A possible relationship between large scale changes in global ice volume, variations in the earth's magnetic field, and short term climatic cooling is investigated through a study of the geomagnetic and climatic records of the past 300,000 years. The calculations suggest that redistribution of the Earth's water mass can cause rotational instabilities which lead to geomagnetic excursions; these magnetic variations in turn may lead to short-term coolings through upper atmosphere effects. Such double coincidences of magnetic excursions and sudden coolings at times of ice volume changes have occurred at 13,500, 30,000, 110,000, and 135,000 YBP

Rampino, M. R.

English

NASA Technical Reports Server

Paper No. 57
VARIATIONS OF THE EARTH'S MAGNETIC FIELD AND RAPID
CLIMATIC COOLING: A POSSIBLE LINK THROUGH CHANGES IN
GLOBAL ICE VOLUME
Michael R, Rampino, Goddard Institute for Space Studies, New York,
New York 10025
ABSTRACT
A possible relationship between large-seale changes in global
ice volume, variations in the earth's magnetic field, and short-
term climatic cooling is investigated through a study of the geo-
magnetic and climatic records of the past 300,000 years. The
calculations suggest that redistribution of the earth's water
mass can cause rotationaliv_+_bi!itieswhich lead to geomag-
netic excursions; these magnetic variations inturn may lead
to short-term coolings through upper-atmosphere effects.
Such double coincidences of magnetic excursions and sudden
coolings at times of ice-volume changes have occurred at
13,500, 30,000,110,000, and 185,000 YBP.
Introduction. A relationship between variations in the earth's
magnetic field and changes in climate has been suggested by many au-
thors (e. g., Harrison and Prospero, 1974; Wollin et al., 1971). The low
field strengths at the times of magnetic reversals or excursions should
lead to an increase in the cosmic-ray flux in the upper atmosphere. It
has been proposed that this might cause increased upper-atmosphere
ionization and cloud formation or perhaps a catastrophic depletion of the
ozone layer. These are conditions that could ultimately result iu in-
creased high altitude cloudiness and increased precipitation and cooling
in the mid-latitudes (Harrison and Prospero, 1974; Reid et al., 1976).
It has also been suggested that long-term climatic changes which
cause major fluctuations in global ice volume, and hence in the redistri-
bution of water mass on the earth's surface, could lead to rotational in-
stabilities and therefore result in changes in the magnetic field through
core-mantle effects (Doake, 1977; MOrner, 1977 ). A glacio-eustatic sea
level change of about 100 meters would cause a change in rotational ener-
MYof 1.9 x 1024 J. In this case, the fractional chang_ in angular veloci_
ty, length of day and moment of Inertia would be 10 -_ (Doake, 1977). In
the model of Doake, the changes in core euerMY involved are of the same
order of magnitude (a rate of energy dissipation of 10 I2 W) as the ener-
gy required to drive the geodyuamo. Doake (1978) has noted a statistical
correlation between magnetic reversals and climatic change.
There is thus an indication in the geologic record of a correlation
between long-term, large-scale changes in ice volume (and therefore sea
level) and excursions of the earth's magnetic field. The magnetic excur-
sions, which occupy a relatively short time span, may produce rapid
climatic coolings. It is therefore worthwhile to search for a further co-
341
https://ntrs.nasa.gov/search.jsp?R=19790012519 2020-03-20T18:30:03+00:00Z
incidence; magnetic excursions which occur during a time of large-scale
melting or growth of ice sheets may be accompanied by a significant
cooling and short-term growth of ice sheets (Fig. 1)°
Study of climatic and geomagnetic records. A first step in
this problem is to examine the climatic and geomagnetic records of the
past several hundred thousand years in search of evidence for such dou-
ble coincidences of major ice/wa_er redistributions, magnetic excur-
sions, and rauid coolings. One such double coincidence at the time of
the Gothenburg Magnetic Excursion _13,500 YBP, has been documented
by Fairbridge (1977). This event came at about the midpoint of the mel-
ting of the latest Pleistocene northern hemisphere ice sheets. Further-
more, the magnetic excursion appears to correlate with a time of short-
term rapid climate cooling and ice buildup. Sea level dropped more
than 10 meters between 13,000 and 14,000 YBP and glaciers on North
America readvanced over an area of some 500,000 square kilometers.
Several other magnetic excursions are reported to have occurred
during the past 300,000 years. The two excursions considered to rest
on the best supporting evidence are the Lake Mungo Excursion ate30, 000
YBP and the Blake Event at _110,000 YBP (Verosub and BanerJee,
1978). Furthermore, study of a core from Lake Biwa, Japan has indi-
cated the presence of the Blake Event (dated at _110,000YBP) as well as
two other magnetic excursions, estimated to date from _185,000 YBP
(the Biwa I Event) and _295,000 YBP (the Biwa II Event) (Fig. 2). These
excursions are coincident with pronounced lows in organic carbon in the
Lake Biwa sediments (Fig. 3). The decrease in organic carbon is be-
lieved to be related to climatically controlled changes in the productivity
of the lake (Kawai et al., 1975).
The Blake Event has previouslybeeu correlated with a time of
quite sudden climatic cooling and ice buildup, foUowing the largo-scale
melting of the ice sheets which marked a change from full-glacial to full-
interglacial conditions (M0ruer, 1977). A cooling at about 110,000 YBP
might be expected from considerations of earth orbital variations (the
MUankovitch mechanism) (Kukla, 1975). However, the actual cooling
and glacier buildup was extremely rapid. Studies of changes in sea level
(Matthews, 1972) and of changes in the oxygen-isotope ratios in deep-sea
cores (Shackleton, 1976) indicate that sea level fell rapidly, 60-70
meters In a few thousand years. These rapid rates of change in global
climate and ice volume might be explained as being a result of the alter-
ations of atmospheric circulation and precipitation that have been sug-
gested to accompany magnetic-field fluctuations (Fairbrtdge, 1977).
The Lake Mungo Excursion at _ 30,000 YBP was also associated
with a time of apparent rapid cooling and glacier advance. This cooling
came soon after the global warming and large-scale melting of ice as-
sociated with an interstadial interval. Evidence from Long Island, New
York in the form of radiocarbon-dated marine deposits points to the pos-
sibility that the sea at _30,000 YBP rose to within 20 meters of modem
sea level (MSL) and then dropped to more than -100 meters MSL by
about 20,000 YBP (Rampino and Sanders, 1976). Pollen analyses from
the same deposits indicate a very rapid cooling Just after 28,000 YBP.
Temperate-forest vegetation on Long Island was replaced by boreal type
forests within a few hundred years. Ice sheets readvauced to the Long
Island area by 23,000 YBP (Sirkin, 1977).
342
ORBITAL VARIATIONS
_IIISIRINII_ OF ICE i WATER
CHANGE IN MOMENT OF INERTIA
CORE-MANTLE INTERACTIONS
&
MAGNETIC EXCURSIONS
CLIMATIC CHANGE
& 0 II
0 100 200 300 400 Xi'iOyr
Fig. 1 (left). Diagram of possible relationships between the redistribution
of global water mass, magnetic excursions, and short-term climatic
cooling.
Fig. 2 (right). Record of global ice volume for the last 400,000 years as
inferred from oxygen-isotope records in sub-Antarctic deep-sea cores
(HaYs etal., 1976). Low values of 8018 indicate small ice volumes; high
U U-- %,_J.iJ.es LI..LU.,L',.,;CX.I,_ .LO,,.L_ ,L',,.,._:} V'J,L'-,U.LL_.,_. ,.k.LJ,,,,,., _V_l,,,,..,,*.,. LA _ _V v_ _
eccentricity of the earth's orbit. The times of five reasonably well-
established magnetic excursions are shown by arrows.
90° • ' _.
0"
<o. : I i
tAKE _]@A E_RE
[49-18 RCII-120 RCl2-225
80 's _0 '_ 30 _
4.0 _.5 3.O 25 20_./,' _,5 30 25 20 ,_&*, 40 3.5 $,O 2,5 ._*_,
• _a!, i°i . / I'l_
• _ II7 6_, * i : 34 , J
• - : i ' "_'_ '" _
% _w_*lc_s % Hem*a_c_ % _mid_sc_
Fig. 3 (left). Magnetic inclination and percent organic carbon in the Lake
Biwa sediment core. The positions of the Blake, Biwa I and Biwa II
magnetic events are shown by arrows (Kawai et al., 1975).
Fig. 4 (right). Oxygen-isotope record (solid line) and percent abundance
of the diatom Hemisdiscus lmrstenii in sections of sub-Antarctic deep-
sea cores. The last appearance of H. karsteuii is shown by the diagonal
hatched areas (Burckle et al., 1978). The date of the Biwa I magnetic
event, as inferred from the Lake Biwa core, is shown by arrows.
343
The sequence of events at %30,000 YBP could be an example of a
climatic warming induced by changes In seasonal insolation (the Milan-
kovttch mechanism) which was cut short by magnetically induced cooling.
The original warming and melting of ice sheets led to changes in the
earth's rotation and therefore to magnetic instabilities; the magnetic in-
fluences on climate in turn caused a pronounced short-term cooling.
The magnetic excursion estimated to have occurred at % 185,000
YBP (the Biwa I Event) also appears to be correlated with a time of
rapid growth of ice as indicated by oxygen-isotope records in deep-sea
cores (Fig. 2). It is estimated that at about 190,000 YBP summer sea-
surface temperatures in the sub-Antartic declined approximately 2° C
(from 9° C to 7° C). This time also marked the last appearance of the
diatom Hemidiscus lmrstenii in sub-Antarctic deep-sea cores (Burckle
et al., 1978) (Fig. 4). This probable extinction might be related to the
environmental stress generated by the climatic cooling, magnetic excur-
sion, or some combination of the two.
The Biwa H Event at %295,000 YBP was apparently not accompan-
ied by rapid changes in ice-volume as indicated by oxygen-isotope curves
(Fig. 2), although the Lake Biwa Core shows a marked decrease in prod-
ucttvity, intepreted as a cooling of the climate at that time (Fig. 3). How-
ever, a very short period of rapid ice-sheet growth might be beyond the
resolving power of the isotope record in mos_ deep-sea cores.
Divcu88ion. An association of events such as chauges in global
ice volume, magnetic excursions and short-term rapid cooling and gla-
ciation of course does not prove that any cause and effect relationship
exists. Several magnetic excursions that have been reported in the lit-
erature (including the Btwa H event mentioned here) are apparently not
associated with times of ice-volume changes or rapid cooling as record-
ed in oxygen-isotope curves (for a review of reported excursions see
Verosub and Banerjee, 1977). This argues against a one-to-one cause
and effect relationship. However, some of these reported excursions
are very likely spurious or poorly dated (Verosub and Banerjee, 1977).
Furthermore, the climatic record in many deep-sea cores may have
poor resolution of events shorter than a few thousand yearst as a result
of slow deposition, bioturbatiou and/or dissolution of calcium carbonate.
A more definitive answer to the question of possible relationships
between magnetic excursions and climate change will depend upon fur-
ther study of the response of the core and mantle to changes lnthe earth*s
rotation, and upon a better understanding of the possible effects that geo-
magnetic variatious might have on climate through upper-atmospheric
mechanisms. Further empirical tests of the validity of the relationship
between magnetic excursions and short-term climate cooling can be ob-
tained from analyses of sedimentary sequences with high rates of depo-
sition, and from closely spaced paleomagnctic determinations In suitable
materials.
Aoknowledgements. The author is grateful to Dr. Rhodes Fair-
bridge for helpful discussions. This work was carriedout while the
author was a NAS-NRC Research Associate at the Goddard Institute for
Space Studies.
344
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Variations of the earth's magnetic field and rapid climatic cooling: A possible link through changes in global ice volume

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