Ecology and E olu ion. 2017;1–13.  
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1
www.ecole ol.o g
Recei ed:28June2016
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Re ised:18Janua y2017
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Accep ed:7Feb ua y2017
DOI: 10.1002/ece3.2841
ORIGINAL RESEARCH
Oxygen and ca bon isoscapes o he Bal ic Sea: Tes ing hei
applicabili y in ish mig a ion s udies
Jy ki To niainen1 | Anssi Lensu2 | Pekka J. Vuo inen3 | Eloni Sonninen4 |
Ma ja Keinänen3 | Roge I. Jones2 | William P. Pa e son5 | Mikko Kiljunen2
Thisisanopenaccessa icleunde  he e mso  heC ea i eCommonsA ibu ionLicense,whichpe mi suse,dis ibu ionand ep oduc ioninanymedium,
p o ided heo iginalwo kisp ope lyci ed.
©2017TheAu ho s.Ecology and E olu ionpublishedbyJohnWiley&SonsL d.
1Na u alHis o yMuseum,Uni e si yo 
Jy askyla,Jy askyla,Finland
2Depa men o BiologicalandEn i onmen al
Science,Uni e si yo Jy askyla,Jy askyla,
Finland
3Na u alResou cesIns i u eFinland,Helsinki,
Finland
4Labo a o yo Ch onology,Uni e si yo 
Helsinki,Helsinki,Finland
5Saska chewanIso ope
Labo a o y,Depa men o Geological
Sciences,Uni e si yo Saska chewan,
Saska oon,SK,Canada
Co espondence
Jy kiTo niainen,Na u alHis o yMuseum,
Uni e si yo Jy askyla,Jy askyla,Finland.
Email:[email p o ec ed]
Funding in o ma ion
MajandTo NesslingFounda ion,G an /
Awa dNumbe :2010150,2011105,2012506
and2013040;Academyo Finland,G an /
Awa dNumbe :34139
Abs ac
Con en ional agsapplied oindi idualsha ebeenused oin es iga eanimalmo e-
men ,bu  heseme hods equi e aggedindi idualsbe ecap u ed.Mapso  egional
iso opic a iabili yknownas“isoscapes”o e po en ial o  a iousapplica ionsinmi-
g a ion esea chwi hou  aggingwhe einiso ope alueso  issuesa ecompa ed o
en i onmen aliso ope alues.In hiss udy,wep esen  hespa ial a iabili yinoxygen
(
δ18
OH
2O
)anddissol edino ganicca bon(δ13CDIC)iso ope alueso Bal icSeawa e .
Wealsop o ideanexampleo how heseisoscapescan e ealloca ionso indi idual
animal iaspa ialp obabili ysu acemaps,using hehigh- esolu ionsalmono oli h
iso opeda a omsalmondu ing hei sea- eedingphasein heBal icSea.Aclea la i-
udinaland e icalg adien was ound o bo h
δ18
OH
2O
andδ13CDIC alues.Thedi -
e encebe weensumme andwin e in heBal icSea
δ18
OH
2O
 alueswasonlysligh ,
whe easδ13CDIC aluesexhibi edsubs an ialseasonal a iabili y ela ed oalgalp o-
duc i i y.Salmono oli hδ18Oo oandδ13Co o aluesshowedclea di e encesbe ween
eedinga easandseasons.Ou exampledemons a es ha dualiso opeapp oacho -
e sg ea po en ial o es ima ingp obable ishhabi a sonceissuesinmodelpa am-
e e iza ionha ebeen esol ed.
KEYWORDS
iso opiclandscape,mic omilling,modele alua ion,Salmo sala ,spa ialassignmen ,
spa ialin e pola ion
1 | INTRODUCTION
Se e al ma king app oaches ha e been employed o add ess ques-
ionsinmig a ionecology.Un il ecen ly,con en ionalex insicma k-
e s(i.e., ags)applied oindi idualsha ebeenused oin es iga e hei 
mo emen (Lucas&Ba as,2000),bu  heseme hods equi e agged
indi idualsbe ecap u ed oacqui espa ialin o ma ion.Du ing ecen 
yea ssomein es iga ionsha ebeenconduc ed os udylong- e m
mo emen so indi idualadul A lan icsalmon(Salmo sala L.;Figu e1)
in heseausing ags ha  eco den i onmen alcha ac e is icsalong
hemig a ion ou es(e.g.,Chi enden,Ådlands ik,Pede sen,Righ on,
&Rika dsen,2013).Howe e ,due o hep esen sizeo  he ags, he
s udied ishha e obela geand, he e o e,dono necessa ily ep e-
sen  hemajo i yo  hepopula ion.
In insicbiochemicalma ke ssuchass ableiso opescanp o ide
anal e na i eapp oach o ackindi idualmo emen so e la gegeo-
g aphical dis ances such as be ween con inen s (Hobson & No is,
2008).All animals a e iso opically ma ked by he en i onmen  hey
li einandby hei die .Theassignmen o anindi idual oace ain
a eawo ksbyes ima ingp obabili ieso occu ence o animalindi-
idualsbycompa ing aluesob ained om issuesamples oiso opic
landscapes(i.e.,isoscapes;Wunde ,2010).Ag ea ad an ageinusing
2
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TORNIAINEN ET Al.
biochemical ma ke s is ha  hey can be linked o hose indi iduals
ha  ac ually su i ed he mig a ion o hei  b eeding habi a s, and
he e o e,be e  ep esen  hepopula ion.As isho oli hsa ealmos 
comple ely mine alized om he ca bona e o  he en i onmen al
wa e (Kim,O′Neil,Hillai e-Ma cel,&Mucci,2007;Pa e son,Smi h,
&Lohmann,1993;Solomone al.,2006),analysisandcompa isono 
o oli handwa e s ableiso opescan e eal heloca ionswhe e he
o oli ho anindi idual ishis o med.Howe e ,i  hechosen issues/
ma e ials a e dissimila , spa ial assignmen  (ma ching o  issue and
sou ceiso ope alues)needs ac iona ionequa ionsbe ween hecho-
sen issueandsou ceiso ope aluesdue o hedi e en  ac iona ion
o  heelemen iso opes iaen i onmen alandphysiological ac o s.
Isoscapeso e po en ial o  a iousapplica ionsinen i onmen al
andecological esea ch(Bowen,Wassenaa ,&Hobson,2005;Dawson
&Siegwol ,2007;Hobson&Wassenaa ,2008),whe eby heiso ope
alueso selec ed issuesa e ela ed oen i onmen aliso ope alues,
andno jus oneelemen ,bu se e alelemen s(i.e.,mul i-iso opeiso-
scape;e.g.,Hobsone al.,2012;Ga cía-Pé ez&Hobson,2014).The
mos ambi iousapp oachesha ebeen hecons uc ionso isoscapes
onaglobalscale(e.g.,Amundsone al.,2003;Bowen&Re enaugh,
2003;LeG ande&Schmid ,2006),whe ese e als udiesha eled o
con incing esul s ega dinganimalmig a ionamongmany axain e -
es ialandaqua icen i onmen s(Bes &Schell,1996;Chambe lain,
Bensch, Åkesson, & Ande sson, 2000; Hanson, Wu s e , EIMF, &
Todd,2010,2013;Hobson&Wassenaa ,1996;Wassenaa &Hobson,
1998).Howe e ,al houghin o ma ionabou animalmo emen sand
spa ialusageo  hei habi a sa  hein e con inen alscaleisimpo an 
inecological esea chandconse a ion,manyc uciale en soccu also
a smalle scaleswi hin hedis ibu iono smalle dis ancemig an s.
Un o una ely, hea ailabili yo isoscapeda a o s udiesa amo e
localspa ialscaleappea s obespa seo  hedis anceo  hesu ey
s a ionso globalisoscapeda amaybe oola ge o adequa elocal
iso opicdisc imina ion(seeBowen&Re enaugh, 2003).The e o e,
addi ionaliso opicda aa eneeded oinc ease he esolu iono global
isoscapes oenablemo ep ecise econs uc iono animalloca ions
andmo emen .
Theaimso  hiss udywe e(1) op o ideho izon aland e ical
iso opicg iddedda ase s(i.e.,isoscapes)o oxygen(
δ18O
H
2O
)anddis-
sol edino ganicca bon(δ13CDIC) o  hewa e o  heBal icSea.(2)
Asanexamplewedemons a e hepo en ialo  heseisoscapesusing
woA lan icsalmon indi iduals om he Ri e  Simojoki.Combined
wi h heiso opeda a om hesalmonandspa ialp obabili ysu ace
maps,weshowp obableloca ionso indi idual ishin a ious ime
poin sdu ing hei sea- eedingmig a ionphasein heBal icSea.We
alsodemons a ehowpa ame e iza iono  hemodelsin luenceson
loca iones ima es.
2 | MATERIAL AND METHODS
2.1 | Sampling and iso ope analyses o wa e
Bal icSeawa e sampleswe ecollec eddu ing h eedi e en c uises
by heR/VA andao  heFinnishEn i onmen Ins i u e(SYKE).To
e alua eapossibleseasonalimpac onseawa e iso ope alues,we
collec ed wosumme se sandonewin e se o samples.Theda es
o  hec uiseswe e(1)24May o11June2010,(2)9Augus  o27
Augus 2010,and(3)17Janua y o3Feb ua y2011.The i s c uise
co e ed hewholeBal icSea om heBo hnianBay o heSou he n
Bal icP ope ,excluding heGul o Finland(Figu e2),whichwas he
onlya easampleddu ing hesecondc uise.The hi dc uise,inwin-
e ,co e ed heBal icSeaexcep a eassou ho Go land.Seawa e 
wassampleda adep ho 10m ome e ysamplings a ion(al o-
ge he 316samples om134s a ion isi s,blackdo sinFigu es3
and4).F om25s a ions,wa e wasalsosampled e icallya 5–50m
FIGURE1 A lan icsalmon(Salmo sala )
FIGURE2 Mapo  heBal icSeawi h heloca iono  heRi e 
Simojoki(uppe mos  igh co ne ).Thema kedpa hwaysshow
ansec sused o c ea ing e icalin e pola ionsinFigu e4
|
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TORNIAINEN ET Al.
in e alsdependingonwa e dep ha  hesi e(Figu e4).Maximum
dis ancesbe weensamplings a ionswe eless han100km.Wa e 
samples we e aken using a CTD/Rose e sample  (Rose e 1015,
Seabi d,SBE911/Gene alOceanics,SIS:Plus500).
Rose esample  eco dsconduc i i y, omwhichsalini ywasau-
oma icallycalcula ed.F ome e ysamplingoccasiono wa e  o iso-
opeanalysispu pose,salini ywas eco ded.Samplewa e collec ed
o  δ13CDICanalysis,we einjec edin o12-mlbo osilica eExe aine 
ials(ca .no438B;LabcoL d.,HighWycombe,UK)p epa edin he
labo a o y,whe e0.2mlo 85%o hophospho icacid(H3PO4)was
addedin oeach ial,whichwas hensealedwi hacap(con aininga
ubbe sep um)and lushedand illedwi haheliuma mosphe e.In
he ield2–4mlo seawa e  omeachs a ionandsampledep hwas
injec ed h ough he ubbe sep umin o he ial.Samplewa e  o 
δ18O
H
2O
analysiswe ecollec edin20-mlglassscin illa ion ialsand
illed ullensu ingnoai bubbles.Allsampleswe es o edinanunli 
FIGURE3 In e pola edmaps o  he
Bal icSeao 
δ18
OH
2O
 alues(a,b)and
δ13CDIC alues(c,d) om10me e sin
summe (a,c)andwin e (b,d).Blackdo s
ep esen samplingloca ions
(a)
(c)
(b)
(d)
Longi ude(E)
La i ude(N)
–7
–8
–9
–10
2
1
0
–1
–2
510 15 20 25 30 35 510 15 20 25 30 35
66
64
62
60
58
56
54
66
64
62
60
58
56
54
Summe Win e
δ18O(‰)δ
13C(‰)
FIGURE4 In e pola edc oss-sec ional
su aceso  e ical
δ18
OH
2O
andδ13CDIC
alues.
δ18
OH
2O
 alues omsou h ono h
in(a)summe and(b)win e ,and omwes 
oeas in(c)summe and(d)win e .δ13CDIC
alues, omsou h ono hin(e)summe 
and( )win e ,and omwes  oeas in
(g)summe and(h)win e .Blackdo s
ep esen samplingloca ionsanddep hs
(a) (b)
(c) (d)
(e)
(g)
( )
(h)
δ18O (‰)δ
13C (‰)
Dep h(m)
0
100
200
300
0
50
100
150
–5
–6
–7
–8
–9
–10
–11
–5
–6
–7
–8
–9
–10
–11
20 22 24 26 28 20 22 24 26 28
56 58 60 62 64 56 58 60 62 64
Longi ude(E)
2
1
0
–1
–2
–3
–4
–5
2
1
0
–1
–2
–3
–4
–5
0
100
200
300
0
50
100
150
20 22 24 26 28 20 22 24 26 28
56 58 60 62 64 56 58 60 62 64
La i ude(N)
Longi ude(E)
La i ude(N)
Summe Win e
4
|
TORNIAINEN ET Al.
e ige a o (+4°C)inada k oompendinglabo a o yanalysis.In he
labo a o y,simila  ialsasused o δ13CDICsampleswe e illedwi h
0.5mlseawa e andequilib a edwi hCO2 o a leas 24h a 25°C.
Analyseso sampless a edwi hinaweeka e a i al o helabo a-
o y, i s  heδ13CDICsamplesimmedia elya e a i al.Theδ13CDIC
aluesa eexp essed ela i e oVPDB(ViennaPeeDeeBelemni e),
measu ed and calib a ed/no malized agains  in e na ional IAEA
(In e na ionalA omicEne gyAgency[IAEA])s anda dsNBS19(o TS-
Limes one;Calciumca bona e,δ13C=+1.95‰)andLSVEC(Li hium
ca bona e,δ13C=−46.6‰);±0.14‰.Valuesa eexp essed ela i e o
VSMOWandcalib a ed/no malized o heVSMOW(ViennaS anda d
Mean Ocean Wa e  [VSMOW], δ18O=0‰)—SLAP (S anda d Ligh 
An a c icP ecipi a ion,δ18O=−55.5‰)scale;±0.1‰.Allwa e sam-
pleswe eanalyzed o bo hδ13CDICand
δ18O
H
2O
a  heLabo a o y
o  Ch onology, Finnish Museum o  Na u al His o y, Uni e si y o 
Helsinki, using a GasBench II and Del a Plus XL (The mo Fishe 
Scien i ic,B emen,Ge many).
S a is ical es ingo seasonaldi e encesin
δ18O
H
2O
andδ13CDIC
alues(pai edsamples  es )waspe o medusingPASWS a is ics18
o Windows(SPSSInc.,Chicago,IL,USA).In e pola edisoscapes o 
δ13CDICand
δ18O
H
2O
we econs uc edusingOceanDa aView(ODV)
so wa e e sion4.5.5(Schli ze ,2002,2011).
2.2 | O oli h sampling, mic omilling and s able
iso ope analysis
In o de  o es  applicabili y o  Bal ic Sea isoscapes in ish mig a-
ions udies,weanalyzedo oli hs om woexample emaleA lan ic
salmon(he ea e Bal icsalmono salmon)o iginallycaugh ,as hey
we e e u ning o heRi e Simojoki(Figu e2) ospawnin2008,by
heNa u alResou cesIns i u eFinland(LUKE)aspa o  hep og am
omoni o yolk-sac ymo ali y(M74synd ome:e.g.,Keinänene al.,
2012; o iginal LUKE code numbe s SS5447 and SS5461, he ea e 
FISH1and2, espec i ely).Bo hsalmonhadspen  woyea s eed-
ingin he sea.Theo igin (wild o ha che y- ea ed) andage o  he
salmonwasde e mined om hescalenucleusandscaleg ow hpa -
e n(Hiili i a,Ikonen,&Lappalainen,1998).FISH1waso wildo igin
(5,300g,80cm)andFISH2waso ha che y- ea edo igin(6,300g,
81cm). Bo h sagi al o oli hs we e emo ed om he head o  he
salmon,cleanedindeionizedwa e  o emo eany emainingo ganic
issue,andd iedo e nigh a 60°C.
Bo ho oli hswe esampled o δ13Candδ18Oanalysisusing he
cus om-buil  h ee-dimensional compu e -con olled mic omilling
sys emin heSaska chewanIso opeLabo a o ya  heUni e si yo 
Saska chewan ollowing he p ocedu e o  Wu s e , Pa e son, and
Chea ham(1999).Thissys emallowed31–32samplingpa hs obe
ollowed conco dan wi h g ow h banding in bo h o oli hs. Iso ope
a ios o  samples we e de e mined using a Finnigan MAT 253 di-
ec lycoupled oaKiel-IVau oma edca bona ep epa a ionde ice
(The mo–Fishe  Scien i ic).Accu acy and p ecision we e moni o ed
by ou ineanalysiso NBS-19s anda d,yieldingas anda dde ia ion
o  eplica es anda ds ha wasconsis en lyless han0.09 o bo h
δ13Oandδ18O alues.Allo oli hiso opemeasu emen sa e epo ed
in hes anda ddel ano a ion(pe mil) ela i e o heVPDBs anda d
asδ18Oo oandδ13Co o.F om heo oli hda ao eachsalmon, h ee
samplemillingpa hswe eselec ed o close inspec ion,namely1s 
seawin e (1SW), he ollowingsumme (2SS),and he2ndseawin e 
(2SW) oassign hesalmon oBal icSeaa eas o eachpe iod.Du ing
heseamig a ionphase,Bal icsalmonexpe iencehighseasonal luc-
ua ions in ambien  empe a u e.These pe iods a e clea ly seen in
heo oli hs,aso oli hca bona ewi h he highes δ18Oo o aluesis
acc e eddu ingcoldwin e pe iod,while helowes δ18Oo o alues
ep esen highes  empe a u esin hesumme (Figu e6;Wu s e &
Pa e son,2003).
2.3 | C ea ing iso opic (isoscapes) and empe a u e
maps o he Bal ic Sea
Isoscapes o δ13CDICand
δ18O
H
2O
aswellas empe a u emapswe e
cons uc edusingODVso wa e.Usedmapda a o ho izon aliso-
opemapswe e ecei ed om heda abaseo  heLeibnizIns i u e
o  Bal ic Sea Resea ch Wa nemünde (IOW; Sei e , Taube , &
Kayse ,2001)and o bo hho izon almapsand e icalp o iles om
he Gene al Ba hyme ic Cha  o  he Oceans (GEBCO_08 G id).
GEBCO_08G idhad obecon e edin oNe CDF o ma compa -
iblewi hODVwi hRS a is icsso wa e 3.0.1(RCo eTeam,2013)
using package RNe CDF (Michna, 2012). In e pola ed maps we e
p oducedusingDa aIn e pola ingVa ia ionalAnalysis(DIVA)g id-
dingso wa e(T oupine al.,2012)includedinODV(DIVApa am-
e e s:scaleleng hschosenau oma ically;signal- o-noise a io=40;
quali ylimi =3.0;excludingou lie s).Ve icalp o ileswe ealsoc e-
a edusingDIVAg idding(scaleleng hschosendependingonused
da a;signal- o-noise a io=40;quali ylimi 3.0;excludingou lie s).
Thecoas linesin hemapsa ebasedon heGlobalSel -consis en 
Hie a chical High- esolu ion Sho elines da abase  2.1 (Wessel &
Smi h,1996).
As hespa ialco e ageo collec ed
δ18O
H
2O
was ela i elyspa se
o assignmen models,andsomela ge a easlackedmeasu emen s,
wec ea edp edic i emodels o es ima e
δ18O
H
2O
 alues om he
Bal icSeawa e salini y(S)da awhichisanexcellen p edic o  o 
δ18O
H
2O
andiscommonlyused oes ima eoceanseawa e iso ope
alues(e.g.,LeG ande&Schmid ,2006).The
δ18O
H
2O
–S ela ionship
is equen lylinea ly ela ed(LeG ande&Schmid ,2006),bu in he
Bal ic eshwa e in low omla ge i e sin oGul o Bo hniaandGul 
o Finlandha eane ec on he ela ionships.The e o e,wec ea ed
sepa a emodels o  heGul o Bo hnia, heGul o Finlandand o 
he es o  he emaininga eao  heBal icSea.Shapeo  hep edic i e
model o eacha eawasselec edbasedongoodnesso  i andmodel
esidualswe ee alua edusingquan ile–quan ileplo s.Modelswe e
u he applied oseawa e salini ysamplingsu eysob ained om
Bal icMa ineEn i onmen P o ec ionCommission(HELCOM)da a-
base(Ande sson,2014) oc ea eseasonal
δ18O
H
2O
maps o  heBal ic
Sea.Da aonly o summe (July–Augus )andwin e (Feb ua y–Ma ch)
o  hepe iod hes udysalmonhadspen in hesea(2007–2008)
we eselec ed.Aswe ounds a is icallysigni ican seasonaldi e ence
in measu ed
δ18O
H
2O
 alues, h ee sepa a e
δ18O
H
2O
 maps [win e 
|
5
TORNIAINEN ET Al.
2007(1SW),summe 2007(2SS)andwin e 2008(2SW)]we ec e-
a ed obeusedinassignmen models.Modeled alueswe ecombined
wi hmeasu ed alues om hesameseason ogainbe e spa ialco -
e age. Ma ked wi hin-season di e ences we e no  ound be ween
HELCOMandou ownmeasu emen sbasedon isual alida iono sa-
lini yda a,ob ained omdep hs5–15m,indica ing ha also
δ18O
H
2O
aluesbeha e hesameway.
Salmon summe  empe a u es we e ixed a  11.5°C, calcula ed
omp e e ed ue10ms ayingdep hso salmoninBal icsalmon
da a s o age ag s udy by Wes e be g, S u laugsson, Ikonen, and
Ka lsson(1999).Fo win e  empe a u es(2007–2008),weusedall
a ailable empe a u e p o iles collec ed om HELCOM da abase
(Ande sson,2014)co e ing hewholeBal icSea(mean empe a u es
omdep hs5–15m)andc ea edanin e pola edsu ace o  hep e-
e ed10ms ayingdep h.In e pola edme abolicallyde i edbica -
bona eδ13Cdie  alueswe ede i ed omδ13C alueso salmondie a y
speciesa ound heBal icSea(AppendixS3).
2.4 | C ea ion o o oli h- ela ed isoscapes om
δ18OH2O, δ13CDIC, δ13Cdie and wa e empe a u e
Unde s anding he dependence o  ambien  wa e  empe a u e and
δ18O
H
2O
 alues on δ18Oo o is necessa y o ob ain compa able al-
ues o  δ18Oo o and
δ18O
H
2O
 o  spa ial assignmen  o  salmon (e.g.,
Pa e sone al.,1993).Mo eo e , heδ13Co o alueisamixo bica -
bona eδ13CDIC omambien wa e andme abolicallyde i edbica -
bona e δ13Cdie  (Solomon e al., 2006; Wu s e  & Pa e son, 2003).
We he e o eco ec ed
δ18O
H
2O
andδ13CDIC aluesusingli e a u e-
de i ed ac iona ionequa ions,a e which heco ec ed aluesa e
conside edas“o oli hisoscape”o bo helemen s(AppendixS1).This
pe mi sadi ec compa isono o oli handBal icSeawa e iso opes,
he ebyp o idingap obabilis icspa ialassignmen o salmondu ing
hei sea- eedingphase.
Ini ially,
δ18O
H
2O
 alues a e calcula ed ela i e o he VSMOW
scaleandδ18Oo o alues ela i e o heVPDBscale om heIAEA.
To enable di ec  compa ison o  δ18Oo o(VPDB) wi h δ18Owa e (VSMOW),
δ18Owa e (VSMOW) alues we e con e ed o VPDB using ollowing
equa ion( omCla k&F i z,1997):
Oxygen iso ope alues o  o oli hs e lec  hose o  he ambien 
wa e (Campana,1999;Fa ell&Campana,1996;Tho old,Jones,&
Campana, 1997), wi h a empe a u e-dependen  ac iona ion (e.g.,
Pa e sone al.,1993).Followingcommonp ac ice,weused helinea 
empe a u e-dependen  ac iona ion(e.g.,Pa e sone al.,1993).
whe e Tis empe a u e(103/K),whe eKisambien wa e  empe a-
u einKel in,andpa ame e α is he ac iona ion ac o be ween
o oli h and ambien  wa e  [α=(δ18Oo o(VPDB)+1,000)/(
δ18O
H
2O
(VPDB)+1,000)]. Model ac iona ion cons an s a and b in ou  p e-
ious s udies co e ing salmonid ishes a e a iable (a=−41.14,
b=20.43:Godiksene al.,2010;a=−33.43,b=17.88:Hansone al.,
2013; a=−33.49, b=18.56:Pa e sone al., 1993and a=−41.69,
b=20.69:S o m-Suke,Dempson,Reis ,&Powe ,2007).Toe alua e
hee ec and a ia iono di e en pa ame e s osalmonassignmen ,
henume icallymos dis an pa ame e s omeacho he (i.e.,Hanson
e al.,2013;Pa e sone al.,1993)we eselec ed o salmonassign-
men (i.e., o p obabili ysu aces),he ea e Model3andModel1,
espec i ely.Alsoana e ageo all ou models(a = −37.44,b = 19.39)
wascalcula edandusedacco dingly,he ea e Model2(AppendixS2).
The ollowingequa iongi es heo oli h- ela edδ18O(VPDB)isos-
cape aluesin ela ion owa e  empe a u e(T)and
δ18O
H
2O
(VPDB) al-
ues, ha canbecompa ed oδ18Oo o aluesenabling heassignmen 
o salmon oseaa easbasedon hei o oli hiso ope alues:
Ano oli h- ela edδ13Co oisoscapewascalcula edas ollows(e.g.,
Solomone al.,2006;Wu s e &Pa e son,2003) oallowcompa ison
be weenδ13CDICandδ13Co o:
whe e δ13Cdie isameanδ13C alueo salmonp ima yp eyspeciesin
heBal icSea(sp a [Sp a us sp a us],Bal iche ing[Clupea ha engus
memb as]and h ee-spineds ickleback[Gas e os eus aculea us])ina
pa icula loca ion(AppendixS3)andMis hep opo iono me abolic
ca bonin hesalmono oli h(She wood&Rose,2003):
whe e Kcaud(A lan icsalmoncaudal in a io;Minns,King,&Po ,
1993)is2.4.
2.5 | Salmon assignmen using o oli h and wa e
iso ope alues
Toes ima e heloca ionso salmonindi idualsin hei 1SW,2SS
and second 2SW om δ18Oo o and δ13Co o alues, we calcula ed
p obabili ydensi ysu aces o eachsalmonbyusingade e min-
is icg idco e ing heBal icSea ollowing heapp oachp esen ed
inWunde (2010)wi hRS a is icsso wa e 3.0.1(RCo eTeam
2013).We i s had o ein e pola eallDIVAin e pola ion esul s
(wa e and die -basediso opes, empe a u es,e c.which we ein
di e en kindso nonde e minis icg ids) omODVin oade e -
minis icg id oenableus ocalcula e he ac iona ionequa ions
o allg idloca ions.This ein e pola ionwaspe o medwi hlocal
(Nmax =4) in e se-dis ance weigh ing in e pola ion a ailable in
heRpackagegs a (Pebesma,2004).Thep obabili ydensi ysu -
ace calcula ion app oach assumes wa e - empe a u e-dependen 
δ18O(VPDB) aluesandDIC-die -basedδ13C alues obeno mallydis-
ibu eda eachg idpoin and hencalcula es hep obabili ieso 
ob aining hemeasu ed alueso  heo oli h omno maldis ibu-
ionswi hmeanpa ame e sacco ding o heVPDB-co ec edin e -
pola ediso ope alues.S anda dde ia ionso δ18Oandδ13C alues
we ees ima edbasedonobse ed a ia ionso 
δ18
O
H2O
(ɛ=0.019)
andδ13CDIC(ɛ=0.216) aluesob ained om hesameloca ionand
dep h,and he a ia iono obse edδ18Oo o aluesin heo oli hs
δ18
O
H2O(VPDB)
=0.97002×δ
18
O
H2O(VSMOW)
−
29.98.
1,000×ln α=a+b∕T,
δ18
O
(VPDB)
=e
(
a+b∕T
)
∕
1,000
×(δ
18
O
H2O(VPDB)
+1,000)−
1,000.
δ13
C
o o =
M
×δ13
C
die +
(1
−
M)
×δ13
C
DIC,
M=0.025+0.066×Kcaud,

6
|
TORNIAINEN ET Al.
o se e al ishindi iduals(ɛ=0.207es ima ed omGodiksene al.,
2010).
The esul ing p obabili y su aces do no  ep esen  wo-
dimensionalp obabili ysu aces( o alp obabili yineachmapsisno 
scaled obe1)and heminimumandmaximump obabili y aluesa e
no  hesameinallmapsasiscommonin hiskindo app oach(see
e.g.,Wunde ,2010).Ins ead, hesesu aces isualizewhe e hep ob-
abili yo ob aining hemeasu ed alueo  heo oli h(o  hep obabili y
o p esenceo pa icula indi iduala ace ain ime)is heg ea es ,
andwhe ei is(much)lowe .In hosemapswhe ebo hoxygenand
ca bon iso opes ha e been aken in o accoun , p obabili ies we e
calcula ed by mul iplying iso ope-wise p obabili ies, assuming inde-
pendence,whichmayno bes ic ly ue o  hiskindo phenome-
non.Howe e ,ou da adidno allow o  ulles ima iono co a iance
be ween ueda a aluesdue opa iallydi e ingmeasu emen o 
obse a ion loca ions. Ne e heless, he co a iance o  in e pola ed
su aceswasabou 10- oldsmalle  han he a ianceso indi idual
iso opes.The e o e,weexpec  ha anypossiblee o in he esul s,
due odependenceiniso ope alues,issmall.
Tos udy,howsensi i eou app oachis omeasu emen e o s
ela ed o hes ableiso opes,weconduc edasimplesensi i i yanal-
ysisbyaddingand/o sub ac ing heobse eds anda dde ia ionso 
wa e samples(basedonli e a u e)o δ13Candδ18O o/ om heac-
ualmeasu ed alues,andpe o med hecalcula iono  hep obabili y
o p esence o FISH2on he i s win e (1SW)using hemodelby
Hansone al.(2013) o  ac iona ion.Theamoun ±SDo wa e iso-
opemeasu emen  a ia ion(basedonli e a u e)waschosenbecause
i also e lec sabou ±2SDo ou ownes ima eo measu emen ac-
cu acy(0.09)o o oli hiso ope alues.So, heselimi sa ealso a he 
close obeingabou 95%con idencein e alo  hemeasu ediso ope
alues.
3 | RESULTS
3.1 | δ18OH2O, and δ13CDIC alues in he Bal ic Sea
Di e encein
δ18O
H
2O
 aluesbe weenseasonsa 10mdep ha  he
same loca ions was s a is ically signi ican  (Pai ed samples T es :
N = 31,p < .001).Howe e , hemean(±SD) alueso 
δ18O
H
2O
we e
e y simila  (meansumme : −7.9‰±0.83, meanwin e : −7.6‰±0.74).
Inaddi ion,
δ18O
H
2O
 aluesshowedaclea sou h ono hla i udinal
dec ease oma ound−6‰ oa ound−10‰(Figu e3a,b).Aweake 
longi udinaldec ease oma ound−6‰ oa ound−7.5‰occu ed
om heeas e nendo  heGul o Finland o hewes e nsideo  he
No he nBal icP ope (Figu e3a,b).Dis inc di e encesin
δ18O
H
2O
aluesbe weenadjacen basinswe ealsoobse ed(Bo hnianBay—
Bo hnianSea—Bal icP ope —Gul o Finland),bu  heBo hnianSea
and heGul o Finland,e en houghno di ec lyconnec ed,had e y
simila  alues(Figu e3a,b)due o hein luxo  eshwa e  om i e s.
Mean (±SD) δ13CDIC alues we e signi ican ly di e en  (Pai ed
samplesT es :N = 31,p < .001)be weensampling imes(meansum-
me :0.3‰±0.81,meanwin e :−0.9‰±0.54).δ13CDIC aluesdec eased
wi hla i udeinsumme  oma ound2‰ oa ound−2‰(Figu e3c).
The di e encewas smalle  in hewin e  (Figu e3d).An inc easing
endwasobse edinδ13CDIC alues om heGul o Finland o he
Bal icP ope inbo hseasons, oma ound−1‰ oa ound2‰in
summe and oma ound−2‰ oa ound0‰inwin e (Figu e3c,d).
Ve icalin e pola iono  he ansec sshowed ha 
δ18O
H
2O
 aluesin
heCen alBal icP ope we ehighe below~50m oma ound−6.5‰
oa ound−5.5‰a  hebo omandashighas−4‰in heSou he n
Bal icP ope (Figu e4a,b),whe easaclea dec easing endinsumme 
δ13CDIC alues oma ound−1‰ oa ound−5‰a  hebo omwas
obse ed (Figu e4e, ). Ve ical in e pola ion also showed s abili y o 
δ18O
H
2O
 aluesbe weensumme andwin e ,whe easδ13CDIC alues
exhibi ed a ia ion be ween summe  and win e  in he uppe  wa e 
laye  (up om ~50m; Figu e4e–h). Below ~50m bo h alues we e
a he s ableo e  ime,excep in helesssalinea eas( heBo hnianSea,
heBo hnianBayand heGul o Finland)whe eδ13CDIC aluesshowed
mino dec easesdue oau umnwa e column u no e (Figu e4).
The ewasa s ong
δ18O
H
2O
–S ela ionshipand he coe icien s
o de e mina ion o all hemodelswe eclose o1.Rela ionshipap-
pea ed obelinea only o Sou he nBal icSea(R2=.98),whilein
Gul o Finland(R2=.97)andGul o Bo hnia ela ionshipswhe eo 
loga i hmicshape(R2=.99;Figu e5).
3.2 | Ca bon and oxygen iso ope alues o
salmon o oli hs
S ableiso opeanalysis iamic omilling om heo oli hnucleus o he
o oli hedgeshowedclea  a ia ionino oli hiso ope alues.Inaddi-
ion,bo hiso ope alueso  he woo oli hsanalyzedshowedsimila 
li e-his o y ends om henucleus o heo oli hedge.δ18O aluesin
heo oli hnucleus(FISH1:−10.9‰;FISH2:−10.6‰)we ema kedly
lowe  han hehighes  aluesobse edin heou e pa o  heo oli h
adius(FISH1:−5.9‰;FISH2:−6.6‰),andwi h helowes  aluesa 
heedgeo  heo oli h(bo ho oli hs:−11.6‰;Figu e6a,b).
FIGURE5 Rela ionshipsbe weenseawa e salini yand
δ18
OH
2O
measu edin(a)Gul o Bo hnia,(b)Gul o Finlandand(c)Bal ic
P ope .P esen edmodelswe eappliedwhenes ima ing
δ18
OH
2O
 o 
eacha ea
–12
–11
–10
–9
–8
–7
–6
–5
–4
0246810121
41
6
a
c
b
Salini y (‰)
δ18O(‰)
y = 0.263x - 8.684
R2= 0.98
y = 2.245ln(x) - 11.243
R2 = 0.97
y = 3.447ln(x) - 13.664
R2= 0.99
|
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TORNIAINEN ET Al.
Fo bo ho oli hs,δ13C aluesalsoshowedclea  a ia ionalong
he o oli h adius, om lowes  δ13C alues in he o oli h nucleus
(FISH1:−16.1‰;FISH2:−14.4‰) ohighes in heou e pa o 
heo oli h adius(FISH1:−3.4‰,FISH2:−3.1‰),wi hin e media e
aluesa  heedgeo  heo oli h(FISH1:−11.1‰;FISH2:−10.8‰;
Figu e6a,b).Bo ho oli hnuclei(i.e.,du ing heju enilephase)exhib-
i edlowδ13Co oandδ18Oo o alues.Theju enilephaseiso ope alues
o FISH1 ended obeless a iable han hoseo FISH2.Theo oli h
iso ope alueso appa en pos -smol mig a ion om he eshwa e 
omo esalinea e hemos dis inc be ween hese wosalmon.FISH
1o oli h δ18O alues inc eased o hehighes  aluesmo esha ply
han hoseo FISH2, o whichδ13C aluesinc easedinamo elinea 
manne .O oli hδ18O alues o FISH1we ehighe du ing he i s 
seawin e  han hose o FISH2,while aluesdu ing hesecondsea
win e andappa en spawningmig a ion(s eepdeclineinbo hiso ope
aluesa e 2SW)we esimila  o bo hsalmon(Figu e6a,b).
3.3 | P obabili y su aces o salmon loca ions in he
sea- eeding phase
Basedon heModel1(Hansone al.,2013)assignmen s, hemos 
p obable i s seawin e loca iono FISH1wasin heBal icP ope 
(Figu e7a).Du ing henex summe and hesecondwin e ,FISH1
appea ed ooccupywa e sclose o heGul o Riga,and hea easo 
hesou hwes andno he nBal icP ope , espec i ely(Figu e7b,c).
The esul s o FISH2we e e ysimila ,excep  ha in he i s win e 
i appea ed obeloca edin heBo hnianSeao in heGul o Riga
(Figu e7d– ).Compa ed o heModel1,assignmen so  heModel
3(Pa e sone al.,1993)we eloca edmo eno he nandalsocolde 
a easo  oa easwi hlowe salini y( heGul o Finland;Figu e7).
Model2( hea e agemodelo  ou modelsusedin hes udy)salmon
assignmen swe ebe weenHansone al.(2013)andPa e sone al.
(1993)models(Figu e7).Someo  heassignmen so  hemodels2
and3we econ ined osuchasmalla ea ha  esul so  hemodels
we eno  e y isiblein heassignmen maps(Figu e7).
To al o  eigh  di e en  esul s (Figu e8) we e ob ained om
hesensi i i yanalysisinaddi ion o he esul ob ainedwi hac ual
measu ed alues.Inc easing heo oli hδ18O aluecauses hemos 
p obablea eain heGul o Bo hnia oshi sligh ly owa dwes ,and
dec easingi causes hemos p obablea ea oshi sligh ly owa d
eas .Inc easingδ13C alueseems omake heassignmen mo econ-
cen a eda oneloca ionanddec easingi causes he esul  obeless
de e mined.
4 | DISCUSSION
4.1 | Iso ope alues o he Bal ic Sea
Wep esen ed hedis ibu iono δ13CDICand
δ18O
H
2O
 aluesin he
Bal icSeadu ingbo hsumme andwin e  iain e pola edho izon al
FIGURE6 Iso ope alueso  wo
exampleRi e Simojokisalmono oli hs
mic o-milledandanalyzed o oxygenand
ca bons ableiso opes:(a)FISH1(wild
o igin)and(b)FISH2(ha che y- ea ed).
Openci cles ep esen δ13C aluesand
illedci clesδ18O alues.Iso opepoin 
aluesusedin hesalmonassignmen  o
hep obableloca ionsin heBal icSea
du ing hei  i s (1SW)andsecondsea
win e (2SW)andsecondseasumme 
(2SS)a eindica ed
–20.0
–18.0
–16.0
–14.0
–12.0
–10.0
–8.0
–6.0
–4.0
–2.0
–12.0
–11.0
–10.0
–9.0
–8.0
–7.0
–6.0
δ
13
C(‰)δ
13
C(‰)
δ18O(‰)
–20.0
–18.0
–16.0
–14.0
–12.0
–10.0
–8.0
–6.0
–4.0
–2.0
–12.0
–11.0
–10.0
–9.0
–8.0
–7.0
–6.0
020406080100
Dis ance om nucleus (%)
δ18O(‰)
(a)
(b)
1SW 2SS 2SW
1SW 2SS 2SW
8
|
TORNIAINEN ET Al.
iso opicmaps omadep ho 10mandalso ia e icalc oss-sec ions.
Di e encesbe weenseaa easinbo hiso ope alueswe eobse ed.
Ho izon alδ13CDIC aluesclea lydi e edbe weensumme andwin-
e ,whe eas
δ18O
H
2O
 alues emained a he simila .Ve ical
δ18O
H
2O
alues emaineds ablebe weensumme andwin e ,whe easδ13CDIC
showedma keddi e encesbe weensumme andwin e ,especially
nea  hesu ace.
The dis inc i e hyd ologic cha ac e is ics o  he Bal ic Sea a e
clea ly e lec edinou measu emen s.
δ18O
H
2O
 aluesin heBal icSea
a emainlycon olledby hein lux om heDanishs ai so dense ,
mo e saline wa e  wi h highe 
δ18O
H
2O
 (see e.g., Dickson, 1973;
Ma häus&Lass,1995)and he eshwa e wi hlowe 
δ18O
H
2O
 alues
unningo  om heca chmen a ea.Theobse ed e icalg adien in
iso ope aluesisalsodue o hepene a iono mo esalinewa e wi h
highe
δ18O
H
2O
 aluesunde  helessdense eshwa e wi hlowe 
δ18O
H
2O
 alues.Thisdense wa e s agna esin hedeepe basinsiso-
la edby hesillsbe weendi e en Bal icSeaa eas(Ma häuse al.,
2008)andleads o hea ealseg ega iono 
δ18O
H
2O
 alues.Asimila 
phenomenoncanbeseeninma ineen i onmen sa ound hewo ld
(Schmid , Bigg, & Rohling, 1999) and has been eco ded om he
Sou he nBal icSea(F ohlich,G abczak,&Rozanski,1988;Punning,
Vaikmae,&Maek i,1991).Tempe a u e- ela edau umno e u no 
hewa e columnb eaksdown hesumme s a i ica ionandmixes
hewa e abo e hehalocline(down o~50m),bu  hedeepe wa e 
FIGURE7 P obabili ysu aceso 
loca ions o  woexampleRi e Simojoki
A lan icsalmons(FISH1and2)du ing hei 
eedingphaseo  i s seawin e (1SW;a
andd, espec i ely),secondseasumme 
(2SS;bande, espec i ely)andsecond
seawin e (2SW;cand , espec i ely)in
heBal icSea.Calcula ionsa ebasedon
salmono oli handBal icSeawa e δ18O
andδ13C alues.Whi eandhigh-sa u a ion
colo sindica e ha all aluesu aces
usedin hecalcula iono p obabili ies
( empe a u e,
δ18
OH
2O
,δ13CDICandp ey
iso ope alues)a e eliableincon as  o
lowcon idencep obabili iesindica edin
g ayandg ayishcolo s.P obabili ysu ace
esul sindica edin ed ep esen high
p obabili yo p esenceacco ding o he
usedmodelo Hansone al.(2013)(Model
1),g eencolo indica eshighp obabili y
o p esencewi h hea e agemodelo 
all ou usedmodelsin hiss udy(Model
2;Godiksene al.,2010;Hansone al.,
2013;Pa e sone al.,1993;S o m-Suke
e al.,2007)andbluecolo  ep esen s
highp obabili yo p esenceon hemodel
p obabili ieso Pa e sone al.(1993)
(Model3)
La i ude
(a)
Model 1 high p ob.
Model 2 high p ob.
Model 3 high p ob.
Low p obabili y
Low con idence
La i ude
(b)
Model 1 high p ob.
Model 2 high p ob.
Model 3 high p ob.
Low p obabili y
Low con idence
Longi ude
La i ude
(c)
Model 1 high p ob.
Model 2 high p ob.
Model 3 high p ob.
Low p obabili y
Low con idence
(d)
Model 1 high p ob.
Model 2 high p ob.
Model 3 high p ob.
Low p obabili y
Low con idence
(e)
Model 1 high p ob.
Model 2 high p ob.
Model 3 high p ob.
Low p obabili y
Low con idence
54 56 58 60 62 64 6654 56 58 60 62 64 66
10 15 20 25 30
54 56 58 60 62 64 66
10 15 20 25 30
Longi ude
( )
Model 1 high p ob.
Model 2 high p ob.
Model 3 high p ob.
Low p obabili y
Low con idence
FISH 1 FISH 2
|
9
TORNIAINEN ET Al.
column emains a he s ablemain ainingmo ema inecha ac e is ics
(Lass&Ma häus,2008).Howe e ,inou s udy,
δ18O
H
2O
 alues e-
maineds ablebe weensumme andwin e ,andonlyoccasionals ong
sal wa e pulses(e.g.,Dickson,1973;Ma häus&Lass,1995)could
change his si ua ion. Lack o  win e  iso ope measu emen s sou h
om Go land migh  ha e a ec ed he in e pola ed alues deno ed
in hemapswi hg ayishcolo s).TheFinnishEn i onmen Ins i u e
(SYKE;h p://www.i ame ipo aali. i/en_GB/:2.6.2014)andHELCOM
(Ande sson,2014)ha e epo eds ablehyd ologyandsalini yo  he
Bal icdu ing hes udiedyea s.Basedon hosea ibu es,i isno  e y
likely ha 
δ18O
H
2O
 aluesinsumme wouldbe e ydi e en  om he
aluesobse edinwin e .
δ13CDIC aluesa econ olledbysimila mechanismsas hose ha 
con ol he wa e  column cha ac e is ics and
δ18O
H
2O
.The clea es 
dis inc ion be ween he mechanisms based on empe a u e- ela ed
bioac i i y. P e e en ial inco po a ion o  12C du ing pho osyn hesis
FIGURE8 Sensi i i yanalysiso p obabilis icspa ialassignmen Model1 o FISH2in1s win e a  hesea(1SW).O iginalo oli hδ18Oand
δ13C alues( igu ein hemiddle)we eadjus ed±1SD.Highp obabili ymeanswhe e hep obabili yo ob aining hemeasu ed(o de ia ed)
alueo  heo oli h(o  hep obabili yo p esenceo  hisindi iduala 1SW) om hec ea edo oli hisoscapeis heg ea es by heused
model.Theha ched(low-sa u a ioncolo ed)a easindica e egionswhe e hedensi yo  ealobse a ionso a leas oneisoscape(usedin he
calcula iono p obabili yo p esence)is oolow o  eliablep edic ion
10 15 20 25 30
δ18Oa uppe , δ13Ca lowe limi
High p obabili y
Low p obabili y
10 15 20 25 30
δ18O a uppe limi
High p obabili y
Low p obabili y
10 15 20 25 30
Bo h a uppe limi
High p obabili y
Low p obabili y
10 15 20 25 30
δ13C a lowe limi δ13C a uppe limi
High p obabili y
Low p obabili y
10 15 20 25 30
Bo h iso opes as measu ed
High p obabili y
Low p obabili y
10 15 20 25 30
High p obabili y
Low p obabili y
10 15 20 25 30
54 56 58 60 62 64 6654 56 58 60 62 64 6654 56 58 60 62 64 66
Bo h a lowe limi
High p obabili y
Low p obabili y
10 15 20 25 30
δ18O a lowe limi
High p obabili y
Low p obabili y
10 15 20 25 30
54 56 58 60 62 64 66
54 56 58 60 62 64 66
54 56 58 60 62 64 66
54 56 58 60 62 64 66
54 56 58 60 62 64 66
54 56 58 60 62 64 66
δ18Oa lowe , δ13C a uppe limi
High p obabili y
Low p obabili y
Longi ude
La i ude
O oli hδ13C alue inc eases →
O oli h δ18O alue inc eases →
10
15
20
2
5
30
High
p o
b
a
bili
y
L
o
w p o
b
a
bil
i
y
10 1
5
20
25
30
High
p o
b
a
bili
y
L
o
w p o
b
a
bili
y
10
1
5
20
25
30
High
p o
b
a
bili
y
L
o
w p o
b
a
bili
y
10
15
20
25
30
δ
1
3
C
a
l
o
w
e
l
i
m
i
δ
1
3
C
a
u
ppe
li
m
i
Hi
g
h p obabili
y
L
o
w p obabili
y
10
15
20
25
30
Bo h iso o
p
es as measu ed
H
i
g
h p obabili
y
L
o
w p obabili
y
10
15
20
25
30
Hi
g
h p obabili
y
L
o
w p obabili
y
B
o
h
a
l
o
w
e
limi
Hi
g
h p obabili
y
L
o
w p obabili
y
δ
1
8
O
a
l
o
w
e
l
i
m
i
H
i
g
h p obabili
y
L
o
w p obabili
y
5
4
5
6
5
8
6
0
6
2
6
4
6
5
4
5
6
5
8
6
0
6
2
6
4
6
5
4
5
6
5
8
6
0
6
2
6
4
66
5
4
5
6
5
8
6
0
6
2
6
4
6
6
5
4
5
6
5
8
6
0
6
2
6
4
66
5
4
5
6
5
8
6
0
6
2
6
4
6
6
δ
1
8
O
a
l
o
w
e
,
δ
1
3
C
a
u
p
p
e
l
i
m
i
Hi
g
h p obabili
y
L
o
w p obabili
y