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VARIATIONS OF δ18O AND Cl- IN THE ICE CORES OF SPITSBERGEN
J.-M. Punning, R. Vaikmäe, K. Tóugu
To cite this version:
J.-M. Punning, R. Vaikmäe, K. Tóugu. VARIATIONS OF δ18O AND Cl- IN THE ICE CORES OF SPITSBERGEN. Journal de Physique Colloques, 1987, 48 (C1), pp.C1-619-C1-624.
�10.1051/jphyscol:1987185�. �jpa-00226450�
JOURNAL DE PHYSIQUE
Colloque C1, supplgment au n o 3, Tome 48, mars 1987
VARIATIONS OF bl'O AND C1- IN THE ICE CORES OF SPITSBERGEN
J.-M. PUNNING, R. V A I K M ~ ~ E and K . T ~ G U
Institute of Geology of the Academy of Sciences, Estonia 7 , Tallinn, 200101, Estonian SSR, USSR
R6sum6. Les recherches d'isotope-geochimiques dans 1 'a r c h i p e l du Spitsbergen o n t & t & f a i t e s pour d&terminer l e s c o r r e l a t i o n s e n t r e l e s composi t i o n s i s o t o p i q u e s e t g6ochimiques du n6v& e t de l a glace e t l e s changements dans l e s c o n d i t i o n s natu- r e l l e s . Les c i n q p r o f i l s i s o t o p i q u e s des c a r o t t e s de glace du Spitsbergen i n d i q u e n t de grandes v a r i a t i o n s des c o n d i t i o n s c l i m a t i q u e s d u r a n t l e s 800-900 d e r n i e r e s ann'ees.
Le mecanisme d'accumulation de C1, Na e t K e s t p l u s compliqu'e, a i n s i que l a concen
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t r a t i o n d e ces 'elements e t l e u r s r a p p o r t s s o n t d i f f e r e n t s ; i l s dependent de l a s i t u a
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tiong'eographique des g l a c i e r s e t de l e u r type d ' a l i m e n t a t i o n .
Abstract. The isotope-geochemical i n v e s t i g a t i o n s on t h e a r c h i p e l a g o o f S p i t s - bergen (Svalbard) were aimed a t f i n d i n g o u t c o r r e l a t i o n s between t h e i s o t o p i c and geochemical compositions o f f i r n and i c e and changes i n n a t u r a l c o n d i t i o n s . The i s o - t o p i c curves by a l l t h e 5 Spitsbergen i c e cores d i s p l a y g r e a t v a r i a t i o n s r e f l e c t i n g t h e changes i n t h e c l i m a t i c c o n d i t i o n s d u r i n g t h e l a s t 800-900 years. The accumula- t i o n mechanism o f C1, Na and K i s more complicated, as t h e c o n c e n t r a t i o n o f these elements, as w e l l as t h e i r r a t i o n s d i f f e r depending on t h e geographical l o c a t i o n o f t h e g l a c i e r s and t h e i r t y p e o f feeding.
INTRODUCTION
Isotope-geochemical s t u d i e s c o n s t i t u t e an i m p o r t a n t p a r t o f t h e research program o f t h e Spitsbergen a e r o - g l a c i o l o g i c a l e x p e d i t i o n on t h e I n s t i t u t e o f Geography o f t h e Academy o f Sciences, USSR. They a r e aimed a t r e c o n s t r u c t i n g t h e g l a c i o - c l i m a t i c con- d i t i o n s d u r i n g t h e l a s t centuries. The t a s k was s e t t o study t h e f o r m a t i o n mechanism o f t h e oxygen i s o t o p e and chemical compositions o f f i r n and i c e masses i n temperate g l a c i e r s under t h e c o n d i t i o n s o f s t r o n g me1 t i n g and meltwater i n f l u e n c e . The analyses o f 8g80 i n atmospheric p r e c i p i t a t i o n , c a r r i e d o u t by us s i n c e 1975, revealed t h a t though t h e c o r r e l a t i o n between 6180 and t h e condensation temperatures i n s i n g l e pre- c i p i t a t i o n i s o f t e n v i o l a t e d , t h e c o r r e l a t i o n c o e f f i c i e n t f o r a l o n g e r l i n e o f data
-
0,52
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s t i l l a l l o w s t o use t h e i s o t o p i c curves i n p a l a e o c l i m a t i c r e c o n s t r u c t i o n s . The p r i m a r y i n f o r m a t i o n contained i n seasonal sediments c e r t a i n l y undergoes d e f i n i t e changes i n t h e processes o f m e l t i n g and metamorphism. Our i n v e s t i g a t i o n s on t h e Gron- f j o r d - F r i d t j o f i c e d i v i d e and t h e Lomonosov p l a t e a u showed t h a t t h e amplitude o f 6180 v a r i a t i o n s i n snow and f i r n d e p o s i t s decreases i n time, a s h i f t o f t h e mean 6q80 v a l u e toward h i g h e r values i s a l s o marked. But, as a Pule, these changes do n o t i n - f l uence t h e general morphology o f i s o t o p i c curves. The primary chemical composition i s s t i l l b e t t e r preserved. T h i s i s i n d i c a t e d by t h e sharp peaks on t h e p a c t i v i t y curves and t h e seasonal rhythm i n t h e v a r i a t i o n s o f Na, K and C1 C11.I n o r d e r t o determine t h e r o l e o f general c l i m a t i c changes and l o c a l i n f l u e n c e s i n t h e f o r m a t i o n o f the isotope-geochemical composition o f i c e we s t u d i e d 5 g l a c i e r s s i t u a t e d i n d i f f e r e n t geographical areas o f t h e archipelago and belonging t o d i f f e - r e n t f e e d i n g types ( f i g . 1). Table 1 presents t h e main data o f these g l a c i e r s t o - gether w i t h t h e average values of t h e analysed components.
SAMPLING AND METHODS
A f t e r t h e c o r e ' s surface had c a r e f u l l y been cleaned by removing 3-5 nun o f i c e , even l a y e r s from fragments o f t h e core, which had accumulated i n 5-10 y e a r s on t h e
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987185
JOURNAL DE PHYSIQUE
Fig. 1. Location of studied g l a c i e r s (see Table 1).
Table 1. Average 6180 and C1 values i n the investigated i c e cores.
No. on Glacier Feeding Elevation, Length Mean ac- 6180, C1-,
f i g . 1 type m of cumulat- %O mg/l
core, m ion of i c e , cm/y r
1 Westfonna cold 580 208 88 -15,5 1,5
(Nordaustl andet) f i rn
2 Austfonna cold 700 202 97 -17,9 1,O
(Nordaustlandet) f i r n
3 Lomonosov plateau cold 1000 20 1 85 -14,2 5,5
(West-Spitsbergen) f i r n
4 Grijnfjord-Fridt- f irn- 450 20 1 62 -10,8 30-40
jof i c e divide i c e ( West-Spi tsbergen)
5 Amundsen g l a c i e r warm 700 368 ? - 1 1 , O 0,5 ( West-Spi tsbergen) f i r n
average were taken a s samples. In order t o investigate seasonal changes 1,5-2,5-me- t e r s long fragments of core were taken every 30-50 m, which i n turn were sampled every 5-10 mm. Samples i n the form of water were poured i n t o clean vessels of glass and polyethylen and then hermetically closed. The 6180 values were determined on the MI
-
1201 and "Delta-E" mass-spectrometers, C1 on a culometric detector, Na and K by means of flame emission photometry. Various methods were used f o r s t r a t i f y i n g the i c e cores: t h e determination of reference layers, seasonal variations of 6180 and1 correlation of abrupt increases in sulphur concentration with volcanic eruptions F2jy C31.
DISCUSSION OF THE RESULTS
As a l l the studied i c e cores cover approximately t h e same time span (800-900 years) and t h e number of analytical data i s comparable, the average 6180 and C1 va-
lues of t h e i c e cores characterize i n general t h e formation processes of the isotope and chemical compositions of ice. Differences i n the values a r e connected with diffe- rences in t h e geographical location and t h e elevation. Changes i n the 6180 values f i r s t of a l l r e f l e c t variations in mean condensation temperatures together with the influence of t h e type of i c e formation. For example, the isotope composition of the f i r n and i c e masses i n the cores from t h e Gronfjord-Fridtjof i c e divide and the Amundsen plateau might have been influenced by t h e long stay (30-40 years) of pre- c i p i t a t i o n in t h e i n f i l t r a t i o n zone with recurrent phasal t r a n s i t i o n s , thus causing the concentration of isotope 180. AS t h e course of yearly temperatures and, corre- spondingly, t h e 6180 variations i n atmospheric p r e c i p i t a t i o n a r e i r r e g u l a r there i s no reason t o presume s t r i c t seasonal variations of t h e 61B0 values i n f i r n and i c e masses, Likewise, we did not succeed t o determine seasonal layers on the basis of 6180 variations anywhere.
Seasonal changes i n t h e concentration of C1 i n atmospheric p r e c i p i t a t i o n a r e b e t t e r displayed. Much a t t e n t i o n has been paid t o t h e variation mechanism of chemi- cal elements i n atmospheric precipitation. Many reports on t h e symposium "Isotopes and impurities i n snow and ice' were dedicated t o these questions C41, C51. The re- s u l t s a r e contradictory as y e t
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in Antarctica t h e investigators, as a r u l e , have found no seasonal variations 161, t h e concentrations of some elements i n the i c e cover of Greenland show regular f l u c t u a t i o n s 141. Investigating t h e d i s t r i b u t i o n of elements i n t h e seasonal snow cover, Y .T. Gjessing C71 came t o t h e conclusion t h a t t h e increased concentrations of C1 and Mg, as well as NOs and NHy i n t h e layers of snow, accumulated in Nordaustlandet during t h e winter of 1974, were caused by stormes which broke the i c e cover on t h e surrounding aquatory. Our s t u d i e s give support t o the conclusions of Gjessing. In summer-autumn months t h e concentration of C1 i n the samples of atmospheric p r e c i p i t a t i o n collected a t the meteostation of Barentsburg exceeds the winter values by tens, sometimes hundreds of times. The concentration of C1, an element of marine o r i g i n , sharply decreases a t a greater distance from open sea o r a t a greater a l t i t u d e (see a l s o Table 1 ) . For t h i s reason i t i s evident, t h a t only those g l a c i e r s which a r e located near enough t o an open aquatory of changing i c e conditions can r e f l e c t seasonal variations. Naturally, the process of metamorphic a l t e r a t i o n s can cause c e r t a i n r e d i s t r i b u t i o n of primary concentrations, such a s an increased concentration of C1 in i n t e r l a y e r s of i c e C71.Fig. 2. Variations i n the concentrations of C1, Na and 6180 values in-fragments of core from Austfonna.
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A t a greater distance from t h e open aquatory the atmosphere quickly loses t h e ele- ments of marine origin and t h e determination of seasonal layers becomes complicated.
On t h e basis of variations of C1 i n t h i s layers we succeeded i n determining seasonal layers in the cores from Westfonna C21 and the Vavilov i c e dome on Severnaya Zemlya archipelago C81, i n Austfonna, s i t u a t e d f a r t h e r o f f , seasonal rhythmicity could not be detected ( f i g . 2).
Fig. 3. Variations of 6180 ( % c ) i n i c e cores: 1) Westfonna, 2) Austfonna, 3) Lomo- nosov plateau, 4 ) Gronfjord-Fridtjof i c e divide,
Distribution trends of chemical elements and t h e oxygen isotopic composition a r e of g r e a t e s t i n t e r e s t i n palaeogeographfc reconstructions. Fig. 3 presents the 61S0 curves f o r four Spitsbergen g l a c i e r s . The most c h a r a c t e r i s t i c feature of the oxygen- -isotope curves i s the presence of r e l a t i v e l y negative 6180 values i n t h e layers which accumulated from t h e f i r s t half of the XVII century t o the beginning of the present one, a t which the more s i g n i f i c a n t decrease periods of 6q80 i n precipitation almost i d e a l l y coincide on a l l the curves. Hence, two conclusions: 1) climatic changes a r e well r e f l e c t e d on isotopic curves ( a f t e r a l l , t h i s i s t h e S.C. L i t t l e Ice Age) and 2) t h e mechanism of formation and transportation of atmospheric moisture, as well as i t ' s general source had t o be q u i t e similar a l l over t h e archipelago. The central p a r t s of t h e curves accumulated during a change from r e l a t i v e l y warm t o severe c l i m a t i c conditions, d i f f e r a b i t i n morphology, In t h i s time span t h e forrna- tion of the i s o t o p i c composition of f i r n and i c e might greatly have been influenced by the unstable regime of atmospheric c i r c u l a t i o n and the feeding regime of glaciers.
After a1 I , i n a1 tered external conditions many g l a c i e r s could have changed t h e i r type of feeding. I t i s also not excluded t h a t short-term changes i n meteorological conditions i n various parts of Spitsbergen could have shown temporary s h i f t s o r proceeded i n an opposite direction.
Fig. 4.
1 2 3 0 1 2 3 5 7
I--
aY
3 - 2
a>
-.
2'190
- =
1200
-
1
2 3Variations i n t h e concentration of C1 (mg/l) i n i c e cores:
2 ) Austfonna, 3) Lomonosov plateau.
1 ) Westfonna,
Our investigations indicate t h a t l a s t i n g changes i n the concentration of C1 re- f l e c t the dynamics of pack i c e cover on t h e aquatory surrounding t h e archipel ago C91.
S a t i s f a c t o r y c o r r e l a t i o n of t h e concentration trends of C1 i n t h e i c e core from the Lomonosov plateau and the i c e conditions on the surrounding aquatories (reconstruct- ed on the basis of h i s t o r i c a l data as well as those from instrumental observations) stand as proof of this. The correlation c o e f f i c i e n t between t h e variations of C1 and t h e dynamic of pack i c e near the coast of Iceland 1500-1800 y.a. [lo] i s -0,78, and even -0,9 according t o t h e data on t h e changes i n i c e d i s t r i b u t i o n on t h e Sea of Greenland during the present century C111. The e f f e c t of short-term meteorological conditions, having great influence on t h e seasonal course of t h e concentration of C1 i n atmospheric precipitation, i s smoothed in case of durable trends and becomes of secondary importance. Our conclusions a r e a l s o supported by the s a t i s f a c t o r y correla- tion between the curves of 6180 and C1 i n the cores from t h e Lomonosov plateau and t h e Vavilov i c e dome [I], Variations of C1 in t h e cores from t h e i c e domes of Nord- austlandet a r e considerably smaller, as t h e r o l e of local influence decreases due t o t h e bigger distance from the open sea ( r e l a t i v e t o t h e interval i n the seasonal dyna- mics of t h e pack i c e cover) ( f i g . 4).
Na and K were also determined i n the core from Austfonna (Nordaustlandet). Table 2 presents the data and t h e correlation matrix according t o 98 samples.
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Table 2. Correlation matrix, mean concentrations of C1, Na, K and mean 61s0 values i n t h e i c e core from Austfonna.
The good c o r r e l a t i o n between C1 and Na, a s well as t h e closeness of t h e Cl/Na r a t i o (2,13) i n i c e t o t h a t i n s e a water (1,8) speak of t h e i r common source
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open sea aquatory. Instead, t h e weak c o r r e l a t i o n of Na and C1 w i t h K and t h e r e l a t i v e l y small r a t i o n of Na/K p o i n t t o t h e p a r t i a l l y continental o r i g i n of K.REFERENCES
111
Vaikmae, R., Punning, J.-M. In: Correlation of Quaternary chronologies. (Ed.Mahaney, W.C., Geo Books, Toronto), (1984), 385-394,
C2l Punning, J.-M., Martma, T., T6ugu, K., Vaikmae, R., Pourchet, M., Pingelot, F.
Data of g l a c i o l o g i c a l s t u d i e s , c h r o n i c l e , discussion. (Moscow), Publ. 52, (1985), 202-205.
C31 Punning, J.-M., Vaikmae, R. In: Glaciology of Spitsbergen. (Ed. Kotljanov, V.M., Moscow), (1985), 148-159.
141 Langway, C.C., Klouda, G.A., Herron, N.M., Cragin, J.H. IAHS-AISH, Publ
.
118,(1975), 302-306.
C51 Weiss, H.V., Koide, M., Bertine, K.K., Goldberg, E.D. IAHS-AISH, Publ. 118, (1975), 103-107.
C61 Lorius, C., Baurdin, G., Cittanova, J., P l a t z e r , R. T e l l u s , XXI, (1969), 136- -148.
C7] Gjessing, Y.T. Atmospheric Environment, 11, (1977), 643-647.
C81 Vai kmae, R.A., Punning, J .-M.K. Data of Glaciological s t u d i e s , c h r o n i c l e , discussion. (Moscow), Publ
.
44, (1982), 145-149.C91 Punning, J.-M.K., Vaikmae, R.A., P i l l , M.A., Gugu, K. In: Isotope and geo- chemical methods i n biology, geology and archaeology. (Ed. Liiva, A , , Tar- t ~ ) , (1981), 108-111.
[lo] Lamb, H.H. Cl irnate: present, p a s t and f u t u r e . (London
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New-York), (19771, 833.[ll] Budyko, M.I. Recent c l i m a t i c changes. (Leningrad), (1977), 216.
