Reprint from:
B. Frenzel (ed.) l99l: Klimageschichtliche Probleme der letzten 130 000 Jahre' 451 pp. G. Fischer, Stuttg"tt] New York. (Paleoklimaforschung Volume l)'
The Scandinavian Ice Sheet through the last interglacial/ glacial cYcle
J,c,N MlNcE,nuo
Abstract
After the Last Interglacial (the Eemian) the Scandinavian Ice Sheet started to grow slightly later than the ice sheets in Antarctica and/or North America. A major ice sheet developed during isotope stage 5d (around I l0 000 before present) but melted away during isotope stage 5c (the Brorup interstadial). Another ice sheet formed during isotope stage 5b (around 90 000 B'P') and disappeared during stage 5a (the Odderade interstadial). Apparently the last ice sheet started to grow around the isotope stage 5/4 transition (75 000 B.P.) and the central areas of Scandinavia were not deglaciated until around 9000 B.P. However, the coastal areas were ice- free several times between 75 000 and 30 000 8.P., and the final expansion towards the Late Weichselian maximum did not take place until after 28 000 B'P'
Kurzfassungr
Das skandinavische Inlandeis begann etwas spdter nach dem Ende des Letzten Interglazials (Eemian) anzuwachsen als das Eis in der Antarktis und/oder von Nordamerika' Eine groBere Inlandeisdecke entstand wdhrend des r8O-Isotopenstadiums 5d [gegen 110 000 vor heute (v.h.)1, schmolz aber wdhrend des Isotopenstadiums 5c (Brorup-Interstadial) wieder ab. Ein weiteres Inlandeis bildete sich wihrend des lsotopenstadiums 5b (gegen 90 000 v'h') und ver- schwand erneut im Isotopenstadium 5a (Odderade-Interstadial). Das letzte Inlandeis begann of- fenbar, sich an der Grenze zwischen dem Isotopenstadium 5 und 4 zu entwickeln (vor 75Ofi) Jahren). und das Zentrum Skandinaviens blieb bis etwa 9000 v. h. eisbedeckt. Demgegeniiber warenaberdieKiistengebietemehrfachzwischenT5 000und30 000v.h.eisfrei,unddasletzte Anwachsen des Eises zum maximalen Stand wdhrend der Jiingeren Weichselzeit erfolgte erst nach 28 000 v.h.
Introduction
The most dramatic expression of climatic changes caused by the small perturbations o[ the Earth's orbit (often called Mrr-eNKovtrcH forcing) are the mid-latitude ice sheets (Bancen et al., 1984). Global ice volumes, as monitored by the ocean oxygen isotope composition, have also been one of the most important parameters in the palaeoclimatic modelling on MrL,r,NxovrrcH wave lengths. However, to unravel the history of each individual ice sheet.
even for the last interglacial/glacial cycle, is an extremely difficult task because the ice during I Ubersetzung: B. FneNzPI-
308 . le,n Mexcenuo
llrc llrst ttlaxitttuttt t'ctttttvctl ttttlst ol'llrc scdinrcntary rcc.rd f'rr)rrr oldcr cvcnts. l.htrs a rrr^ j'r pr.- blem is simply to find sediments within the glaciated areas that survived the subsequent erosion.
still' to reconstruct the history of each ice sheet must be attempted, at least for the last in- terglacial/glacial cycle, if we try to understand how the Earth's climatic system responds to or_
bital forcing' The glacial history provides a fascinating challenge for scientists who are willing to search for an answer where no results are guaranteed.
To construct the history of an ice sheet is like nraking a three or four dinrensional puzzle. Most pieces (sedimentary sequences) will fill in only a short segment of the time dimension in the
\ 60"
, ' 1
I j
I t)
I
/ " ,
24.
*'---/-
^r.,,",1",r",.
"'it----
t
\
\ _
weichselian names used in the text are marked. srightry modified after sveNosnN & MeNcnnuoand Younger Dryas ice margins of the Scandinavian Ice Sheet. Localities Fig. l: The Late
and geographical ( r 9 8 7 ) .
The Scandinavian Ice Sheet through the last interglacial/glacial cycle . 309
puzzle, just a point in the areal dimensions, and normally provide no information on the ice thickness dimension (volume). In the puzzle I am constructing in this paper, most pieces are floating in this three/four dimensional space without touching each other, leaving large uncer- tainties both in time correlations and in areal/volume extent of the ice at different times. Still the model represents a major improvement compared to what we knew some few years ago.
Paradoxically most of the important pieces are not glacial sediments, but non-glacial sediments indicating when a site was ice-free.
In this paper I reconstruct the Scandinavian Ice Sheet through the last interglacial/glacial cycle, based on available geological observations. The information is still so sparse that I only con- struct a simplified model with time as the one dimension, and linear ice-extent (instead of arealvolume) as the other (Fig. 5). I will emphasize when the proximal areas were ice-free, and not discuss the timing of the Late Weichselian in the peripheral areas. I will also discuss the Ear- ly Weichselian (isotope stage 5) more thoroughly than the younger part of the cycle, and I have omitted the deglaciation after 20 000 before present (B.P.). Unavoidably, discussion will in particular be concentrated upon sites which I know from my own field experience.
The stratigraphic framework
My opinion on the stratigraphy of Northern Europe outside the Weichselian glaciation limits will first be presented, because this stratigraphy provides the framework to which the more fragmentary record within the glaciated areas has to be correlated. I will also correlate the Euro- pean stratigraphy with the deep sea oxygen isotope stratigraphy, partly because thc latter represents a global framework, and partly because the ages ofthe stage boundaries are relative- ly well established (MnnrtNsoN et al., 1987). In fact, sites in Western Norway where amino acid age estimates are available, can be more securely correlated with the deep sea isotope stratigraphy than to the European stratigraphy, because no independent datings exist fbr the Early Weichselian units in Europe.
The Eemian, with its stratotype along the Eem River in the Netherlands (Zrcwl:N, l96l ), has for a century been considered the Last Interglacial in the sense used in Northern Europe; an in- terglacial is defined by the occurrence of mixed oak forests in north-western Europe, and nor- mally a transgression along the North Sea coasts, i.e. climates and environments similar to pre- s e n t d a y c o n d i t i o n s . H o w e v e r , K u r u ( 1 9 7 1 - ) , B o w e ru (1 9 7 g ) , a n d w o n _ r . n n o ( 1 9 7 g ) q u c s - tioned that the stratotype Eemian represents the Last Interglacial. I consider this problem as solved by the amino acid correlation of Mrlr-pn & MnNcenuo (1986): The Eemian is indeed the Last Interglacial in Europe, and different sites can in most cases be correlated unambiguous- ly by the characteristic pollen stratigraphy of the Eemian. The correlation oI thc Ecmian with the deep sea oxygen isotope stage 5e, first proposed by SH.lcxleroN ( 1969), is now well estab_
lished (MnNcERUD et al., 1979; TunoN, l9g4).
worrlnno's (1975, 1978, worr-r-,,',nn & Moox, l9g2) study of the Grande pile in Northern France was a benchmark in European Quaternary stratigraphy, as this was the first site discovered with a continuous lacustrine sequence from the Eemian up to the present. Above the
3 1 0 . J n N M l N c r , R u p
-
aO)
o) o ( n a (o G)
t l o l 0 O -v
g o
6 1 8 o ( r t o r r t t a l i z e ( l ) 0
I
a (o
d l
U'
C h r o n o s t r a t i g r a P t r Y
. l
u r a n q e
| r u w E u r o p e
F , i l e I
3
a Vl -
- a Y o J -
g , g E s E
E 3 * i a o S " U ' : E I
d E e d 3 =
t 2 2 4
0 - - - { s e
o - = - z 4
r - 7 8 s
2 - - -
-/
9 33 - - - - - - - - {
( _ 1 0 s
4 - - .
J ' '
= __ _ .___ _ =__-
o <--- 130
I H o l o c e n e 2
3
4
'=
a
?
B
o,)a.\
f
o
=
D e n e k a m p H e n g e l o G l i n d e f oo, O e r e l I
5 a S t . G e r n r a i n l l
o3
J
O d d e r a d e
s b M e l i s e y ll R e d e r s t a l l
5 c S t . G e r m a i n I B r o r u p
5 d M e l i s e y I H e r n i n g
5 e E e m i a n
6
Fig.2: The "normalized" oxygen isotope curve from MenrtNsoN et al. (1987) with their "orbitally tun- ed" timescale. To the left on the curve are indicated some of the events given by them. The traditional EurlrnNr-SHAcKLEToN lettering of the isotope stages, which I use in this paper, is given with approximate ages of the boundaries as identified from the curve. The chronostratigraphy of the Grande Pile core is from Wollr-eRn (1978, only older units included). For north-western Europe, the subdivision of the Weichselian into Lower, Middle and Upper follows Mencenun etal. (1974), except that the middle/up- per boundary is moved to around 25 000 yr. (MnNcERUD & BnncluNo, 1978, CHnuNe et al., 1980).
The identification and naming of the interstadials/stadials (chronozones) follows MeNxe & TvNNt (1984) and/or BEHne & Lnnr (1986). I also follow MENru (1982), and MpNxE & TvNNI (1984) including the Amersfoort as the lower part of the bipartite Brorup. The curve of environmental changes in Germany.
The Netherlands reflects mainly the summer temperature, and is based on ZlcwllN ( 1975), MeNre &
TyNNr (1984) and Besnn & LnoE (1986). Generally the warmer interstadials can be more precisely characterized than the cold tree-less periods, and I have therefore mainly marked the warm peaks. Note that the time scale for the older half of the curve is based on the correlation to the isotope curve, argued for in the text.
Eemian in Grande Pile are two warm periods that Wotr.l.ARD identified as true interglacials (St. Germain I and II) and she concluded that they stratigraphically should be placed between the Eemian and the Early Weichselian interstadials Brsrup and Odderade of Northern Europe ( A N o e n s r N , 1 9 6 1 ; Z A G W T J N , l 9 6 l ; A v r n o t e c r , 1 9 6 7 : s e e re v i e w i n M p N r c & T v N t t t , 1 9 8 4 ) . The main reason why WoTILARD maintained St. Germain I and II not to correlate with the in- terstadials of Northern Europe, is that St. Germain I and II palynologically show a development to a full interglacial type of mixed oak (climax) forest suggesting that this vegetation could not
The Scandinavian Ice Sheet through the last interglacial/glacial cycle . 3l I
exist contemporaneously with the coniferous (taiga type) forests of the Brorup and OdiJerade in Northern Europe.
WollleRo's correlations have been challenged by several authors (e.g. Gnucnn; 1979a, b;
MeNcsnuo et al. ,1979; wrLreN, l98l; MrNru, 1982 MeNrB & TvNNr, 1984; Brsnr &
LlDe , 1986), whoallacceptedheridentificationoftheEemian, butsuggestedthatSt. Germain I and II should indeed be correlated with the Brorup and Odderade interstadials, respectively (Fig. 2). The main argument for this correlation is the similar stratigraphical position: In a large number of lacustrine basins in Northern Germany the first "warm-climate units" above the Eemian are the Brorup and the Odderade (MrnrE & TyNNl, 1984; Brsnn & Leoe, 1986). It is completely improbable that any warm interstadial or interglacial should be missing between the Eemian and the Brsrup in so many closed basins. Similarily St. Germain I and II were the first warm periods after the Eemian in Grande Pile (WoTLLARD, 1978), and this is confirmed in another basin in France (on BnluI-tru & RuLrr, 1984). The correlation of the Brorup and Odderade with St. Germain I and II, respectively, is supported by the amplitude of environmen- tal/climatic change: In both areas these were the two warmest periods after the Eemian, and in- deed the only interstadials that were really forested. Grande Pile is situated much further to the south than the interstadial localities mentioned in the Netherlands and Germany, and therefore the Grande Pile area during warm interstadials had a forest similar to the interglacial forests far- ther north in Europe. The correlation of St. Germain I and II with Brsrup and Odderade implies some steeper ecological/climatical north-south gradients in middle Europe than today, which I do not find difficult to accept.
Wott-lnno (1978) and WoIILARD & Moox (1982) suggested that St. Germain I and II should be correlated with the deep sea oxygen isotope stages 5c and 5a, respectively, accepting that 5e correlates to the Eemian. The correlation of St. Germain I with stage 5c is also supported by pollen analysis of a marine core with an isotope curve (TuRoN, 1984). I find these correla- tions probable, and thus that the Brorup and Odderade should correlate to isotope stages 5c and 5a, respectively. To some extent this correlation is a matching of curves (Fig. 2): Both, in Europe and the deep sea, these are the first warm peaks above the Eemian/Se, and in both cases they are the highest peaks between the Eemian and the Holocene. The causative arguments are the following: On the wavelength and amplitude of change we consider here, the environmen- tal/climatical curve for Northern Europe (Fig. 2) has to be roughly parallel to the volume change of the Scandinavian lce Sheet. A similar argument can be used for the major ice sheets on either side of the North Atlantic. The discussed parallelisms are both demonstrated for the last glacial maximum and deglaciation. Thus on this wavelength and amplitude the climatic curve for Northern Europe should approximate a Northern Hemisphere glaciation curve, as does the isotope curve. The only argument I can see against the proposed correlation, is that it predicts marine transgressions in the North Sea area during the Brsrup and Odderade, because the eustatic sea levels during stages 5a and 5c were not much lower than during 5e (Cuenrell & SHecKLEToN, 1986; SnecxlrroN, 1987), but such transgressions are not iden- tified.
312 ' JrN MnNcenuo
When did ice start to accumulate in Scandinavia after the peak of isotope stage 5e?
For the Fjosanger site in Western Norway the amino acid analyses given by Mlr-lrn &
Me,Ncnnuo (1986) have neither provided unambiguous results as to whether it represents the Eemian, nor an older interglacial. However, further analyses of the amino acids and other a r g u m e n t s ( S e r n u r , 1 9 8 7 ) , i n c l u d i n g u n p u b l i s h e d T L d a t e s ( M n r o n H I - & M n N c e R u o ) , s t r o n g - ly suggests that the Fjosangerian indeed is the Eemian, as originally suggested by MeNcnRun et al. (1979 , 198 1), and this is accepted here without further discussion.
At Fjosanger sea level dropped eustatically some l0 to 25 m when mixed oak forests, succeeded by spruce forests, surrounded the site, both forest types indicating a climate that excluded growth of any ice sheet in Scandinavia (MINGERUD et al. ,1979,1981). This implies that the first part of the sea-level drop after the peak of 5e was due to ice accumulation outside Scan- dinavia, probably in North America and/or Antarctica.
For the Netherlands ZncwuN (1983) has constructed a much more accurate curve, showing a drop of sea-level of at least 32m at the Eemian/Weichselian boundary. ZncwllN's curve (Fig.3) shows that around 20 m of the drop occurred within the Eemian. However, during the latest part of the Eemian there were pine (Pinus) forests in the Netherlands, and this may be compatible with growth of ice in the Scandinavian mountains. I conclude that sea level dropped eustatically between l0 and 20 m before any significant ice-growth occurred in Scandinavia.
However, the total drop in eustatic sea level from peak 5e to the trough 5d was nearly 70 m
0 m 5 m l0m
1 5 m 2 O m 2 5 m i 0 m 3 5 n l 0 n t S m
0cPlh Delov ,'escnl Scol3|r0l
-Amersloorl
/a
,jSchornqanlum/
-Amersloorl I
I
\- Pett"n _-lx--
'p Comperdurn
\\
I lAmslerdom
I I
-lvorlh Seo
N o r l h S e o
Lote S o o l i o n
I L S I
1 2 3o 3 u t o 4 u 5 o 5u 6 o 6 u E o r l Y
W e i c h s e l i o n ( E W I o l E e m r o n ( E l
Fig. 3: A sea level curve (high tide levels) forthe Eemian in The Netherlands, reproduced from ZecwtrN
( r983).
The Scandinavian Ice Sheet through the last interglacial/glacial cycle . 313
(CHnneet,l- & SnecKLEroN, 1986), so the time-lag in inception of the Scandinavian Ice Sheet compared to others was probably not large. As discussed below, certainly a major ice sheet developed during 5d.
The Weichselian glaciation(s) west of the Scandinavian mountains
The mountains in Scandinavia are like a major asymmetrical backbone running from south to north. The western side is steep, with deep fiords, and receives large amounts of precipitation with the westerly winds. The eastern side is gentle, and is in the rain shadow. Further to the east there are large plains (Finland, Estonia, etc.), and the broad depression of the Baltic Sea. The Scandinavian mountains are actually not very high, the highest summit today being 2469 m a.s.l., but they are situated at a high latitude, from 58o to more than 7l oN. From the described topography one might expect that the glacial development was different on each side of the mountain chain, so I will first discuss the west side, and subsequently the east side.
Earlier versions of the glaciation curve for the west side are given in MnNcsnuo ( l98l , 1983), where an extensive review of earlier literature is also provided. In the following I will concen- trate on sites that give key informations for dating the glacial advances.
Bo, Karmoy Skjonghelleren, Sunnmore
m l o
E
G r a v e l F = F a n a i n t e r s t
-_Silly gravel H F jo s a n g e r i a n
( = E e m i a n ) P a r a d i s T i l l
H a u g e s u n d D i a m i c l o n
1 0 B o
S a n d
K a r m o y 5
D i a m i c t o n - Torvastad Sand
A v a l d s n e s S a n d ( E e m i a n )
0
B l o c k B = H o l o c e n e D i a m . G = A l e s u n d in t e r s l
B l o c k K
B l o c k M
"r""oYrXho,,
. "r"yo3ha;
"o**r,-t^
-a
Fig. 4: Simplified lithostratigraphy for some sites in western Norway. Fjosanger modified from MnNcenuo et al. (1981). Bo, Karmoy modified from ANoERSEN et al. (1983); in this figure the names for the lithostratigraphical units are used also for stadials (Haugesund and Karmoy), interstadials (Bo and Torvastad), and the Avaldsnes interglacial. Skjonghelleren cave, modified from LnRsEN et al. (1987);
note that block/diamicton beds in this case were deposited during ice free periods, the clay beds during glaciations.
Fjosanger
3 1 4 ' J n N M , r N c e n u o
Fjosanger
Above the Eemian beds at Fjosanger is a thick glaciomarine silt (G on Fig. a) which demonstrates that glaciers at that time were calving some few km from the site (MnrucrnuD et al., 1981). All observations (lithostratigraphy, pollen, foraminifers, amino acids) suggest that there is no major unconformity between the Eemian beds and the glaciomarine silt: thus this
C o a s t D e n m a r k
q)
o
I
FE
6 c)
o 0)
o oo c
a
o I
6
;
U) M o u n l a i n
e a s t
T o r v a s t a d *
F a n a F o r n e s
A v a t d s n e s @ H o v d e n
@ F i o s a n g e r i a n
M o u n l a i n s F in l a n d w e s l / n o r t h
Y o u n g e r D r y a s
^ : - - r l . -
! , i ' . . 4 U d r s l U V
o 6
tt- f,o ;
o
o
E o
I
N S w c d e r t
P e r e p o h i o l a
T e p s a n k u m p u a n d o l h e r F i n n i s h s i l e s Leveiniemi
O . D o s e b a c k a r
t2
@ Fauna suggesting climale as today, ot warmer.
* Fauna with Allanlic Curent'guide lossils.'
Fig 5: Schematic glaciation curves for the last interglacial/glacial cycle in Fennoscandia. The left curve is for the west side of the mountains, the right curve for the east side in the mountain-proximal areas (N.
Sweden and Finland) and towards south (Denmark) in the distal parts. The horizontal scales are somewhat arbitrary because sites scattered over a huge area are "projected" into a theoretical linear cross-section.
Ages for isotope stage boundaries from MnnrrNsoN et al. (1987), compare with Fig. 2.
The Scandinavian Ice Sheer through the last interglacial/glacial cycle 3 I 5
g l a c i a t i o n i s u n d o u b t c d l y o f i s o t o p c s t a g e - 5 d o r H c r n i n g s t a d i a l a g e (F i g . 5 ) . I t ( l c m o n s t r a r c s that in this area the glaciers were nearly as large during 5d as they were during the younger Dryas. Ifthe correlation is correct, there must have been a considerable glacio-isostatic depres- sion to keep the site below sea level, as eustatic sea level dropped nearly 70 m from the peak 5e to the trough 5d (Cuernrll & SHecrl-EroN, 1986). Thus the Scandinavian Ice Sheet must have been correspondingly large.
Above the glaciomarine silt is a gravel deposited during a milder period, the Fana interstadial (Fig. a). Amino acid analysis strongly suggests that the Fana should be correlated with isotope stage 5c (Mrllrn et al., 1983; Selnup, 1987), and thus the Brorup (Fig. 5). originally we (Mance nun et al. , 1981) suggested that Fana is older than Brorup, because the fauna suggested colder climate than we expected for the Brorup. If we now accept the age, the unexpected cool fauna can be explained in two ways: l) The warmest part of the interstadial is missing. 2) The difference in summer temperature between the present and the Brorup was larger in Western Norway than further east in Europe. This latter is supported by temperature gradients deduced from pollen sequences in Europe, and I assume it is at least a part of the explanation.
Three observations have led us to conclude that there is no unconformity between silt E and the Bsnes Till (Fig. a)' and thus that the Bsnes Till is of isotope stage 5b or Rederstall stadial ase ( F i g . 5 ) :
l ) I n t h r e e o u t o f f o u r e x c a v a t i o n s t h e t i l l c o n f o r m a b l y o v e r l i e s t h e 0 . 5 m t h i c k s i l t E . I t w o u l d be most surprising if glacial erosion had stopped at several different places just at this s t r a t i g r a p h i c a l l e v e . .
2) Upglacier, in the deeper part of the fiord, the glacier eroded marine sediments that it over- rode, and therefore the till is full of transported fossils. These fossils may all be correlated with the Eemian and Early Weichselian beds at Fjosanger; there are no hints of younger fossils.
3) A large number of amino acid analyses of shell fragments in the till gave only ratios cor- responding to the beds at Fjosanger, suggesting that the glacier did not erode any younger beds.
Godoya
A t G o d o y a , S u n n m s r e ( F i g . l ) , L n N o v l x & Mencenun (1985) d e s c r i b e d a s a n d u r t h a t th e y , and also LANnvtx & Hn Msonc ( 1987), interpreted to be of Middle Weichselian age. However, several thermoluminescence dates now suggest it is of isotope stage 5d age (JuNcNen et al.,
1989). I will not discuss the reliability of these dates here, just state that if they are correct the ice reached much further west during stage 5d than during the Younger Dryas in this area.
Karmoy
Excavations in the Bo claypit at Karmoy (Fig. l) reached beds (the Avaldsnes Sand, Fig. 4) where pollen-, mollusc-, foraminifera-, and amino acid stratigraphy all suggest an Eemian age ( A N o e n s t l N e t a l . , 1 9 8 3 ; S c l n u p , t 9 8 7 ) . D i r e c t l y o n t o p o f t h c i n t c r g l a c i a l b c c l s l i c s t h c T g r -
3 1 6 . l e N M A N c E R U D
vastad (interstadial) Sand, where the marine fossils suggest conditions comparable to the north- ernmost tip of Norway today (SEJRUT, 1987). The pollen assemblage indicates an open vegeta- tion with some birch, but it is difficult to interpret it because of the large amount of redeposited pollen in these marine sediments (ANoanseN et al., 1983). Amino acid racemization suggests an age of the Torvastad interstadial of 78 000 + 7000 B. P. (Mlr-lrn et al., 1983), and thus a cor- relation with the isotope stage 5a and the Odderade interstadial in Europe (Fig. 5). This suggests a major hiatus between the Avaldsnes and the Torvastad Sands.
Above the Torvastad interstadial is a basal till (the Karmoy Diamicton, Fig. a) showing that rhe site was overridden by a glacier reaching the open sea. Between this till and the Late Weichselian till (the Haugesund Diamicton) is the Bs Sand, demonstrating another ice-free (Bo) interstadial. Several radiocarbon dates gave finite ages around 40 000 B.P. (ANornsEN et al., 1983) for this interstadial, an age supported by amino acid analyses of molluscs, whereas amino acids on foraminifera suggested an age around 60 000 B. P. (Mrr-len et al., 1983). Even though neither the age nor the duration can be fixed exactly, the site demonstrates a Middle Weichselian interstadial, certainly predating c. 40 000 B.P., with sea surface temperatures like in northernmost Norway today (Sr-rnup, 1987).
From the ages given above for the Torvastad and Bs interstadials, the glacial advance demonstrated by the Karmoy Diamicton can most reasonably be correlated with isotope stage a (Fig. 5), even though this is a correlation with week constraints.
Karst caves, Nordland
Speleothems in karst caves can only be precipitated when the cave is not covered by an ice sheet, because beneath the ice the cave would be filled with water, or alternatively it would be frozen.
LeuRlrzrN (1984, 1986, oral communications 1988) has performed uranium series dating of more than 90 speleothems from caves along the valleys and in the mountains west of the water- shed in Nordland (Fig. l). The distribution of the dates shows major peaks around the ages of isotope stages I (the Holocene) and 5e (the Eemian), but also enough dates from the rest of isotope stage 5 to demonstrate that these mountains were also ice-free after 5e, probably during both 5a and 5c.
In fact Leururznn has discovered three speleothems which he assumes grew continuously from around 130000 to 95000 B.P.. If correct, this will contradict the extensive glaciation I have concluded for isotope stage 5d (Fig. 5). Alternatively one could postulatc diffcrent glacial histories for the different areas. To some extent that is certainly right, but that can not explain the referred contradiction.
Skjonghelleren, Sunnmere
Skjonghelleren is a 100 m long wave-cut cave with a unique on-off signal of glaciations (LnnsEN et al., 1987): When it was overridden by glaciers an ice-dammed lake was formed, and laminated clay deposited (beds L, J-I, and F, Fig. 4); when it was ice-free stones fell from the roof, and animals lived in the cave.
The Scandinavian Ice Sheet through rhe last interglacial/glacial cycle 3 | 7
The last ice-free period (the Alesund interstadial, letter G on Figs. 4 and 5) is well dated to around 30000 B.P. by radiocarbon dates on bones and U-series dates on speleothems. The fossils show marine conditions so warm that a branch of the North Atlantic current must have entered the Norwegian Sea at that time. The clay F from the last glacial overriding has a characteristic palaeomagnetic signature correlated with the Lake Mungo excursion, dated to around 28 000 B.P. (LensEN et al., 1987; LsvrtE & SaNoNes, 1987).
Below the Alesund interstadial is a sequence showing two more glaciations and two ice-free periods. These are not as well dated as the last cycle, but palaeomagnetic correlations suggest that the lastof these glaciations (letters I and J, Fig. 4) occurred between 36 000 and 42 000 B.P.
ago.
The extent of the Late Weichselian maximum
I shall not discuss this topic here, just mention some recent results. On the basis of extensive field studies Rvs et al. (1987) and Nrstr et al. (1987) concluded that summits in Sunnmsre (Fig. l) and areas south and east of Sunnmsre, in Western Norway remained ice-free nunataks throughout the Late Weichselian, a topic discussed for a century. This provides strong con- straints on the thickness of the ice. Srrnup et al. ( 1987) demonstrated that the Scandinavian and the British ice sheets probably did not meet in the North Sea. VoRneN et al. (1988) showed that Andoya (Fig. l) was ice-free around 20 000 B.P., and after a short glacial overrun during the Late Weichselian maximum, finally deglaciated around l8 500 B.P.
Discussion and conclusions for the western flank of the ice sheet
A couple of decades ago, the view was that most of Scandinavia was continuously glaciated dur- ing the entire last ice age. This view is now completely changed, but a logical approach is still to assume that it was ice-covered during all those periods where we cannot demonstrate ice-free conditions. One reason for this approach is that the age and duration of ice-free periods can be shown by fossil-bearing sediments, whereas basal tills cannot be dated. An exception for this is the Skjonghelleren cave discussed above, and hopefully other similar caves, where glacial periods are recorded by laminated clays which in fortunate stratigraphic positions might be dated by palaeomagnetic correlations. The approach described here leads to a history with a minimum number of events. New localities probably will show a larger number of glacial ad- vances and ice-free periods than shown on Fig. 5. If during some periods there was a high fre- quency forcing of climate, as e.g. suggested by DlNscr,r.no (1987) for parts of the Middle Weichselian, the Younger Dryas may provide an example of the glacial response: In Western Norway there was during the Younger Dryas a major re-advance of the ice sheet that lasted for some few hundreds of years only (Mnncrnun, 1987).
The glaciation curve (Fig. 5) is a conceptual curve that ideally should show glacial advances and retreats from the mountains in the east to the coast in the west. However, the sites are spread out along the coast from north to south, and the configuration of the ice-front was certainly dif-
3 1 8 ' l e N M e N c e n u o
ferent at different times. Here I have followed the same approach as I have done earlier (MlNcrnuo, l98l); the coastal sites (Fjosanger, Karmoy, Sunnmore) are plotted relative to their distance to the Younger Dryas end moraines. However, the main pattern of the curve would not change with a different way of plotting. I will point out that both the Karmoy and Sunnmsre sites are close to the open sea, so when the glacier overrode the sites it locally ended in the open ocean.
The curve is drawn after different rules before and after 50 000 B. P. For the older part I have simply placed the advances and retreats at the time of the isotope stage boundaries , even though that correlation is strictly demonstrated only for the 5el5d boundary. For the younger part I have followed the datings.
I consider the main pattern through the isotope stages 5e-5d-5c as established, because we could demonstrate that the first glaciation at Fjosanger followed soon after the Eemian. The nearly complete deglaciation of Scandinavia during the Brorup (5c) is documented by several sites discussed in the next chapter, and the Fsrnes site (VonntN & Ronloser, 1977) located in the western mountains. Therefore, the glacial/deglacial cycle of stages 5d/5c is demonstrated even if the Fana interstadial should be older than the Brorup, as assumed in the earlier version o f t h e c u r v e ( M n N c e n u o , 1 9 8 l ) . H o w e v e r , t h e c o n s e q u e n c e f o r t h e i s o t o p e s t a g e 5 b g l a c i a t i o n might be more important; if the Fana is older than stage 5c, the Bsnes tilt should also be older, and no record of a 5b glaciation is known.
A basal till between the Torvastad and Bs interstadials demonstrate unambiguously that there was at least one glaciation in that time interval. I have plotted that glaciation to isotope stage 4, based on amino acid ratios, but the precision of these age assignments are too poor to really demonstrate that this was a stage 4 glaciation. Also the correlation of clay L in Skjonghelleren to the discussed glaciation (Fig. 5), is mainly by "counting from the top".
I have drawn a more extensive deglaciation for isotope stages 5c and 5a than for the younger interstadials, because for the two former a deglaciation of Central Scandinavia is demonstrated (see below). Inland sites with reliable finite radiocarbon dates are not demonstrated yet.
However, the fauna in both Bs and Alesund interstadials suggests warmer conditions than the fauna in Fana, and as warm a climate as in Torvastad. In both Bs and Alesund the faunas com- p a r e t o t h e A l l e r o d f a u n a ( M A N G E R U D , 1 9 7 7 ) , f o r w h i c h w e a s s u m e t h a t a b r a n c h o f t h e A t l a n t i c Current entered the Norwegian Sea. During Allersd there was still a considerable ice sheet over Scandinavia, even though it certainly would have shrunk much more in the easterly areas if the mild climate had lasted longer.
ANnrnsrN et al. (1981) inferred a short-lived, large glaciation close to 40000 B.P. at Jeren.
A glaciation of that age is also postulated from Skjonghelleren (LansrN et al., 1987). However, in neither case is the glaciation reliably dated. The timing of the last advance is better known:
The glacier front passed Skjonghelleren close to 29000 B.P. on its way towards the Late Weichselian maximum position at the edge of the continental shelf.
The Scandinavian lce Sheet through the last interglaciar/glaciar cycre 3 l9
The Weichselian glaciations in the central areas and on the east side of the Scandinavian mountains
A glaciation curve for the east side is developed by LuNoqursr (1974, l9gl, 19g3, 19g6), LrrunNrn (1984), LtNotlsn et al. (1984), and Manr.ran (1969,lggl). The main modifications I have made to LuNnQutsr's curve is to stretch the time scale for the older part by correlating the Brorup and odderade to isotope stages 5c and 5a, respectively, and to accept two Early weichselian ice-free periods. Similar interpretations of the time scale and correlations have earlier been presented by Fonssrnou (1984), but he used the oxygen isotope curve more direct- ly as a glaciation curve for Scandinavia.
In Northern Germany the Brorup and Odderade interstadials were the last forested periods before the Late weichselian glacial maximum (MrNxe & TvNNr, l9g4; BEHnE & Lnoe,
1986), and therefore I consider these interstadials as also the last periods that forests possibly could have existed in Fennoscandia. Accepting the correlation to the deep sea- isotope stratigraphy, this means that forested sires have a minimum age of 75 000 B.p. (Fig. 2). Boih finite and infinite radiocarbon dates have been obtained for such sites. with the assumptions I have made here, apparent radiocarbon ages (finite or infinite) cannot be used for correlations of sites where the existence of forests is demonstrated.
The stratigraphy of Northern Finland
Northern Finland (Lapland and periipohjola regions, Fig. r) is for two reasons a key area ( r e v i e w s i n H r n v e s e t a l . , lggl and Hrnvns & NENoNEN, l 9 g 7 ) ;
l) More interglacial and interstadial sites (more than 100, Hrnvns & NrNoNsN, l9g7) are known from this area than from any other area within the borders ofthe Scandinavian Ice Sheet.
2) The area is a lowland plain, so that till beds can be mapped over large areas.
Interglacials are defined by a pollen-flora similar to, or in fact slightly more warrn-clernanding than the Holocene, e.g. with pin us, Betura, and some pjc ea, and Arnus(Hlnvas & KurlNsuu,
198 I ) ' An interglacial age on that basis is unquestionable, and most of the srtes are assumed to b e E e m i a n ( H l n v n s , 1983).
Fig..6: Sketch showing the principle for constructing the stratigraphy in Finland: Till beds, especially the direction of ice-flow that deposited them, are used for lateral correlations;
organic (and other non-glacial) beds are used lor ..clatinc...
- - I - 1
t l
l * l -
t * b " d \ \ - '- H
- - - -i"lJPontottf'...''...]
r i i l b e d i l l \ l _ t l
Eemian
3 2 0 l e N M e x c r n u o
Ahove thc youngcst intcrglacial hcds f<rllows a till (Till bcd lll) that is latcrally corrclatc6 hy n r e a n s o f i t s ti l l f a b r i c ( F i g s . 5 a n d 6 ) . H l n v e s & N e N o N e N ( 1 9 8 7 ) c o r r e l a t e t h i s ti l l o v e r la r g c parts of Northern Finland (Lapland and perripohjola. Fig. l). SurlNEN (t9g4) nrappcd end moraines correlated with that till in the southern part of Perzipohjola. There seems to be a general agreement in Finland that till III does not occur further south, and thus that the moraines
C H R O N O . ST RAT I GRAPHY
L A T E A N O M ID D L E W E I C H S E L I A N
P E R A P O H J O L A I N T E R S T A D I A L I J A M T L A N D .
8 R 9 R U P )
E A R L Y W E I C H S E L I A N
L A 5 T I NTERGL AC I A L { E E M , L E V E A N I E M I , M I K U L I N O )
S A A L I A N
C E N T R A L L A P L A N D
€ g h r r v o 3 e l o t 1 9 7 7
<..
- / S A N O aNO
\ - - _ ! R A v E L r t r r ard---_
I N T E R S T A O I A L P E A T G Y T I J A ,
S I L T , E T C
t
I N I E R G L A C I A L P E A ] 6 Y T ] J A
E T C
r I L L 8 E D
tr
S I L T S A N D
r I L L 8 E O
:a
{::^J
r { L h t ( l
€ E H I N I E R G L A C I A I
G Y T T J A
l_'-
' " 0 i
;r
Fig' 7: Correlation of the stratigraphy of Northern Finland. Note that the given sequence fbr each area
I
is a synthesis of many sites; two organic beds do not occur above each other at any single locality. Repro- duced from Hrnvrs & NeNoNrN (l997).
L O W E S I I I L L A € O
The Scandinavian Ice Sheet through the last interglacial/glacial cycle . 32 I
mapped by SurrNeN represent the limit of the pre_perripohjola glaciation (: isotope stage 5d g l a c i a t i o n ) .
At many sites organic and other non-glacial sediments are found on tills identified as till bed III. The pollen flora in these sediments is always dominated by Beturaand herbs (Fig. 7), sug_
gesting a birch forest, and thus cooler conditions than during the Holocene. All these sites are referred to the Perdpohjola interstadial, first defined by Ko-nre r-a (1969). and generally cor- related with the Brorup (HInvns et al. ' 1981). As discussed above, the only alternative period within the weichselian that could allow a birch forest to thrive there is the odderade.
T h e c o n c l u s i o n b y H t n v n s e t al. (1981), H l n v e s & N r N o N r N (19g7), a n d m a n y e a r l i e r a u t h o r s cited by them' is that during the weichselian there were in Northern Finland two glaciations, separated by one single ice-free period, the Periipohjola interstadial, correlated with rhc Brorup' The strength of this model is that it apparently explains all observations. I will especial- ly point out that if sites from two differeni ice-free periods were grouped together in the Periipohjola interstadial,
this should have led to different till fabricsLelow and/or above the beds from the different interstadiats (Fig. 6), and such sites are not found.
I will briefly mention the interesting site of oulainen (Fig. l) further south in Finland. which h a s u p t o 9 0 % p i n u . s p o i l e n . F o n s s r n o u ( 1 9 g 2 , 1 9 g 4 , l9g5) assumed a n i n r e r g l a c i a r a g c , w h e r e a s D o N N e n ( 1 9 g 3 ) , HvvAnrNEN (19g5), and Fonssrnau et ar. (19g7) a s s u m e d a Periipohjola (Brorup) interstadial age, Iater supported by many TL dates (JuNcNe n, l9g7). If the latter conclusion is correct, it would mean that the northern boundary of pine forests was bctwcen oulainen and{hc classical Pcrripohjola sitcs. This is surprisingly I'ar north c.nrparcd to the vegetation
in middle and Northern Euiope (MENrr & TyNNl, | 9g4), and wourd require a lower temperature gradient between Germany and Finland during the Brorup than at present.
if the climatic pattern
was similar. However, during the Brarup there possibly was a more con- tinental climate with steeper summer temperature gradients towards the cooler west coast. If oulainen is of Brorup age' some other sites earlier assumed to be Brorup probably represent other ice-free periods, e.g. the Odderade.
The central area of Sweden and Norway
M a n y s i t e s w i t h s u b - t i l l s e d i m e n t s , m o s t o f t h e m w i t h onry minerogenic s e d i m e n t s , a r e k n . w n from areas close to the watershed of the Scandinavian mountai; (e.g. LuNoqulsr, r967, BencrnseN & GnnNes, 198 l). when these sites were ice-free, nearly all glacier ice in Scan- dinavia must have been gone. A recent review is given by LuNnqursr (19g6), who assumed that all sites are from one single ice-free period, the Brorup interstadial (fbr which he assumed a much lower age than in this paper).
T w o k e y s i t e s are Brumunddar ( H e l l e et al., lggr) and pirgrimstad ( L u N o g u r s r , 1967), because they contain organic sediments that offered tne posiiuitity of constructing pollen diagrams' At Brumunddal (Helu et al., l98l) the lithostratigraphy (till/pear/riil) and the pollen stratigraphy show a full environmental or climatic cycle: Glaciation/tundra/birch forest/tundra/glaciation,
where the ice-free period did not ,each the temperature of an in-
322 ' lxr't M,rxcenuo
terglacial. The frequent occurence of lnrix and also the occurence of Picea, within the Betula forest suggests a correlation to the Brorup, even though both trees also occurred during the Od- derade in Northern Europe. The underlying till suggests a glaciation between the preceding in- terglacial and the Brumunddal interstadial. The pollen diagram from Pilgrimstad (LuNnqursr,
1967) is very similar to the one from Brumunddal, except that lnrix is missing, and probably correlates to the same interstadial.
Evidences of more than one Lower weichselian ice-free interstadial
As discussed above, the stratigraphy in Northern Finland indicates that there was only one Lower Weichselian ice-free interstadial, the Periipohjola. Lulroeursr (1986) also concluded that there was only one ice-free interstadial in the central areas of Sweden and Norwav. which
--.ot- Alnus
+ Pinus ----*- picea
Fig' 8: Pollen diagram from Permantokoski, Perdpohjola, the type area for the periipohjola interstadial.
Reproduced from Konpell (1969); the original German rext is translated. Note ttuiin tf,. total diagram the amount of herb pollen (NAP) is given relative to 100 tree pollen (AP), so that throughout the peal bed Betula Sirch) pollen constitutes more than 70 to j5% of the total amount of pollen.
r $ 9 :
o o > ; i - 6
, * , t * : E s F - f ; r c 5 ! c
;EffiTtr3si 5 5,"3g5E
Upper lill
T i l l witi o r 9 a n i c m a l l a r
The Scandinavian Ice Sheet through the last interglacial/glacial cycle . 323
he correlated with the Periipohjola and the Brorup. However, in Northern Germany the Brorup was only slightly wanner than the Odderade (MeNxr & TyNNr, 1984; Brnnr & Lene. 1986).
Furthermore, if the correlation in Fig. 2 is correct, the duration of the Odderade (isotope stage 5a) and the Brorup (5c) should be similar, and indeed approximately as long as the Eemian (5e) and the Holocene (stage 1), all periods having a duration between l0 000 and 13 000 years.
These considerations lead me to examine if there is evidence of more than one ice-free period in central areas covered by the Scandinavian Ice Sheet.
First I will simply state that a reliable mutual correlation of the many individual sites correlated with the Jiimtland, Gudbrandsdalen, Brumunddalen and other ''Brorup"
interstadials in Swe- den and Norway is impossible. Theoretically, different sites may stem from many different in- terstadials, and even different glacials (MeNcenuo, l98l). When they all were grouped into one single interstadial (e.g. LuNnqutsr, 1986), it was partly because this was the simplest model which explained all observations. Up to now this model has not been contradicted.
The most obvious evidence for more ice-free interstadials is presented by LncrnnAcx, who from Northern Sweden (around Junosuando, Fig. l) reported three sites with two interstadial beds separated by a till (LacrnnAcr, 1986; HrrrlnoRc et al., 1986). Based on till fabric and pollen stratigraphy LncensAcx & RonrnrssoN (1988) correlate the lower interstadial with the Periipohjola. Also the upper, named the Tirendci interstadial, has an infinite radiocarbon age, and is tentatively correlated with the odderade (LncrnnAcr & Ronenrssor.r, 1988).
LuNnquIsr(1967)describedsub-tillclayandsiltatVilbacken,nearPilgrimstadonFig. l,and included these sediments in the Jiimtland interstadial. ManNrn ( I 981) found that the Vilbacken sediment has a palaeomagnetic signal similar to the signal of event F in St. Germain II in the Grande Pile, and different from the signal in St. Germain I. The correlations given in Fig. 2 reflect ihat Vilbacken is of Odderade age.
Ice-free periods with finite radiocarbon ages?
Many finite radiocarbon dates with ages above 20 000 B. P. have been obtained from the central p a r t s o f S c a n d i n a v i a ( s e e L u N o q u r s r , 1 9 8 l , 1 9 8 6 ; H r n v l s e t a l . , 1 9 8 1 , M a N c B n u o , lg g l f o r further references). Many of them can be demonstrated to be minimum ages only, e.g. because they date forested periods. In my opinion no finite date from Central Scandinavia, e.g. the area proximal to the Younger Dryas endmoraines, can at present be convincingly argued to be cor- rect. This may be changed in the future, but with Fig. 5 I have assumed that the central areas were covered by ice from 500m to 12000 B.P..
BrncensrN & THonnseN (oral communication 1988) recently obtained a TL date of 37 000 B.P. for windblown sediments from Gudbrandsdalen (Fig. l). LeunnznN (oral communica- tionl988)obtainedU-seriesdatesaround30000B.P.onspeleothemsfromNordland(Fig. l).
Both these cases have to be re-tested, and I have conservatively not included them in the diagram (Fig. 5). Still they open exciting ways of dating ice-free periods to cold, or to short, for organic production. If they are correct, each of them would demonstrate that central areas indeed were ice-free.
3 2 4 . t t n M r x c r n u o
Discussion and conclusions for the eastern flank of the ice sheet
It seems quite clear that there was a glaciation in the central areas during the Herning stadial (isotope stage 5d): All interglacial beds are directly overlain by a till (and not a "mild" in- terstadial), and all interstadial beds are found on till (and not on an interglacial). A main problem in mapping the geographical extent of that glaciation is that interglacial and interstadial sites hardly exist between the central area and the marginal zone of the Weichselian glacial max- i m u m .
The most proximal site with Eemian and Brorup sediments not separated by a till is Stenberget ( F i g . l ) i n S o u t h e r n S w e d e n ( B e n c r u r u n & L n c r , n r - u N n , l 9 8 l ) . I f t h e d a t i n g o f t h e ti l l I I I i n Finlancl is correct, Lapland and PerZipohjola districts were glaciated, whereas Osterbotten (around the site Oulainen, Fig. l) remained ice-free during stage 5d. The Brumunddal site in N o r w a y (F i g . l ) ( H r l l e e t a l . , l 9 8 l ) s u g g e s t s a g l a c i e r w i t h a m i n i m u m e x t e n s i o n o f n e a r l y t h e Y o u n g e r D r y a s s i z e . M a i n l y b a s e d o n T L d a t e s , M o r s x t ( 1 9 8 0 , 1 9 8 5 ) , G a l o N ( 1 9 8 2 ) . Lrr.roNen ( 1984), and LINnNE n et al. ( 1984) concluded that the lowest Weichselian till bed along the lower Vistula valley in Poland is of pre-Brorup age, which would suggest a stage 5d glacia- tion considerably larger than the Younger Dryas, and incompatible with the conclusions drawn from Finland. However, this age is not proven by overlying Brorup sediments, and Kozensrt ( 1980), for example, postulates a Late Weichselian age for that till.
The pattern of glaciation during the Herning and the Late Weichselian maximum was quite dif- ferent. During the Herning the ice-shed remained in the mountains to the west (Hrnve,s &
Ne,NoNeN, 1987; Hlnvls et al., 1986) whereas during the Late Weichselian it was far to the east. Based on the given observations, I conclude that the size of the Herning time glacier was of the same order of magnitude as the Younger Dryas glacier west of the mountains, and pro- bably somewhat smaller on the east side.
I also conclude that there were two (or possibly more) interstadials, of ages beyond the range of radiocarbon dating, when areas close to the mountains were ice-free. The older of these cor- relates with the Periipoh.jola (LlceneAcx & RoerRrssoN, 1988), or at least with some of the localities grouped together as Periipohjola, and probably with the Brorup. The logical assump- tion will then be that the younger Tdrendri interstadial correlates with the Odderade. The cor- relation, or rather the splitting, of the other Swedish and Norwegian sites into the two in- terstadials is difficult, simply because most of them lack any criteria for both relative and ab- solute ages. The most promising techniques for solving this problem are TL dating and palaeomagnetic correlations with areas outside the Wcichselian glaciation.
The scale of the glaciation between the two interstadials (that should be Rederstall stadial : isotope stage 5b) is unknown. LecsnsAcx (written communication 1988) assumes that it had a considerable extent in Northern Sweden and Finland, even though a till bed of this age is not reported from Northern Finland.
The extension of the isotope stage4 glaciation is unknown, too. Both for this, and for the earlier advances. Poland may be the key area. Dnozoowsxl (1980), Dnozoowsxr & Feoonowrcz ( 1 9 8 7 ) . M o l s x t ( 1 9 8 0 , 1 9 8 5 ) , L t N o n r n ( 1 9 8 4 ) , a n d L t N o N r n c t a l . ( 1 9 8 4 ) c o n c l u d e , r n a i n l y
T h e S c a n d i n a v i a n l c e S h e e t t h r o u g h t h e l a s t in t e r g l a c i a l / g l a c i a l c y c l e 3 2 5
on the basis ofTL dates, that the Scandinavian Ice Sheet transgressed Poland around this time, and that the ice front approached the limit of the Late Weichselian maximum. However. this is not yet generally accepted (Koznnsxl, 1980).
The Dssebacka site, near Gotenburg in south-western Sweden has several till beds, too, separated from one another by horizons suggesting ice-free conditions, mostly as wind abraded s u r f a c e s w i t h s o m e o r g a n i c m a t t e r ( H t l r - e n o n s , 1 9 7 4 , 1 9 8 6 ) . T h e d a t i n g i s p r o b l e m a t i c t y e t t h e stratigraphy suggests that the ice overrode this area several times during the Weichselian. A TL date gave about 50 000 B. P. for an interstadial bed (Hrllrrons, 1986); if correct it may suggest that the underlying till is of isotope stage 4 age.
PrrrnsnN (1984) assumed that a till at Holmstrup (correlated with the oldest Weichselian till in Ristinge Klint) in Denmark was deposited by a glacier flowing from the Baltic at a time that may correlate with isotope stage 4. If he is right. the ice sheet must also have transgressed Poland, and thus his conclusion is indeed compatible with the similar conclusion for poland given above. However, HoutraRx-NTELSEN ( 1987) postulated the same till to be of pre-Eemian age. LlcenluNn (1987) concluded that the first Weichselian ice advance over southernmost Sweden, and thus Denmark, postdate the Gdrdslsv beds (Mrr-lrn , 1977) from which there are several radiocarbon dates in the range 2l 000 to 30 000 B. P. I still consider the time of the first Weichselian ice advance to Denmark as unsolved.
Towards climatic and glaciological models for the Weichselian glaciations
Glaciological models for the Weichselian have been developed by, for example, DeNroN &
H u c n e s ( 1 9 8 1 ) ; B o u l r o N e t a l . ( 1 9 8 5 ) , a n d L A c s n L u N n ( 1 9 8 7 ) . S u c h m o d e l s a r e e x t r e m e l y important to improve the understanding both of the climatic role of the ice sheets, and fbr several other geological problems. A crucial boundary condition in all such models is the type of observations discussed in this paper: Field data on the size of the ice sheet at different times.
I shall not discuss the models here, but only present some thoughts originating in the geological observations presented here.
The Weichselian was not one simple glacial cycle from an interglacial to a glacial maximum.
In fact ice sheets developed (at least) three times, each time from virtually no glacier ice.
However, only the first of these started from a full interglacial climate, with an ocean to the west as warm as at present. In contrast, the last major expansion to the Late Weichselian maximunt started (around 30000 B.P.) from an ice sheet that already was relatively large. There are all reasons to believe that the different starting points and different climates during thc cycles caus- ed quite different types of development of the geometry of the ice shcets mentioned.
Allobservations suggest that the first glaciation (stage 5d) remained a mountain centcre6 glacia- tion, with the ice-shed remaining in the mountains throughout the glaciation. This contrasts strongly with the Last Glaciation, when the ice-shed moved far east and south of the watershed in Sweden and Norway (LuNoqutsr, 1974, BancenseN & GnnNBs, 1983). Whether this was a slow movement during several thousand years, or whether it had happened rapidly around the time of the maximum glaciation, is unknown. Further north Hrnves et al. (l98l) and Hrnvns
326 . sex MeNcsnuo
& NTNoNEN (1987) did not find any fabric in the till suggesting that this Last Glaciation started in the western mountains, and their observations would rather lead to a model of instantaneous glacierization of large areas of Northern Finland.
Acknowledgements
A draft of this manuscript was widely distributed to Nordic colleagues early February l9gg, and I received a large number of written and orar comments, noruuiy from J. J. DoNNen, M.
EnoNeN, L. FonssrRdu, H. HrRv,rrs, and K. NTNoNEN from Finiand; R. LecrnnAcx, E.
LAcERr-uNn, J. Lunoqursr, and A. M. RosrnrssoN from sweden; M. Hourrllnr_NlErspN and K' S. Perrnsrhr, Denmark; B. G. ANoe nsEN, o. F. Bnnornsrp, J. LaNnvrx, E. LlnssN, s' E' LnunrrzrN, A. Nrs*, H. p. Sarnup, and M. THoREsnN, Norway. MrcHneL Tnlsor corrected the English language. To all these friends I offer my sincere thanks. The project was financially supported by the Norwegian Research council for Science and Humanities ( N A V F ) .
References
A N o E n s E N ' B.P. at Jaren-Karmoy B . G . , N v o n r - , in southwestern R . , w n n c e N , o . p . & o s r r , . r o , Norway. Boreas s . R . (r 9 g l ) : w e i c h s e r i a n b e f o r e 10, 2g:'_314. r 5 0 0 o y e a r s -, Sr'rnup, H. p. & KrnrHus, 6. (r9g3): Eemian and weichselian a.pnrit, at Bo on Karmoy, SW Nor_
. way: A preliminary report. Norges geologiske undersskerse 3g0, ig9-20r.
ANornsrN' (last glacial). s' T' (1961): Danmarks vegetation Geologiske and Undersskelse. its-environment II Rekke 75, r_r75.in Denmark in the Earty weichselian Glacial AVERDIECK, tersradiale F' R. (1967): Die vegetationsentwicklung von Odderade/Schleswig_Holstein. Fundamenta 4., n..-int..gi"ri.r, und der Frtihwiirm-ln-2, l0t _ i2S.
BrnuLtEu, Lyon, France. J' L' nr & Rrlue, M. 1t9441: Boreas f-i, lll_132. A long Upper pleistocene pollen record from Les Echets, near BeHnn' K' E' & Le'pe, u' {1986): Eine Folge von Eem und 4 weichsel-lnterstadialen in oerel/Nieder-
* sachsen und ihr Vegetarionsablauf. EiszJitalter u. Gegenwa rt 36, ll-36.
Bencrn, NATO ASI Series A., Irrrsn|E, J., Hevs, 126 (2 volumes), J., Kuxle, G. & SAirzrueN, D. Reidel, Dordrecht.B. (eds.) (19g4): Milankovitch and climare.
BsncensEN' terstadial and the following o' F' & GrnNss, glaciation. K. (1981): Boreas weichselian 10, 315-322.in central South Norway: The Gudbrandsdal In- - & - (1983): Glacial deposits in the culmination zone ofthe Scandinavian ice sheet. In: EslEns, J.
- (ed'): Glacial deposits in north-wesr Europe, zg-40. A. A. Batkemo, noii.roor.
BencluNo' B' E' & LecBnLuNo, Boreas 10, 323-362. E. (1981j: Eemian and weichselian stratigraphy in south Sweden.
BoulroN' G' s', Srrrrrn, of the last mid-latitude ice sheets. G. D., JoNrs, J. Geol. Soc. London A. s. & Nrwsorrlr, 142,44i474.J. (19g5): Glacial georogy and graciorogy BownN, D. e. (197g): euaternary Geology. p".garnon press, Oxford.
tt:il?
i;;i?l:;Jrlfi MEYER. x."o. *sE')' Report on trre sfmposium Visturian srrarigraphy,
c H r p p c L t - , J ' & s H , c , c x l - s r o N , N . J . . . ( 1 9 8 6 ) : o x y g e n i s o t o p e s a n d s e a l e v e l . N a t u r e 3 2 4 , 1 3 7 - . 1 4 0 . De*screno, w' (1987): L' D. (eds.): Abrupt crimatic Ice core change, evidence NATO A'sI Series of abruit climatic c. 216,223_234. changes.l;,;;";.*, w. H. & Lensynrr,D. Reider, Dordrecht.
The Scandinavian Ice Sheet through the last interglacial/ glacial cycle . 327 D e x r o N , G . H . & H u c s p s , T . J . ( e d s . ) ( 1 9 8 1 ) : T h e l a s t g r e a t i c e s h e e t s . J o h n W i l e y & S o n s , N e w Y o r k . DonNEn, J. (1983): The identification of Eemian interglacial and Weichselian interstadial deposits in
Finland. Annales Academiae Scientiarum Fennica. Series A 136, l-38.
Dnozoowsrt, E. (1980): Chronostratigraphy of the Vistulian glaciation on the lower Vistula valley.
Quatern. Studies in Poland 2, 13-20.
- & FBponowlcz, S. (1987): Stratigraphy of Vistulian glaciogenic deposits and corresponding ther- moluminescence dates in the lower Vistula region. Boreas 16, 139-153.
Fonssrnou, L. (1982): The Oulainen interglacial in Ostrobothnia, western Finland. Acta Universitatis Oufuensis. Series A 136, l-125.
- (1984): Eemian and Weichselian correlation problems in Finland. Boreas 13, 301-318.
- (1985): Further observations on Weichselian and Eemian correlations in Finland: A reply to Hannu Hyvdrinen. Boreas 14, 2&-266.
- , E n o N r r , M . & G n O N l u N o , T . ( 1 9 8 7 ) : O n m a r i n e p h a s e s a n d s h o r e l e v e l s o f t h e E e m i a n l n t e r g l a c i a l and Weichselian interstadials on the coast of Ostrobothnia, Finland. Geological Survey of Finland.
Special Paper 2,3742.
Grt-oN, R. (1982): On the stratigraphy and chronology of the last glaciation (Vistulian) in Poland.
Quatern. Studies in Poland 3,3'748.
Gnucrn, E. (1979a): Die Seeablagerungen von Samerberg/Obb. und ihre Stellung im Jungpleistoziin.
Eiszeitalter u. Gegenwart 29, 23-34.
- (1979b):Commenton"GrandePilepeatbog:Acontinuouspollenrecordforthelastl40000years"
by G. M. WorLLnno. Quatern. Res. 12, 152-153.
Hlr',rsonc, M., Hrnvns, H., Le,cBnsAcK, R., MAKTNEN, K., NeNoxen, K., OrsrN, L., RoHoe, L., SurtNeN, R. &THonrsBN, M. (1986):Mapof Quaternarygeology, sheet4: Quaternary stratigraphy, Northern Fennoscandia, 1: I mill., Geological Surveys of Finland, Norway and Sweden.
Her-ls, M., SoNsrrcelno,8., coopB, R. G. & Rve, N. (1981): Early weichselian peat at Brumund- dal, southeastern Norway. Boreas .10, 369-379.
Hlllrrons, A. (tSU+): The stratigraphy and genesis of the Drisebacka and Ellesbo drumlins. A contribu- tion to the knowledge of the Weichsel-glacial history in western Sweden. Geologiska Foreningens i Stockholm Forhandlingar 96, 355-37 4.
- (1986): The Dtisebacka interstadials, 17. Nordiska geologmotet, Helsingfors Universitet, 54.
Htnve,s, H. (1983): Correlation problems of interglacial deposits in Finnish Lapland. Quaternary Glacia- tions in the Northern Hemisphere, IGCP project 24, Report 9, 129-139, paris.
-, Konpele, K. & Kul,c'Nsuu, R. (1981): Weichselian in Finland before 15 000 B.P. Boreas 10,
42343t.
- & KurnNsuu, R. (1981): Quaternary stratigraphy and chronology in northern Finland. In: Gon-
BUNov, G. I. (ed.): Glacial deposits and glacial history in eastern Fennoscandia, Kola branch of the USSR Academy of Sciences, Aparity, 5-15.
- , L l c B n g A c K , R., MAKINEN, K . , M r N e r _ 1 , H . , N n n o n p N , K . , O r s e N , L . , R o H o r , L . , S u r r r . r e N , R .
& TsonesBN, M. (1986): Map of Quaternary geology, sheet 5: Ice flow directions, Northern Fen- noscandia. Geological Surveys ofFinland, Norway and Sweden.
- & NnNoneN, K. (1987): The till stratigraphy of Finland. Geological Survey of Fintand Special paper 3 , 4 9 - 6 3 .
Houturnx-NtersEN, M. (1987): Pleistocene stratigraphy and glacial history of the central part of Den- mark. Bull. Ceol. Soc. Denmark -i6, l-189.
HvvAntNEN, H. (1985): Weichselian and Eemian correlations in Finland: A discussion. Boreas 14, 262-263.
JuNcxen, H. (1987): Thermoluminescence dating of sediments from Oulainen and Vimpeli, Ostrabothnia, Finland. Boreas 16, 231-236.
-, LeNovIx, J. & MnNcenuo, J. (1989): Thermoluminescencedatesof Weichselian sediments in west- ern Norway. Boreas ,18, 23-29.
328 lnN MnNcenuo
Konpnle, K. (1969): Die Weichsel-Eiszeit und ihr Interstadial in Perdpohjola (n<irdliches Nordfinland) im Licht von submoriinen Sedimenten. Annales Academia Scientiarum Fennicie Series A III 99.
r - t 0 9 .
Kozensrl, S. (1980): An outline of vistulian stratigraphy and chronology of the grear poland lowland.
Quatern. Studies in Poland 2,21-36.
Kuru, G. l. (1977): Pleistocene land-sea correlations. Earth science Rev. 1-1, 301-374.
LncE nsicx. R. ( I 986): SGU: s kvartdrgeologiska kartliiggning i skala I : 100 000 inom norra Sverige, I 7.
Nordiska geologmotet, Helsingfors Universitet, 91.
- & RosenrssoN, A.-M. (1988): Kettle holes - stratigraphical archives for Weichselian geology and paleoenvironment in northern-most Sweden. Boreas 17, 439_-469.
LecEnl-uNo, E. ( 1987): An alternative Weichselian glaciation model with special reference to the glacial history ofSkine, South Sweden. Boreas 16, 433-459.
LrNovtx, J. Y. & Hnltnonc, M. ( 1987): Weichselian glacial episodes in outer Sunnmore, western Nor- way. Norsk geologisk tiddskrift 67, 107-123.
- & Mlr'rcEnuo, J. (1985): A Pleistocene sandur in western Norway: Facies relationships and sedimen- tological characteristics. Boreas I 4, 16l-|i4.
L n n s r r u , E . , G u r - r - r x s r N , s . , L e . u n r r z E N , S . 8 . , L r a , R . , L o v L r E , R . & M e N c r n u o , J . ( 1 9 g 7 ) : C a v e stratigraphy in western Norway; multiple Weichselian glaciations and interstadial vertebrate fauna.
B<rrcas /6, 267-292.
Lrunt t ztN, S. E. ( 1984): Speleothem dating in Norway: An interglacial chronology. Norsk geogralisk tidsskrift J8, 198.
- (1986): Karstformer iNordland, Report to Direktoratet for Naturforvaltning. 152 p, Oslo.
LINonrn, L. ( 1984): An outline of Pleistocene chronostratigraphy in Poland. Acta Geologica polonica 34. 27 -49 .
-, Menxs, L. & Pprnu, K. (1984): Late Quaternary glacial episodes in the Hornsund resion of Spitsbergen. Boreas /J, 35-4'7.
LuNoqutsr, J. (1967): Subntordna sediment iJ:imtlands liin. Sveriges Geologiska Undersokning Serie
c 6 t 8 , t- 2 6 7 .
- (1971): The interglacial deposit at the Leveaniemi mine, Svappavaara, Swedish Lapland. Sveriges Geologiska Undersokning Serie C 658, l-163.
- (1974): Outlines of the Weichsel Glacial in Sweden. Geologiska Foreningens i Stockholm Fsrhand- lingar 96,327-339.
- (1981): Weichselian in Sweden before l5 000B.p. Boreas,l0, 395_402.
- ( 1 9 8 3 ) : T h e g l a c i a l h i s t o r y o f S w e d e n . I n : E H l r n s , J . ( e d . ) : G l a c i a l d e p o s i r s i n n o r t h - w e s r E u r o p e , 77-82, A. A. Balkema. Rotrerdam.
- (1986): Stratigraphy of the central area of the Scandinavian glaciation. euatern. Science Rev. j,
25r-268.
l-svttB, R. & Snr'roNss, A. (1987): Paleomagnetic excursions recorded in mid-Weichselian cave sediments from Skjonghelleren, Valderoy, W. Norway. Physics of the Earth and planetary Interiors 45 , 337 -348.
MnNcenuo, J. (1977):
.Late Weichselian marine sediments containing shells, foraminifera, and pollen, at Agotnes, wesrern Norway. Norsk Geologisk Tidskrift 52, n_,1.
- ( 1 9 8 1 ) : T h e E a r l y a n d M i d d l e w e i c h s e l i a n i n N o r w a y : A r e v i e w . B o r e a s / 0 , 3 g l - 3 9 3 .
- ( 1 9 8 3 ) : T h e g l a c i a l h i s t o r y o f N o r w a y . I n : E s l e n s , J . ( e d . ) : G l a c i a l d e p o s i r s i n n o r t h - w e s t E u r o p e , 3-9, A. A. Balkema, Rotrerdam.
- ( I 987) : The Allersd/Younger Dryas boundary. In: Bencrn, w. H. & Lesnynre, L.
climatic change - Evidence and implications. NATo ASI Series c 216, 163-li | . recht.
D . ( e d s . ) : A b r u p l D. Reidel, Dord- -, ANDERSEN, s. T., BrncLuNo, B. E. & DoNNrn, l. J. (191,4): euaternary srratigraphy of Norden,
a proposal for terminology and classification. Boreas 3, l}g_l2j.
