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the past 200 ka. Subsequently, this work has been
extended to the last 800 ka and then to the past 2 Ma
(Guyodo & Valet 1996, 1999; Valet
et al
. 2005 ). In the
200 ka study, they used 18 normalized paleointensity
records from the world ocean and produced the
S
int
200
record of geomagnetic fi eld intensity variations. They
have normalized their stacked record to have a mean
intensity equal to unity and can therefore report a
running standard deviation for
S
int
200. The average
value of the standard deviation is about 0.37 and gives
a good sense of the repeatability of relative paleointen-
sity DRM records. Some of this variability is due to
non - dipole fi eld effects because the records were col-
lected globally and the non-dipole fi eld is expressed
locally, and some variability is due to errors in the
recording process. It is not possible to separate the two
effects in the
S
int
200 record, but Brachfeld & Banerjee's
(2000) relative paleointensity work on Lake Pepin sedi-
ments offers some insight into the relative importance
of non-dipole and recording error effects.
Directional accuracy of the paleomagnetism of
recent sediments can be assessed in Lund & Keigwin's
(1994) record of paleosecular variation of the fi eld
(PSV) from North Atlantic Ocean Bermuda Rise marine
sediments (Fig. 1.1). Lund and Keigwin compare the
natural remanent magnetizations (NRMs) of two adja-
cent gravity cores. Digitization and evenly spaced sam-
pling of the inclination and declination records plotted
by Lund and Keigwin show that the inclination records
differ by a minimum of 0.04° to a maximum of 12.9°,
while declination records differ by a minimum of 0.4°
to a maximum of 15.2°. The median difference in
either inclination or declination for these two marine
cores is about 3°. Lund and Keigwin also collected a
box core from the top 50 cm of marine sediment and
sampled it with four subcores. These data showed
GGC-2
40
INCLINATION
GGC-1 INCLINATION
GGC-2 DECLINATION
GGC-1 DECLINATION
150
200
60
40
60
50
100
10 kybp
10 kybp
12 kybp
12 kybp
13 kybp
13 kybp
13.8
kybp
13.8
kybp
14.5
kybp
14.5
kybp
(a)
(b)
Fig. 1.1
Paleomagnetic records from the marine sediments of the Bermuda Rise showing reproducibility of paleomagnetic
directions from two adjacent gravity cores: (a) inclination and (b) declination. Reprinted from
Earth & Planetary Science Letters
,
volume 122, SP Lund and L Keigwin, Measurement of the degree of smoothing in sediment paleomagnetic secular variation
records; an example from late Quaternary deep-sea sediments of the Bermuda Rise, western North Atlantic Ocean, 317-330,
copyright (1994), with permission from Elsevier.
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