Clim. Pas , 10, 1473–1487, 2014
www.clim-pas .ne /10/1473/2014/
doi:10.5194/cp-10-1473-2014
© Au ho (s) 2014. CC A ibu ion 3.0 License.
Tes ing long- e m summe empe a u e econs uc ion based on
maximum densi y ch onologies ob ained by eanalysis o ee- ing
da a se s om no he nmos Sweden and Finland
V. V. Ma sko sky1and S. Helama2
1Ins i u e o Geog aphy, Russian Academy o Sciences, Moscow, Russia
2Finnish Fo es Resea ch Ins i u e, No he n Uni , Ro aniemi, Finland
Co espondence o: V. V. Ma sko sky (ma sko sk[email p o ec ed])
Recei ed: 13 Augus 2013 – Published in Clim. Pas Discuss.: 16 Oc obe 2013
Re ised: 1 June 2014 – Accep ed: 11 June 2014 – Published: 5 Augus 2014
Abs ac . He e we analyse he maximum la ewood densi y
(MXD) ch onologies o wo published ee- ing da a se s:
one om To ne äsk egion in no he nmos Sweden (TORN;
Mel in e al., 2013) and one om no he n Fennoscan-
dia (FENN; Espe e al., 2012). We paid pa icula a en-
ion o he MXD low- equency a ia ions o econs uc
summe (June–Augus , JJA) long- e m empe a u e his o y.
We used published me hods o ee- ing s anda diza ion: e-
gional cu e s anda diza ion (RCS) combined wi h signal-
ee implemen a ion. Compa isons wi h RCS ch onologies
p oduced using single and mul iple (non-clima ic) ageing
cu es ( o be emo ed om he ini ial MXD se ies) we e
also ca ied ou . We de elop a no el me hod o s anda diza-
ion, he co ec ion implemen a ion o signal- ee s anda d-
iza ion, ailo ed o de ec ion o pu e low- equency signal
in ee- ing ch onologies. In his me hod, he e o in RCS
ch onology wi h signal- ee implemen a ion is analy ically
assessed and ex ac ed o p oduce an ad anced ch onology.
The impo ance o co ec ion becomes ob ious a lowe e-
quencies as smoo hed ch onologies become p og essi ely
mo e co ela i e wi h co ec ion implemen a ion. Subsam-
pling he FENN da a o mimic he lowe ch onology sam-
ple size o TORN da a shows ha he ch onologies bi u -
ca e du ing he 7 h, 9 h, 17 h and 20 h cen u ies. We used
he wo MXD da a se s o econs uc summe empe a u e
a ia ions o e he pe iod 8 BC h ough AD 2010. Ou new
econs uc ion shows mul i-decadal o mul i-cen ennial a i-
abili y wi h changes in he ampli ude o he summe empe a-
u e o 2.2◦C on a e age du ing he Common E a. Al hough
he MXD da a p o ide palaeoclima e esea ch wi h a highly
eliable summe empe a u e p oxy, he bi u ca ing dend o-
clima ic signals iden i ied in he wo da a se s imply ha u-
u e esea ch should aim a a mo e ad anced unde s anding
o MXD da a on dis inc issues: (1) in luence o pas popu-
la ion densi y a ia ions on MXD p oduc ion, (2) po en ial
biases when calib a ing di e en ly p oduced MXD da a o
p oduce one p oxy eco d, (3) in luence o he biological age
o MXD da a when in oducing young ees in o he ch onol-
ogy o e he mos ecen pas and (4) possible ole o wa e -
logging in MXD p oduc ion when analysing ee- ing da a o
ipa ian ees.
1 In oduc ion
Dend och onology is one o he mos common me hods o
ob aining he la e Holocene econs uc ions o pas clima e
a iabili y because ee- ing ch onologies a e high- esolu ion
indica o s o exac ly da ed paleoclima e in o ma ion (F i s,
1976). Mo eo e , ee- ing ch onologies a ound he ex a -
opical No he n Hemisphe e con ain clea clima ic signals
o summe empe a u es (B i a e al., 2002). This dend ocli-
ma ic associa ion is no ably high o di e en ee species
g owing nea hei pola and alpine ange o dis ibu ion.
Ye he s eng h o his dend oclima ic esponse depends
on he measu ed ee- ing pa ame e . While he use o ee-
ing wid h ch onologies as indica o s o pas clima e a i-
abili y has a long adi ion in dend oclima ology, he de el-
opmen o X- ay-based es ima es o wood densi y luc ua-
ions (Schweing ube e al., 1978) has inc eased he alue
o dend och onology as an in eg al pa o paleoclima ology.
Published by Cope nicus Publica ions on behal o he Eu opean Geosciences Union.
1474 V. V. Ma sko sky and S. Helama: Tes ing summe empe a u e econs uc ion
Se e al s udies ha e shown ha he measu emen s o maxi-
mum la ewood densi ies (MXD) yield ch onologies wi h an
imp o ed clima ic signal (B i a e al., 2002). Consequen ly,
he MXD ch onologies om se e al egions a ound Eu asia
and No h Ame ica ha e been used o summe empe a u e
econs uc ions (Hughes e al., 1984; Da i e al., 2003; Luck-
man and Wilson, 2005; Bün gen e al., 2008).
Simila s udies ha e been conduc ed in no he n
Fennoscandia whe e a ew econs uc ions o summe
empe a u es (JJA) o e he Common E a ha e been based
on MXD eco ds o li ing and sub ossil pines (B i a e
al., 1988, 1990, 1992, 1996; B i a and Schweing ube ,
1992; G udd, 2008; Bün gen e al., 2011; Espe e al., 2012;
McCa oll e al., 2013; Mel in e al., 2013). While he
ea ly s udies concen a ed on ma e ials om no he nmos
Sweden, pa icula ly he To ne äsk egion (Schweing ube
e al., 1988; B i a e al., 1990, 1992, 1996; G udd, 2008),
he ee- ing ma e ials om no he n Finland (E onen e
al., 2002) ha e ecen ly been exploi ed o MXD analyses.
These ma e ials ha e no ably inc eased he a ailable MXD
sample size and empo ally ex ended he ch onology o he
egion o 138 BC (Bün gen e al., 2011; Espe e al., 2012).
In a ecen dend oclima ic analysis Mel in e al. (2013) used
upda ed and adjus ed sub ossil (Schweing ube e al., 1988)
and li ing- ee (G udd, 2008) MXD da a om To ne äsk.
A b ie li e a u e e iew exempli ies se e al inconsis en-
cies in he published palaeoclima e eco ds. While he i s
o hese econs uc ions (B i a e al., 1992) s o e o de-
ine he deg ee o he 20 h-cen u y wa m h in he con ex o
he las 1500y , he subsequen s udy (G udd, 2008) demon-
s a ed a posi i e empe a u e anomaly o abou 0.7–1.5◦C
(30y mean) o he Medie al Wa m Pe iod (MWP) ela-
i e o he 20 h-cen u y condi ions (1951–1970 mean). I
also showed a cooling phase (up o 1.1◦C nega i e anomaly
o 30y mean) o he Li le Ice Age (LIA). Howe e ,
Bün gen e al. (2011) did no ind e idence o a cool pe-
iod du ing he LIA in e al. Espe e al. (2012) s a ed ha
he p e iously es ima ed wa m h o he MWP may be no-
ably unde es ima ed. Ano he de ailed dend oclima ic anal-
ysis (Mel in e al., 2013) p esen ed MWP empe a u es a a
le el simila o he mode n ones in he egion sugges ing an
o e es ima ion o he medie al wa m h published by G udd
(2008). Mel in e al. (2013) showed ha he G udd (2008)
s udy con ained sys ema ic bias and should no be consid-
e ed sui able o use as a clima e econs uc ion. The esul s
o McCa oll e al. (2013) sugges ed ha he 20 h and 17 h
cen u ies we e wa mes and coldes in he egion, while sim-
ila ly wa m spells we e expe ienced du ing he 11 h cen u y.
While he pos -1700 inconsis encies in a pa o he MXD
da a (B i a e al., 1992; G udd, 2008) ha e been cla i ied
(Mel in e al., 2013), he wo da a se s (Mel in e al., 2013;
Espe e al., 2012) ha e no been analysed collec i ely o e-
cons uc an MXD-based long- e m empe a u e a iabili y
o e he whole o no he n Fennoscandia. This si ua ion is
e en mo e unsa is ac o y, i no wo isome, conside ing he
impo an ole o he pa icula MXD da a in se e al hemi-
sphe ic and equen ly ci ed paleoclima e econs uc ions o
he Common E a (e.g. Jones e al., 1998; Espe e al., 2002;
Osbo n and B i a, 2006; Mann e al., 2009; Ljungq is e al.,
2012).
We assume ha he clima e a iabili y wi hin he egion
is likely oo uni o m o ha e caused he epo ed de ia ions
in he published empe a u e econs uc ions om adjacen
egions o no he nmos Sweden (To ne äsk) and Finland.
Ins ead, he easons o hese de ia ions may mo e ealis i-
cally s em om he ee- ing s anda diza ion and mic oden-
si ome ic me hods, as well as non-clima ic noise inhe en
o he a ia ions in a ailable samples and hei si e cha ac-
e is ics. A p oblem associa ed wi h he dend oclima ic im-
p o emen , consis ing o he de elopmen om he adi ion
o simply egis e ing he wid hs o he ings o he mo e so-
phis ica ed MXD, is he complexi y o me hods equi ed o
p oduce he high- esolu ion wood densi y p o iles. As a pi -
all, e en ma ginal changes in he mic odensi ome y me h-
ods may p oduce signi ican ly al e ed MXD da a (Helama
e al., 2010d, 2012). T ee- ing s anda diza ion is a necessa y
p ocess whe e he ini ial measu emen se ies a e ans o med
in o dimensionless indices o emo e he biological (i.e. non-
clima ic) g ow h a ia ions p io o dend oclima ic in e p e-
a ions (F i s, 1976). Di e en s anda diza ion me hods p o-
duce ch onologies wi h de ia ing cha ac e is ics, and pa ic-
ula ly he long- e m (i.e. low- equency) es ima ion o den-
d oclima ic signals is sensi i e o he applied me hod (B i a
e al., 1992; Espe e al., 2002; Helama e al., 2004). In-
deed, he ecen eanalysis o he To ne äsk MXD da a de-
ailed a se o es ima ion biases o igina ing om changes
in he mic odensi ome y p ac ices and ee- ing s anda d-
iza ion (Mel in e al., 2013). I is essen ial o no e ha all
he discussed s udies used he same ype o s anda diza ion
me hod, he egional cu e s anda diza ion (RCS; B i a e
al., 1992), o p oduce he MXD ch onologies as a p oxy
o empe a u e econs uc ions, bu selec ed di e en op-
ions which migh explain di e ences be ween he esul -
ing ch onologies. While his pa icula me hod is capable o
p oducing ch onologies wi h p ese ed low- equency a ia-
ions (B i a e al., 1992; Espe e al., 2002; Helama e al.,
2004), i is also mo e sensi i e o da a he e ogenei y and
he e o e equi es highe sample eplica ion han o he com-
monly applied s anda diza ion me hods (B i a and Mel in,
2011). Mo eo e , ecen yea s ha e seen a di e si ica ion o
he o iginal RCS me hod, wi h de elopmen o i s signal- ee
implemen a ion (Mel in and B i a, 2008) and i s subsequen
co ec ion (Ma sko sky, 2011), as well as mul iple cu e ap-
p oaches o RCS (Helama e al., 2005b; Nicaul e al., 2010;
Mel in e al., 2013). The ecen e sions o he To ne äsk
and Fennoscandian ch onologies ha e used he RCS along
wi h i s a ia ions (Espe e al., 2012; McCa oll e al., 2013;
Mel in e al., 2013) bu so a no sys ema ic s udy exis s o
p esen he cons uc ion o he esul ing MXD ch onologies
using consis en ee- ing s anda diza ion.
Clim. Pas , 10, 1473–1487, 2014 www.clim-pas .ne /10/1473/2014/
V. V. Ma sko sky and S. Helama: Tes ing summe empe a u e econs uc ion 1475
Figu e 1. Sub ossil and li ing-pine si es loca ion o FENN and
TORN da a se s.
He e we eanalyse and compa e wo MXD da a se s om
To ne äsk (Mel in e al., 2013) and om a la ge egion o
Fennoscandia (Espe e al., 2012) using di e en s anda d-
iza ion me hods. MXD a ia ions in he da a we e iden i ied
in de ail and he same ypes o RCS me hod we e applied o
bo h da a se s. We calib a es anda dized MXD da a o ins u-
men al JJA empe a u es o he To nedalen clima e eco d lo-
ca ed in no he n Sweden and co e ing he las 200y (Kling-
bje and Mobe g, 2003). Then we con inue o econs uc e-
gional summe empe a u e in he Common E a.
2 Ma e ials and me hods
2.1 Geog aphical se ing
This s udy is based on X- ay-based mic odensi ome ic da a
o mode n and sub ossil Sco s pine (Pinus syl es is L.) ee
ings. We use published and online a chi ed MXD da a om
no he nmos Sweden (i.e. To ne äsk egion) and no he n
Fennoscandia. These da a se s a e e e ed o as TORN
(Schweing ube e al., 1988; G udd, 2008; Mel in e al.,
2013) and FENN (o iginally named N-Scan; Espe e al.,
2012).
O iginally, he collec ion o he TORN ma e ial was ca -
ied ou in i e indi idual si es a ound Lake To nes äsk
(68.17–68.33◦N, 19.75–20.75◦E; 400–470ma.s.l.; Fig. 1).
Th ee o hese locali ies p o ided sub ossil ee ings o ex-
ending he ch onology back in ime o AD 436 (Ba holin
and Ka lén, 1983; Ba holin, 1987). The MXD ch onology
o TORN was p oduced by Schweing ube e al. (1988)
and upda ed wi h mo e ecen ma e ial o li ing ees by
G udd (2008) and Mel in e al. (2013). The TORN da a now
co e he pe iod AD 441–2010 and can be downloaded ia
h p://www.c u.uea.ac.uk/c u/pape s/mel in2012holocene/.
The sub ossil FENN ma e ial o E onen e al. (2002)
o igina es om he egion o no he n Finland. A po ion
o his ma e ial, co e ing oughly he pas wo millennia
(since 138 BC) was la e used o build a new MXD ch onol-
ogy o he egion (66.80–69.50◦N, 23.00–29.00◦E; 190–
340ma.s.l.; Fig. 1). The sub ossil ma e ial was upda ed
wi h li ing- ee ma e ial om no h-wes Finnish Lapland
and no he nmos Sweden (Espe e al., 2012). In ac ual
ac , one o he li ing- ee si es included in he FENN da a
se is om he To ne äsk egion. As a esul , he mod-
e n pa o he FENN da a se is weigh ed owa ds he
wes , while he eas e n hal o egion is ep esen ed only by
sub ossil si es. Mo eo e , wo o he h ee li ing- ee si es
(67.90◦N, 20.10◦E; 68.20◦N, 19.80◦E) a e a ou side he
ne wo k o sub ossil si es. The FENN da a can be down-
loaded ia h p://www.blogs.uni-mainz.de/ b09clima ology/
iles/2012/03/Da a.pd . Fo subsequen analyses FENN da a
we e ans o med in o “mean ee” se ies, i.e. mul iple mea-
su emen s o each ee we e a e aged in o one se ies. This
was done o a oid a i icial educ ion o e o ma gins and o
b ing he wo da a se s in o co espondence.
2.2 Sampling si es
The ee- ing ma e ial o igina es om ou di e en ypes o
sampling si es: mode n samples o li ing pines ep esen ing
d y (inland) en i onmen s and lake ipa ian habi a s, sub os-
sil samples p ese ed in subae ial condi ions and sub ossils
p ese ed in lacus ine sedimen s. I is no able ha he sub-
ossil ma e ial o he TORN da a se o igina es me ely om
subae ial condi ions (Ba holin and Ka lén, 1983; Schwein-
g ube e al., 1988). In o he wo ds, he e is no sub ossil
ma e ial om lacus ine sedimen s included in he Swedish
MXD da a (G udd, 2008). On he o he hand, he FENN
assemblage consis s o sub ossil samples collec ed a lakes
only (E onen e al., 2002). The mode n pa o FENN MXD
da a ( om li ing ees) was p oduced by using ee- ing sam-
ples om only lake ipa ian si es (Espe e al., 2012).Thus,
he p incipal di e ence be ween he TORN and FENN da a
se s s ems om he s udied habi a : he TORN da a include
d y si es whe eas he FENN da a a e ep esen ed by lake
sho e en i onmen s.
2.3 Mic odensi ome y
X- ay-based mic odensi ome y p oduces adial wood den-
si y p o iles o each ee- ing sample. Each ing exhibi s an
annualdensi y cyclewhe e he woodo low densi yis o med
du ing he ea ly g owing season (i.e. ea lywood), wi h in-
c easingly high densi ies owa ds he la e summe and au-
umn (i.e. la ewood). The in a-annual poin whe e he den-
si y eaches i s highes alue is aken as he maximum densi y
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1476 V. V. Ma sko sky and S. Helama: Tes ing summe empe a u e econs uc ion
(MXD) o ha ing. The consecu i e MXD alues o each
sample ep esen he indi idual MXD se ies. These se ies
a e o special in e es in dend oclima ology because o hei
s ong co ela ions wi h g owing season empe a u es as ob-
se ed b oadly ac oss he ci cumpola bo eal o es s oday
(B i a e al., 2002).
Commonly, li ing ees a e co ed a b eas heigh , and
he inc emen co es exposed o mic odensi ome ic analy-
ses. Sub ossil pinewood ma e ial can ei he be ound lying
on d y g ound o p ese ed in he sedimen o small lakes.
In he ield, he unea hed logs a e sawn in o disks. Subse-
quen ly, in he wo kshop, adial la hs a e sawn pe pendicula
o he ing bounda ies o be analysed using mic odensi ome-
y. I is impo an o no e ha e en sligh di e ences in he
labo a o y p o ocol du ing he X- ay p ocess may p o oundly
al e he esul ing MXD da a (G udd, 2008; Helama e al.,
2010d, 2012). MXD da a may become al e ed depending on
he me hods ha a e used o emo e he wood ex ac i es (o -
ganic, non-cell-wall componen s) p io o analyses (Helama
e al., 2010d), he wood mois u e con en du ing he mea-
su emen (Helama e al., 2012) and he adial s ep size o he
densi y scanning (G udd, 2008; Helama e al., 2012).
The wo MXD da a se s analysed he e (TORN and FENN)
we e p oduced using di e en X- ay me hods and da a analy-
sis. The TORN da a se consis s o da a p oduced in di e en
decades and labo a o ies (G udd, 2008; Mel in e al., 2013).
I has been shown o TORN da a ha he old MXD alues
(Schweing ube e al., 1988) exhibi lowe s anda d de ia ion
o densi y a iabili y han he MXD alues p oduced using
he e ol ed echnical p ope y o he X- ay scanne (G udd,
2008). In o de o deal wi h his bias, G udd (2008) educed
he a iance in new MXD da a o ma ch wi h he old a i-
ance. Mo e ecen ly, Mel in e al. (2013) added mo e da a o
he TORN da a se . These da a we e p oduced in a di e en
labo a o y. Compa isons wi h he di e en ly p oduced MXD
da a showed a need o addi ional adjus men s o mean and
s anda d de ia ion o he da a because o he di e en labo a-
o y p o ocols (Mel in e al., 2013). In his s udy, we a e us-
ing hese adjus ed TORN da a (S88G1112A.mxd da a om
h p://www.c u.uea.ac.uk/c u/pape s/mel in2012holocene/).
2.4 S anda diza ion me hods
2.4.1 Regional cu e s anda diza ion
Ou analyses a e based on egional cu e s anda diza ion
(RCS) (B i a e al., 1992, 1996; B i a and Mel in, 2011)
wi h he signal- ee implemen a ion (Mel in and B i a,
2008; B i a and Mel in, 2011) and RCS wi h a p oposed
co ec ion (Ma sko sky, 2011). In he o iginal RCS ech-
nique p esen ed by B i a e al. (1992), he same s anda d-
iza ion cu e is used o de end each se ies o ee- ing mea-
su emen s. The s anda diza ion cu e is assumed o display
egionally ep esen a i e cambial ( ha is, biological and hus
non-clima ic) ends in he o al ee- ing a iabili y (B i a
e al., 1992, 1996). The e o e, his end can be de i ed as a
single mean cu e o he da a aligned acco ding o hei cam-
bial ages. The p ocess o a e aging he se ies e eals ee-
ing a ia ions ela ed o ageing and he expec ed age- ela ed
componen can be de ec ed as he mean cu e. As is ypical
o he con en ional RCS me hod, his cu e is assumed o be
no a ec ed by clima e. Subsequen o a e aging, he mean
cu e is commonly smoo hed o educe he e ec o an-
dom luc ua ions. Time- a ying esponse smoo hing (TVRS;
Mel in e al., 2007) wi h he ou ine o Mel in e al. (2007;
see hei Appendix A) was used whe e SSY (spline s i ness
o each yea ) equalled he cambial age in yea s plus 15y .
We used a cubic spline wi h 50% a iance cu -o (Cook and
Pe e s, 1981) on he equency pe iod o SSY yea s. Using
his me hod, he RCS is ca ied ou wi h a single egional
cu e ( e e ed he ea e as RC1) o s anda dize all ee- ing
se ies and he ee- ing indices a e de i ed as a ios be ween
he obse ed ee- ing alue and he alue expec ed by he
RC1. This p ocess is expec ed o emo e a la ge po ion o
age- ela ed a ia ions p esen ed in he ini ial se ies o mea-
su emen s. Pa s o each ee- ing se ies con ibu ing o he
egional cu e o e he weakly eplica ed old cambial ages
(wi h eplica ion less han 10) we e emo ed be o e using
he RCS me hod.
2.4.2 Signal- ee app oach
The con en ional RCS me hod can be combined wi h he
signal- ee (SF) app oach ( hus, RC1SF) as sugges ed by
B i a and Mel in (2011) and as al eady applied in se e al
s udies (Helama e al. 2010b; Bjö klund e al., 2013; Mel in
e al., 2013; Coope e al., 2013; Wilson e al., 2013). In con-
as wi h con en ional RCS, his me hod assumes ha he
es ima e o he s anda diza ion cu e as jus an a e age o all
a ailable se ies is biased by clima e because he ini ial ee-
ing se ies hemsel es con ain a signi ican clima ic compo-
nen . The eby he mean cu e may e ain a la ge p opo ion
o clima ic in luence, which becomes e ec i ely emo ed
om ee- ing indices because he g ow h componen ep-
esen ed by he cu e is emo ed om he ini ial se ies. As
an al e na i e, a mo e non-clima ic mean cu e could be p o-
duced om signal- ee measu emen s whose clima ic signal
is emo ed p io o es ima ion o he s anda diza ion cu e.
Following Mel in and B i a (2008), he emo al o he cli-
ma ic a ia ions is done h ough a p ocess whe e he ini ial
ee- ing measu emen s, aligned by hei calenda yea s, a e
i s di ided by he index alues o he con en ional RCS
ch onology. The esul ing SF measu emen s a e a e aged,
aligned by hei cambial yea s, ollowing he ypical RC1
p ocedu e (see abo e). The new mean cu e is hen emo ed
om he ini ial ee- ing measu emen s o p oduce SF indices
and a new (RC1SF) ch onology. The p ocess is epea ed un-
il no imp o emen in ch onology es ima ion is achie ed (see
Mel in and B i a, 2008, 2013 o de ails).
Clim. Pas , 10, 1473–1487, 2014 www.clim-pas .ne /10/1473/2014/
V. V. Ma sko sky and S. Helama: Tes ing summe empe a u e econs uc ion 1477
2.4.3 Co ec ion p ocedu e
An imp o emen o he ch onology es ima ion, subsequen
o RCS and SF me hods, was p e iously a ained by applying
a co ec ion (C) me hod ( hus, RC1SFC; Ma sko sky, 2011).
This me hod, RC1SFC, is a no el applica ion o he RCS and
SF me hods, ailo ed o de ec ion o a pu e low- equency
signal in ee- ing ch onologies. The e o in RC1SF ch onol-
ogy is assessed and subsequen ly ex ac ed om he da a in
o de o p oduce an RC1SFC ch onology.
Fo ou pu poses ee g ow h can be hough o as a
p oduc o clima ic and non-clima ic componen s. When
a e aging non-clima ic componen s om di e en samples
( ees) we ge non-clima ic componen s in he ch onology.
These ypes o ch onology a ia ions o igina e om he non-
uni o m dis ibu ion o indi idual se ies in ime and uncom-
mon indi idual ee g ow h peculia i ies and depend on he
da a se p ope ies; hus he e o associa ed wi h hese a i-
a ions is deno ed as “da a se e o ”. In p ac ice i is di icul
o ob ain an ideal da a se wi hou such inhomogenei ies. SF
and “co ec ion” a e used o emo e his non-clima ic com-
ponen om he ch onology, ocusing on di e en equen-
cies. SF deals only wi h high equencies. “Co ec ion” is
designed o deal wi h lowe equencies. The co ec ion p o-
cedu e consis s o h ee s eps: (1) building a ch onology om
smoo hed SF measu emen s (o SF cu es – ini ial se ies
o measu emen s wi hou clima ic signal and high- equency
a ia ions): his ch onology ep esen s he da a se e o ; and
(2) sub ac ing his e o om he ini ial ch onology, hus
co ec ing i . See he de ailed algo i hm o he co ec ion p o-
cedu e in he Supplemen .
2.4.4 Mul iple-RCS me hod
Ou ou h ype o s anda diza ion me hod u ilizes mul i-
ple RCS cu es (ins ead o a single cu e used in he RC1,
RC1SF and RC1SFC me hods) o emo e he non-clima ic
a ia ions (B i a and Mel in, 2011; Mel in e al., 2013).
Following he p e ious sugges ions (Mel in e al., 2013), we
used wo egional cu es ha we e buil using he SF ou ine
( hus, RC2SF) and RC2SF wi h Ma sko sky’s (2011) co ec-
ion ( hus, RC2SFC). The p ocess o de ining he mul iple
RCS cu es began wi h calcula ing he mean o SF measu e-
men s o he cambial ages 1–100y o each ee. These al-
ues we e di ided by he mean o he i s 100y o a single
RC1SF cu e (c ea ed using all ees) o yield ela i e g ow h
a e (sensu B i a and Mel in, 2011) o MXD p oduc ion
o each ee. All ees we e a anged by his ela i e g ow h
a e and he ull se o ees was acco dingly di ided in o wo
equally la ge g oups (in p ac ice, one g oup was la ge by
one ee i he o al numbe o se ies in ha ch onology was
odd). The egional cu e was p oduced o each g oup o de-
ending each MXD se ies in he co esponding g oup. He e
again we unca ed all he se ies o ee- ing measu emen s o
achie e eplica ion o a leas 10 samples o e e y egional
cu e alue and TVRS spline was used o smoo hing o e-
gional cu e. Compa isons be ween he ch onologies we e
ca ied ou only o he pa s o ch onologies wi h eplica-
ion o a leas six se ies. The e o e, he common pe iod was
limi ed by eplica ion o TORN da a se and was se o AD
542–2006.
2.5 Design o expe imen s
Fi e ypes o s anda diza ion me hods we e used o com-
pa ison unde he assump ions ha TORN and FENN da a
se s a e p oxies o mean summe empe a u e (JJA) and ha
empe a u e is spa ially homogenous o he whole egion.
Co ela ion be ween he JJA empe a u es (AD 1959–2007)
as obse ed a Abisko and Sodankylä me eo ological s a ions
is 0.83. Unde hese assump ions, imp o ed co ela ion be-
ween any pai o di e en ly s anda dized TORN and FENN
ch onologies demons a es a highe common (i.e. empe a-
u e) signal.
We compa ed i e ypes o ch onologies (RCS, RC1SF,
RC1SFC, RC2SF and RC2SFC) o TORN and FENN da a
se s and also used low-pass il e ed ch onologies wi h N-yea
smoo hing splines (Cook and Pe e s, 1981) o ocus on low-
equency signals (N=50,100,200 and 300y ). De ailed
compa ison o low- equency signals be ween he TORN
and FENN da a se s was ca ied ou using hei RC2SFC
ch onologies. We also used subsampled FENN da a because
o hei highe eplica ion. Subsampling was supposed o
highligh any di e ence a ising in he FENN da a se when
a i icially educed o he sample dep h o he TORN da a se .
Fo de ails o he subsampling algo i hm see he Supplemen .
2.6 Tempe a u e econs uc ion me hods
While he FENN da a se bene i s om i s g ea e sample
size and eplica ion o e he common pe iod (since ca. AD
700), he bene i s o TORN da a lie in hei homogenei y and
hei s onge co ela ion o empe a u e. Bo h ma e ials ha e
hei bene i s and ollowing hei high o e all co ela i i y, i
was jus i iable o combine he da a in o an enhanced MXD-
based paleoclima e econs uc ion. The use o a combined
da a se could be seen o bene i om se e al o he ci cum-
s ances (see McCa oll e al., 2013). Including a highe num-
be o si es p oduces a mean se ies ha is s onge and yields
an unce ain y es ima e ha inco po a es he in o ma ion o
changes in bo h da a se s o e ime. This app oach also e-
duces he e ec s o ecological o cul u al (i.e. non-clima ic)
dis u bance e en s in he ch onology. Combining he da a
om si es o e a la ge a ea also p oduces a econs uc ion
ha is ep esen a i e o he clima e o he ex ended a ea (Mc-
Ca oll e al., 2013). The empe a u e econs uc ion was p o-
duced om a combina ion o TORN and FENN da a se s
(called FULL da a se ). The FULL da a se includes 430 se-
ies and co e s he pe iod 216 BC–AD 2010 (8 BC–AD 2010
wi h eplica ion o mo e han i e se ies). The combined
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1478 V. V. Ma sko sky and S. Helama: Tes ing summe empe a u e econs uc ion
da a se has exp essed popula ion signal (EPS; Wigley e
al., 1984) alues consis en ly la ge han 0.85 a e AD 535,
mo e han o he TORN and FENN da a se s indi idually.
We used AD 1802–2010 as he common pe iod o compa -
isons be ween he MXD p oxy and ins umen al da a (Kling-
bje and Mobe g, 2003). I is no able ha he ins umen al
eco d used he e was co ec ed o inhomogenei ies (Klingb-
je and Mobe g, 2003, as ci ed in he ex ). Mo eo e , a ecen
s udy (Helama e al., 2013) did no show inc easing inhomo-
genei ies in he 19 h-cen u y pa o his eco d, in compa i-
son o he 20 h-cen u y pa . The da a o he yea AD 1815
(wi h missing ins umen al da a) we e excluded om all he
dend oclima ic compa isons. The common pe iod o ins u-
men al and MXD da a was di ided in o wo pe iods (AD
1802–1905 and AD 1906–2010) o be used as calib a ion
and e i ica ion pe iods and ice e sa o p oducing a JJA
empe a u e econs uc ion om he FULL-RC2SFC MXD
ch onology. We used he ollowing commonly used s a is-
ics o assess he quali y o he econs uc ion: Pea son co -
ela ion coe icien ( ), coe icien o de e mina ion (R2), e-
duc ion o e o (RE), coe icien o e iciency (CE) and oo
mean squa e e o (RMSE) (Cook e al., 1994). The s a is ics
o R2, and RMSE we e calcula ed o calib a ion, e i ica-
ion and common (1802–2010) pe iod wi h ins umen al da a
(no e ha CE is ac ually R2 o e i ica ion pe iod).
MXD-based JJA empe a u es we e econs uc ed using
non-smoo hed and smoo hed a iance adjus men and linea
eg ession me hods (Lee e al., 2007, de ails in he Supple-
men ).
2.7 Unce ain y es ima es o he econs uc ion
The unce ain ies o he econs uc ion a ising om h ee in-
dependen sou ces we e es ima ed as ollows:
1. The unce ain y o eplica ion by he egional cu e
(RC): his ype o unce ain y a ises om he RC
eplica ion unce ain y ha gene ally inc eases owa ds
highe cambial ages. This unce ain y will a ec he un-
ce ain y o e e y MXD index, depending on i s cambial
age. Since we used wo RCs, his ype o unce ain y is
also dependan on he RCs we used and hence on he
mean MXD o he i s 100y .
2. The unce ain y o eplica ion by he mean ch onology:
his unce ain y p o ides he con idence in e al o he
a e age o all MXD indices o each calenda yea ( ak-
ing in o accoun he unce ain y 1)
3. The unce ain y om calib a ion: he unce ain y ac-
coun s o he unce ain y o mean and a iance (as we
use mean and a iance adjus men econs uc ion ech-
nique) in he calib a ion pe iod ( aking in o accoun un-
ce ain ies 1 and 2).
As he h ee ypes o unce ain iesa e assumed obe indepen-
den , he unce ain y ha a ises om each sou ce can be de-
Figu e 2. Sample eplica ion o FENN and TORN ull da a se s,
dense and less dense coho s ( ees wi h highe and lowe a e age
MXD alues o he i s 100y ) (a) and a ios be ween eplica ions
o dense and less dense coho s o TORN and FENN da a se s (b).
i ed by sub ac ing p e ious unce ain ies on he same con i-
dence le el. Fo his eason, he esul s in Fig. 7 show ela i e
alues o all he h ee unce ain ies. Fo de ails o unce ain y
es ima ion, see he Supplemen .
3 Resul s
3.1 Sample size eplica ion
The FENN da a se con ains 1.5–3 imes mo e samples han
he TORN da a se h ough mos o he common pe iod
(Fig. 2a). The eplica ion o TORN ch onology emains be-
low 20 samples o e he sub ossil pe iod. The sample size
a ia ion o e he pas 200y is explained by he high numbe
o co e samples om li ing ees du ing his pe iod. O e he
20 h cen u y, he absolu e inc ease o young pines is highe
o FENN da a in compa ison o TORN da a (Fig. 2a).
TORN and FENN ull sample se s we e spli in o ees
wi h dense (“ ees wi h good g ow h”) and less dense (“ ees
wi h poo g ow h”) MXD alues. The e seem o be almos
equal amoun s o ees g owing well and poo ly g owing
ees h oughou he s udy pe iod (Fig. 2). The isual inspec-
ion shows ha he a ios be ween he numbe o dense and
less dense ee samples do no co ela e in he FENN and
TORN da a se s ( =0.08; Fig. 2b). Since he da a se s o igi-
na e om nea by egions, he desc ibed asynch ony indica es
ha he examined g ow h componen ( ela i e g ow h a e)
is no ela ed o low- equency clima e a iabili y. The e o e
we assume ha his inding suppo s he use o mul iple RCS
ha will emo e his g ow h componen om he esul ing
ch onology.
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V. V. Ma sko sky and S. Helama: Tes ing summe empe a u e econs uc ion 1479
Figu e 3. Regional cu es (a) and ch onologies (b) o TORN,
FENN and FULL da a se s and di e en ypes o s anda diza ion.
All he ch onologies a e smoo hed wi h 100y splines. Va iance and
mean s anda dized o he pe iod AD 1802–2006, 15y smoo hed
da a a e used o a iance adjus men . S88G1112A (Mel in e al.,
2013) and N-SCAN (Espe e al., 2012) a e o iginal ch onologies
o he TORN and FENN da a se s, espec i ely.
3.2 MXD ch onologies
Subsequen ly, he ini ial MXD alues we e ans o med in o
RC1, RC1SF, RC1SFC, RS2SF and RS2SFC indices us-
ing he co esponding egional cu es (Fig. 3a) and a -
e aged in o a co esponding se o mean MXD ch onolo-
gies (Fig. 3b). The co ela ions be ween he di e en ly s an-
da dized ch onologies decline owa ds lowe equencies o
g ow h a iabili y (Supplemen Table S1). On a e age, he
non-smoo hed ch onologies ag ee wi h a mean co ela ion
coe icien o =0.66, whe eas he 50y , 100y , 200y and
300y smoo hing esul s in mean co ela ion coe icien s o
=0.54, =0.49, =0.46 and =0.49, espec i ely. The
obse ed endency o lowe co ela i i y a lowe equencies
indica es he inc easing unce ain ies in es ima ing pa icu-
la ly he long- e m empe a u e a ia ions by MXD p oxy
da a.
In a iably, he highes co ela ions be ween he ch onolo-
gies o he same s anda diza ion me hod we e hose ob-
ained by RC1SFC p ocedu e (Supplemen Table S1), ha
is, using a single egional cu e bo h wi h signal- ee and
Ma sko sky’s (2011) co ec ion implemen a ions. This e-
sul becomes e en mo e ob ious o co ela ions calcu-
la ed a lowes equencies (Supplemen Table S1). I be-
comes e iden ha he applied Ma sko sky’s (2011) co ec-
ion (C) subsequen o SF implemen a ion imp o es he ac-
ual SF es ima ion, and in pa icula he es ima ion o he
low- equency ee- ing a ia ions, as al eady sugges ed in
he o iginal me hodological s udy (Ma sko sky, 2011). Ap-
plying mul iple-RCS echnique (RC2SF and RC2SFC) p o-
duces an imp o emen in FENN ch onologies, bu no in
TORN ch onologies. This may be, a leas in pa , owing o
a smalle sample size o he TORN da a se ha may no be
su icien o obus es ima ion o mul iple RCs. This may be
he eason o highes co ela ions ob ained be ween TORN-
RC1SFC and FENN-RC2SFC on a ying imescales (Sup-
plemen Table S1).
Di e en ly p oduced FENN and TORN ch onologies
show consis en bu also bi u ca ing dend oclima ic signals
(Fig. 3b). Apa om many common ea u es wi h syn-
ch onously amelio a ed and de e io a ed g ow h pe iods, i
is ound ha he FENN ch onologies exhibi no ably highe
g ow h p io o AD 900 and du ing he 17 h cen u y. Rega d-
less o he s anda diza ion me hod, he TORN ch onologies
indica e highe g ow h du ing he ecen decades and a end
inc easing owa ds he p esen day (Fig. 3b).
Since he TORN da a se is cha ac e ized by lowe sample
eplica ion h ough he common pe iod (Fig. 2a), an expe -
imen was pe o med o es whe he he obse ed g ow h
bi u ca ions (Fig. 3b) could be explained by his p ope y.
The FENN da a se was andomly subsampled o mimic he
TORN eplica ion (Fig. 4a). We ound ha he di e ence in
sample eplica ion be ween he wo da a se s was no likely
a eason o he de ia ing MXD luc ua ions in FENN and
TORN o he abo e-men ioned pe iods (Fig. 4b).
The low- equency luc ua ions could be de ailed in he
con ex o oscilla o y modes domina ing he mul i-decadal
o cen ennial MXD a ia ions o FENN and TORN da a
(Fig. 5). Bo h ch onologies showed nea ly iden ical 54–56y
and 67–70y pe iodici ies, as well as p ecisely iden ical 113
and 133 pe iodici ies. Howe e , he TORN ch onology was
also cha ac e ized by he 33y , 244y and 488y pe iodici-
ies, whe eas he FENN ch onology exhibi ed an addi ional
sub-cen ennial oscilla ion o 86y pe iodici y (Fig. 5).
3.3 Clima e-p oxy compa isons
Compa isons be ween he ch onologies and ins umen al cli-
ma e eco ds demons a e ha bo h ch onologies co ela e
wi h summe empe a u es wi h a ange o coe icien s =
0.76−0.79 (Table S2). A low equencies, howe e , he co -
ela ions a e highe when using TORN ch onologies han
wi h FENN ch onologies ( =0.95 and =0.84, espec-
i ely). This is no an issue o s anda diza ion me hod since
he dend oclima ic co ela ions a e in a iably highe in he
case o TORN, ega dless o he me hod used (Table S2).
Ra he , he FENN ch onologies show wa ming du ing he
pe iod 1802–1815 when he TORN and ins umen al da a
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1480 V. V. Ma sko sky and S. Helama: Tes ing summe empe a u e econs uc ion
Figu e 4. Replica ion o TORN, FENN and subsampled FENN da a
se s (a) and compa ison o RC2SFC ch onologies o di e en da a
se s (b). Red shading shows he a ea be ween 2.5 h and 97.5 h pe -
cen iles o FENN subsampled da a se s. Ve ical ed line shows
h eshold o well- eplica ed da a se s (mo e han i e se ies). All
se ies smoo hed wi h 100y splines. Va iance and mean s anda d-
ized o he pe iod AD 1802–2006; 15y smoo hed da a a e used o
a iance adjus men .
indica e cooling (Fig. 6). Mo eo e , he FENN ch onologies
unde es ima e empe a u e a ound 1900 and since he 1950s.
In addi ion, no malized FENN ch onologies show in la ed
alues ela i e o TORN and ins umen al eco d z-sco es
du ing he ea ly-20 h-cen u y wa ming ha occu ed in he
egion in he cou se o he 1920s and 1930s (Fig. 6).
The FULL ch onologies’ co ela ions wi h ins umen al
empe a u es each 0.8 a e mul iple RCs and signal- ee im-
plemen a ion (Table S2). He e, he FULL-RC2SFC ch onol-
ogy was used o econs uc ing he JJA empe a u e because
successi e implemen a ion o mul iple RCS and signal- ee
and Ma sko sky’s (2011) co ec ion ou ines leads o e-
mo al o high- and low- equency non-clima ic signals om
ee- ing ch onology (Sec . 2.4) and because i was indica ed
(Sec . 3.2, Supplemen Table S1) ha co ec ion p ocedu e
imp o es p oxy quali y on longe imescales.
3.4 Summe empe a u e econs uc ion
Ou new empe a u e econs uc ion is shown wi h h ee sep-
a a e ypes o unce ain ies since 216 BC (Fig. 7). EPS is usu-
ally used as a heo e ical limi o ex ension o econs uc ion
Figu e 5. TORN-RC1SFC (a) and FENN-RC2SFC (b) spec um.
Red line shows powe spec um o ed noise wi h lag 1 au oco ela-
ion es ima ed om he se ies. Pe iod: AD 542–2006.
in o he pas . Fo he FULL da a se EPS is consis en ly la ge
han0.85 only a e AD 535. We don’ es ic ou econs uc-
ion o his yea because he unce ain y es ima es p o ided
could be used o he same pu pose mo e easonably. Clea ly,
he unce ain ies a ising om MXD da a a e conside ably
na owe han he clima e-p oxy calib a ion unce ain y (un-
ce ain y 3), especially o e he pas hi een cen u ies. O e
he ea lie imes, he unce ain ies o he MXD da a in-
c ease, consis en ly wi h he dec ease in he sample eplica-
ion (Fig. 2a). A low equencies, he Common E a o he e-
cons uc ion is go e ned by he wa m clima ic phases culmi-
na ing in he 10 h and 20 h cen u ies. The peak empe a u es
du ing hese pe iods a e compa able wi h each o he , whe eas
he wa m h o he 1s cen u y BC shows sligh ly highe em-
pe a u es. Ne e heless, he empo al leng h o he medie al
wa m h om he 8 h o 11 h cen u ies o e shadows he o he
wa m pe iods. The cooles clima ic phases p e ailed du ing
he 6 h and 7 h, as well as he 13 h h ough 19 h cen u ies,
he la e o e lapping wi h he iming o he Li le Ice Age.
The wa mes and cooles 30y pe iods occu ed AD 27–56
and AD 536–565, espec i ely, when JJA empe a u es a e -
aged 15 and 12.8 ◦C, ansla ing in o maximal mul i-decadal
empe a u e ampli ude o 2.2◦C. The econs uc ion exhibi s
pe iodic oscilla ions on dis inc ly mul i-decadal (55 o 66y ),
cen ennial (86 o 128y ), mul i-cen ennial (171 o 513y )
and millennial (1027y ) imescales (Fig. 8).
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V. V. Ma sko sky and S. Helama: Tes ing summe empe a u e econs uc ion 1481
Figu e 6. TORN, FENN and FULL ch onologies wi h To nedalen
JJA empe a u es (a) and esiduals o he ch onologies om
To nedalen JJA empe a u es (b). Va iance and mean adjus ed o
AD 1802–2006 using 15y smoo hed da a. All he da a smoo hed
wi h 50y splines. S88G1112A (Mel in e al., 2013) and N-SCAN
(Espe e al., 2012) a e o iginal ch onologies o he TORN and
FENN da a se s, espec i ely.
4 Discussion
4.1 Compa ison o da a se s
Focusing on low- equency luc ua ions, he TORN (Schwe-
ing ube e al., 1988; G udd, 2008; Mel in e al., 2013) and
FENN (Espe e al., 2012) da a se s show se e al common
anomalies o synch onously high and low MXD alues, as
well as se e al common pe iodici ies. Despi e high co ela-
ion wi h summe empe a u es and o e lapping p o enance
o he o iginal ee- ing ma e ial, he MXD da a do no show
ully consis en g ow h a ia ions h oughou he s udy pe-
iod. The mos ob ious pe iods wi h he bi u ca ing dend o-
clima ic luc ua ions occu ed in he 7 h, 9 h, 17 h and 20 h
cen u ies (Fig. 3b). Ye , he esul s om spec al analysis in-
dica e dispa a e dend oclima ic signals in he o m o sig-
ni ican oscilla o y modes (Fig. 5). I is easonable o a gue
ha hese dissocia ions likely ep esen MXD a ia ions no
closely ela ed o he egional clima ic signal. The e o e, be-
o e in e p e ing he ob ained paleoclima e in o ma ion on
he summe empe a u es, i may be use ul o discuss a.
Samples o he wo ch onologies o igina e om adjacen
and pa ially o e lapping geog aphical se ings in no he n
Fennoscandia and we sugges ha esul s showing di e ging
MXD luc ua ions be ween he ch onologies a e no d i en
by spa ial anomalies in egional clima e. Indeed, one con-
lic ing esul was iden i ied o he la e 20 h cen u y when
bo h da a se s con ain ee- ing ma e ials om li ing ees
o he same (To ne äsk) egion and hus o he pe iod o
supposedly enhanced homogenei y o p o enance. Ins ead o
clima e, he e a e six likely sou ces o he e ogenei y: (i) da a
quan i y, (ii) biogeog aphical di e ences in sou ce ma e ials,
(iii) a ying mic odensi ome ic and (i ) ee- ing s anda d-
iza ion me hods, ( ) cambial age s uc u e o he ch onology
and ( i) habi a o ipa ian and inland pines.
4.1.1 Da a quan i y
Da a quan i y is a ac o ha dis inc ly di ides he o igi-
nal ee- ing ma e ials acco ding o ch onologies wi h high
(FENN) and low (TORN) eplica ions (Fig. 2a). The sample
eplica ion and he law o la ge numbe s should no be o e -
looked in he cou se o any dend och onological p ocedu e
(F i s and Swe nam, 1989). Mo eo e , i may be gene ally
com o able o ely on massi e sample eplica ion in den-
d och onology (Bün gen e al., 2012). E en so, an inc easing
sample eplica ion may no necessa ily emo e he sys em-
a ic e ec s i p esen in he da a. Subsampling o he mo e
deeply eplica ed da a se (FENN) e ealed, howe e , ha he
di e ging MXD luc ua ions could no be ep oduced by an-
domly educing he quan i y o ha da a se (Fig. 4b). Thus,
we a gue ha he da a quan i y may no be a p ima y ac-
o p oducing he di e ences as obse ed be ween he TORN
and FENN ch onologies.
4.1.2 Biogeog aphical aspec s
The p ima y di e ence be ween he TORN and FENN
da a se s s ems om hei spa ial cha ac e is ics (Fig. 1).
While he TORN was collec ed om a es ic ed locali y
o To ne äsk in no he nmos Sweden (Ba holin and Ka -
lén, 1983; Schweing ube e al., 1988; G udd, 2008), he
sub ossil sampling si es o FENN a e sp ead o e no h-
e n Finnish Lapland (E onen e al., 2002). Two o he h ee
mode n FENN si es a e loca ed in no he n Sweden, in-
cluding To ne äsk (Espe e al., 2012). Despi e his p ox-
imi y o he mode n sampling si es in he wo collec ions,
he wo ch onologies in ac di e ged in iguingly a e AD
1950 wi h no ably highe g ow h obse ed o he TORN
ch onologies (Fig. 6). Since he ee- ing ma e ial o FENN
and TORN o his pe iod comes om neighbou ing si es,
i canno be he biogeog aphical aspec s which play a c u-
cial ole in he obse ed di e gence. I is in e es ing, how-
e e , ha he p eceding pe iods o di e gence (du ing he
7 h, 9 h and 17 h cen u ies) showed an opposed misma ch (in
espec o he 20 h cen u y) whe e he FENN ch onologies
come wi h highe g ow h. In a biogeog aphical con ex , he
MXD may no be insensi i e o s and densi y a ia ions, as
shown by hinning expe imen s. These s udies indica e ha
www.clim-pas .ne /10/1473/2014/ Clim. Pas , 10, 1473–1487, 2014
