cherise martin final 1809856
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Honours!Dissertation! ! ! !!!!!!!!!!! ! !!!!!!!!!!!!!!!!Earth!Science
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November!2015!
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Sodium!concentrations!in!speleothems!
as!a!proxy!and!archive!for!past!wind!
conditions!and!storm!events!!
Cherise!Martin!
The!University!of!Auckland!
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Word!count!
(Includes!abstract,!chapter!1>4!&! ! ! 8,!827!!words!
conclusion,!excludes!figure!captions):!! ! !
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Total!word!count:!! ! ! ! 11,!098!words!
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!
Sodium!concentrations!in!speleothems!as!a!proxy!and!!
archive!for!past!wind!conditions!and!storm!events!
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by!
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Cherise!Martin!
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A!dissertation!submitted!to!fulfil!
the!requirements!for!a!
Bachelor!of!Science!(Hons)!
for!the!School!of!Environment!
at!
The!University!of!Auckland!
!
Professor!Joel!Baker!
&!
Simon!Barker!
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Date!submitted!
16th!November!2015!
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Keywords:!speleothem,!sodium,!paleoclimate,!wind!and!storm!events,!ICP>MS!
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Acknowledgments!
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I! could! not! have! completed! my! dissertation! without! the! help! of! several! individuals,!
whom! I! deeply! thank.!My! advisor,! Professor! Joel! Baker,! whom! offered! the! incredible!
opportunity! to!work!with!state!of! the!art!and! innovative! technology! in!Wellington.!He!
matured!and!evolved!my!understanding!in!the!geochemistry!world.!Dr!Simon!Baker!who!
was! continuously! there! to! guide!my!understanding.! !Both!have! given!me! support! and!
constructive! criticism.! Dr! Paul! Williams! who! was! available! for! all! my! questions! and!
provided!me!with!my! two! speleothems.!My! friends,!which! I! am! fortunate! to! have! too!
many! to!name! individually,!whom!promoted!balance.!My! family,!both! far!and!near! for!
the!unconditional!encouragement.!I!am!also!thankful!for!the!financial!contributions!from!
the!Faculty!of!Science!for!my!research.!I!greatly!appreciate!help!in!the!laboratories!from!
Andreas,!Dan,!Simon,!Joel,!Neville,!as!well!as!analytical!assistance!from!Michael!Rowe.!
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Abstract((
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Trace!element!data!were!measured!by! laser!ablation! inductively!coupled!plasma!mass!
spectrometry! in! two! speleothems! from! Waitomo! (GG5;! western! North! Island)! and!
Wairoa!(DS;!eastern!North!Island)!over!the!period!0–800!AD.!The!focus!of!this!study!was!
to!investigate!if!Na!concentrations!in!speleothems!provide!a!proxy!and!archive!for!past!
wind!conditions!and!storm!events.!The!Waitomo!speleothem!has!significantly!higher!Mg!
concentrations!as!compared!with!the!Wairoa!speleothem,!interpreted!to!reflect!greater!
cave! depth! at! Waitomo.! Mg/Ca! ratios! in! the! Wairoa! speleothem! show! clear! cyclical!
variations!with!distinct!peaks,!which!are!most!likely!recording!past!climatic!variations.!
The!Wairoa!speleothem!is!a!more!sensitive!archive!that!better!records!climatic!change!
relative!to!the!Waitomo!speleothem!due!to!the!former!being!a!shallower!cave!system.!As!
such,! Na! was! normalised! to! Mg! in! order! to! minimise! the! effect! of! cave! depth! on!
speleothem!chemistry.!Na/Mg!ratios!are!higher!on!average!and!show!larger!peaks!in!the!
Wairoa!speleothem!than!in!the!Waitomo!speleothem,!which!most!likely!reflects!the!fact!
that!the!Wairoa!speleothem!was!taken!from!a!site!relatively!close!to!the!coast.!Large!Na!
peaks!in!the!Wairoa!speleothem!between!0–120,!470–550!and!680–830!AD!correspond!
with!periods!of! increased!storms! identified! from!the!character!of!sediments! in!nearby!
Lake!Tutira.!Cyclicity!of!smaller!Na!peaks!in!the!speleothems!appear!to!correspond!with!
the! frequency! (ca.! 10–15! yr)! of! the! El!Niño! –! La!Nina! cycle.! The! results! of! this! study!
indicate! that! Na! concentrations! in! speleothems! hold! considerable! promise! for!
reconstructing! paleoWwind! and! Wstorm! conditions! related! to! large! storm! events! and!
climate!cycles!that!affect!New!Zealand!and!elsewhere.!
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Table(of(contents(!Acknowledgements………………………………………………………………………………………………!Abstract……………………………………………………………………………………………………………….!Preface…………………………………………………………………………………………………………………!!Chapter(One…………………………………………………………………………………………...………….! 1!1.0!Introduction!!
1.1#Objective…………………………………………………………………………………..………….! 1!1.2#Background……………………………………………………………………………….…………# 1!# 1.2.1#Speleothems#formation…………………………………………………………….# 1!# 1.2.2#Speleothem#geochemistry…………………………………………………………! 2#
1.2.3#δ18O#and#δ13C#stable#isotopes…………………………………………………….! 3## 1.2.4#UraniumDseries#dating………………………………………………………..……! 4!# 1.2.5#Sodium………………………………………………………………….………………..! 5## 1.2.6#Late#Holocene#climate#and#cycles#in#New#Zealand…..………………….! 5## 1.2.7#Storm#Events……………………………………………………….………………….! 7#
# 1.2.7.1#Historic#storm#events………………………………………………….! 7!# 1.2.7.2#Prehistoric#storm#events……………………………………….…….! 9
! # # 1.2.8#Structure#of#thesis…………………………………………………..…….! 9!#
Chapter(Two……………………………………………………………………………………………………..! 10!2.0!Methodology…………………………………………………………………………………………………! 10!! 2.1#Selection#of#speleothems#for#study………………………………………………………….! 10## 2.2#Speleothem#GG5#(Waitomo)#………………………………………………………..………..! 11## # 2.2.1#GG5#sample#preparation…………………………………………………………..! 11!# 2.3#Speleothem#DS#(Wairoa)#………………………………………………………………………! 12!############### 2.3.1#DS#sample#preparation#(DS)……………………………………………..………! 12!# 2.4#Data#collection#techniques…………………………………………………….………………! 13!# # 2.4.1#Laser#ablation#inductively#coupled#plasma#mass#spectrometry……! 13#
2.5!Data!processing!techniques………………………………………………………………….! 15!! ! 2.6.1!Iolite!data!processing……………………………………………….…………….! 15!!Chapter(Three…………………………………………………………………………………………………...! 16!3.0!Results…………………………………………………………………………………………………………..! 16!! 3.1!Trace!element!data!normalised!to!Ca……………………………………………………! 16!! 3.2!Trace!element!normalised!to!Mg……………………………………….………………….! 22!! 3.3!Trace!element!correlations…………………………………………………………………..! 26!!!!!!
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Chapter(Four……………………………………………………………………………………………………..! 30!4.0!Discussion……………………………………………………………………………………………………..! 30!! 4.1!Similarities!and!differences!for!Mg/Ca,!Sr/Ca,!and!Ba/Ca…….………………..! 30!! 4.2!PaleoWclimate!inferences!from!Mg/Ca,!Ba/Ca!and!Sr/Ca………………….….…! 35!! 4.3!PaleoWclimate!inferences!from!Na/Ca………………………………………...…………! 37!!Chapter(Five………………………………………………………………………………………………………! 44!5.0!Conclusion……………………………………………………………………………………………………..! 44!!List(of(figures…………………………………………………………………………………………………….!
1. Cave!environment…………………………………………………………………………………….! 2!2. Uranium!decay!chain………………………………………………………………………………..! 4!3. El!Niño!wind!anomalies…………………………………………………………………………….! 6!4. La!Niña!wind!anomalies……………………………………………………………………………! 6!5. Rainfall!for!New!Plymouth………………………………………………………………………..! 6!6. Rainfall!for!Napier……………………………………………………………………………………! 7!7. Landslide!and!soil!erosion!from!cyclone!Bola…………………………………………….! 8!8. Location!of!DS!and!GG5…………………………………………………………………………….! 10!9. Cross!section!of!GG5…………………………………………………………………………………! 11!10. Cross!section!of!DS…………………………………………………………………………………...! 12!11. ICPWMS!experimental!setup………………………………………………………………………! 14!12. TimeWseries!of!Na/Ca………………………………………………………………………………..! 16!13. TimeWseries!of!Mg/Ca………………………………………………………………………………..! 18!14. TimeWseries!of!Sr/Ca…………………………………………………………………………………! 19!15. TimeWseries!of!Ba/Ca………………………………………………………………………………..! 20!16. TimeWseries!of!U/Ca………………………………………………………………………………….! 21!17. TimeWseries!of!Na/Mg………………………………………………………………………………..! 22!18. TimeWseries!of!Sr/Mg………………………………………………………………………………...! 23!19. TimeWseries!of!Ba/Mg………………………………………………………………………………..! 24!20. TimeWseries!of!U/Mg…………………………………………………………………………………! 25!21. Mg/Ca!vs!Na/Ca………………………………………………………………………………………..! 27!22. Sr/Ca!vs!Na/Ca…………………………………………………………………………………………! 28!23. U/Ca!vs!Na/Ca………………………………………………………………………………………….! 29!24. TimeWseries!of!Mg/Ca………………………………………………………………………………..! 30!25. TimeWseries!of!Mg/Ca!for!GG5!&!DS!vs!Nettlebed……………………………………….! 33!26. TimeWseries!of!Sr/Ca!for!GG5!&!DS!vs!Nettlebed…………………………………………! 34!27. TimeWseries!of!Mg/Ca………………………………………………………………………………..! 36!28. TimeWseries!of!Na/Ca………………………………………………………………………………..! 38!29. Mg/Ca!vs!Na/Ca………………………………………………………………………………………..! 39!30. Sr/Ca!vs!Na/Ca…………………………………………………………………………………………! 39!31. U/Ca!vs!Na/Ca………………………………………………………………………………………….! 39!32. TimeWseries!of!Na/Mg………………………………………………………………………………..! 41!33. TimeWseries!of!Na/Mg!&!Mg/Ca………………………………………………………………….! 43!
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!List(of(tables……………………………………………………………………………………………...………!
1. Wind!patterns!record!cyclone!A)!Drena,!B)!Gisele,!C)!Bola!&!D)!Fergus……....! 8!2. Stormy!periods!from!deposits!in!Lake!Tutira……………………………………………..! 9!3. Reference!values!for!NIST!SRM610……………………………………………………………! 13!4. Reference!values!for!NIST!SRM612……………………………………………………………! 13!5. Pearson!linear!correlation…………………………………………………………………………! 26!6. Mg,!U,!Ba!&!Sr!concentrations!for!Nettlebed!speleothem…………………………….! 32!7. Pearson!linear!correlation…………………………………………………………………………! 34!
(References……………………………………………………………………………………..…………………..! 46!!Electronic(Appendix(One:(Analytical(Data……………………………………..…………………….!(((((
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!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!Chapter!1!!
1.0!Introduction!!
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1.1#Objectives#
Historic!climatic!records!in!New!Zealand!only!extend!back!for!the!last!ca.!100!years!(The!
National!Climate!Database!(NIWA);!retrieved!15!August!2015).!In!order!to!improve!our!
understanding!of!climatic!changes!and!events!beyond!this!timeframe,!it!is!necessary!to!
use!quantitative!proxies!of!past! environmental! conditions!and!apply! them! to!dateable!
archives! that! can! then! be! used! to! reconstruct! past! environmental! conditions.! Recent!
studies! have! shown! that! speleothems! (secondary! cave! carbonate! deposits)! are!
important!paleoclimate!archives,!due!to!the!fact!that!speleothems!can!be!reliably!dated,!
and! the! composition! of! the! precipitated! carbonate! varies! according! to! external!
parameters! and! during! their! systematic! growth.! Speleothems! have! the! potential! to!
reconstruct! past! climatic! conditions! at! annual! to! subannual! resolution.! This! study!
investigates! the!potential! to! use! speleothem! trace! element! chemistry,!with! a! focus! on!
sodium!(Na)!contents,!to!track!wind!conditions!and!storm!events!for!a!period!of!800!yr.!
Two! speleothems!have!been! studied! from! two!different! cave! systems! from! (near)! the!
west!and!east!coasts!of!the!North!Island!of!New!Zealand!over!the!time!interval!of!0–800!
AD.!
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1.2#Background#
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1.2.1#Speleothem#formation#
Speleothems!are!secondary!mineral!deposits!of!calcium!carbonate!formed!on!the!ceiling,!
walls! and! floors! of! caves.! The! precipitation! of! speleothems! relies! on! meteoric! water!
seeping!through!the!carbonatePrich!lithologies!(limestone)!found!above!caves!(Calaforra!
et! al.,! 2008).! As! the!water! enters! the! atmosphere! and! seeps! through! the! upper! soil! it!
incorporates!carbon!dioxide!from!the!atmosphere!as!well!as!from!the!organic!material!
trapped!within! the! soil,! which!makes! the!water! acidic.! The! acidic!water! continues! to!
leach! downwards! and! partially! dissolves! carbonatePrich! rocks.! As! the!meteoric!water!
enters! the! cave! system,! the! carbon! dioxide! is! lost! to! the! cave’s! atmosphere! and!
previously! dissolved! minerals! precipitate! out! to! form! speleothems! (Figure! 1).!
! 2!
Speleothems! can! take! various! forms,! depending! on! a! cave’s! internal! atmosphere.! The!
water! can!drip,! seep,! condense!or! flow,!which! creates!different! secondary! formations.!
The! four! major! formations! include! dripstones,! flowstones,! pore! deposits! and! pool!
deposits!(Huang!et!al.,!2001).!The!two!speleothems!in!this!study!are!from!different!caves!
with!varying!conditions!and!thus!illustrate!two!different!types!of!speleothems.!GG5!is!a!
stalactite! and! grows! downwards! from! the! caves! roof,! whereas! DS! is! a! flowstone! and!
grows!as!water!flows!and!leaves!a!film!of!calcite.!These!two!processes!are!illustrated!in!
Figure!1.!!!
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1.2.2#Speleothem#geochemistry#
Speleothems!are!regarded!as!valuable!archives!of!past!climatic!conditions!due!to! their!
relatively!simple!geometry,!and!the!fact!that!they!can!be!precisely!dated!(Ma!et!al.,!2010;!
Harms! et! al.,! 2008).! The! trace! element! chemistry! and! stable! isotopic! compositions! of!
speleothems!can!be!used! to! infer!past! climate! (McDermott,!2004;!Harms!et!al.,!2008).!
Study! of! the! youngest! parts! of! speleothems! can! be! used! to! calibrate! the! relationship!
between! climate! and! speleothem! chemistry! by! crossPcomparison! with! historic!
Figure!1:!Schematic!of!a!typical!cave!environment!illustrating!key!processes!in!the!precipitations!of!speleothems!(adopted!from!Fairchild!et!al.,!2012).!!
Stalagmite)
Stalac+te)
Soil) Decay)of)plant)li2er)producing)CO2))
Slow)drips)allow)for)degassing)of)CO2))at)the)roof)of)the)cave)to)form)a)stalac+te)
Fast)drips))allow)for)degassing)of)CO2)at)the)floor)of)the)cave)to)form)a)stalagmite)
Flowstone))
Carbonate)rich)Country)rock)
Atmosphere) Plant)respira+on)producing)CO2)
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meteorological!records!from!The!National!Climate!Database!(NIWA).!The!stable!isotopic!
compositions! of! speleothems! can! provide! climatic! proxies! for! diverse! environments!
including!low!latitude!and!elevation!(Bieniok!et!al.,!2011)!environments!to!high!latitudes!
and!elevation!environments!(Cruz!et!al.,!2015:!Orland!et!al.,!2014).!
Speleothems! incorporate! minor! and! trace! elements! into! their! calcite! matrix! during!
growth.!Stable!oxygen!and!carbon!isotopes!are!common!proxies!that!have!been!applied!
in!speleothem!paleoclimate!studies!(McDermott,!2004;!Cruz!et!al.,!2015;!Li!et!al.,!2014),!
along! with! some! trace! element! studies! (e.g.,! Mg,! Sr,! Ba! and! U).! These! geochemical!
variations!have!been!used!to!reconstruct!regional!changes!in!precipitation,!temperature!
and! paleoPvegetation! (Ku! and! Li,! 1998;! McDermott,! 2004).! Mg,! Sr! and! Ba! have!
previously!been!used!by,! for!example,!Fairchild!et!al.! (2012),!Orland!et!al.! (2014)!and!
Huang!et!al.!(2001)!to!infer!hot–wet!and!cold–dry!periods.!Low!Mg/Ca!ratios!with!high!
Sr/Ca!and!Ba/Ca! ratios! characterise! relatively!warmPwet!periods!whereas! the! inverse!
signals!coldPdry!periods!(Cross!et!al.,!2015;!Cruz!et!al.,!2015).!
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1.2.3##δ18O#and#δ13C#stable#isotopes#
Oxygen!and!carbon! isotopes!have!been!extensively!studied! in!speleothems! in!order! to!
interpret! past! climate! events.! For! example,! Frappier! et! al.! (2007)! identified! δ18O!
excursions!in!a!stalagmite!extracted!from!a!cave!in!central!Belize.!The!variations!in!δ18O!
are!associated!with!11! tropical! cyclone!events.!The!study!achieved!weekly! to!monthly!
temporal!resolution!and!found!that!major!negative!δ18O!excursions!coincided!with!the!
landfall!of! tropical! cyclones!near!Belize!during! the!period!1977–2000.!This! stalagmite!
(ATM7)!was!collected!three!months!after!Hurricane!Keith,!but!the!fingerprint!of!this!was!
not! observed! in! the! stalagmite,! suggesting! that! infiltration! rates! cause! a! lag! time!
between!such!events!and!their!incorporation!into!speleothems.!This!implication!of!lags!
in! the! isotopic! signals! in! speleothems! was! recognised! by! McDermott! (2004)! and!
attempts!to!analyse!D/H!ratios!in!fluid!inclusions!trapped!in!speleothems.!A!speleothem!
from!Devil’s!Hole!recorded!continuous!δ18O!variations!for!500,000!yr.!These!speleothem!
variations! were! shown! to! be! consistent! with! the! Vostok! ice! core! record! and! broadly!
delineated! interglacial! and! glacial! periods! using! stable! isotope! data! (Legrand! et! al.,!
1988;!Winograd!et!al.,!1992).!
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1.2.4#UraniumDseries#dating#
Speleothems! have! been! established! as! one! of! the! best! terrestrial! archives! for!
paleoclimate! reconstruction! as! they! can! be! precisely! dated! by! UPseries! techniques.!
UraniumPseries!dating!measures!the!equilibrium!between!238U!and!230Th.!238U!decays!to!234Th! through! alpha! decay! at! a! rate! of! 4.5! x! 109! yr.! The! decay! continues! through! a!
number!of!other!decay!steps!(234Pa;!1.2!min),!(234U;!2.5!x!105!yr)!and!then!further!decays!
to! 230Th! (7.7! x! 104! yr)! (Figure! 2)! (Ulusoy! et! al.,! 2014).! UraniumPseries! age!
determinations! allow! growth! intervals! and! rates! for! individual! speleothems! to! be!
determined!with!exquisite!resolution!(years!to!centuries).#The!banding!in!speleothems!
illustrates! variable! periods! of! growth,! with! the! surface! of! the! speleothem! being! the!
youngest!age,!and!the!interior!getting!progressively!older!towards!the!centre.!Each!band!
can!be!dated!by!measuring!how!much!uranium!has!decayed!into!thorium!(Maher!et!al.,!
2014;!Ulusoy!et!al.,!2014).!The!uranium!from!the!surrounding!bedrock! is! leached! into!
the!subsurface!and!is!incorporated!into!the!speleothem!matrix!(Maher!et!al.,!2014).!It!is!
presumed!that!there!is!no!initial!230Th.!The!concentration!of!the!daughter!isotope!230Th!
is!directly!related!to!the!decay!of!the!parent!isotopes!238U!and!234U!(Ulusoy!et!al.,!2014).!
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238U!4.5x109!years!
234Th!24.1!days!
234Pa!1.17!minutes!
!!!234U!2.4x105!years!
!!!230Th!7.7x104!years!
!!!226Ra!1600!years!
Element!!UP!Uranium!ThP!Thorium!PaP!Protactinium!RaP!Radium!
α"
α"α"
β"
β"
Figure!2:!Uranium!238!decay!chain!(adopted!from!Ulusoy!et!al.,!2014).!
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1.2.5#Sodium#(Na)#
New! Zealand! is! a! narrow! and! seaPsurrounded! landmass! and,! as! such,! atmospheric!
particles!delivered!to!land!are!strongly!influenced!by!sea!salts!from!marine!aerosols.!The!
soluble!Na!in!aerosols!comes!solely!from!sea!salts,!which!are!higher!in!summer!than!in!
winter,!and!higher!at!coastal!regions!relative!to!inland!areas!(Wang!and!Shooter,!2001).!
Aerosol!concentrations!of!Na!are!strongly!affected!by!wind!direction!and!mildly!affected!
by!wind!speed!(Wang!and!Shooter,!2001).!!Atmospheric!Na!is!transported!by!wind!and!
is!dissolved!in!precipitation!and!deposited!on!land.!Na!is!thought!to!be!leached!into!the!
subsurface! and! groundwater! and! then!may! be! incorporated! in! speleothems! found! in!
caves.!Other!possible!sources!of!Na!in!speleothems!could!come!from!rock!surrounding!
the! cave! environment.! This! dissolved! Na! from! the! country! rock! would! be! a! constant!
background! phenomenon! and! anomalous! concentrations!might! be! able! to! be! inferred!
from!wind!and!storm!events!(Bieniok!et!al.,!2011)!
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1.2.6#Late#Holocene#climate#and#cycles#in#New#Zealand##
In! New! Zealand,! El! Niño! and! La! Niña! cycles! significantly! influence!wind! direction.! El!
Niño!and!La!Niña!refer!to!opposite!ends!of!a!climate!spectrum!and!are!weather!patterns!
that!occur!periodically!across!the!Pacific!Ocean!characterized!by!variable!levels!of!winds!
and! rainfall! in! different! parts! of! New! Zealand! (NIWA).! During! an! El! Niño! event,! New!
Zealand! summers! tends! to! experience! stronger/more! frequent! winds! from! the! west,!
which!typically!leads!to!a!drought!on!the!east!coast!and!more!rain!on!the!west!coast.!In!
winter,!southerly!winds!dominate,!bringing!colder!conditions! to!both!the! land!and!the!
surrounding! ocean.! In! spring! and! autumn! southwesterly! winds! are! more! common!
(Figure!3).!During!El!Niño! it! is! expected! that! summer!periods!will! result! in!higher!Na!
aerosols!on!the!west!coast!and! lower!Na!on!the!east!coast.!Similar! inferences!apply! to!
spring!and!autumn,! although! in! lower! concentrations.!Winter!periods! should! result! in!
low!Na!aerosols!for!both!east!and!west!coasts.!La!Niña!events!have!contrasting!impacts!
on! New! Zealand's! climate.! Northeasterly! winds! dominate,! which! tend! to! bring! rainy!
conditions! to! the!northeast! of! the!North! Island,! and! reduced! rainfall! to! the! south! and!
southwest!of!the!South!Island.!During!a!La!Niña!event!Na!aerosols!should!be!higher!on!
the!east!coast!relative!to!the!west!coast!(Figure!4).!!
! 6!
!#
#
#
#
#
#
#
#
#
!In!1997–1998!there!was!a!strong!documented!El!Niño!event!that!caused!severe!droughts!and!floods!in!New!Zealand.!New!Plymouth!on!the!west!coast!of!the!North!Island!had!high!rainfall!events!with!some!days!reaching!a!maximum!rainfall!of!480!mm.!During!this!period,!Napier!on!the!east!coast!on!the!North!Island!had!relatively!very!little!rainfall!with!a!maximum!rainfall!for!a!given!day!of!28!mm.!(The!National!Climate!Database!(NIWA);!retrieved!15!August!2015)!(Figures!5!and!6).!
#
#
Figure!3:!Typical!El!Niño!wind!anomalies!(adopted!from!NIWA).!
Figure!4:!Typical!La!Niña!wind!anomalies!(adopted!from!NIWA).!
Figure!5:!Rainfall!pattern!for!New!Plymouth!(west!coast)!during!the!1997–1998!El!Niño!event!(The!National!Climate!Database!(NIWA);!retrieved!15!August!2015).!
0"
100"
200"
300"
400"
500"
17/12/95" 4/07/96" 20/01/97" 8/08/97" 24/02/98" 12/09/98" 31/03/99" 17/10/99"
Precipita
)on,(m
m),
Date,
! 7!
#
#
1.2.6#Storm#events#
1.2.6.1%Historic%storm%events%%
Between! December! and! April,! storms! from! the! tropics! move! south! towards! New!
Zealand.! As! these! storms! reach!New! Zealand!waters,! they! bring! damaging!winds! and!
heavy!rain.!In!April!1968,!Tropical!Cyclone!Gisele!moved!over!New!Zealand,!producing!
winds!gusting!to!75!m/s!in!Wellington!(Sinclair,!1993).!Cyclone!Bola!precipitated!over!
900! mm! of! rain! and! produced! hurricanePforce! winds! in! regions! of! northern! New!
Zealand! in! March! 1988! (Sinclair,! 1993),! More! recently,! Cyclones! Fergus! and! Drena!
brought!heavy!rain!and!stormPforce!winds!to!the!North!Island!in!December!1996.!New!
Zealand’s! climatic! records! of! such! events! are! stored! on! a! National! Climate! Database!
(CliFlo).!CliFlo!is!a!web!system!and!stores!climatic!records!from!as!early!as!1850.!CliFlo!
generates! outputs! that! are! hourly! to! yearly! raw! data.! The! tropical! cyclones! (Drena,!
Gisele,!Fergus!and!Bola)!are!recorded!in!CliFlo!as!shown!in!Table!1.!
!
!10$
0$
10$
20$
30$
40$
50$
60$
70$
80$
90$
100$
1/01/95$ 20/07/95$ 5/02/96$ 23/08/96$ 11/03/97$ 27/09/97$ 15/04/98$ 1/11/98$
Precipi
ta)o
n,(mm),
Date,
Figure!6:!Rainfall!pattern!for!Napier!(east!coast)!during!the!1997–1998!La!Niña!event!(The!National!Climate!Database!(NIWA);!retrieved!15!August!2015).!
! 8!
!
! !
! !
!
!
!
!
!
!
!
!
!
!
!
!
!
!Table!1:!Cyclones!A)!Drena,!B)!Gisele,!C)!Bola,!and!D)!Fergus!recorded!by!NIWA!using!wind!speed!data!(The!National!Climate!Database!(NIWA);!retrieved!26!June!2015).!!!!
!
!
!
!
%
%
%
%
%
%
%
%
Station Date(NZST) Time(NZST) Speed(m/s)26/12/96 8:00 027/12/96 8:00 3.128/12/96 8:00 029/12/96 8:00 2.630/12/96 8:00 4.631/12/96 8:00 6.71/01/97 8:00 3.12/01/97 8:00 3.63/01/97 8:00 0
Whakatane4Aero
Station Date(NZST) Time(NZST) Speed(m/s)1/01/97 8:00 2.62/01/97 8:00 2.63/01/97 8:00 2.64/01/97 8:00 2.65/01/97 8:00 6.76/01/97 8:00 2.67/01/97 8:00 2.68/01/97 8:00 2.69/01/97 8:00 2.610/01/97 8:00 2.611/01/97 8:00 15.412/01/97 8:00 2.613/01/97 8:00 114/01/97 8:00 0
Te0Kuiti0High0School
Station Date(NZST) Time(NZST) Speed(m/s)4/03/88 8:00 4.65/03/88 8:00 06/03/88 9:00 4.67/03/88 9:00 6.78/03/88 9:00 9.89/03/88 9:00 12.410/03/88 9:00 2.611/03/88 9:00 4.612/03/88 9:00 6.713/03/88 9:00 4.6
Napier4Nelson4Park
Station Date(NZST) Time(NZST) Speed(m/s)5/04/68 9:00 4.16/04/68 9:00 3.17/04/68 9:00 2.68/04/68 9:00 3.69/04/68 9:00 7.710/04/68 9:00 2.111/04/68 9:00 0.512/04/68 9:00 3.113/04/68 9:00 3.6
New1Plymouth1Aero
A)"Drena"(09"January"1997)" " ! B)"Gisele"(9/10"April"1968)" !
C)"Bola"(4"March"1988)" "" !
D)"Fergus"(30"December"1996)"" " !
Figure,7:"Landslides"and"soil"erosion"on"the"east"coast"of"New"Zealand"after"Cyclone"Bola""(Manatū"Taonga"Ministry"for"Culture"and"Heritage)."
! 9!
1.2.6.2%Prehistoric%storm%events%
It!is!difficult!to!identify!prehistoric!storm!events.!However,!storm!events!cause!massive!landslips! and! slides,! which! may! be! recorded! in! geomorphic! and! geological! features!
(Figure! 7)! ! (Manatū! Taonga! Ministry! for! Culture! and! Heritage).! A! fraction! of! New!
Zealand’s!prehistoric!storm!events!are!recorded!by!lake!sediments!on!the!eastern!side!of!
the!North!Island!at!Lake!Tutira.!Lake!Tutira!terrigenous!deposits!are!a!direct!response!
to! rainfall! induced! erosion! (Page! et! al.,! 2010).! Sedimentary! cores! were! analysed! and!
dated!back!to!ca.!7200!a.!The!cores!contain!very!abrupt!sedimentary!packages!recording!
storm! events.! Numerous! stormy! periods! were! recorded! as! listed! in! Table! 2.! This!
prehistoric!record!provides!a!template!with!which!to!compare!the!results!of!this!thesis!
research.!
Storm!Periods!(AD)! Duration!(yr)!
1750–1650! 100!
1570–1540! 30!
1450–1270! 180!
830–680! 150!
550–470! 80!
120–0! 120!
!Table!2:!Storm!periods!identified!from!sedimentary!deposits!in!Lake!Tutira!(Page!et!al.,!2010).!# #
1.3#Structure#of#thesis#
This!thesis!is!structured!and!presented!as!follows:!!
Chapter! 1! introduces! this! thesis! by! presenting! the!main! objectives! of! this! research.! It!
then!provides!a!synthesis!of!relevant!background!material.!
Chapter!2!describes! the! samples! that!were!analysed!as!part!of! this! study,! justifies! the!
sample! selection,! and! details! the! analytical! methods! that! were! used! to! collect! and!
process!the!data.!!
Chapter!3!presents!the!geochemical!results!obtained!on!the!two!speleothems.!!
Chapter!4!discusses!the!results!in!terms!of!whether!it!is!possible!to!use!the!geochemistry!
of!speleothems!to!track!paleoPwind!and!Pstorm!events.!
! 10!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!Chapter!2!!!
2.0!Methodology!
!
2.1!Selection!of!the!speleothems!for!study!
Two!speleothems!were!selected!from!the!University!of!Auckland!speleothem!collection!
according! to! their! geographical! locations! (Figure! 8)! and! age.! Two! speleothems! were!
selected! from! the! (near)! west! (Waitomo)! and! east! coast! (Wairoa)! regions! of! North!
Island,! New! Zealand,!which! had! previously! been! dated! by! uraniumGseries! techniques.!
The! two! study! sites! are! both! warm,! temperate! regions! and! experience! high! average!
rainfall,!but!different!wind!patterns.!The!Waitomo!region!experiences!an!average!annual!
temperature!of!22.2°C!and!an!average!rainfall!of!1102!mm!per!year.!Wairoa!experiences!
an!annual!temperature!of!22.5°C!and!a!slightly!higher!average!rainfall!of!1187!mm!per!
year!(Metservice);!retrieved!17!September!2015).!!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
! Figure!8:!Map!of!the!North!Island!showing!the!location!of!speleothem!samples!(grey)!and!major!cyclone!events!(blue).!!
!1968%Gisele%
%1988%Bola%
!1996%Fergus%
!1996%Drena%
GG5!
DS!
!!N!
200km!
! 11!
2.2!Speleothem!GG5!(Waitomo)!
The!speleothem!GG5!was!collected!by!Prof.!Paul!Williams!in!2005!from!Gardeners!Gut!
cave!in!Waitomo!near!the!west!coast!of!North!Island.!!Gardeners!Gut!cave!has!a!passage!
length!of!12.2!km!and! is!120–180!m!above! sea! level.!The! cave! is!35!km! inland!and! is!
developed! in! gently! dipping!Oligocene! limestones,! overlain! by!Miocene! siltstones! and!
volcanic! ash! soils! (P.!Williams,! pers.! comm.).!GG5!was! actively! growing! at! the! time!of!
collection!and!is!75!mm!in! length,!with!clear!growth!bands!(P.!Williams,!pers.!comm.).!
U/Th!dating!of!the!speleothem!indicates!that!the!interior!dates!back!to!12200!±!300!yr!
(Figure!9).!However,!there!is!a!significant!hiatus!in!growth!at!ca.!5000!yr,!marked!by!a!
distinct!change! in!the!colour!of! the!growth!bands!at!a!depth!of!45!mm!(Figure!9).!The!
outer!45!mm!of! the!speleothem!provides!a!highGresolution!record! from!2300!yr!BP!to!
the!modern!day!as!it!was!actively!dripping!at!the!time!of!sampling.!
!
2.2.1!GG5!sample!preparation!
GG5! was! prepared! by! cutting! through! the!
sample! with! a! diamond! saw! perpendicular! to!
the!growth!bands.!It!was!then!mounted!flat!on!
a!glass!slide!and!the!surface!was!polished!and!
cleaned.!The!smooth!surface!was!microGdrilled,!
and! previously! dated! by! U/Th! series!
techniques! using! a! thermal! ionisation! mass!
spectrometer! (TIMS).! Prior! to! trace! element!
analysis! the! surface! of! the! speleothem! was!
cleaned! with! methanol! and! preGablated! to!
remove! any! surficial! contamination.! The! preG
ablated! surface! was! then! reGablated! and!
analysed.!
!
!
!
!
!
!
Figure!9:!HighGresolution!crossGsectional!view!of!GG5,!showing!clear!growth!bands!with!annotated!uraniumGseries!dates.!!
1.680%ka%
2.012%ka%
2.334%ka%
1.207%ka%
! 12!
2.3!Speleothem!DS!(Wairoa)!
The! speleothem!DS!was! collected!by!Prof.! Paul!Williams! in!
1992! from!the!east! coast!of!New!Zealand! in!Disbelief!Cave.!
Disbelief!Cave! is! located! in! the!Wairoa!River! catchment! ca.!
29! km! northeast! of! Wairoa! township! in! northern! Hawkes!
Bay.!The!cave!is!approximately!120!m!long!and!600!m!above!
sea!level!and!developed!in!Late!Pliocene!limestone,!which!is!
overlain! by! early! Pleistocene! sediments! (P.!Williams,! pers.!
comm.).! DS! is! a! flowstone/shawl! that! was! not! actively!
growing!at!the!time!of!collection.!It!has!been!dated!by!TIMS!
techniques! to! be! ca.! 7600! yr! BP! in! age! and! the! tip! of! the!
speleothem!is!<1000!yr!BP!in!age!!
(P.! Williams,! pers.! comm.).! Speleothem! DS! is! 150! mm! in!
length! with! clear! growth! bands! throughout! the! sample!
(Figure!10).!!
!
2.3.1!DS!sample!preparation!
Due!to!this!speleothem!being!very!fragile,!it!was!embedded!
in! epoxy! resin,! which! supported! its! structure! prior! to!
cutting.! DS! was! then! prepared! by! cutting! through! the!
sample! with! a! diamond! saw! perpendicular! to! the! growth!
axis,!in!close!proximity!to!the!regions!microGmilled!for!U/Th!
series!dating!(Figure!10).!The!sample!was!then!polished!and!
cleaned.! DS! was! then! mounted! in! preparation! for! trace!
element! analysis.! Prior! to! ablation,! the! surface! of! the!
speleothem!was!once!again!cleaned!with!methanol!and!preG
ablated!to!minimise!surficial!contamination.!!
!
The!time!interval!chosen!for!analysis!in!both!speleothems!is!
0–800! AD,! given! that! both! samples! have! similar! growth!
rates!over!this!time!period.!!
!
!
Figure!10:!HighGresolution!crossGsectional!view!of!DS!with!annotated!uraniumGseries!dates.!
! 13!
!
2.4!Data!collection!techniques!
!
2.4.1!Laser!ablation!inductively!coupled!plasma!mass!spectrometry!
Trace! element! analysis! was! undertaken! by! laser! ablation! inductively! coupled! plasma!
mass! spectrometry! (LAGICPGMS)! at! Victoria! University! of! Wellington.! This! system!
comprises! a!Resonetics! S155GSE,!193!nm!excimer! laser! ablation! system!coupled! to! an!
Agilent!7500!series!ICPMS.!This!is!an!analytical!technique!with!excellent!sensitivity,!high!
analytical! throughput! and! high! spatial! resolution.! Calibrated! standards! were! run! as!
unknowns!to!monitor! instrumental!drift!and!the!precision!and!accuracy!of! the! ICPGMS!
throughout!analytical!sessions.!The!reference!material!used!for!this!study!are!the!NIST!
610! standard,!NIST!612! standard! and!MACS3,! and! reference! data! for! these! standards!
were! acquired! from! georem.mpchGmainz.gwdg.de.! Data! for! the! NIST! standards! are!
summarized!in!Tables!3!and!4.!NIST!610!standard!was!used!as!the!primary!calibrating!
standard,!whereas!NIST!612!was!used!to!confirm!the!accuracy!and!the!precision!of!the!
data.!
!
NIST!610!
Element! Value! Uncertainty! Unit!
Ba! 452! 9! µg/g!
Mg! 432! 29! µg/g!
Na2O! 13.4! 0.3! %m/m!
Sr! 515.5! 1! µg/g!
U! 461.5! 1! µg/g!
! ! Table!3:!Reference!values!for!NIST!SRM610!(GeoReM,!2015).!!
!
NIST!612!
Element! Value! Uncertainty! Unit!
Ba! 39.3! 0.9! µg/g!
Mg! 68! 5.1! µg/g!
Na2O! 13.7! 0.3! %m/m!
Sr! 78.4! 0.2! µg/g!
U! 37.38! 1.2! µg/g!
! ! Table!4:!Reference!values!for!NIST!SRM612!(GeoReM,!2015).!!
! 14!
Inductively! coupled! plasma! mass! spectrometry! (ICPGMS)! is! a! technique! capable! of!detecting!metals! and! several! nonGmetals! at! concentrations! as! low! as! one! part! in! 1015!(ppq)!on!nonGinterfered!lowGbackground!isotopes.!This!can!be!achieved!by!firing!a!laser!beam!onto!the!surface!of!the!speleothem,!with!the!energy!of!the!laser!beam!transferred!to!the!speleothem!and!causing!material!to!be!removed/ablated.!The!ablated!material!is!transported! by! a! flow! of! helium! gas! passing! through! the! sample! chamber! and!transported!to!an!ICPGMS.!As!the!material!passes!into!the!plasma!of!the!ICPMS,!elements!are!ionized.!The!ions!are!separated!in!the!mass!spectrometer!according!to!their!massGtoGcharge!ratio!and!then!detected!and!counted!on!an!electron!multiplier!detector.!!!
!!!
!
!
!
!
!
!
!
Figure!11:!Schematic!of!an!ICPGMS!experimental!setup!(Latkoczy!and!Ghislain,!2006).!!
!
!
!
!
!
!
!
!
!
!
! 15!
!
2.5!Data!processing!techniques!
!
2.5.1!Iolite!data!processing!
!
All! the! raw! LAGICPGMS! data! were! processed! using! Iolite! software.! Iolite! is! data!
processing!software!used!for!large!mass!spectrometry!datasets!(Paton!et!al.,!2011).!The!
data! processing! involves! a! background! correction! as! well! as! normalising! the! trace!
element!ratios! from!the!speleothems!to! the!ratios!measured! in! the!NIST!610!standard!
relative!to!their!known!values!(Table!3).!
!
! 16!
!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!Chapter!3!!!
3.0!Results!
This! chapter! presents! detailed! geochemical! data! for! the! Wairoa! and! Waitomo!
speleothems.!The!data!was!collected!by! ICP=MS!methods!and!processed!using! Iolite!as!
described!in!Chapter!Two.!
!!
3.1!Trace!element!data!normalised!to!Ca!
The!Wairoa!and!Waitomo!speleothems!are!largely!comprised!of!calcium!carbonate!and!
thus!the!measured!trace!element!data!are!presented!normalised!to!calcium.!This!
technique!is!a!conventional!method!used!in!speleothem!science!(Fairchild!et!al.,!2012;!
Huang!et!al.,!2001).!!
!
!
Figure!12:!Time=series!of!Na/Ca!ratios!in!the!speleothems!GG5!(Waitomo;!blue)!and!DS!(Wairoa;!red).!!
From!0–800!AD!Na/Ca!ratios!in!both!the!Wairoa!and!Waitomo!speleothems!have!almost!
identical! average! values! (4.34! x! 10–5! and! 4.32! x! 10–5,! respectively).! The! Waitomo!
speleothem! has! Na/Ca! ratios! that! vary! from! a! minimum! value! of! 1.59! x! 10=5! ! to! a!
maximum!value!of!1.01!x!10–4!!and!there!appears!to!be!cyclical!changes!from!31–110!AD,!
110–142!AD,!142–182!AD!and!182–275!AD.!The!cyclical!variations!are! less!marked! in!
0.00E+00!
2.00E=05!
4.00E=05!
6.00E=05!
8.00E=05!
1.00E=04!
1.20E=04!
1.40E=04!
1.60E=04!
1.80E=04!
0! 100! 200! 300! 400! 500! 600! 700! 800!
Na/Ca!
Age!(AD)!
Waitomo!Na!
Wairoa!Na!
! 17!
the! period! 275–714! AD.! There! are! distinct! peaks! in! Na/Ca! ratios! in! the! Waitomo!
speleothem!at!110!AD,!142!AD,!182!AD,!275!AD!and!714!AD.!Na/Ca!ratios!in!the!Wairoa!
speleothem!in!a!general!sense!behave!similarly!to!that!of!the!Waitomo!Speleothem!and!
show!cyclical!variation!between!150–227!AD,!227–261!AD,!261–387!AD,!387–557!AD,!
557–750!AD!and!750–768!AD.!There!are!also!distinct!Na/Ca!peaks!at!150!AD,!227!AD,!
261!AD,!387!AD,!557!AD,!750!AD!and!786!AD!in!the!Wairoa!speleothem.!Na/Ca!ratios!in!
the!Wairoa!speleothem!vary!from!a!minimum!value!of!2.14!x!10–5!to!a!maximum!value!of!
3.72!x!10–4.!The!Wairoa!speleothem!has!significantly!higher!Na/Ca!peaks!relative!to!the!
Waitomo!speleothem.! In!general,!Na/Ca!peaks! in! the! two!speleothems!do!not!occur!at!
the!same!time.!However,!there!are!intervals!where!smaller!scale!Na/Ca!peaks!in!the!two!
speleothems!do!correlate! (142–153!AD,!173–210!AD,!239–272!AD,!319–341!AD,!511–
531!AD,!547–557!AD,!659–691!AD,!705–760!AD!and!775–800!AD),!and! there!are!also!
intervals!where!the!Na/Ca!ratios!in!the!speleothems!appear!to!be!anti=correlated!(52–72!
AD,! 76–101! AD,! 115–126! AD,! 153–157! AD,! 227–239! AD,! 269–289! AD,! 363–393! AD,!
479–491!AD,!534–548!AD,!617–647!AD!and!750–775!AD).!
!
!
!
!
!
!
!
!
!
!
!
!
!
!!
! 18!
!
Figure!13:!Time=series!of!Mg/Ca!ratios!in!the!speleothems!GG5!(Waitomo;!blue)!and!DS!(Wairoa;!red).!
!
From!0–800!AD,!Mg/Ca!ratios! in!both! the!Wairoa!and! the!Waitomo!speleothems!have!
very!different!trends!and!values.!The!average!Mg/Ca!value!for!the!Wairoa!speleothem!is!
4.03!x!10–4!and!8.27!x!10–4!for!the!Waitomo!speleothem.!The!Waitomo!speleothem!has!a!
minimum! value! of! 3.71! x! 10–5! and! a!maximum! value! of! 1.12! x! 10–3.! From! 0–400!AD,!
Mg/Ca!ratios!in!the!Waitomo!speleothem!increase!substantially!and!then!at!460!AD!the!
Mg/Ca!ratios!drop!from!1.06!x!10–3!to!6.73!x!10–4.!!After!the!drop,!Mg/Ca!ratios!increase!
back! to! 1.03! x! 10–3! for! ~90! years! where! the! Mg/Ca! values! stabilise! and! show! less!
variability!until!800!AD.!There! is!no!clear!evidence! for!cyclicity! in! the!Mg/Ca!ratios!of!
the! Waitomo! speleothem.! However,! Mg/Ca! ratios! in! the! Wairoa! speleothem! show!
clearer! cyclical! trends.!The!Wairoa! speleothem!has!a!minimum!Mg/Ca!value!of!3.09!x!
10–4!and!a!maximum!value!of!7.02!x!10–4!and!peaks!at!52!AD,!154!AD,!257!AD,!384!AD,!
518! AD,! 647! AD,! 693! AD! and! 774! AD.! The! two! Mg/Ca! trends! from! the! different!
speleothems!are!not!well!correlated,!and!do!not!show!similar!trends!or!spikes.!
!
4.00E=04!
5.00E=04!
6.00E=04!
7.00E=04!
8.00E=04!
9.00E=04!
1.00E=03!
1.10E=03!
1.20E=03!
2.80E=04!
3.80E=04!
4.80E=04!
5.80E=04!
6.80E=04!
7.80E=04!
0! 100! 200! 300! 400! 500! 600! 700! 800!
Mg/Ca!
Age!(AD)!
Wairoa!
Mg!
Waitomo!
Mg!
! 19!
!
Figure!14:!Time=series!of!Sr/Ca!ratios!in!the!speleothems!GG5!(Waitomo;!blue)!and!DS!(Wairoa;!red).!!
From!0–800!AD,! Sr/Ca! ratios! in! both! the!Wairoa! and! the!Waitomo! speleothems! have!
significantly! different! average! values! (3.42! x! 10–4! and! 1.04! x! 10–4,! respectively).!
Waitomo!Sr/Ca!values!varies!from!a!minimum!value!of!3.77!x!10–5!to!a!maximum!value!
of! 1.91! x! 10–4! and! there! are! no! clear! cyclical! changes.! In! the! Waitomo! speleothem!
between! 0–350! AD! there! is! more! variation! in! Sr/Ca! ratios! over! shorter! timesclaes!
relative! to! 350–800! AD! where! varations! tend! to! be! more!muted.! Sr/Ca! ratios! in! the!
Wairoa!speleothem!vary! from!a!minimum!value!of!1.66!x!10–4! to!a!maximum!value!of!
4.73! x! 10–4.! The!Wairoa! speleothem! has! higher! Sr/Ca! ratios! relative! to! the!Waitomo!
speleothem.! In! general,! the! trends! for! the! two! speleothems! show! some! degree! of!
correlation.! There! appear! to! be! common! trends! for! the! two! speleothems,! with! the!
exception!of!between!400–500!AD,!at!0–100!AD,!120–242!AD,!250–400!AD,!500–650!AD!
and!650–800!AD.!!!
!
!
!
0.00E+00!
5.00E=05!
1.00E=04!
1.50E=04!
2.00E=04!
2.50E=04!
0.00E+00!
1.00E=04!
2.00E=04!
3.00E=04!
4.00E=04!
5.00E=04!
6.00E=04!
0! 100! 200! 300! 400! 500! 600! 700! 800!
Sr/Ca!
Age!(AD)!
Wairoa!Sr!Waitomo!Sr!
! 20!
!
Figure!15:!Time=series!of!Ba/Ca!ratios!in!the!speleothems!GG5!(Waitomo;!blue)!and!DS!(Wairoa;!red).!!
From! 0–800! AD,! Ba/Ca! ratios! in! both! the! Wairoa! and! Waitomo! speleothems! have!
significantly! different! average! values! (9.49! x! 10–6! and! 2.82! x! 10–5,! respectively).! The!
Waitomo! speleothem! shows! a! slight! trend! to! lower! Ba/Ca! ratios!with! time! that! vary!
from!a!minimum!value!of!7.33!x!10–6!to!a!maximum!value!of!5.28!x!10–5.!The!Waitomo!
speleothem!shows!slight!cyclical!variations!with!large!peaks!at!75!AD!and!250!AD,!and!
smaller!peaks!at!417!AD,!507!AD,!580!AD,!640!AD!and!730!AD.!At!690!AD,!Ba/Ca!ratios!
drop!from!2.4!x!10–5!to!7.33!x!10–6!and!steeply!increase!back!to!2.9!x!10–5.!The!Wairoa!
speleothem! has! a! slight! increase! in! Ba/Ca! values! through! time! that! vary! from! a!
minimum! value! of! 3.48! x! 10–6! to! a! maximum! value! of! 1.67! x! 10–5.! The! Wairoa!
speleothem!has!stronger!cyclical!variations!than!that!of!the!Waitomo!speleothem,!with!
peaks!in!Ba/Ca!at!90!AD,!180!AD,!265!AD,!310!AD,!357!AD,!435!AD,!547!AD,!622!AD,!684!
AD,!714!AD!and!782!AD.!There!are!some!similarities!in!the!data!for!the!two!speleothems!
whereby!some!peaks!and!lows!correlate!(e.g.,!67–157!AD!and!693–794!AD).!
!
!!
!
!
!
0.00E+00!
1.00E=05!
2.00E=05!
3.00E=05!
4.00E=05!
5.00E=05!
6.00E=05!
0.00E+00!
5.00E=06!
1.00E=05!
1.50E=05!
2.00E=05!
0! 100! 200! 300! 400! 500! 600! 700! 800!
Ba/Ca!
Age!(AD)!
Wairoa!Ba!
Waitomo!Ba!
! 21!
!
Figure!16:!Time=series!of!U/Ca!ratios!in!the!speleothems!GG5!(Waitomo;!blue)!and!DS!(Wairoa;!red).!!
Average!U/Ca!ratios!in!the!Waitomo!and!Wairoa!speleothems!are!very!different!(6.87!x!
10–8!versus!5.23!x!10–7).!The!Wairoa!speleothem!has!a!wider!range!of!U/Ca!ratios!with!a!
minimum!value! of! 1.15! x! 10–7! and! a!maximum!value! of! 8.76! x! 10–7! and! exhibits! very!
noisy!variations.!There!are!some!clear!U/Ca!peaks!(72!AD,!150!AD,!196!AD,!267!AD,!307!
AD,!383!AD,!429!AD,!552!AD,!637!AD,!677!AD!and!753!AD)!and!lows!(109!AD,!149!AD,!
208! AD,! 283! AD,! 328! AD,! 397! AD,! 518! AD,! 580! AD! and! 694! AD).! The! Waitomo!
speleothem!has! lower!U/Ca!values! than! that!of! the!Wairoa!speleothem!with!a! smaller!
range!in!values!from!1.51!x!10–4!to!22!x!10–7.!There! is!a!period!at!660!AD!where!U/Ca!
values! in! the!Waitomo!speleothem! increase!significantly! to!4.22!x!10–7,!but!most!peak!
U/Ca! values! are! ca.! 1! x! 10–7.! U/Ca! in! the! two! speleothems! do! not! appear! to! exhibit!
similar!trends.!
!
!!
!
!
!
!
!
!
0.00E+00!
5.00E=08!
1.00E=07!
1.50E=07!
2.00E=07!
2.50E=07!
0.00E+00!
2.00E=07!
4.00E=07!
6.00E=07!
8.00E=07!
1.00E=06!
0! 100! 200! 300! 400! 500! 600! 700! 800!
U/Ca!
Age!(AD)!
Wairoa!U!
Waitomo!U!
! 22!
!
3.2!Trace!elements!normalised!to!Mg!
Trace!element!data!for!the!Wairoa!and!Waitomo!speleothems!were!also!normalised!to!
Mg!to!examine!how!variations!with!respect!to!this!element!changed!over!time.!!
!
!Figure!17:!Time=series!of!Na/Mg!ratios!in!the!speleothems!GG5!(Waitomo;!blue)!and!DS!(Wairoa;!red).!!
!
From!0–800!AD,!Na/Mg!ratios!in!the!Wairoa!speleothem!have!a!slightly!higher!average!
value! than! the! Waitomo! speleothem! (1.05! x! 10–1! versus! 5.32! x! 10–2).! The! Waitomo!
speleothem!varies!from!a!minimum!value!of!2.51!x!10–2!to!a!maximum!value!of!1.4!x!10–1!
and!there!appears!to!be!cyclical!changes!between!31–105!AD,!105–134!AD,!134–142!AD,!
142–182!AD!and!182–275!AD.!The!cyclical!variations!are!less!marked!in!the!period!275–
720!AD.!There!are!distinct!peaks! in!Na/Mg!ratios! for! the!Waitomo!speleothem!at!110!
AD,! 142! AD,! 182! AD,! 275! AD! and! 714! AD.! Na/Mg! ratios! in! the! Wairoa! speleothem!
behave! similarly! to! the! Waitomo! speleothem,! in! that! it! shows! cyclical! variations!
between!150–227!AD,!227–261!AD,!261–!325!AD,!325–387!AD,!387–557!AD,!557–750!
AD!and!750–768!AD.!There!are!also!distinct!peaks!at!227!AD,!261!AD,!387!AD,!557!AD,!
750! AD! and! 786! AD.! The! Waitomo! speleothem! has! Na/Ca! ratios! that! vary! from! a!
minimum!value!of!6.02!x!10–2! to!a!maximum!value!of!9.58!x!10–1!and!has!significantly!
higher!Na/Ca!peaks!relative! to! the!Waitomo!speleothems.! In!general! the! timing!of! the!
peaks!in!the!two!speleothems!do!not!correspond!with!each!other.!
0.00E+00!
2.00E=02!
4.00E=02!
6.00E=02!
8.00E=02!
1.00E=01!
1.20E=01!
1.40E=01!
1.60E=01!
0.00E+00!
2.00E=01!
4.00E=01!
6.00E=01!
8.00E=01!
1.00E+00!
1.20E+00!
0! 100! 200! 300! 400! 500! 600! 700! 800!
(Na/Mg)!
Age!(AD)!
Wairoa!
Na!
Waitomo!
Na!
! 23!
!Figure! 18:! Time=series! of! Sr/Mg! ratios! in! the! two! speleothems!GG5! (Waitomo;! blue)!and!DS!(Wairoa;!red).!
!
From!0–800!AD,!Sr/Mg!ratios! in!both! the!Wairoa!and! the!Waitomo!speleothems!have!
significantly! different! average! values! (8.65! x! 10–1! and! 1.27! x! 10–1,! respectively).! The!
Waitomo!speleothem!has!Sr/Ca!ratios!that!vary!from!a!minimum!value!of!5.57!x!10–2!to!
a! maximum! value! of! 3.12! x! 10–1! and! there! are! no! apparent! cyclical! changes.! In! the!
Waitomo!speleothem!between!0–350!AD!there!is!more!variation!over!shorter!timescales!
relative!to!350–800!AD!where!varations!tend!change!more!gradually.!Sr/Mg!ratios!in!the!
Wairoa!speleothem!vary! from!a!minimum!value!of!3.85!x!10–1! to!a!maximum!value!of!
1.46.!Wairoa! has! higher! Sr/Mg! ratios! relative! to! that! of! the!Waitomo! speleothem.! In!
general,! the! trends! of! the! two! speleothem! show! some! degree! of! correlation.! There!
appear!to!be!common!trends!for!the!two!speleothems!with!the!exception!of!between!0–
100!AD,!120–242!AD!and!650–800!AD.!!
!
!
!
!!
!
0.00E+00!
5.00E=02!
1.00E=01!
1.50E=01!
2.00E=01!
2.50E=01!
3.00E=01!
3.50E=01!
0.00E+00!
2.00E=01!
4.00E=01!
6.00E=01!
8.00E=01!
1.00E+00!
1.20E+00!
1.40E+00!
1.60E+00!
0! 100! 200! 300! 400! 500! 600! 700! 800!
(Sr/Mg)!
Age!(AD)!
Wairoa!Sr!
Waitomo!
Sr!
! 24!
!Figure! 19:!Time=series!of!Ba/Mg! ratios! in! the! two! speleothems!GG5! (Waitomo;!blue)!and!DS!(Wairoa;!red).!!
From!0–800!AD,!Ba/Mg!ratios!in!both!the!Wairoa!and!Waitomo!speleothems!have!very!
similar! average! values! (2.32! x! 10–2! and! 3.51! x! 10–2,! respectively).! The! Waitomo!
speleothem! has! a! slight! negative! trend! in! Ba/Mg! ratios! with! time! that! vary! from! a!
minimum!value!of!1.11!x!10–2!to!a!maximum!value!of!1.00!x!10–1.!Waitomo!shows!slight!
cyclical! variations!with! large!Ba/Ca!peaks!at!75!AD,!200!AD,!250!AD!and!269!AD!and!
smaller!peaks!at!450!AD,!507!AD,!580!AD,!640!AD!and!730!AD.!The!Wairoa!speleothem!
has!a!slight!increase!in!Ba/Mg!values!through!time!that!vary!from!a!minimum!value!of!
8.14! x! 10–3! to! a!maximum! value! of! 5.20! x! 10–2.! The!Wairoa! speleothem! has! stronger!
cyclical!variations!in!Ba/Ca!ratios!than!in!the!Waitomo!speleothem,!with!peaks!at!34!AD,!
108!AD,!117!AD,!180!AD,!276!AD,!310!AD,!357!AD,!435!AD,!547!AD,!615!AD,!680!AD,!714!
AD!and!782!AD.!!
!
!
!
!
!
!
!
!
!
0.00E+00!
2.00E=02!
4.00E=02!
6.00E=02!
8.00E=02!
1.00E=01!
1.20E=01!
0! 100! 200! 300! 400! 500! 600! 700! 800!
(Ba/Mg)!
Age!(AD)!
Waitomo!Ba!
Wairoa!Ba!
! 25!
!
Figure!20:!Time=series!of!U/Mg!ratios!in!the!two!speleothems!GG5!(Waitomo;!blue)!and!DS!(Wairoa;!red).!!!
Average!U/Mg!ratios!in!the!Waitomo!and!Wairoa!speleothems!are!very!different!(8.43!x!
10–5!versus!1.27!x!10–3).!Wairoa!has!a!wider!range!of!U/Ca!ratios!with!a!minimum!value!
of!2.45!x!10–4!and!a!maximum!value!of!2.46!x!10–3!and!exhibits!very!noisy!variations.!
There!are!some!clear!peaks!(96!AD,!129!AD,!189!AD,!267!AD,!307!AD,!356!AD,!460!AD,!
552!AD,!622!AD,!677!AD!and!753!AD)!and!lows!(37!AD,!109!AD,!159!AD,!220!AD,!283!
AD,!328!AD,!391!AD,!518!AD,!554!AD,!694!AD!and!767!AD)!in!U/Ca!ratios.!The!Waitomo!
speleothem!has!lower!U/Mg!ratios!than!the!Wairoa!speleothem!with!a!smaller!range!of!
values!from!2.04!x!10–5!!!to!4.76!x!10–4.!There!is!a!period!at!660!AD!where!U/Mg!values!
increase!significantly!to!4.76!x!10–4,!but!most!peak!U/Mg!values!are!ca.!1!x!10–4.!U/Mg!
ratios!in!the!two!speleothems!do!not!appear!to!exhibit!similar!trends.!!
!
!
!
!
!
!
!
0.00E+00!
5.00E=05!
1.00E=04!
1.50E=04!
2.00E=04!
2.50E=04!
3.00E=04!
0.00E+00!
5.00E=04!
1.00E=03!
1.50E=03!
2.00E=03!
2.50E=03!
3.00E=03!
0! 100! 200! 300! 400! 500! 600! 700! 800!
(U/M
g)!
Age!(AD)!
Wairoa!U!
Waitomo!U!
! 26!
!
3.3!Trace!element!correlations!
The!following!section!presents!Pearson’s!linear!correlations!between!trace!element!data!
in!the!speleothems.!The!Pearson’s!linear!correlation!coefficient!is!a!statistical!measure!of!
the!strength!of!a!linear!relationship!between!paired!data.!The!closer!the!value!is!to!1!or!–
1,!the!stronger!the!correlation!between!two!elements.!!Pearson’s!linear!correlation!(R2)!
defines!values!of!±0! to!±0.19!as!very!weak,!±0.20! to!±0.39!as!weak,!±0.40! to!±0.59!as!
moderate,! ±0.60! to! ±0.79! as! strong! and! ! ±0.80! to! ±1! as! very! strong! correlations.!!
Elements! with! strong! correlations! suggest! that! similar! processes! control! their!
variability.!!
!
!! Na/Ca! Mg/Ca! Sr/Ca! Ba/Ca! U/Ca!
Na/Ca! 1!
(VW)!!!!!
0.05132!
(VW)!!!!!
0.03193!
(VW)!!!
0.12207!
(W)!!!!!!!!
0.23617!
Mg/Ca!(VW)!!!!!
0.08311! 1!
(VW)!!!=
0.11014!
(W)!!!!=
0.33975!
(VW)!!!!=
0.12718!
Sr/Ca!
(VW)!!!!=
0.00287!
(VW)!!!!=
0.11608! 1!
(VS)!!!!!
0.83152!
(W)!!!!!!!!
0.33829!
Ba/Ca!(VW)!!!!!
0.10882!
(M)!!!!!!=
0.42067!
(VS)!!!!!!!
0.85081! 1!
(W)!!!!!!!!
0.35519!
U/Ca!(W)!!!!!!!!
0.26525!
(VW)!!!!!!!!
0.1521!
(W)!!!!!!=
0.21277!
(VW)!!=
0.02331! 1!
Table! 5:!Pearson! linear! correlation! table! for! elemental! ratios! in! the! two! speleothems!(GG5!=!blue;!DS!=!red)!(VW!=!very!weak,!W!=!weak,!M!=!moderate!and!VS!=!strong).!
!
None!of! the!elements!correlate!strongly!except! for!Sr/Ca!and!Ba/Ca! (Waitomo!–!0.85;!
Wairoa!–!0.83).!A!weak!positive! correlation! is!observed! in! the!Wairoa! speleothem! for!
U/Ca!with!Sr/Ca!and!Ba/Ca!(0.34!and!0.36)!and!a!weak!negative!correlation!for!Ba/Ca!
with! Mg/Ca! (–0.34).! ! A! weak! negative! correlation! is! observed! in! the! Waitomo!
speleothem!for!Ba/Ca!and!Mg/Ca!(–0.42).!There!are!no!element!ratios!that!have!a!strong!
or!moderate!correlation!with!Na/Ca,!although!a!weak!correlation!is!exhibited!between!
Na/Ca!and!U/Ca!in!both!speleothems.!
!
!
! 27!
!Figure!21:!Mg/Ca!versus!Na/Ca!ratios!for!speleothem!DS!from!Wairoa.!!
The! R2! (0.05)! value! for! Mg/Ca! and! Na/Ca! illustrates! that! there! is! no! statistical!
correlation!between!the!two!ratios.!However,!qualitatively!there!appears!to!be!a!cluster!
of!values!for!Na/Ca!from!2.43!x!10–5!to!6.58!x!10–5!and!Mg/Ca!from!3.15!x!10–4!to!5.53!x!
10–4.!!!
!
!
!
!
!
!
0.00E+00!
2.00E=04!
4.00E=04!
6.00E=04!
8.00E=04!
1.00E=03!
1.20E=03!
0.00E+00! 5.00E=05! 1.00E=04! 1.50E=04! 2.00E=04! 2.50E=04! 3.00E=04! 3.50E=04! 4.00E=04!
Mg/Ca!
Na/Ca!
Wairoa!
! 28!
!
Figure!22:!Sr/Ca!versus!Na/Ca!ratios!for!speleothem!DS!from!Wairoa.!!!
The!R2!(0.03)!value!for!Sr/Ca!and!Na/Ca!illustrate!that!there!is!no!statistical!correlation!
between!the!two!ratios.!However,!qualitatively!there!appears!to!be!a!cluster!of!values!for!
Na/Ca!from!2.44!x!10–5!to!6.62!x!10–5!and!Sr/Ca!from!1.88!x!10–4!to!5.16!x!10–4.!
!
!
!
!
!
!
0.00E+00!
1.00E=04!
2.00E=04!
3.00E=04!
4.00E=04!
5.00E=04!
6.00E=04!
0.00E+00! 5.00E=05! 1.00E=04! 1.50E=04! 2.00E=04! 2.50E=04! 3.00E=04! 3.50E=04! 4.00E=04!
Sr/Ca!
Na/Ca!
Wairoa!
! 29!
! !Figure!23:!U/Ca!versus!Na/Ca!ratios!for!speleothem!DS!from!Wairoa.!!
The! R2! (0.2)! value! for! U/Ca! and! Na/Ca! illustrates! that! there! is! statistically! a! weak!
correlation!between!the!two!ratios,!which!is!also!evident!from!Fig.!25.!There!appears!to!
be!a!cluster!of!values!for!Na/Ca!from!2.38!x!10–5!to!7.62!x!10–5!and!U/Ca!from!2.09!x!10–7!
to!8.66!x!10–7.!
0.00E+00!
2.00E=07!
4.00E=07!
6.00E=07!
8.00E=07!
1.00E=06!
1.20E=06!
0.00E+00! 5.00E=05! 1.00E=04! 1.50E=04! 2.00E=04! 2.50E=04! 3.00E=04! 3.50E=04! 4.00E=04!
U/Ca!
Na/Ca!
Wairoa!
! 30!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!Chapter!4!!!
4.0!Discussion!
The! trace! elements! magnesium! (Mg),! strontium! (Sr)! and! barium! (Ba)! have! been!measured!routinely! in!speleothem!studies!worldwide!(Fairchild!et!al.,!2012;!Orland!et!al.,! 2014;! Huang! et! al.,! 2001).! The! chemistry! of! these! three! elements! is! quite! well!understood! and! much! is! known! about! what! controls! their! incorporation! into!speleothems.! As! such,! this! discussion! first! focuses! on! the! similarities! and! differences!observed!between!the!two!speleothems!with!regards!to!Mg,!Sr!and!Ba.!It!then!continues!by!focusing!on!paleoclimatic!interpretations!from!Mg,!Sr!and!Ba.!The!last!section!of!this!discussion!then!explores!the!main!focus!of!this!thesis!by!examining!if!Na!can!be!used!to!track!paleoNstorm!and!Nwind!events.!!4.1!Similarities!and!differences!in!Mg/Ca,!Sr/Ca,!and!Ba/Ca!values!in!Waitomo!and!
Wairoa!speleothems!
!Figure!24:!TimeNseries!of!Mg/Ca!ratios! for!the!speleothems!GG5!(Waitomo;!blue)!and!DS!(Wairoa;!red).!!!!!
4.00EN04!
5.00EN04!
6.00EN04!
7.00EN04!
8.00EN04!
9.00EN04!
1.00EN03!
1.10EN03!
1.20EN03!
2.80EN04!
3.80EN04!
4.80EN04!
5.80EN04!
6.80EN04!
7.80EN04!
0! 100! 200! 300! 400! 500! 600! 700! 800!
Mg/Ca!
Age!(AD)!
Wairoa!Mg!Waitomo!Mg!
! 31!
The! firstNorder! observation! for! the!Mg/Ca! record! in! the! two! speleothems! is! that! the!
Waitomo!speleothem!has!significantly!higher!Mg!concentrations!as!compared!with!that!
of!the!Wairoa!speleothem.!The!Waitomo!speleothem!has!a!higher!average!Mg/Ca!of!8.3!x!
10N4,! whereas! the! average! Mg/Ca! ratio! in! the! Wairoa! speleothem! is! 4.0! x! 10N4.! The!
difference!in!this!ratio!could!be!due!to!differences!of!the!two!sites!in!terms!of:!
1. The!depth!of!the!cave!(hydrology).!
2. The!amount!of!precipitation!(climate).!
As!meteoric!water!percolates!through!the!rocks!overlying!a!cave! it! incorporates!Mg.! If!
there!is!less!precipitation!it!takes!longer!for!the!water!to!percolate!through!the!overlying!
rocks!and!thus!higher!Mg/Ca!ratios!are!expected.!The!same!process!can!be!envisaged!to!
occur! for! deeper! cave! systems,! as! the! meteoric! water! has! to! pass! through! a! greater!
volume! of! overlying! rock! and,! therefore,! the! deeper! the! cave,! the! higher! the! Mg/Ca!
values.!The!annual!rainfall!at!Waitomo!is!1102!mm/yr!and!Wairoa!has!a!similar!average!
rainfall! of! 1187!mm/yr! (Metservice);! retrieved!17! September! 2015).!When!Prof.! Paul!
Williams!collected!the!Waitomo!(GG5)!and!Wairoa!(DS)!speleothems!he!noted!that!the!
Waitomo! cave!was! 50!m! below! the! surface,! whereas! the!Wairoa! cave!was! just! 10!m!
below! the! surface.! The! annual! rainfalls! for! Waitomo! and! Wairoa! are! less! than! 10%!
different!and!are!broadly!similar,!thus!the!different!average!Mg/Ca!ratios!for!Waitomo!
(GG5)!and!Wairoa!(DS)!most!likely!reflects!cave!depth,!rather!than!regional!climate!(i.e.,!
precipitation)!variations.!!
!!
A!secondNorder!observation!of!the!Mg/Ca!record!for!the!two!speleothems!is!that!there!
are!cyclical!variations!superimposed!on!these!larger!scale!differences!in!Mg/Ca!values.!
Mg/Ca! ratios! in! the! Wairoa! speleothem! show! clear! cyclical! variations! with! distinct!
peaks,!whereas!the!Mg/Ca!ratios!in!the!Waitomo!speleothem!do!not!show!clear!cyclical!
changes.!The!Mg/Ca!ratios!in!the!Wairao!speleothem!have!an!average!cyclical!time!of!ca.!
100!yr!between! the!peaks! (50–154!AD,!154–270!AD,!270–380!AD,!380–520!AD,!520–
660! AD,! 660–700! AD! and! 700–770! AD).! The! absence! of! cyclical! variations! in! Mg/Ca!
ratios!in!the!Waitomo!speleothem!may!be!due!to:!!
1. A!more!stable!regional!climate!at!Waitomo!as!compared!with!Wairoa.!
2. The!sensitivity!of!the!cave’s!hydrological!system!to!overlying!changes!in!regional!
climate!such!as!mean!annual!rainfall.!
! 32!
The!Wairoa!and!Waitomo!regions!are!not!located!far!away!from!each!other!(Figure!8).!Events! that! affect! the! amount! of! precipitation! and!wind! such! as! El! Niño! and! La!Niña!events!should!be!recorded!in!both!speleothems.!With!prehistoric!storm!events!recorded!in!Lake!Tutira!(Page!et!al.,!2010)!and!historic!wind!anomalies!recorded!by!the!National!Climate!Database! it! is! clearly!evident! that!climate!varies!and!has!not!been!stable!over!the!course!of! the!period!0N800!AD.!Variations! in!Mg/Ca! for!each!speleothem!are!most!likely!responses!to!climate!variations.!However,!the!Wairoa!speleothem!appears!to!be!a!more! sensitive! archive! that! better! records! climatic! change! relative! to! the! Waitomo!speleothem.! Again,! this! sensitivity! may! be! a! reflection! of! the! Wairoa! cave! being! a!shallower!system!than!that!at!Waitomo.!!Hellstrom! et! al.! (2000)! carried! out! an! ICPNMS! trace! element! study! of! a! speleothem,!which!was!a!flowstone!collected!from!a!deep!cave!system!200!m!below!the!surface!on!the! west! coast! of! the! South! Island,! New! Zealand! in! Nettlebed! cave.! The! speleothem!covered! 30,000! yr! of! growth! and! thus! showed! trace! element! (Mg,! Sr,! Ba! and! U)!variations! between! glacial! and! interglacial! periods.!Hellstrom!et! al.! (2000)! found! that!trace!element!chemistry!showed!glacial!conditions!rapidly!ended!around!15,000!yr!BP.!This!change!from!glacial!to!interglacial!conditions!is!marked!by!increases!and!decreases!in!different!trace!elements.!During!the!glacial!period!there!are!relatively!higher!Mg!and!U!concentrations!and!relatively!lower!Ba!and!Sr!concentrations.!!!! !
Glacial!
!
Interglacial!
Change!in!magnitude!from!glacial!
to!interglacial!period!Concentration! Normalised!
to!Ca!Concentration!
Normalised!to!Ca!
Concentration!
Normalised!to!Ca!
Percentage!
Mg! 470!ppm!! 1.2!x!10N3! 340!ppm! 8.5!x!10N4! 130!ppm! 3.3!x!10J4! 38.8%!
U! 125!ppb! 3.1!x!10N7! 55!ppb! 1.4!x!10N7! 70!ppb! 1.8!x!10J7! 128.6%!
Ba! 1900!ppb! 4.8!x!10N6! 3000!ppb! 7.5!x!10N6! 1100!ppb! 2.8!x!10J6! 37.3%!
Sr! 25!ppm! 6.3!x!10N5! 36!ppm! 9.0!x!10N5! 11!ppm! 2.8!x!10J5! 31.1%!
Table! 6:! Mg,! U,! Ba! and! Sr! concentrations! and! element/Ca! ratios! in! a! South! Island!speleothem.!Highlighted!values!show!the!change! from!glacial!conditions!to! interglacial!conditions!for!this!relatively!deep!cave!system!(adopted!from!Hellstrom!et!al.,!2000).!!
! 33!
!Figure!25:!TimeNseries!of!Mg/Ca!ratios! for!the!speleothems!GG5!(Waitomo;!blue)!and!DS!(Wairoa;!red).!Also!shown!are!the!magnitude!of!the!glacial!and!interglacial!changes!in!Mg/Ca!values!from!a!South!Island!(Nettlebed)!speleothem!(Hellstrom!et!al.,!2000).!!
The! Nettlebed! speleothem! shows! significant! Mg/Ca! variations! associates! with! large!
climate! variations! from! the! most! recent! glacial! to! interglacial! period.! The! Waitomo!
speleothem!has!similar!average!Mg/Ca!values!to!the!Nettlebed!speleothem.!The!largest!
change! in!Mg/Ca!values! for! the!Waitomo! speleothem! is! 3.5! x! 10N4! and! for! the!Wairoa!
speleothem! is! 2.4! x! 10N4.! These! changes! are! broadly! similar! in! magnitude! to! those!
observed! in! the! Nettlebed! speleothem,! despite! the! fact! that! both! the! Waitomo! and!
Wairoa!speleothems!grew!wholly!within!the!Holocene!(0–800!AD).!For!some!reason,!the!
chemistry! of! the! Waitomo! and! Wairoa! speleothems! are! more! sensitive! to! change! in!
climate! than! the! Nettlebed! speleothem.! A! plausible! reason! for! the! large! variations! in!
Mg/Ca! ratios! for! the! Waitomo! and! Wairoa! speleothems! is! that! they! reflect! more!
sensitive!recorders!to!climate!variations!due!to!their!relative!shallow!cave!depth!relative!
to! the! Nettlebed! speleothem.! Similar! size! magnitude! variations! are! observed! in! the!
Nettlebed!speleothem,!which!is!known!to!cover!large!climate!variations!between!glacial!
and!interglacial!periods!(Hellstrom.,!et!al,!2000).!!!
!
!
!
!
4.00EN04!
5.00EN04!
6.00EN04!
7.00EN04!
8.00EN04!
9.00EN04!
1.00EN03!
1.10EN03!
1.20EN03!
2.80EN04!
3.80EN04!
4.80EN04!
5.80EN04!
6.80EN04!
7.80EN04!
0! 100! 200! 300! 400! 500! 600! 700! 800!
Mg/Ca!
Age!(AD)!
Wairoa!Mg!Waitomo!Mg!
28.2%!
41.1%!
Glacial!value:!1.2$x$10'3$!!!Interglacial!value:!8.5$x$10'4$
Magnitude$change:$38.8%!
! 34!
!! Na/Ca! Mg/Ca! Sr/Ca! Ba/Ca! U/Ca!Na/Ca! 1! 0.05! 0.03! 0.12! 0.24!
Mg/Ca! 0.08! 1! –0.11! –0.34! N0.13!
Sr/Ca! –0.00! N0.12! 1! 0.83! 0.34!
Ba/Ca! 0.11! –0.42! 0.85! 1! 0.36!
U/Ca! 0.27! 0.15! –0.21! –0.02! 1!Table! 7:! Pearson! linear! correlation! table! for! selected! element/Ca! ratios! in! the! two!studied!speleothems!(GG5!=!blue;!DS!=!red).!!
Sr/Ca! and! Ba/Ca! are! well! correlated! in! both! the! Waitomo! and! Wairoa! speleothems!
(Table!7).!As!such,!discussion!of!Sr/Ca!ratios!can!be!combined!with!that!for!Ba/Ca!ratios.!!
!
!
Figure!26:!TimeNseries!of!Sr/Ca!ratios!for!the!speleothems!GG5!(Waitomo;!blue)!and!DS!(Wairoa;!red).!!!
The!Waitomo!and!Wairoa!speleothems!have!very!different!Sr!concentrations!compared!
with! the! Nettlebed! speleothem.! However,! the!Waitomo! speleothem! has! Sr/Ca! values!
closer!to!the!Nettlebed!speleothem!relative!to!the!Wairoa!speleothem.!Cave!depth!could!
be! a! plausible! factor! to! this! variation! as! the!Waitomo! cave! system! is! deeper! than! the!
Wairoa!cave.!The!annual!rainfall!for!Nettlebed!is!812!mm/yr!(Metservice);!retrieved!17!
September!2015).!!Therefore,!another!reason!for!the!Sr/Ca!variations!could!be!that!the!
Waitomo!and!Wairoa!regions!experience!slightly!higher!average!rainfalls!as!mentioned!
previously,!and!thus!have!a!warmer!and!wetter!climate!relative!to!the!Nettlebed!region.!!
!
0.00E+00!
5.00EN05!
1.00EN04!
1.50EN04!
2.00EN04!
2.50EN04!
0.00E+00!
1.00EN04!
2.00EN04!
3.00EN04!
4.00EN04!
5.00EN04!
6.00EN04!
0! 100! 200! 300! 400! 500! 600! 700! 800!
Sr/Ca!
Age!(AD)!
Wairoa!Sr!Waitomo!Sr!
277.8%!
168.9%!
Glacial!value:!6.3$x$10'5$Interglacial!value:!9.0$x$10'5$
Magnitude$change:$31.1%$!
! 35!
!
4.2!Paleoclimate!inferences!from!Mg/Ca,!Ba/Ca!and!Sr/Ca!ratios!
These! three! element/Ca! ratios! have! been! chosen! to! infer! paleoclimate! because! they!
have!been!previously!well!studied!and!understood!(Fairchild!et!al.,!2012;!Orland!et!al.,!
2014;!Huang!et!al.,!2001),!and!are!now!conventionally!used!as!paleoclimate!indicators.!
!
Huang! et! al.! (2001)! investigated! the! variations! in! trace! element! concentrations! in!
speleothems!from!the!Ernesto!cave!(northeast!Italy).!The!results!showed!that!Mg!largely!
has!a!negative!covariation!with!Sr! in!bandings! formed!in!the!1990s,!and!a!positive!coN
variation! with! bandings! formed! in! the! 1960s.! These! were! in! response! to! changes! in!
hydroNenvironmental!conditions!and!climate!variations.!Therefore,!it!has!been!proposed!
that! during! cold–dry! periods,! speleothems! will! have! relatively! high! Mg/Ca! with!
relatively! high! Sr/Ca! and! Ba/Ca! ratios.! On! short! timescales,! New! Zealand’s! warm!
periods! are! associated! with! less! rainfall! (warm/dry),! whereas! cold! periods! are!
associated!with!more!rainfall!(cold/wet).!The!resolution!of!the!dataset!presented!in!this!
study!is!only!applicable!to!larger!timescales!and!therefore!the!assumption!of!warm/wet!
periods!and!cold/dry!periods!are!applicable.!
!
In! the! Waitomo! speleothem,! Mg/Ca! ratios! increase! between! 250–400! AD! and! Sr/Ca!
ratios!decrease!between!250–400!AD!(Figures!25!&!26).!However,!Sr/Ca!ratios!do!not!
drastically!decrease.!This!subdued!inverse!relationship!indicates!that!during!the!period!
of! 250–400! AD,! Mg/Ca! ratios! changed! in! response! to! climate! change.! Therefore,!
between! 250–400! AD! there! would! have! been! less! rainfall,! with! moderately! warmer!
temperatures.!Between!700–710!AD!and!460–480!AD!Mg/Ca! ratios! increase,!whereas!
Sr/Ca! ratios! are! relatively! low.! These! periods! represents! a! time! of! less! rainfall! and!
relatively!warmer!conditions.!!
!
For! the!Wairoa! speleothem,! periods! between! 60–140! AD,! 160–250! AD,! 260–370! AD,!
400–500! AD,! 540–630! AD! and! 700–780! AD! have! relatively! low! Mg/Ca! ratios! and!
periods! between! 60–100! AD,! 260–360! AD,! 410N507! AD,! 540–620! AD! have! relatively!
high!Sr/Ca!ratios.!!These!periods!reflect!warmer!and!wetter!conditions!(Figure!27).!
! 36!
!Figure!27:!TimeNseries!of!Mg/Ca!ratios!in!the!speleothems!GG5!(Waitomo;!blue)!and!DS!(Wairoa;! red).! The! timeNseries! highlights! peaks! in! Mg! for! the! Wairoa! speleothem!showing!warm–wet!climatic!conditions!(red!triangles)!and!periods!noted!as!prehistoric!stormy!periods!recorded!in!lake!sediments!from!Lake!Tutira!(black!boxes).!Green!boxes!show!warm–wet!periods!(Low!Mg,!High!Sr).!!
Changes!in!the!sediment!character!of!cores!taken!from!Lake!Tutira!can!be!interpreted!to!
represent! changing! climatic! conditions! such! as! the! occurrence! of! major! storms! and!
droughts!(Page!et!al.,!2010).!These!events!recorded!in!the!sedimentary!layers!will!only!
capture!or!record!paleoNstorms!that!were!associated!with!extreme!rainfall!events.!Such!
storm!events!would!be!needed!to!have!large!amounts!of!precipitation!in!order!to!wash!
and! erode! detritus!material! into! the! lake! from! the! surrounding! hills,! and! thus! not! all!
storms!(in!terms!of!windiness)!are!likely!to!be!recorded.!Page!et!al.!(2010)!identified!0–
120!AD,!470–550!AD!and!680–830!AD!as!periods!of!major!storms.!These!time!periods!
described!by!Page!et!al.!(2010)!correspond!to!a!decreasing!Mg!peak!between!0–120!AD,!
after!a!low!Mg!trough!for!470–550!AD!and!at!a!trough!in!Mg!between!680–830!AD.!The!
low! Mg! concentrations! in! the! Wairoa! speleothem! are! located! around! these! stormy!
events,!however!the!storm!periods!vary!somewhere!around!the!low!Mg!concentrations!
either! due! to! a! lag! in! time! from! the! event! or! because! the! storms! were! perhaps! not!
always!large!enough!to!cause!detritus!material!to!be!eroded!from!near!by!hills.!Page!et!
al.!(2010)’s!findings!as!well!as!low!Mg!concentrations!are!consistent!with!a!warm–wet!
climate!between!60–140!AD,!470–500!AD!and!680–770!AD!(Figure!27).!!
!
! 37!
!
4.3!Paleoclimate!inferences!from!Na/Ca!values!in!speleothems!
As!described! in!section!4.1,! cave!depth!and!hydrology!provide!a! firstNorder!control!on!
the!speleothem!Mg!concentration!and,!as!such,!the!effects!of!this!have!been!normalised!
out!by!normalising!Na!to!Mg!concentrations.!!
!
Using! this! approach,! it! is! evident! that! the! Wairoa! speleothem! has! higher! Na!
concentrations! relative! to! the! Waitomo! speleothem.! The! Wairoa! speleothem! has! an!
average!Na/Mg!ratio!of!1.1!x!10–1!and!the!Waitomo!speleothem!has!an!average!Na/Mg!
ratio!of!5.3!x!10N2.!Intuitively,!this!might!be!expected!as!sea!salt!spray!will!be!higher!at!
(nearN)! coastal! regions! (i.e.,! Wairoa)! relative! to! more! inland! regions! (i.e.,! Waitomo).!
Thus,!the!different!Na/Mg!averages!for!the!two!speleothems!may!be!due!to!Wairoa!being!
closer!to!the!coast!than!Waitomo!(Figure!8).!!
!
A!secondNorder!observation!is!that!Wairoa!has!significantly!larger!Na/Mg!peaks!than!the!
Waitomo!speleothem.!Wairoa!has!seven!significant!Na/Mg!peaks,!where!distinct!influxes!
of!Na! entered! into! the!hydrological! system!and!were!ultimately! incorporated! into! the!
speleothem.!The!peaks!for!Wairoa!are!observed!at!150!AD,!227!AD,!261!AD,!320!AD,!383!
AD,!557!AD!and!752!AD.!In!contrast,!Waitomo!has!more!subdued!Na/Mg!peaks!that!are!
less!defined!than!the!Wairoa!Na/Mg!peaks.!The!Na/Mg!peaks!for!Waitomo!are!observed!
at!31!AD,!103!AD,!134!AD,!192!AD,!275!AD,!487!AD!and!714!AD.!Previous!discussion!of!
variations! in!Mg/Ca!values! (section!4.1),! as!well! as! the!Na/Mg!variations!discussed! in!
this! section,! illustrate! again! that! cave! depth! appears! to! control! the! sensitivity! of! the!
speleothem!chemistry!to!environmental!factors.!
!
! 38!
!
Figure!28:!TimeNseries!of!Na/Mg!ratios!in!the!speleothems!GG5!(Waitomo;!blue)!and!DS!(Wairoa;!red).!The!timeNseries!highlights!peaks!in!Na!for!the!Wairoa!speleothem!(green!rectangles)! corresponding! to! prehistoric! stormy! periods! recorded! in! lake! sediments!from!nearby!Lake!Tutira!(grey!boxes)!and!antiNphase!correlations!for!Na!concentrations!in!the!Wairoa!and!Waitomo!speleothems!(black!dotted!lines).!!
The! grey! rectangles! mark! periods! where! major! prehistoric! storm! events! took! place.!
Some!storms!may!be!associated!with!only!windy!or!wet!conditions,!whereas!others!may!
be!associated!with!both!windy!and!wet!conditions.!Not!only!do!the!deposits!rely!on!the!
type!of!storm!but!also!the!size!of!the!storms.!This!complexity!might!explain!why!not!all!
Na!peaks!have!corresponding!storm!records! from!Lake!Tutira.!The!Na!peaks! in!Figure!
28! highlighted! in! green! do! have! correlated! stormy! periods! recorded! in! Lake! Tutira.!
Thus,!the!storms!observed!in!the!records!had!both!windy!and!wet!conditions.!!
!
!
!
!
!
!
!
! 39!
!Figure!29:!Mg/Ca!versus!Na/Ca!ratios!for!the!Wairoa!speleothem.!!The!R2! (0.05)!value! for!Mg/Ca!and!Na/Ca!illustrates! that! there! is! a! very! weak!correlation!between!the!two!ratios.!There!appears!to!be!a!cluster!of!values!for!Na/Ca!from!2.43!x!10N5!to!6.58!x!10N5!and!Mg/Ca!from!3.15!x!10N4!to!5.53!x!10N4.!!
!
!!!!Figure!30:!Sr/Ca!versus!Na/Ca!ratios!for!the!Wairoa!speleothem.!!The! R2! (0.03)! value! for! Sr/Ca! and! Na/Ca!illustrates! that! there! is! a! very! weak!correlation!between!the!two!ratios.!There!appears!to!be!a!cluster!of!values!for!Na/Ca!from!2.44!x!10N5! to!6.62!x!10N5!and!Sr/Ca!from!1.88!x!10N4!to!5.16!x!10N4.!!
!
!
!
!
Figure! 31:! U/Ca! versus!Na/Ca! ratios! for!the!Wairoa!speleothem.!The! R2! (0.2)! value! for! U/Ca! and! Na/Ca!illustrates!that!there!is!statistically!a!weak!correlation!between!the!two!ratios.!There!appears!to!be!a!cluster!of!values!for!Na/Ca!from!2.38! x! 10N5! to! 7.62! x! 10N5! and!U/Ca!from!2.09!x!10N7!to!8.66!x!10N7.!!
!
!
Mg/Ca!
!
0.00E+00!
1.00EN04!
2.00EN04!
3.00EN04!
4.00EN04!
5.00EN04!
6.00EN04!Wairoa!
0.00E+00!
2.00EN04!
4.00EN04!
6.00EN04!
8.00EN04!
1.00EN03!
1.20EN03! Wairoa!
0.00E+00!
2.00EN07!
4.00EN07!
6.00EN07!
8.00EN07!
1.00EN06!
1.20EN06! Wairoa!
Sr/Ca!
!U/Ca!
!
Na/Ca!!
! 40!
The!data!plotted!in!Figures!28–30!all!show!considerable!variations!in!Mg,!Sr!and!U,!but!
these! are! only! weakly! (U)! or! not! correlated! at! all! with! Na! concentrations,! which!
randomly!extend!to!high!values.!These!points!are!controlling!and!lowering!the!R2!values!
in!these!plots.!The!clusters!can!be!interpreted!as!the!normal!climatic!conditions!and!the!
points!that!deviate!away!from!the!trend!are!the!events!(i.e.,!storms)!that!are!anomalous!
and!deliver!Na!to!the!land!surface!and!cave!hydrological!systems.!!
!
Where!Na/Ca!is!high!(>2.4!x!10N5),!Mg/Ca!varies!from!3.5!x!10N4!to!1.0!x!10N3!and!Sr/Ca!
varies! from!1.7! x!10N4! to!4.0! x!10N4.! The! (generally)!high!Mg/Ca!and! low!Sr/Ca!values!
when! anomalous! Na! peaks! occur! are! diagnostic! of! warm–wet! conditions.! Warm–wet!
conditions! are! historically! associated! with! stormy! periods! as! it! forces! surface! air!
pressures! to! drop,! creating! extreme! air! pressure! differences! and! thus!windy! and!wet!
conditions.!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
! 41!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
! 42!
!
El!Niño!and!La!Niña!cycles!significantly!influence!wind!direction!and!climate!patterns!in!
New!Zealand.!Historic! records! for!El!Niño!and!La!Niña!events!only!extend!back! to! the!
late! 1970s/early! 1880s! and! show! that! the! El! Niño! and! La! Niña! occurs! on! a! frequent!
basis!between!every!ca.!5–15!yr!(Folland,!2002).!Figure!32!highlights!smaller!Na!peaks!
to! occur! on! average! every! ca.! 10–20! yr,! with! larger! peaks! occurring! with! infrequent!
intervals! of! 75,! 35,! 65,! 55,! 170! and! 200! yr.! The! frequency! of! the! smaller! Na! peaks!
corresponds!with!the!frequency!of!the!El!Niño–!La!Niña!cycle.!As!historical!records!for!El!
Niño!do!not!extend!back!to!the!period!between!0–800!AD,!a!plausible!explanation!for!the!
larger!Na!peaks!is!extreme!El!Niño!events!or!nonNEl!Niño!tropical!storms.!
La! Niña! events! lower! seaNsurface! temperatures! in! the! Pacific! Ocean! and! thus! New!
Zealand!experiences! cooler! temperatures!during!a!La!Niña!on! the!west! coast! (NIWA);!
retrieved! 13! August! 2015).! The! El! Niño! cycle! raises! seaNsurface! temperatures! in! the!
Pacific! and! thus! New! Zealand! experiences! a! warmer! and!wetter! climate! on! the! west!
coast.!During!a!La!Niña,!the!east!coast!experiences!northNeasterly!winds,!while!during!an!
El!Niño!the!west!coast!experiences!southNwesterly!winds.!Due!to! the!dominating!wind!
patterns!as! a! result!of! the!El!Niño!and!La!Niña!events,! it! is!observed! that!during!a!La!
Niña! event,! the! Wairoa! speleothem! has! Na! peaks,! while! during! an! El! Niño! event,!
Waitomo! has! Na! peaks.! This! is! seen! in! ! ! ! Figure! 28! where! the! small! scale! cyclicity!
between!Wairoa!and!Waitomo!Na!concentrations!are!antiNphased!(dotted!black!lines!in!
Figure! 28).! These! antiNphased! periods! are! seen! where:! Wairoa! has! increased! Na!
concentrations!and!Waitomo!have!decreased!Na!concentrations!(20!AD,!84!AD,!170!AD,!
227!AD,!305!AD,!764!AD)! and!Wairoa!has!decreased!Na! concentrations! and!Waitomo!
have!increased!Na!concentrations!(97!AD,!115!AD).!
!
!
!
!
!
!
!
!
!
! 43!
!
!Figure!33:!TimeNseries!of!Mg/Ca!(purple)!and!Na/Mg!(green)!ratios!for!the!Wairoa!speleothem.!.!The!timeNseries!highlights!corresponding!Mg!peaks!and!troughs!for!peaks!in!Na.!The!correlations!between!Mg!and!Na!infer!climatic!conditions.!!
Figure! 33! compares! Mg! and! Na! concentrations! for! the! Wairoa! speleothem! to! infer!
correlations!of!wet!periods!from!the!low!Mg!values!with!that!of!high!Na!values.!At!~80!
AD,!~180!AD,!~320!AD,!~580!AD,!~610!AD,!~680!AD!there!are!small!peaks!in!Na!and!
low!Mg! values.! These! periods! can! be! justified! as! little! storm! events! that! had!wet! and!
relatively!little!wind.!At!~150!AD,!~220!AD,!~260!AD,!~390!AD!there!are!peaks!in!both!
Na!and!Mg!values.!These!periods!can!be!thought!as!wind!events!with!no!rain.!At!~550!
AD! and!~750!AD! there! are!massive!Na! peaks!with! low!Mg! values.! These! periods! are!
thought!to!be!larger!storm!events,!which!were!both!rain!and!wind!events.!!
!
! 44!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!Chapter!5!!!5.0$Conclusions$
$
A!trace!element!study!of!two!speleothems!from!the!Waitomo!and!Wairoa!regions!of!the!North!Island!of!New!Zealand!has!shown!that:!!
1. The!Waitomo!speleothem!has!significantly!higher!Mg!concentrations!compared!with!that!of!the!Wairoa!speleothem,!and!that!the!different!average!Mg/Ca!ratios!for!the!two!speleothems!are!likely!to!be!primarily!due!to!cave!depth!at!each!site!rather!than!regional!climate!variations.!!
2. Mg/Ca!ratios!in!the!Wairoa!speleothem!show!clear!cyclical!variations!with!distinct!peaks,!which!are!most!likely!in!response!to!climate!variations.!The!Wairoa!speleothem!appears!to!be!a!more!sensitive!archive!that!better!records!climatic!change!relative!to!the!Waitomo!speleothem.!
3. A!previously!studied!speleothem!from!northwest!Nelson!(reference)!shows!changes!in!trace!element!chemistry!during!glacial!and!interglacial!periods.!Similar!sized!changes!are!observed!for!Mg!during!the!period!0–800!AD!in!both!the!Waitomo!and!the!Wairoa!speleothems,!but!not!for!Sr.!These!Mg/Ca!changes!support!the!conclusion!that!Mg!in!speleothems!is!partly!related!to!cave!depth.!The!cave!depth!also!alters!the!sensitivity!of!the!trace!element!chemistry!in!the!speleothems!to!changing!environmental!conditions.!The!deeper!the!cave,!the!less!sensitive!the!trace!element!chemistry!of!the!speleothems!is!to!changes!in!environmental!parameters.!!!
4. There!is!a!distinct!Na!difference!between!the!two!speleothems.!The!Wairoa!speleothem!has!higher!Na!concentrations!than!the!Watomo!speleothem.!This!is!due!to!Wairoa!being!a!more!(nearP)!coastal!region!than!that!of!Waitomo,!which!is!relatively!inland!as!compared!with!the!Wairoa!site.!!
5. Spikes!in!Na!concentrations!relate!to!either!windy!storm!events,!rainy!storm!events!or!both!wind!and!storm!events.!Rainy!storm!events!occur!when!Mg!concentrations!are!relatively!low!and!Na!concentrations!are!relatively!high.!Windy!storm!events!occur!when!Na!and!Mg!concentrations!are!relatively!high.!
!
! 45!
Wind!and!rainy!storm!events!occur!when!Na!concentrations!are!very!high!relative!to!a!very!low!Mg!concentration.!
6. Na!concentrations!between!the!two!speleothems!shows!antiPphased!cycles.!It!is!hypothesized!that!during!a!La!Niña!event,!the!Wairoa!speleothem!has!Na!peaks!and!the!El!Niño!has!Na!depletions,!whereas!during!an!El!Niño!event,!Waitomo!has!Na!peaks!and!the!Wairoa!speleothem!has!Na!depletions.!This!is!because!during!a!La!Niña,!the!east!coast!experiences!northeasterly!winds,!while!during!an!El!Niño!the!west!coast!experiences!southwesterly!winds,!thereby!influencing!delivery!of!Na!via!marine!aerosols!to!each!site.!
! 46!
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