absolute Earth’s magnetic field intensity values obtained
from the lava flows are precisely dated using the coupled
K/Ar and
40 Ar/
39 Ar methods. This figure also shows that the
coupled volcanic intensity/dating is consistent with the one
obtained by GLOPIS-75, placed on the GICC05 age model
(Laj et al. 2014).
It also shows that geomagnetic variations observed in the
sediments used to build NAPIS-75 and then GOPIS-75 are
similar to those of the geomagnetic field, recalculated based
on the concentrations of cosmogenic isotopes registered in
Greenland ice (Wagner et al. 2000).
This results from the fact that the Earth’s magnetic field
shields our planet from cosmic and solar radiations and
therefore modulates the production of cosmogenic isotopes
(
10 Be,
36 Cl,
14 C) in the upper atmosphere. Assuming a
constant solar activity, a reduction (increase) in the intensity
of the geomagnetic field leads to an increase (decrease) in
this production. The concentration of these radionuclides,
especially
36 Cl, recorded in Greenland ice, compared to the
reference curve GLOPIS-75, has enabled a precise correlation, independent of climate, to be established between the
ice and sedimentary records.
Transferred to the GICC05 age model, the maximum
peak flow of
10 Be corresponding to the intensity minima of
the Laschamp excursion, is dated at 41.25 ka, in perfect
agreement with the radiometric dating (41.2 ± 1.6 ka; Laj
et al. 2014). In addition, the width of this peak can be
accurately estimated and thus gives a measure of the duration of the excursion as 1.5 ka, again in perfect agreement
with sedimentary data.
If the Laschamp excursion (and also the more recent
Mono Lake excursion) constitutes a critical tie point for all
the stratigraphies (in ice and sediment), it is also observed
that, even outside these instability periods, the intensity
profile and that of
10 Be and
36
Cl are extremely similar in
time and amplitude for the 20–50 ka interval.
These studies show that it is possible to accurately
transfer the ice age model to sedimentary sequences, independently of climate variations. The magneto-stratigraphic
tool based on variations in the intensity of the geomagnetic
field is therefore a very powerful tool, within the limits of its
application.
Paleo-Oceanographic Implications
of High-Resolution Magnetic-Assisted
Stratigraphy
The last glacial period was characterized by very rapid climate changes which have been observed in the upper and
middle northern latitudes. Heinrich (H) and DansgaardOeschger (DO) rapid climatic events, are associated with
iceberg discharges into the ocean and large amplitude
oscillations of air temperature over Greenland (Dansgaard
Fig. 7.9 a GLOPIS-75 curve
(red) (Laj et al. 2004) together
with Earth’s magnetic field
intensity data obtained from dated
lava flows from the Massif central
(black), the Canary Islands
(green) and New Zealand (blue)
(the grey dots are intensities
reported on the age given by the
geological map) (Laj et al. 2014).
b Zoom on the 20–48 ka interval
of the above diagram a with, in
addition, the Earth’s magnetic
field intensity reconstructed from
the
10
Be data (blue) and
36
Cl data
(green) obtained from the
Greenland ice core
112
C. Laj et al.
from the lava flows are precisely dated using the coupled
K/Ar and
40 Ar/
39 Ar methods. This figure also shows that the
coupled volcanic intensity/dating is consistent with the one
obtained by GLOPIS-75, placed on the GICC05 age model
(Laj et al. 2014).
It also shows that geomagnetic variations observed in the
sediments used to build NAPIS-75 and then GOPIS-75 are
similar to those of the geomagnetic field, recalculated based
on the concentrations of cosmogenic isotopes registered in
Greenland ice (Wagner et al. 2000).
This results from the fact that the Earth’s magnetic field
shields our planet from cosmic and solar radiations and
therefore modulates the production of cosmogenic isotopes
(
10 Be,
36 Cl,
14 C) in the upper atmosphere. Assuming a
constant solar activity, a reduction (increase) in the intensity
of the geomagnetic field leads to an increase (decrease) in
this production. The concentration of these radionuclides,
especially
36 Cl, recorded in Greenland ice, compared to the
reference curve GLOPIS-75, has enabled a precise correlation, independent of climate, to be established between the
ice and sedimentary records.
Transferred to the GICC05 age model, the maximum
peak flow of
10 Be corresponding to the intensity minima of
the Laschamp excursion, is dated at 41.25 ka, in perfect
agreement with the radiometric dating (41.2 ± 1.6 ka; Laj
et al. 2014). In addition, the width of this peak can be
accurately estimated and thus gives a measure of the duration of the excursion as 1.5 ka, again in perfect agreement
with sedimentary data.
If the Laschamp excursion (and also the more recent
Mono Lake excursion) constitutes a critical tie point for all
the stratigraphies (in ice and sediment), it is also observed
that, even outside these instability periods, the intensity
profile and that of
10 Be and
36
Cl are extremely similar in
time and amplitude for the 20–50 ka interval.
These studies show that it is possible to accurately
transfer the ice age model to sedimentary sequences, independently of climate variations. The magneto-stratigraphic
tool based on variations in the intensity of the geomagnetic
field is therefore a very powerful tool, within the limits of its
application.
Paleo-Oceanographic Implications
of High-Resolution Magnetic-Assisted
Stratigraphy
The last glacial period was characterized by very rapid climate changes which have been observed in the upper and
middle northern latitudes. Heinrich (H) and DansgaardOeschger (DO) rapid climatic events, are associated with
iceberg discharges into the ocean and large amplitude
oscillations of air temperature over Greenland (Dansgaard
Fig. 7.9 a GLOPIS-75 curve
(red) (Laj et al. 2004) together
with Earth’s magnetic field
intensity data obtained from dated
lava flows from the Massif central
(black), the Canary Islands
(green) and New Zealand (blue)
(the grey dots are intensities
reported on the age given by the
geological map) (Laj et al. 2014).
b Zoom on the 20–48 ka interval
of the above diagram a with, in
addition, the Earth’s magnetic
field intensity reconstructed from
the
10
Be data (blue) and
36
Cl data
(green) obtained from the
Greenland ice core
112
C. Laj et al.