ࡱ> #%"c  jbjbSS 11] FHHHHHH,sgttjFFFF p.5`FF The Pleistocene-Holocene Transition: the Role of Extraterrestrial Accretion Daniel B. Karner Frank Asaro Richard A. Muller published in EOS American Geophysical Union Proceedings of the 1998 Fall Meeting page U31A-03 TI ABSTRACT Rapid glacial terminations during the last 800+ kyr of the Pleistocene have been the focus of much study, but the triggering mechanism has remained elusive. A possible mechanism for glacial terminations is the accretion of extraterrestrial dust. $^{3}$He data, recording interplanetary dust particle (IDP) concentrations in ocean sediment, supports this idea, showing that the flux of IDPs oscillates on an approximate 100 kyr cycle. However, He-3 trapped in IDPs is sensitive to atmospheric entry heating, which is dependent on particle size; large particles de-gas upon entry, so an unusually large particle size distribution for the hypothesized accretion event could go undetected by He-3 measurements. We are measuring iridium, another proxy for extraterrestrial accretion, in sea floor sediment from ODP Site 806. Unlike He-3, iridium is not sensitive to atmospheric entry heating, and so provides a direct measure of accretion. We will show neutron activation analysis data from a continuous strip of sediment covering the approximate time range 20-7 ka , homogenized in increments of about 1 kyr. These data should tell us whether changes in accretion played a role in the last glacial termination. N CJCJ$MN_k}~ $$MN_k}~  / =!"#$%|HH(FG(HH(d'`DFDFZ^9ww)Jg9^F1999B19o{9!1^!Bo{!Ns)Jg9^99F1F1w!^9F1BB9F1!F1!^o{9!1^fTHDF]DF [4@4NormalCJOJPJQJmH <A@<Default Paragraph Font    X^ej qu HK~VclRichard A Muller;7 Gbyte:archives (new): here it is:Karner 1998 AGU abstract@4 q`@GTimes New Roman5Symbol3 Arial3Times"qhw:x:$20KThe Pleistocene-Holocene Transition: the Role of Extraterrestrial AccretionRichard A MullerRichard A Mullerg9!g9)J9^!F19)Jg9!g91ww[DFfTHDF]^DFjjDFfTL!^9F1!!o{wF1Vo{Ns!^o{wVw9VV^^!9F1Ns9w!w )will )be ) presented.( (dvgrd (,Times .+dC0The Pleistocene-Holocene Transition: the Role of+VExtraterrestrial Accretion +. Daniel )%B. )Karner(Frank )"Asaro(Richard A. Muller+published in EOS(American Geophysical Union($Proceedings of the 1998 Fall Meeting+5 page U31A-03 TI+ AABSTRACT(+<Rapid )#glacial )% terminations )Dduring )'the )last )800+ )!kyr )of )the ) Pleistocene )@have )been(8<the )focus )!of )much )!study, )$but )the ) triggering )8 mechanism )>has ) remained )5 elusive. )- )A(E< possible ). mechanism )=for )glacial )% terminations )Dis ) the ) accretion )4of )extraterrestrial )Pdust.(R< $^{3}$He )>data, ) recording )9interplanetary )Pdust ) particle )-(IDP) )"concentrations )Uin(_<ocean )# sediment, )4 supports )1this )idea, )showing )1 )that) )the )flux )of ) )IDPs ) oscillates )4on )an(l< approximate )I100 )kyr )cycle. )& However, ):He-3 )!trapped )0in )IDPs )!is ) sensitive )6to(y< atmospheric )Centry ) heating, )-which )$is ) dependent )<on ) particle )+size; )large ) particles )0de-(<gas )upon )%entry, )'so )an ) unusually )=large )#pa) rticle )#size ) distribution )Gfor )the(< hypothesized )K ) accretion)1 )event )!could )!go ) undetected )?by )He-3 ) measurements.(< ) ) ) ) ) ) ) )We )are ) measuring ): iridium, )*another )-proxy )$for )extraterrestrial )P accretion, )7in )sea(<floor ) sediment )5from )ODP )Site )806. ) )Unlike )*He-3, )#iridium )+is )not )s) ensitive )0to(< atmosph Oh+'0 ( DP l x 'LThe Pleistocene-Holocene Transition: the Role of Extraterrestrial Accretionhe Richard A MulleroloichNormal Richard A Mullerolo1chMicrosoft Word 8.0o@F#@j@)us )whether )/changes )/in ) accretion )5played )(a ) role(<in ) the )last )glacial )% termination.,( (dvgrd (,Times .+7&Glacial Cycles and Interplanetary Dust +_Richard A. Muller(\Department of Physics(h+University of California Berkeley, CA 94720+?published in EOS(American Geophysical Union($Proceedings of the 1998 Fall Meeting+6 page )U22B-04(ABSTRACT(<We )do )not ) understand )7the )origin )of ) the )ice )ages. ) )The ) Milankovitch )Bmodel, )#which ) attributed(<the )ice )ages )to ) changes )*in ) northern ), hemisphere ): insolation, )4is ) unable )#to ) a)ccount )$for )simple(< features )* )seen) )in ) spectral )) analysis )+of )the )data. ) ) )Spectra ))of )global )#ice )proxies ))(oxygen(<isotope )'ratios) )#for )the )last )million )&years )show )a ) single )!narrow )&line )near )period )$100 )ky,(<whereas ))the ) Milankovitch )Atheory )! predicts )(a )triplet )with )stro)ng )power ) at ) 95, )125, )and )400 )ky.(<The ) discrepancy )>cannot )&be ) reconciled )7by )any ) published )5 nonlinear )3model), ) since )they(< preserve ),the )triplet ) structure. )1 )Other ) problems )1with )the ) Milankovitch )Dtheory )$include )(the((<absence )(of ) a )strong )!23 )ky )peak )and ) causality ), )proble)ms ) (glacial )% terminations )= occurring )1prior(4<to ) insolation )1 increases). )5 )Nevertheless, )Athe ) narrowness )9of ) the ) spectral )'line )argues )# strongly )+in(@<favor )of )an ) astronomical )@cause )for )the )the )ice ) )ages.) ) ) (Terrestrial )8 mechanisms )>fail )because(L<they ) invariably )4predict )&bro)ad ) spectral )*lines )-- )unless )$they )are ) arbitrarily )5 narrowed )3by(X< parameter )3 adjustment )9-- )since ) terrestrial )2 processes )4allow )mode ) mixing )'which )"broadens(d< spectral )'lines.)(|< ) ) ) ) ) ) ) )Changes )-in ) the )Earth's )$Orbital )& inclination )6could )account ))for )the )glacial )#cycles. )% )Th) e(< spectrum ).of ) the ) inclination )4is ) a )good )match )to ) the ) spectrum ).of ) the )glacial )!cycles; )#both )have )a(<single )narrow )%line )near )100 )ky) . ) ) Inclination )6 naturally )- accounts )-for )the )absence ))not )only )of(<the )split )peak, )but )also )the ) absences ).of )the )400 )and )23 )ky )features)% ) predicted )0by )standard(< Milankovitch )Atheory.(< ) ) ) ) ) ) ) )Gordon )) MacDonald )<and )I )have ) proposed )0that )the )orbital )# inclination )6cycle ) modulates(<the ) accretion ).of )solar )system )%dust, )and )that )such )dust ) entering )*the ) atmosphere ): triggers ))the(<chang ՜.+,D՜.+,L hp  ,'University of CaliforniaHo: LThe Pleistocene-Holocene Transition: the Role of Extraterrestrial Accretion Title 6> _PID_GUID'AN{AEC7BEB1-87B6-11D3-9E5C-000502EDF71F}ts ),that )this )model ) is ) too )simple; )&however )+ experimental )@ observations )?verify( <that )extraterrestrial )Fdust )does )have )the ) predicted ).100 )ky )cycle.($< ) ) ) ) ) ) ) )Various )+ mechanisms )@that )link ) accreted ),dust )to )climate )'will )be ) discussed. )7 )Direct(0< scattering )1o)f ) sunlight )*is ) insufficient )9unless )"the )dust )serves )!as )a ) seed )for )the ) formation )3of(<<larger ) particles. )/The )timing )$of )the ) appearance ):of ) noctilucent )9clouds )% suggests )/a ) link )to(H< accretion. )1 ) ) Accreted )-dust ) )is) )the )primary ))source )#of )solid )surface )&in ) the )middle )%and )up) per(T<stratosphere, )?and )could )be )the )site )of )heterogeneous )H chemical )- reactions, )0such )as )those )that(`<affect )ozone )above ) Antarctica. )5Extraterrestrial )Hdust )is ) also )a ) significant )5source )#of )bromine )+in(l<the )upper ) atmosphere, )=and )this )too )could )affect )the )ozone )!layer.) ) ) ) Detailed )- calculations(x<would )!require )% particle )&size )distributions )?and )other )aspects )'of )upper ) atmosphere ); chemistry(<that )are ) currently ). unknown. )3 )It ) is ) not )known )$whether )*the )dust )should, )'theoretically, )@cause(<cooling )&or ) warming. )/It ) is ) possible )*that )a )mechanis),m ) other )than )dust )can )be )found ) to ) link )the(<cycles )"of ) glaciation )3to )orbital )$ inclination, )9but ) )no)  )such ) plausible )0 mechanism );has )been(< proposed. )3 )Ice )volume )&proxy ) data )for )the )period )"1 ) Ma )to )2.5 )Ma )shows )#a ) narrow )&41 )ky(r( (dvgrd (,Times .+<2 periodicity. )8 )In ) contrast ))to ) the )recent ) cy) cles, )these )earlier )!ones )may )be )linked )!to ) insolation.(><The )onset )of ) the )100 )ky ) periodicity, )7that )took )place )between ))800 )and )1200 )ky )ago, )could )be(J<due )to ) the ) increase ))of ) solar )system )$dust ) observed )-in ) helium-3 ).records )'for )that )time. ) )Not )all(V<climate ))processe))s ) follow )&the )same )! spectra. )- ) Evidence )3 suggests )2that )local )climate(b<() foraminfera )=size, )lake )bed )depth ) ranks, )"rock )color) )"can )be )linked )$to ) precession )9and(n<eccentricity; )=however ),these )cycles )"are )weak )or )absent )$in )global )#ice )proxies)#.\ ) New )dust(z< measurements )Fbased )on )iridium )% measurements )Gin ) Greenland )5(GISP2) )-ice )samples )*and )sea-(<floor )cores )(Site )806) )will )be  !$Root Entrya.tlb.niraei.siptcrusee.oritacm.laela.tib Fre.scito@ &citu1Table.tibanirsep.ciuter.smataue.refamelatlb.niraei.sipelala.tbinariescip.erutma.seutalar se.pWordDocumentniraei.siptcrusea.anlla.tibanirsep.citlab.niaries.pirutca.seaminaslb.tlipctSummaryInformationa.inamitnosla.tibanirse(.tlaibanries.picerutra.slatib.tiraners.DocumentSummaryInformationciuter.s8ip.stcrues.arts.ydobtra.tlaanibseir.sasCompObjciuter.ssaainla.tibanirsep.ciuter.ssaai.namelrutcsea.sian-indnaiXapraObjectPooler.ssartola.tibanirsep.ciuter.suaotsla.t@ @ sei.tlaibnairsep.ciuter.sabllubtsnigla.tibanirsep.ciuter.scbs-reeisla.tibs-cbreeis.dalt.anibseircip.erutib.stubgasttl.b FMicrosoft Word DocumentNB6WWord.Document.8etion. )8 )We )will(<show )#neutron )0 activation ); analysis )0data )from )a )  ) continuous)< )strip )of )sediment(< covering )4the ) approximate )Gtime )range )#20-7 )ka ), ) homogenized )Nin ) increments )?of(<about )"1 ) kyr. ) )These )"data )should )'tell )us )whether )/changes )/in ) accret