Rock Magnetism Linked LMagnetite New Map for Climate ChangeI
Transcription
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¬ 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