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Magnetic effect on CO
2
solubility in seawater: A possible link between
geomagnetic field variations and climate
Alexander Pazur
1
and Michael Winklhofer
2
Received 17 April 2008; revised 25 July 2008; accepted 29 July 2008; published 30 August 2008.
[1] Correlations between geomagnetic-field and climate
parameters have been suggested repeatedly, but possible
links are controversially discussed. Here we test if weak
(Earth-stren gth) magnetic fields can affect climatically
relevant properties of seawater. We found the solubility of
air in seawater to be by 15% lower under reduced magnetic-
field (20 mT) compared to normal field conditions (50 mT).
The magnetic-field effect on CO
2
solubility is twice as
large, from which we surmise that geomagnetic field
variations modulate the carbon exchange between
atmosphere and ocean. A 1% reduction in magnetic dipole
moment may release up to ten times more CO
2
from the
surface ocean than is emitted by subaerial volcanism. This
figure is dwarfed in front of anthropogenic CO
2
emissions.
Citation: Pazur, A., and M. Winklhofer (2008), Magnetic effect
on CO
2
solubility in seawater: A possible link between
geomagnetic field variations and climate, Geophys. Res. Lett.,
35, L16710, doi:10.1029/2008GL034288.
1. Introduction
[2] Causal and non-causal con nections between the
Earth’s magnetic field and climate have been proposed
repeatedly, mostly on the basis of statistical analyses of
time series of geomagnetic and clima te (proxy) data (for a
recent review, see Courtillot et al. [2007]). Potentially
underlying mechanisms remain a subject of controversy,
however. Doake [1977] suggested that rotational accelera-
tion or deceleration due to waxing or waning ice sheets
might trigger instabilities in the geodynamo and promote
geomagnetic events of large magnitude (excursions or
reversals). Although variations in the Earth’s rotation rate
affect the geodynamo [Le Moue¨l et al. , 1981], it is not
known what magnitude is required for the change in angular
frequency in order to critically perturb a stably running
geodynamo, or how close the geodynamo has to be to the
critical state to be susceptible for such perturbations at all.
Also, there is no convincing statistical evidence for such a
connection in the paleo-record, although possible correla-
tions may be obfuscated by uncertainties in age models, as
was already cautioned by Doake [1977].
[
3] Since luni-solar precession may provide power to the
geodynamo [e.g., Vanyo, 1991; Tilgner, 2007], all effects
that pe rturb or modulate precession (such as obliquity
variations) can potentially influence the geomagnetic field.
However, the statistical evidence for an orbitally modulated
geodynamo from sedimentary paleomagnetic records is far
from firm [Guyodo et al., 2000; Kent and Carlut, 2001;
Roberts et al., 2003; Heslop, 2007; Xuan and Channell,
2008].
[
4] Although absolute paleointensity records derived
from terrestrial lava flows or archaeological artifacts are
discontinuous in time, they have no climatic overpr int,
which makes them in principle better suited for studying
such correlations. For example, Gallet et al. [2005] reported
a remarkable coincidence between major cool episodes and
periods of increased archeomagnetic field strength (AMF)
since 700 AD. AMF variations during the four millennia BC
appear to be interrupted by so-called archeomagnetic jerks,
that is, periods of sharp intensity increase, which coincide
with periods of fastest cooling rates [Gallet et al., 2006].
Unfortunately, the archeomagnetic database is still too
sparse to verify if periods of rapid warming are correlated
with fast dropping AMF values.
[
5]AsCourtillot et al. [2007] remarked, the negative
correlation between magnetic dipole moment and tempera-
ture is at odds with an often invoked mechanism, in which a
diminishing dipole reduces the shielding capacity of the
terrestrial magnetosphere against galactic cosmic radiation,
which in turn enhances the nucleation rate of deep clouds,
entailing a higher albedo and cooler temperatures.
[
6] We test if this inverse correlation can be isola ted from
global time series constructed from instrumental records.
The normalized correlation coefficient c
TM
between global
mean surface temperature T and magnetic dipole moment M
(records shown in Figure 1a) amounts to 0.8, which at
first glance migh t suggest a significant anti-correlation.
Howe ver, when the two curves are detrended or when
comparing their time derivatives, the anti-correlation weak-
ens (c
TM
0.5 for detrended curves and c
TM
0.6 for
derivatives shown in Figure 1b), which implies that the
inverse correlation between the original curves is due to
the fact that M happens to continue decreasing during the
upward trend in the temperature anomaly since the early
20th century, which in turn reflects the anthropogenic
effect on global temperature. Although there appears to
be some correlation between the derivatives shown in
Figure 1b, the phase relationship between the curves is
not consistent. It is clear that longer time series would be
needed to clarify the nature of the correlations. Neverthe-
less, the possibility that geomagnetic field variations affect
climate is worthwhile exploring, even though the instru-
mental records are unlikely to be useful here due to the
human overprint.
[
7] The intent of this Letter is to draw the attention to the
widely unknown effects of magnetic fields on the physico-
chemical properties of seawater, which may present an
GEOPHYSICAL RESEARCH LETTERS, VOL. 35, L16710, doi:10.1029/2008GL034288, 2008
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A
rticl
e
1
Department Biology I, Ludwig-Maximilians-Universi ty, Munich,
Germany.
2
Department of Earth and Environmental Sciences, Ludwig-Maximilians-
University, Munich, Germany.
Copyright 2008 by the American Geophysical Union.
0094-8276/08/2008GL034288$05.00
L16710 1of5
important mechanism linking geomagnetic field variations
and climate, given the major role the ocean has on global
climate. Sever al recent studies suggested that mag netic
fields have a role on the physicochemical properties of
aqueous electrolytic solutions [Beruto et al., 2003; Valle´e et
al., 2005], as well as on kinetics and thermodynamics of
CaCO
3
precipitation [ Holysz et al., 2002; Barrett and
Parsons, 1998]. Those experiments were done in a different
context and the fields used were either strong static mag-
netic fields (100 mT) or weak alternating electromagnetic
fields. Below we show that similar effects can also occur in
weak (Earth-stre ngth) static magnetic fields and propose a
mechanism in which variations of the geomagnetic field
strength affect the gas solubility of sea-water and thereby
modulate the atmospheric CO
2
concentration.
2. Experiments
2.1. Magnetic Field Effects on Viscosity
[
8] Viscosities of seawater and of a 0.62 M (3.5%) NaCl
solution were determined from fluorescence polarization
[Marangoni, 1992], for which purpose the solutions were
dyed with Rhodamine-B (see Figures S1–S3 in the auxil-
iary material for setup and calibration
1
). An electronically
controlled pipette was periodically pumped up and down to
induce a vertical flow in the solution (0– 5 mm/s). The
controlled application of a magnetic field (MF) was through
Helmholtz coils, housed inside a permalloy box screening
out the ambient f ield. When the Helmholt z coils were
switched off, the residual field in the tank was about 1 mT.
The effect of a MF on viscosity was investigated at T = 5 ±
0.1°C. After switching on a MF of 2 mT, the viscosity
continuously increased. The effect is fully reversible when
the MF is reduced to 1 mT again, with a decay time of less
than 10 s (Figure S4). When the samples are agitated, the
viscosity initially increases at much higher rates and reaches
overall higher levels than without agitation. The increase of
viscosity was 8 –10% stronger for the 3.5% NaCl solution
than for seawater. The viscosity enhancement due to a 2 mT
field (relative to 1 mT) is equivalent to a temperature
reduction of 0.7°C (placid) or 1.5°C (agitated). However,
we were not able to quantify the viscosity enhancement due
to an earth strength field (0.05 mT). Although the sign of the
MF effect is the same, the signal-to-noise level here is too
low to obtain decent estimates.
[
9] The MF effect on viscosity increases with decreasing
temperature. Importantly, the viscosity effect vanished after
degassing the salt solutions for 60 s under vacuum, and was
re-established by gassing. The MF effects on the viscosity
of the solution when O
2
or N
2
were used instead of air were
similar, but slightly stronger with CO
2
and virtually absent
with argon, in distilled water, and in a glucose solution
(3.5 weight %). The fact that the MF effect is similar among
the molecular gases suggests that effects seen with air are
not due to the paramagnetic susceptibility of O
2
, which is
too small to explain the observed magnetic-field effects in
terms of magnetization effects.
[
10] The observed MF effect on viscosity obviously
needs a combination of two components; namely, dissoci-
ated salts (electrolytes) and the presence of internal inter-
faces in the solution ( due to air bubbles or pa rticulate
matter). Electrostatically, gas bubbles in water are similar
to colloidal solutes. Both are coated by shells of ions and
counterions, referred to as inner and outer Helmholtz layer,
which together form a dielectric boundary layer (DBL). The
potential that arises on removal of the outer Helmholtz
layer, is called the zeta potential, a measure of the electric
polarization. The zeta potential depends on pH and salt
concentration [Creux et al., 2007], but also on viscosity
according to the Smoluchowski-Einstein equation. The
observed changes in viscosity therefore are likely to repre-
sent a magnetic-field effect on the zeta potential.
2.2. Magnetic Field Effects on Gas Exchange Between
Air and Seawater
[
11] To measure gas concentration in sea-water, we used
an elastic light-scattering technique [Valle´e et al., 2005]
with a monochromatic (400 nm) light source. Elastic light
scattering is sensitive to the presence of gas bubbles, which
have a different refractive index than the solution and thus
act as scatterers. The intensity of the scattered light depends
not only on the concentration of the gas phase in the
solution, but also on bubble size. To minimize the obfus-
Figure 1. (a) Relative variation of the geomagnetic-field
dipole moment M/M
0
(thick line, left scale), with M
0
=
M(1850), and globally averaged surface temperature
anomaly, T (thin line, right scale). Data sources: M from
Jackson et al. [2000], T from Brohan et al. [2006]. (b) Time
derivatives of M/M
0
(thick, left scale) and T (thin, right
scale), respectively. To emphasize a possible anti-correla-
tion, the negative time derivative of M/M
0
is shown. T was
smoothed before differentiation.
1
Auxiliary materials are available in the HTML. doi:10.1029/
2008GL034288.
L16710 PAZUR AND WINKLHOFER: MAGNETIC EFFECT ON CO
2
SOLUBILITY L16710
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cating effects of a broad bubble-size distribution on the
scattering intensity, the solution was not agitated in this
experiment. Under placid conditions, the bubble-size distri-
bution is narrow (bubble sizes well below 1 mm) and the
bubbles are separate d, whilst under turbulent conditions,
bubbles are prone to interact and coalesce, which gives rise
to a broad bubble-size distribution. Thus, for the placid
solution, the scattering intensity can be considered to reflect
the concentration of roughly monodisperse gas bubbles in
the solution.
[
12] The seawater was degassed before the experiment.
Then the surface of the water container was allowed to
exchange gas with the environment (ambient pressure) and
the time course of the scatter intensity was recorded in 1 mT,
20 mT, and 50 mT, respectively. The solution was kept at
4°C. Each regassing experiment follows a similar time
course, characterized by an initially linear increase in scatter
intensity (gas concentration) up to 45 min, followed by an
approach-to-saturation behaviour, with saturation achieved
after about two hours (Figure 2a). The curves are normalized
by the sa turation value for the curve taken at 50 mT.
Importantly, re-gassing rate and saturation values increase
with field strength. Additional experiments were conducted
to determine the MF effect on CO
2
solubility. For 30%
(v/v) CO
2
enriched air, a reduction in field strength from 20
mTto1mT has an even more pronounced effect on gas
solubility compa red to normal air with 380 ppm CO
2
(Figure 2b). For pure CO
2
, the extrapolated MF effect is
twice as strong than for normal air, such that a 1% field
change yields a 0.5% change in CO
2
solubility. Importantly,
the magnetic-field effect is absent in purified water.
[
13] The time course of the gas-solubility experiment
represents the diffusion-limited, molecular transfer of gas
across the air-solution interface. According to the classic
models of air-sea gas exchange [Broecker and Peng, 1974;
Liss and Slater, 1974], the main resistance to gas transport
is due to the stagnant boundary layer, across which the
exchanging gases transfer by molecular processes (diffu-
sion) from the well-mixed atmosphere to well-mixed sur-
face ocean and vice versa. The net flux F of gas into the salt
solution is driven by the concentration gradient Dc/d of gas
across the stagnant film (thickness d),
F ¼ DDc=d ¼ kc
s
c
a
ðÞ ð1Þ
where D is molecular diffusivity of gas in sea water, k = D/d
is the transfer velocity (‘‘piston velocity’’), c
a
and c
s
are the
gas concentrations in air and in seawater (below the
stagnant film), respectively. For O
2
,N
2
, and CO
2
, D (at
4°C) is about 1 10
5
cm
2
/s [Himmelblau, 1964]. Under
low agitation, Broecker and Peng [1974] obtained d values
of 3 10
2
cm, resulting in k values of about 3 10
4
cm/s.
[
14] With c
a
in equation (1) kept constant during the
experiment, the integration of equation (1) yields
c
s
¼ c
sat
s
1 exp kt=LðÞðÞ; ð2Þ
where t is time and L = V/A is the characteristic length, with
V and A denoting the volume (1 cm
3
) and the surface area
(1 cm
2
), respectively, of the liquid container. Fitting the
measured time course to equation (2), we obtain experi-
mental time constants of L/k 30 min, that is, k values of
about 5 10
4
cm/s, in good agreement with literature
data.
3. Discussion
[15] The MF effect on viscosity and gas solubility
requires the presence of dielectric boundary layers (DBL),
because MF effects are absent when destilled water (or a
glucose solution) is used instead of seawater. The MF
effects therefore are expected to occur in the ocean as well,
given the abundance of DBL in the surface ocean, be it due
to submicrometre particles (10
8
–10
9
particles per ml) [Wells
and Goldberg, 1991], be it due to sub-100 nm colloidal
particles (10
8
–10
9
particles per ml) [Isao et al., 1990]). A
conservative estimation of all DBL-generating matter yields
a total surface of tens of m
2
per m
3
seawater.
Figure 2. (a) Time course of air saturation of seawater at
1 mT, 20 mT, and 50 mT, respectively. Each curve presents
the mean over five experiments each and their ±1s standard
deviation (error bars). All curves are normalized to the
saturation level obtained at 50 mT. (b) As in Figure 2a, but
now for air with 30% CO
2
. Averages of three experiments
each, 100% is defined for normal air in 50 mT (see Figure 2a).
L16710 PAZUR AND WINKLHOFER: MAGNETIC EFFECT ON CO
2
SOLUBILITY L16710
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[16] The MF effect on gas-solubility in seawater does not
seem to be directly related to the MF effect on viscosity,
since the latter is much less pronounced. This is also
suggested by the fact that the time scale of gas uptake in
our experiments shows no discernible difference between
normal and reduced MF. The single-most important differ-
ence between gas uptake under normal and reduced MF is
the magnitude of the flux and the saturation level. This
implies a lower gas solubility in seawater in weaker mag-
netic fields and we may conclude that MF strength affects
the equilibrium concentr ation of dissolved gas in the liquid
phase. It is therefore conceivable that geomagnetic field
strength may act as an additional factor that modulates the
air-sea exchange of gas.
[
17] An important unknown is the magnetic-field effect
on the reaction rates in the dissolved inorganic carbon
system. CO
2
as a reactive gas may become hydrated already
in the stagnant film, whereupon concentration gradients of
other inorganic carbon species (HCO
3
,CO
3
2
) would be set
up immediately (given the rapid dissociation of carbonic
acid, compared to the slow hydration reaction under typical
seawater pH conditions), which leads to well-known CO
2
exchange enhancement [Hoover and Berksh ire, 1969;
Wanninkhof and Knox, 1996]. The fact that the MF effect
on solubility is more pronounced for a CO
2
enriched
atmosphere than for the standard atmosphere might also
result from MF effects on the equilibrium constants in the
marine carbonate system, but more experiments are needed
for clarification.
[
18] The theoretical framework describing effects of a
weak static MF on electrolyte solutions, gas solubility, and
equilibrium constants is at a level that does not even allow
us to make qualitative predictions. Obviously, the MF effect
is related to the presence of ionic solutes. Salinity reduces
solubility of hydrophobic gases, and it is possible that the
magnetic field (by exerting a Lorentz force on ionic solutes
at DBL) partly undoes the adverse effect of salinity on gas
solubility. We speculate that under higher fields, the relative
influence of thermal fluctuations on ion movement becomes
weaker (particularly at DBL, where gyration of ions may be
stabilized), which would lead to lower effective temper-
atures, hence higher gas solubility.
4. Conclusions
[19] We have measured viscosity and gas solubility of
seawater at different magnetic field (MF) strengths. While
the MF effect on seawater viscosity is probably too small to
be relevant under naturally occurring field variations, the
MF effect on gas solubility may present a physical link
between geomagnetic field and climate. Our small-scale
laboratory experiments indicate lower solubility of CO
2
in
seawater under reduce d MF intensity. The extra amount of
CO
2
not dissolved due to reduced CO
2
solubility in a
weaker MF would add to the greenhouse effect. This
mechanism therefore has the right sign to qualitatively
explain the observed anti-correlation between archeomag-
netic field strength and global temperature estimates.
[
20] However, the magnitude of the mechanism is small
compared to the magnitude of the preponderant mechanisms
driving the exchange of carbon between ocean and atmo-
sphere, such as water temperature, biological pumpi ng,
overturning circulation. The effect of geomagnetic-field
variations therefore is to modulate the air-sea exchange of
carbon.
[
21] The magnitude of the MF effect is such that CO
2
solubility reduces by a maximum of 0.5% per each %
decrease in MF strength. To provide a quantitative assess-
ment of the MF effect on the global carbon dioxide budget,
we assume that our experimental results can be extrapolated
to the global scale and that a reduction in CO
2
solubility by
0.5% is equivalent to an emission of 0.5% of the total
amount of dissolved inorganic carbon (DIC) in the surface
ocean (700 Pg C) [see Sigman and Boyle, 2000, Figure 2].
A 1% decrease in magnetic dipole moment occurring over a
decade would then add 1 ppm CO
2
per decade to the
atmosphere, that is, 0.35 Pg C/yr. This figure is a magnitude
larger than the CO
2
discharge from subaerial volcanism
(0.03 Pg C/yr) [Kerrick, 2001], from which we surmise that
the MF effect may have played a role in pre-industrial times.
[
22] Given the high anthropogenic emission rate of CO
2
(7 Pg C/yr), it would be preposterous to make the weaken-
ing Earth’s magnetic field responsible for global warming.
Yet, by lowering the capacity of the surface ocean to absorb
excess CO
2
from the atmosphere, the diminishing field acts
in the same direction as the increase in sea-surface temper-
ature and acidity, thereby exacerbating the effects of global
warming.
[
23] Acknowledgments. The authors would like to thank Professor
H. Scheer and two anonymous referees for helpful comments. M. W.
acknowledges funding from the DFG (Wi 1828/4-1).
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A. Pazur, Department Biology I, Ludwig-Maximilians-University, D-80638
Munich, Germany.
M. Winklhofer, Department of Earth and Environmental Sciences,
Ludwig-Maximilians-University, Theresienstrasse 41, D-80333 Munich,
Germany. (michael@geophysik.uni-muenchen.de)
L16710 PAZUR AND WINKLHOFER: MAGNETIC EFFECT ON CO
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SOLUBILITY L16710
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Fig. S1. The experimental setup in the fluorescence spectralphotometer, consisting of
polarizer (Pol) and analyzer filter (Ana), sample holder with cuvette (C), and a pair of
Helmholtz coils (H) that generate the magnetic field. A home built electromechanical sweep
controller immerses a tube periodically into the sample (to mix the solution).
Fluorescence polarization A
F
is calculated as
)(
)(
⊥ΙΙ
⊥ΙΙ
+
−
=
II
II
A
F
where I
║
and I
⊥
are the parallel and orthogonal polarized emission intensities at 597 nm.
Fig. S2. Calibration of fluorescence polarization A
F
, based on the temperature dependence of
viscosity, for freshwater (diamonds), seawater (triangles), and 3.5% NaCl solution (squares).
Each data point represents the mean from 10 experiments each, error bars denote the standard
deviation. The solid line shows reference values for freshwater (Lide, 1986). The right
ordinate refers the viscosity after calibration of the A
F
values to the viscosity of pure water at
293 K. The average slopes dA
F
/dT are -2.5⋅10
-4
K
−1
(water), -2.676 ⋅10
-4
K
−1
(3.5% NaCl)
and -2.667 ⋅10
-4
K
−1
(seawater).
Fig. S3. Effect of salinity changes on fluorescence polarization, for seawater (triangles) and
NaCl solution (squares). The solid lines refer to the linear regressions. A
F
increases with
(6.9±1.3)⋅10
-4
per 1% salinity change for NaCl and (6.0±1.6)⋅10
-4
per 1% salinity change for
the sea salt mixture.
Fig. S4. Magnetic-field (MF) induced changes in viscosity of seawater (black curves) and of a
3.5% NaCl solution (grey curves) after applying a MF of 2 mT at t=10 sec. The values are
normalized to the ones from the control experiment (t=0-10 sec). Graphs 1 and 2 show
immobile solutions, where diffusion processes prevail. Graphs 3 and 4 show samples that
were agitated by periodic sweeping (at a rate of 5 mm/s), as indicated by the signal shown on
the top. Convectional processes should prevail here. For the data shown, 200 records of
complete cycles (40 s/cycle, with a trailing pause of 10 sec each) were averaged for each
experimental situation.
