Table Of ContentMethane Hydrates in
Quaternary Climate Change
The Clathrate Gun Hypothesis
James P. Kennett
Kevin G. Cannariato
Ingrid L. Hendy
Richard J. Behl
AmericGane ophysUicnailo n
Washington,
Publishedu ndert he aegiso f the AGU BooksB oard
Jean-LouiBs ougeretC, hair;G rayE . BeboutC, arlT FriedrichsJ,a mesL . Horwitz,L isaA. Levin,
W. BerryL yons,K ennethR . MinschwaneDr, arrellS trobela, ndW illiam R. Young,m embers.
Library of CongressC ataloging-in-Publication Data
Methaneh ydratesin Quaternaryc limatec hange:t he clathrateg un hypothesis/ JamesP .
Kennett...[et al.].
p.cm.
Includesb ibliographicarl eferences.
ISBN 0-87590-296-0
1. Paleoclimatology--Quaternar2y.. Climatic changes.3 . Methane.I . Title: Clathrate
gun hypotheses.I I. Kennett,J amesP .
QC884.M44 2002
551.6--dc21 2002035623
ISBN 0-87590-296-0
Cover photograph: Methane hydratem ound ((cid:127)-1.5 m diameter) on oceanf loor (540 m)
at Bush Hill, northern Gulf of Mexico, with free gas venting into the water column.
Mound is surroundedb y chemosynthetictu be worms and coveredb y Beggiatoam ats.
Courtesyo f Ian R. MacDonald, Geochemicala nd EnvironmentalR esearchG roup,Texas
A&M University (see SassenR, . et al., 1998, Geology2 6, p 851-854).
Back cover graphics:R ibbonsa re from a sonarr eflectionp rofile (3.5 kHz) througha ctive
hydrocarbong ass eepsa t Coal Oil Point,S antaB arbara,C alifornia.D ark blue curtainsa re
gasb ubblep lumesr isingf rom the oceanf loor.W aterd epth(cid:127) -60 meters.C ourtesyo f Bruce
Luyendyk,H ydrocarbonS eepsS tudyG roup,U niversityo f CaliforniaS antaB arbara.
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Contents
Preface ..................................................... v
Methane Hydrates in Quaternary Climate Change:
The Clathrate Gun Hypothesis
Summary. ................................................... 1
Introduction .................................................. 4
Chapter 1
Late QuaternaryC limate Patterns. ............................... 11
Chapter 2
AtmosphericM ethane Behavior: Ice Core Records. .................. 29
Chapter 3
Methanogenesisa nd Methanotrophy. ............................. 37
Chapter 4
Sourceo f Methane During Rapid Increases.. ....................... 43
Chapter 5
Methane Hydrates as AtmosphericM ethane Source .................. 89
Chapter 6
The ClathrateG un Hypothesis ................................. 105
Chapter 7
Methane Hydratesi n Pre-QuaternaryC limate Change. ............... 109
Chapter 8
Primary Causeo f QuaternaryI nstability of Methane Hydrates ......... 113
Chapter 9
Instabilityo f Methane HydratesD uring the Quaternary.. ............. 125
Chapter 10
Role of Methane in QuaternaryC limate Change. ................... 147
Chapter 11
Role of Methane Hydratesi n QuaternaryC limate Change. ............
Chapter 12
FutureT estso f the Hypothesis. ................................ 163
Chapter 13
Conclusions ............................................... 167
References.. ............................................... 169
List of Abbreviationsa nd Symbols.. ............................. 211
Glossaryo f Terms. ..........................................
Preface
Like mostE arth scientistsw, e are intrigueda nd amazedb y recentd iscoveries
from ice-corea nd marines edimentsth at globalc limatea nd the ocean-atmosphere
systemc an abruptly switch from glacial to near-interglaciatle mperaturesw ithin
decadesR. emarkablyt, his happenedm any times duringa nd at the end of the last
glaciale pisodec, ausinge normousd isruptionisn the globalb iosphereS. uchd iscov-
eriesa re double-edgedh, owever.A long with the excitementt hey promptc omesa
grandc hallenget:h eir explanationW. e, ando thersh, avew onderedw hat factorsc an
possiblyd rive the climates o far and so fast. Where doest he energyc ome from?
Understandings uchp henomenab ecomesp aramounti n a world with increasing
concerna boutt he potentialr ole of humanso n globalc limatec hange.
This booka ddressessu chi ssuesh eado n, if by an unconventionatal ck.W e sug-
gestt hat eacho f the numerousa bruptw arningsd uringt he last ice age was accom-
paniedb y, and in part drivenb y, massiver eleaseso f methanei nto the oceana nd
atmosphersey stemb y dissociatioonf "frozen"m ethaneh ydrates( clathratess) tored
in marines edimentos n the continentaml arginsA. generalc onsensunso w existst hat
methaneh ydratesr epresenat n enormousre servoiro f carboni n the form of frozen
methaneth atb oth storesa ndh ast he capabilityo f suddenlyre leasingfr ee methane
into the oceana nda tmospherwe hene nvironmentacl onditionsa re suitableW. e also
suggestth atr epeatede missionso f methane( a potentg reenhousgea s)p romulgated
otherr apidf eedbacksth at assistedin drivingt he Earth'sc limatea bruptlyf rom gla-
cial to interglaciatl emperaturesW. e refer to this hypothesisa s the ClathrateG un
Hypothesis.
The ClathrateG un Hypothesisin vokesp rocessesth at have been relatively
inactive and unobservedb y human beingsd uring our cultural developmenta nd
recordedh istory--thel ast7 000 years.T his periodrathel atterp art of the Holocene
interglacial--wasa time of high seal evels and warm and relatively stablea tmos-
pherica ndo ceant emperaturesS. uchc onditionsw ere ideal for methaneh ydrates ta-
bility, andc onsequentlym, ajore missionsfr om the reservoira re outsidet he modem
human experienceB. efore the middle Holocene,h owever,o ur human ancestors
experiencedd ramatics hiftsi n climate and sea level, and some may have even
observeda nd experiencedt he effects of massive methane releasesi nto the
ocean/atmospheirne near-coastaalr eas.
Yet, becauset he methaneh ydrater eservoirh as been largely stabled uring
recordedh umane xperiencei,t s potentiali nfluencei s little incorporatedin to gener-
al modelso f pastc limatec hangeA. recentm ajor synthesiso f abruptc limatec hange
relegatesth e potentials ignificancoef methaneh ydratesto the categoryo f "exotica
and surprises.W" e believet hat if methaneh ydratesw ere a currents ourceo f large
methanee missionsin to the atmospheret,h ey almosta ssuredlyw ould have been
long considereda n integralp art of the climates ystem,w hich we suggestth ey are.
Herein,w e presentm uche videnceth att he methaneh ydrater eservoirh asv igorous-
ly interactedw ith the oceana nd atmospherien the recentg eological
Key discoveriems aded uringt he lastd ecadeh avel ed scientisttso recognizeth e
importanceo f three areaso f Earth scienced iscussedin this book: (1) the extreme
sensitivityo f the Earth'se nvironmentasl ystemt o changed uringt he last ice age;( 2)
the abruptnesasn d near-globael xtento f major climate and environmentacl hange
that occurredo ver decadesa; nd (3) an appreciationo f the extento f the methane
hydrater eservoira s a majorc arbonr eservoirT. his bookp resentsa n assessmentht at
links all three into an integratedg lobal hypothesisI.t invokesi nherentlyu nstable
methaneh ydratesa s a critical componento f the climate systemi n providingc ru-
cially needede nergyt o force and acceleratea bruptc limatec hange.
Our interesti n the potentialr elationsb etween climate changea nd methane
hydratesd erivesf rom our studieso f the dramaticp aleoclimatica nd paleoceano-
graphicc hanger ecordeda nd containedi n the methane-richs edimentso f Santa
BarbaraB asin. Specifically,w e begant o formulatet he ideaso utlinedi n this book
upond iscoveryin 1995 of a sequencoe f brief,h ighlyn egativec arbonis otopics pikes
exhibitedi n fossilp lanktonica ndb enthicf oraminifersin SantaB arbaraB asins edi-
ments.T hesei mmediatelyr emindedu s of a carboni sotopics pikei n foraminiferad is-
coveredb y Lowell Stotta ndJ im Kennetta ssociatewd ith thet erminalP aleocenteh er-
mal maximum and major deep-seae xtinction5 7 million years ago, which Jerry
Dickensl ater attributedt o massived issociationo f marinem ethaneh ydratesd ue to
deepo ceanw arming.W e still find it remarkableth atd iscoverieos f the Earth'so per-
ating style in its ancientp ast provide clues and critical insighti nto key climatic
processetsh at may have operatedi n the near-recengt eologicp ast,p rovidingy et
anothere xampleo f the importanceo f the pasta s a key to the presenta ndf uture.
The presenbt ook integratesa nds ummarizesw idely disparatere searchfi eldsi n
a processo f consiliencea; lthoughn o singlep roof existsf or the hypothesisp resent-
ed here,a wide rangeo f evidences upportsit . For thisr easona lone,w e hopet hatt he
book interestsa broadr angeo f Earth scientistsW. e expecti t to be especiallya ppro-
priatef or scientistsc ompelledb y the history,a ndp rocesseso,f the Eartha s an inte-
grateds ystemb ut comingf rom differenta pproachesin, cluding:p aleoceanography,
climate dynamics,p aleobotanyb, iogeochemicacl ycling, methaneh ydrates,a nd
marineg eology.I n formulatingt his integratedh ypothesisw e recognizet hat differ-
ent aspectsa re controversialH. owever,w e hope that the presenth ypothesiss timu-
lates further researcho n possiblel inkagesa nd significanceT. o this end, we have
outlineda numbero f researcha reasa ndt estst hatm ay clarify relationshipasn dp ro-
mote betteru nderstandinogf the causeso f late Quaternaryc limatec hange.
AcknowledgmentIs b: eganw ritingt hism anuscripwt hile on sabbaticalle avea s
a guesti n the Departmento f Earth and OceanS ciencesa t the Universityo f British
Columbia, Canada. I thank the Department,a nd especiallyD rs Tom Pedersen,
StevenC alvert and Richard Chasef or their wonderfulh ospitalitya nd for helping
makem y sabbaticasl o stimulatinga ndp roductiveI. alsot hankL ionel Carter,K eith
Lewis, andN IWA in Wellington,N ew Zealand,f or theirh elp andh ospitalityd uring
initial stageso f this projecti n early 2000. My colleaguesa nd I alsor eceiveda ssis-
tance from severailn dividualsa t theU niversityo f California,S antaB arbara.I n par-
ticular,w e thank Karen Thompsonf or considerablea ssistancien gatheringa nd
compilingr eferencesJ,o A nne Sharpef or secretariaal ssistancien preparingth e first
draft, andD iana Kennettf or assistingin so many ways.I nitial stimulationfo r this
investigationre sultedf rom the innovationso f G. Dickensa nd E. Nisbet.W e thank
numerouso therc olleaguesfo r providingu seful suggestionss,t imulationo, r con-
structivec riticism as this researche volved. These individuals include P. Brewer, H.
Behling,B . Buffett, T B lunier,J . Chappell,J . Clark, G. Denton,P . Glaser,T . Hill,
K. Hinrichs,R . Hyndman,C . Keeling,L . Keigwin, M. Kienast,K . Kvenvolden,D .
Lea, I. Leifer, B. Luyendyk, M. Maslin, H. Nelson, U. Ninnemann,C . Paull, D.
Piper,W . Reiners,M . SamtheinJ, . Schimel,J . SeveringhausC, . Sorlien,L . Talley,
and R. Wrist. We also wish to thankL . PetersonC, . Ruppel, and an anonymous
reviewerf or their most valuablec onstructives uggestionfso r improvementsu pon
readingo f the entirem anuscriptT. he sectionso n methanogenesiasn d methanotro-
phy were considerablyim proveda s a resulto f constructives uggestionbsy D. L.
Valentine.
Dr. Dale Krause provided much stimulation,e ncouragementa, nd valuable
advice throughoutw hile offering useful commentso n the manuscriptW. e also
appreciatet he efforts of Allan Graubard,A cquisitionsE ditor of the American
GeophysicaUl nion booksp rogram,f or constructives uggestionasn d encourage-
ment throughouta nd for his guidancet hrought he review process; in effect, for
makingt hisp ublicationa reality.W e alsot hankT erenceM ulligan, our production
editor,f or carefullyt ransformingo urm anuscripitn to thisv olume.T his researchw as
initially inspireda s a result of OceanD rilling Program( ODP) participationT. he
ODP is sponsorebdy the U.S. NationalS cienceF oundation(N SF) andp articipating
countriesu nder the managemento f Joint OceanographicIn stitutions( JOI) Inc.
Fundingf or this researchw as providedb y the JOUU.S. ScienceS upportP rogram
and NSF (Marine Geologya nd Geophysicsa) nd we especiallyt hank Dr. B il Haq
for his help ande ncouragemenRt.i chardB ehl wishest o make acknowledgmentot
the Donorso f theA mericanC hemicalS ocietyP etroleumR esearchF und,f or partial
supporto f thisr esearch.
About the Authors
JamesK ennett,a marine geologisth, as been a Professorin the Departmento f
GeologicalS ciencesU, niversityo f California,S antaB arbara,s ince1 987, and was
Director of the Marine Science Institute at UCSB from 1987 to 1997. He received his
PhD (1965) andD Sc (1976) from VictoriaU niversityo f WellingtonN, ew Zealand.
Kennett has publishede xtensivelyi n stratigraphym, arine micropaleontology,
marineg eologya nd contributedto wardst he developmenot f paleoceanographHye.
i(cid:127) (cid:127) (cid:127)n ..... (cid:127) ,h(cid:127) (cid:127),,(cid:127),4,.(cid:127) n GeophysicaUl nion (AGU), the AmericanA ssociation
for theA dvancemenot f Sciencea ndt he GeologicaSl ocietyo f Americaa sw ell as a
Member of the U.S. NationalA cademyo f Sciencesa nd HonoraryM ember of the
Royal Society of New Zealand. He has had numerousa ssociationws ith AGU
includingb eing FoundationE ditor of Paleoceanographayn d electioni n 2000 as
EmilianiL ecturerb y the OceanS ciencesS ectiono f AGU.
His contributiontso wardsa bruptc limatec hanged uringt he Quaternaryh avec on-
tinueds ince1 992 with the successfuclo tingo f the outstandinSg antaB arbaraB asin
sequencbe y the OceanD rilling Program.R esultsf rom thisr esearchs timulatedh is
interestin the potentiarl ole of methaneh ydratesin climatec hange.
He and his wife Diana have lived in the U.S. since 1966 and have two grown
children.
Kevin Cannariatoo btaineda PhD (2002) in paleoceanographiny t he Department
of GeologicalS ciencesU, niversityo f California,S antaB arbara.C urrentlyh, e is a
Post-doctoraFl ellow in the Departmento f GeologicalS ciences,U niversity of
SouthernC alifornia.H is primaryi nterestsa re causeso f climatec hangea nd affects
on the biotao f paste nvironmentaclh anges.
Ingrid Hendy obtaineda PhD (2000) in paleoceanographiny the Departmereo f
GeologicalS ciencesU, niversityo f California,S antaB arbara.S he was a Post-doc-
toralF ellow (2000-2002)a t the Universityo f BritishC olumbia,V ancouverC, anada,
and is currentlya n AssistanPt rofessorin the Departmento f GeologicalS ciences,
Universityo f Michigan. She receivedt he Doffs CurtisW omeni n ScienceA ward in
2001 by the GeologicalS ociety of America in recognitiono f her paleoclimatic
researchi n Santa BarbaraB asin. Her interestsc entero n past oceana nd climate
changea s studiedf rom marines edimenrt ecords.
RichardB ehl is AssociateP rofessorin the Departmento f GeologicalS ciences,
California State University,L ong Beach, where he has taught since 1995. He
obtaineda PhD in EarthS ciencesa t the Universityo f California,S antaC ruz (1992),
havingr esearchetdh e sedimentologayn dd iagenesiosf siliceouss edimentasl ongt he
Californiam argina ndi n the deepP acificO cean.F rom 1992 to 1995 he was a Post-
doctoralF ellow in the Marine ScienceI nstitute,U niversityo f California,S anta
Barbaraw, hereh e beganr esearcho n Quaternaryc limatec hangea sr ecordedin Santa
BarbaraB asin.H is primaryi nterestsa re in marines edimentologiyn cludingd iagen-
esis,g eochemistryp,e troleumg eologyp, aleoceanographayn dc limatec hange.
MethaneH ydratesi n QuaternaryC limate Change'
The ClathrateG un Hypothesis
JamesP . Kennett, Kevin G. Cannariato,I ngrid L. Hendy,
and Richard J. Behl
SUMMARY
The remarkables imilarityo f late Quaternarya tmosphericm ethane( CH4) and
temperaturev ariationsr ecordedi n ice coress uggeststh at CH 4 has played a sig-
nificant role in climate change.D issociationo f marine sedimentarym ethane
hydratesli kely inducede pisodeso f rapid climatew arminga t varioust imesi n the
geologicp ast throughg reenhousefo rcing by atmosphericC H 4. We proposet hat
the late Quaternary( last 800 kyr) was also a time of significanti nstabilityo f the
methaneh ydrater eservoir.T his sensitivityr esultedf rom the interactiono f large
changesi n sea level (pressure)a nd fluctuatingc haractero f intermediatew ater
(temperature)i mpinging on upper continental slopes (-400 to 1000 m water
depth);t he zone of potentialm ethaneh ydratei nstability.A fter 800 ka, upperc on-
tinental margin methaneh ydrate reservoirsb ecamem ore stronglye ngagedi n
greenhousea mplificationo f global climate change.T his occurredw hen colder
glacial upperi ntermediatew aterse xpandedm ethaneh ydratea ccumulationin to
shallowerw aters at the samet ime that intermediate-watert emperaturesb ecame
more variable.
Accordingt o the Clathrate Gun Hypothesis,e pisodicC H 4 releaser esulting
from the dissociationo f the sedimentarym ethaneh ydrater eservoirc ontributed
significantlyt o the distinctiveb ehavior of late Quaternaryc limate change on
orbital (Milankovitch) and millennial time scales.R epeatedc hangesb etween
sourcesa nd fluxes of upperi ntermediatew atersc ausedf luctuationsi n tempera-
ture that alternatelya ccumulateda nd episodicallyd issociatedh ydrateso n upper
MethaneH ydratesi n QuaternaryC limateC hange
¸ 2003 by theA mericanG eophysicaUl nion
2 Methane Hydratesi n QuaternaryC limate Change
continentals lopes.T he Clathrate Gun metaphorr efers to the sequentiala nd
repeateds tepso f loadingt he methaneh ydrater eservoir,t riggeringh ydrated is-
sociationb y changesi n intermediate-watert emperature,a nd energeticallyd is-
chargingC H4 into the ocean/atmospherteo amplify late Quaternaryc limate
warming eventst hat were stronglyr einforcedb y other greenhouseg ases,e spe-
cially water vapor.
Accordingt o thish ypothesism, ethaneh ydratess tabilizeda nda ccumulatedd ur-
ing late Quaternaryc ool intervalsw hen cold intermediatew atersb athedu pper
continentalm argins.C oldest intervalso ccurredw hen reinforcemento f orbital
insolation cycles led to largest ice sheetsa nd the greatesta ccumulationo f
methaneh ydrates.C hangesi n thermohalinec irculationt hat causedw arming of
upperi ntermediatew atersr esultedi n methaneh ydratei nstabilitya nd catastroph-
ic releaseo f CH4 into the ocean/atmosphesrey stema ssociatewd ith sedimendt is-
ruptiono n upperc ontinentasl lopesE. pisodeso f major CH 4 releasef rom hydrates
appeart o have beenr ecordedi n late Quaternarys ediments equenceos n different
continentaml arginsb y very negative1 5(cid:127)3Cex cursionisn benthica ndp lanktonic
foraminifera.I t is suggestedth at theser eleasesi,n associationw ith otherc limatic
feedbackm echanismst,r iggeredr apid warmingso f differentm agnitudea nd con-
tributed to the distinctive sawtoothp attern of late Quaternaryc limate change
exhibitedo ver a wide range of time scalesi ncludingt he 100-kyr cycle, Bond
Cycles,a nd individuali nterstadiael vents( Dansgaard/Oeschgeinr terstadials).
Much geologicale videncei ndicatest hat the abruptC H4 increasesa t glacial
and stadial terminationsw ere more likely to have been producedb y methane
hydratest hanb y continentalw etlands.I nundatedf lood plainsa nd organicc arbon
buildup,n ecessaryfo r major CH4 productionh, ad not significantlyd eveloped
duringg laciall owstandso f seal evel, becausein cisedr iversr esultedi n vigorous
freshwaterd ischargef rom the continentsT. hese wetland systemsw ere insuffi-
ciently establishedd uringr apid warmingst o have producedt he dramatica tmos-
phericC H4 increasesth at occurredw ithin decadesT. he large,c omplexm odern
wetland ecosystems(p eatlands,t ropical floodplains,c oastalw etlands)d id not
begin to develop substantiallyu ntil the middle Holocene becauseo f low sea
level, low water tablesa nd drynesso ver largea reaso f the Earth. Extensivem od-
ern high latitudew etlandsw ere not establishedu ntil after the ice sheetsa nd gla-
ciers of the high northernl atitudesm elted, well after the glacial terminations.
Major wetlandsi n non-glaciatedh igh latitude areasa lso did not developu ntil
within the Holocene.F urthermore,m uch paleobotanicaal nd other data indicate
that tropicalw etlandso nly developede xtensivelya fter the middleH olocene,f ol-
lowing sea-levelr ise to modernl evels,i nfilling of incisedr iver channelsa ndf or-
mation of flood plains.I n the absenceo f establishedC H4-producingw etlands,
the rapid increasesin atmosphericC H 4 recordedi n ice coresa re more consistent
with a methaneh ydrate source.
Abrupt atmosphericC H4 increasesa t glaciala nd stadialt erminationss uggest
that the greatestC H4 expulsionsfr om the methaneh ydrater eservoiro ccurred
