fi eld applied in increas-

ingly higher-strength alternating fi elds. This ARM
acquisition experiment allows better resolution of the
coercivity components in the < 100 mT fi eld range.
Modeling of the ARM results shows that two distinct
coercivity components could be distinguished in the
< 100 mT fi eld range for samples collected at depths of
35 and 45 cm in the piston core. These most likely rep-
resent the BH and BS magnetosome components of
Egli (2004) and could suggest contributions from
magnetosomes with different morphologies. It is inter-
esting that only one coercivity component dominates
the ARM acquisition modeling at the shallowest depths
in the lake sediments, suggesting that reduction dia-