Rock Magnetism Linked LMagnetite New Map for Climate ChangeI

Eos, Vol. 75, NO. 15, AprU 12,1994
ing program cannot assess damage to the
man magnetite ctystals are not isolated from
anrrnals.
each other.
"Dramatic, obvious effects, such as
Calibration studies of these interaction
whales floating to the surface will be deeffects done with bacterial magnetites and
tected, but some ed& wilI be too subtlethe more sensitive techniques of anhysteretic
such as changes in reproduction, mortality,
remanent magnetization (ARM) le.g., McNeiI!
and growth rates," Wellgart s a i d . 4 . C~a~lirer-and Kirschuink, 1993)indicate the magnetite
me White
crystals in the brain are present in clumps
with a minimum of 50 or more particles per
clump. Hence, rather than one crystal per
100 brain cells, there is less than 1 cell in
5000 with one of these magnetite clumps.
to
Unfortunately, the rock magnetic data do
not place an upper limit on the number of
crystals present pet cluster-something on
PAGES 17b179
the order of at least 50 is needed, but it
This piece was writfenlo help i n b n scicould just as well be 10,000.
ence teachers, students, and joumoli$&
More recent work suggests that the upper
a b u t some of the lafest d@oelopmentsin
number may be mwe correct. Recently, we
rhe geophysical sciences. I! wilt o/so appear
have found thaZ pellets of the Jurkat strain of
in Earth in Space, published by AGU.
human '6-lymphocyteshave peculiar magnetic dipole patems when viewed with
three-dimensional magnetic resonance imag.
Magnetite has a long and dlstlnguished
career as one of the most important minerals ing (MRI) rnicrosmpy [Ghosh et at,, 19931.
The number density of these patterns, ahng
in geophysics, as it is responsible for most
with the magnetite conmtmtions measured
of the remanent magnetization in marine
with SQUIDmagnetometry, Implied the pressedlrnenrs and the oceanic crust. It may
ence of between I000 and -1 0,000 magnecome as a surprise to discover that it.also
tite crystals per dipole pattern.
ranks as the third or fourth most diverse
We also have evidence that rnagnetocytes
mineral product formed bimhemically by
are naturally present In tissues, rather than
lmng organisms. and forms naturally in a
formed as some bizarre differentiationprodvarieb of human tissues [Kirschuink et at.,
uct in the cell cultures. In collaboration with
19921.
our group, M. H. Nesson oh Oregon State
Jlaqnetite was disc&
in teeth of the
University has disaggregated normal mouse
~ o l ~ l & o ~ h mollusks
ora
over 30 years ago,
brain tissue with rnult~plefreeze-thaw cycles
in maqnetotactic bacteria nearly 20 years
and used our "magnetic finger" technique to
ago. In honey bees and homing pig&ns
pull out magnetic objects. This technique
nearly 15 years ago,but only recentFy in huallows cell fragments only a few microns
man tissue.
across to be extracted, and these fragments
Research in the somewhat obscure gem
phys~calfield of rock magnetism led to many contain hundreds of single-domaln magaetite crystals nearly identical to those in the
of these more recent discoveries, as many of
human brain. The close packing arrangethe instruments and techniques dweloped
ment is precisely what is needed to produce
for these studies lend themselves directly to
the magnetic interaction effects noted above.
the problem of finding ferromagnetic materiThe biological function of these magnetoals in tissue samples.
cytes is as yet unknown. They are definitely
Most recently, extension of these r&not used to detect the geomagnetic field, as
magnetic techniques to biological materials
they d o not contain the linear chains of cryshas pointed to the presence of a biological
surprise: a new cell type loaded with crystals tallographically aligned magnetite crystals as
do magnetotactic bacteria, protozms, miof biogenic magnetite, which we have
gratoly fish, and birds.
d u b M "magnetoqtes."
At the risk of engaging in speculation,
Sweral important clues concerning the
our best guess is that the magnetite aystals
organization of magnetite crystals in the human brain were present in our original mag. are important for biochemisby. The lipidbilayer membranes surrounding the magnener~cdata. which in fast led to the discwely
tite crystals in bacteria contain m m l hunof these new cells. Over the past 20 years,
dred distinct proteins of unknown function.
~eophysicists.workingin the field of rock
It is easy to show that these proteins reside
magnetism have dweloped sensitive techin a local, static magnetic field that ranges
niques to determine whether the magnetic
from 0.2 to 0.5 T (2000 to 5000 Gauss) prowstals wtthln a sample are close to each
duced by the enclosed magnetite crystal.
orher. Ir turns out that the magnetic field of
Although these held strengths are probaone cn.stal upon its neighbor will cause dlsbly too weak to produce significant magnetotlnctke shifts in h e coercwity spectrum of a
mechanical orientations in diamagnetic molsample. This inhibils the acquisition of an
ecules, which need fields approaching 1 T,
so thermal remanent magnetlsrn (IRM) but
they are well within the range needed to proa d s in rts demagnetization 1e.g.. GsowsRi,
duce dramatic effects on the electronic spin
19811.
states of reaction intermediates. Controlling
These erects are present in virtually all
vertebrate tissues m i n e d to date. includthe decay path of a triplet state, for example,
ing the human brain, implying that the huonly requires magnetic fields on the order of
Rock Magnetism Linked
Human Brain
LMagnetite
-10 mT or lC4 Gauss Ic.g, McLaughlin,
19891.
As magnetife bbfomineralization wotved
nearly 2 b.y.a. (Chang and Kixschuink, 19891,
wolulion has had ample opportunity to Incoporate magnetically mediated reactions
into biochernisfry.. Rock rnagnetlsrn may yet
induce another field of study.Joseph L.
Kirsch~link,Coliiomia Insr~ruted TechnolOD, Pasodeno, CffIjI:
Rcftrtnces
Cisowski, S., Interacting vs. non-interacting single-
domain behavior in natural and synthetic mples, Phys, Earth Planer InL, 26,56, 1981.
Ghosh P., R. E,Jacobs, A. KobayashiXirsctwink
and J. L. Kirschmnk, NMR microscopy of biw
genic magnetite (abstract), In Proceedings &Ute
12th Annual Meefing d the Society FOT Magnetic
Resonance Imaging in Medicine, p. 938, New
York, 1993.
Klrschvink, J. L., A. Kobayashi-Wrschvink. and B. d.
Woodford, Mwnetite biomineralization in the
human brain, Pmc, dNatl. Acad. Sci. USA., 89,
7683,1992.
Mclauchlan, K k , Magnetokenetics, mechanistics,
and synthesis, Chem. Brit., 895, September 1989.
McNe~ll,D. F., and J. L. Kirschvink, Early dolomititation of platform carbonates and the preservatlon of magnetic polariw,J. Gmphys. Res., 98,
7977. 1993.
New Map for Climate
ChangeI Ecosystems
Researchers
PAGE 180
A new map of the land cover regions of
the conterminous United States and its accompanying digital data set can provide scientists with a new tool for investigating the
ecosystem effects of climate change.
The map combines satellite i m a m , digital elevation, ecoregion, and climate data
sets to build a database containing 759 separate land cwer regions across the lower 48
states. Each of the map's regions bas a
unique cornbinat~onof vegetation and land
cwer types. Typical vegetation or land c m r
patterns commonly found In each region are
listed in the map's legend.
Additional smaIl-scale maps depict the
length of vegetation greenness, the onset of
greenness, and peak greenness,
The map, "Seasonal Land Cover Regions,'"~available lor $3 from USGS Map
Distribution, Box 25286, MS 306, Denver Federal Center, Denver, CO 80225; the complete
digital data set and dmumentation for the
map are available on CD-ROM for 532 from
Customer Services, EROS Data Center, Sioux
Falls, SD 57198.
Atmospheric
Idomation Available
on Gopher
PAGE 180
The Atmospheric Sciences Department at
the University of Illnois. Urbana-Champaign.
6 opening a new full-scale World Wide Web
0
semer, The Daily Planet. T h ~ envis