glacier mass balance in svalbard since 1912hydrologie.org/redbooks/a208/iahs_208_0313.pdf · direct...

Glaciers-Ocean-Atmosphere Interactions (Proceedings of the International Symposium held at St Petersburg, September 1990). IAHS Publ. no. 208, 1991.

Glacier mass balance in Svalbard since 1912

J.O. HAGEN, B. LEFAUCONNIER & 0. LIEST0L Norwegian Polar Research Institute, P.O.Box 158, N-1330 Oslo, Lufthavn, Norway

ABSTRACT Mass balance investigations on glaciers in Svalbard at high latitudes (78°N) show that the ice masses have been steadily decreasing during the period 1950-1988. Detailed annual observations have been carried out on Braggerbreen since 1966 and Lovénbreen since 1967. The mean specific net balances are -0.43 m

-i -l

year and -0.35 m year water equivalent respectively. Only one year had positive net balance in this period. Zero net balance would be obtained if the summer temperature fell by about 1°C or if the winter precipitation increased by about 50%. Based on summer temperature recordings since 1912, the net mass balance for 1912 -1988 on Br0ggerbreen was reconstructed. The total ice loss in this period was 34.35 m water equivalent corresponding to a mean value of -0.45 m per year. The net balance is negative, but stable. There is no sign of climatic warming through increased melting during the last twenty years.

INTRODUCTION

Mass balance data from extreme high latitudes are sparse. According to the World Glacier Monitoring Service (1988) statistics for 1980-1985 only Meighen Island (79°57'N) and Devon Island (75°25'N) ice caps in north Canada and Br0ggerbreen and Lovénbreen (78°53'N) in Svalbard are measured north of 70°N. In this paper, results of the long time series of measurements in Svalbard are presented. The correlation between mass balance and climatic parameters are discussed and the net mass balance since 1912 is reconstructed.

The results in this paper are based on two papers by Hagen & Liestol (1990) and Lefauconnier & Hagen (1990).

SVALBARD

Svalbard is a group of islands between latitudes 76 N and 81°N, and longitudes 10°E and 35°E. The total area is about 63 000 km where 60% is covered by glaciers.

Ice-free land areas have continuous permafrost with

313

/. O. Hagen et al. 314

thickness varying from less than 100 m near sea level up to 500 meters in the higher mountains (Liestol, 1977) .

The glaciers were close to their Late Holocene (Little Ice Age) maximum extension as late as the end of the nineteenth or beginning of the twentieth century. Like in the rest of the world a general shrinkage of the glaciers occured during the first half of the twentieth century.

Temperature records are available from Svalbard since 1912. At Ny-Alesund weather station close to the investigated area, the mean annual temperature is - 6.0°C (1971-1988). The summer months have mean temperatures above zero, June 2.1°C, July 5.2°C, August 4.1°C, and September 0.1°C. Even the highest areas of the glaciers at about 800 m a.s.l. have some days with temperatures above zero and surface snow melting.

MASS BALANCE INVESTIGATIONS

In 1950 the Norwegian Polar Research Institute started the first systematic mass balance studies on Finsterwalderbreen on the south side of Van Keulenfjorden. In 1966 investigations were started in the Kongsfjord area on Broggerbreen and a year later on Lovénbreen. Both accumulation and ablation were measured every year by the direct glaciological method: snow sounding profiles, pits, and stake readings. Accumulation maps were drawn on basis of the soundings.

Soviet glaciologists started systematic annual mass balance measurements in 1966 on Vôringbreen in Gronfjorden. In the years 1973-1976 they extended the program to three other glaciers on the central west Spitsbergen and one on the east coast.

RESULTS FROM BR0GGERBREEN AND LOVÉNBREEN

Winter accumulation

The precipitation in Svalbard is normally small. At the meteorological stations it used to be 200 - 400 mm year" with maximum in August/September and minimum in April-June (Steffensen, 1982). Reliable measurements of precipitation are difficult because most of it comes in connection with strong winds and snow drift. In Ny-Alesund the meteorological station is situated only 5-6 kilometres from the central areas of the glaciers. However, the correlation between the measured winter precipitation from September to June at the station and the snow accumulation measured by sounding profiles over the entire glacier surface is not high. During the 14-years period, 1974-1975 to 1987-1988, the correlation coefficient was 0.63.

The mean winter accumulation on Br0ggerbreen during the period 1967-1988 is 0.71±0.16 m in water equivalent

315 Glacier mass balance in Svalbard since 1912

and on Lovénbreen 0.73+0.18 m. As can be seen in Fig. 1 and Table 1 the annual variations are fairly small.

FIG. 1 Mass balance results on Br0ggerbreen in the period 1967-1988. The hatched areas represent the net balance.

The altitudinal increase of snow accumulation has a fairly constant gradient db /dz ~ 1 kg m m" .

Superimposed ice gives a significant additional accumulation to the snow precipitation measured on the stakes. Superimposed ice is formed at the snow-ice interface when mild weather or rain soak the snow. This may happen after the first snow fall during the autumn and during the whole summer. The amount of this superimposed ice comes as an additional accumulation being on the average 0.10 to 0.20 m (Liestol, 1975; Wold, 1976), i.e. 10 to 30% of the total snow accumulation.

Trend analysis of the measured winter balance shows a slight increase of the winter accumulation.

Summer ablation

During the observation period (1967-1988) the mean summer balance has been 1.14±0.29 m water equivalent on Broggerbreen and 1.08±0.30 m on Lovénbreen. Ablation values show more fluctuations than the winter balance values. Summer balance (b in m year water equivalent) as a function of the mean temperature for June, July, and August (t in °C) with correlation coefficient r gives:

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b = 0 . 3 6 7 4 t - 0 . 1 6 3 w i t h r = 0 . 7 5 (1)

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If we introduce melting degree days (MDD), the cumulative sum of daily above freezing mean temperatures, for the whole summer season we get a larger correlation coefficient and better regression equation:

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There is no sign of increased melting. The trend for the whole period is stable with a very slight negative trend of the cumulative MDD.

Net balance

The glaciers are not in balance with the existing climate. As can be seen from the altitudinal variations of the net balance (Fig. 2) the ablation near the snout of the glaciers is very high. Summer ablation has been greater than the winter accumulation nearly in all observed years, resulting in steady decreasing ice masses. The annual values for both glaciers are given in Table 1 and are illustrated for Broggerbreen in Fig. 1. The mean annual specific net mass balance is - 0.43 m water equivalent on Broggerbreen and - 0.35 m on Lovénbreen.

BR0GGERBREEN 1966-88 LOVENBREEN 1966-88

-2.0 -1,0 1,0 m -2.0 -1.0

FIG. 2 Mean net mass balance variations related to altitude on Broggerbreen and Lovénbreen. Most extreme years are dotted.

Cumulative net balances are shown in Fig. 5. The total mass loss since the balance year 1967-1968 has been


54.6 106 and 40.5 106 m respectively, which corresponds to an average lowering of the surface by 8.9 and 7.5 m. This is more than 10% of the total volumes.

Only one balance year, 1986-1987, had positive net balance during these twenty years, respectively +0.22 m and +0.24 m for the two glaciers, due to the extraordinary cold summer of 1987.

Based on air photographs from 1977, a glacier map was constructed on scale 1 : 20 000 with contour intervals 10 m. One of the stakes was surveyed in 1985. The vertical difference from 1977 to 1985 at this point of the glacier surface was 5.20. The measured cumulative net balance during the same period was 4.95 m in water equivalent which is 5.50 m of ice. The direct measurements on the map thus agree well with the sum of the annual mass balance figures.

The ice mass transport down the glacier is much less than the ablation in the lower part. Hence the surface gradient gets steeper year by year. This may result in a surge after some years.

RESULTS FROM FINSTERWALDERBREEN

In the years 1950 to 1968 the Finsterwalder Glacier was visited every second year. It was therefore only possible to obtain balances for two-year periods. The measurements were finished in the middle of August. The melting at the end of the ablation periods are therefore added to the following two years balance. The results are given in Table 2.

TABLE 2 Net mass balance on Finsterwalderbreen every second year from 1950-1952 to 1966-1968.

Balance years Net balance (m year water equivalent)

1950-1952 1952-1954 1954-1956 1956-1958 1958-1960 1960-1962 1962-1964 1964-1966 1966-1968

-1.35 + 0.05 -1.20 + 0.20 -0.05 -1.15 -0.10 -0.40 -0.55

Only two of the periods showed positive balance and the result was therefore a decrease of the glacier volume.


The mean annual deficit was -0.25 m water equivalent, which gave a total loss of -4.55 m from 1950 to 1968. Since the velocity below 300 m a.s.l. is negligible, the lowering of the surface here is almost the same as the net balance.

RESULTS FROM SOVIET MEASUREMENTS

Soviet mass balance investigations are given in Table 3 (Gus'kov, 1983; Troitsky, personal communication). The series are shorter but the results are in fairly good agreement with the Norwegian recordings. Their longest series from Vôringbreen shows a correlation coefficient r = 0.81 with the net balance of Br0ggerbreen, while the net balance of Bertilbreen gives r = 0.88. On both these glaciers the results show higher mass deficit than in the Kongsfjord area. The mean net balance on Vôringbreen was -0.65 m in the period 1973/1974 to 1985/1986 while it was -0.70 m on Bertilbreen in the observation period 1975/1976 to 1984/1985. The five years of measurements on the small glacier Daudbreen on the east coast indicate that the glaciers in the east have negative mass balance too and follow the same trends as the central and westerly glaciers.

DISCUSSION

ELA and net balance

The activity index is the balance gradient near the equilibrium line. This index (Sb /5z) is nearly constant for each glacier and thus gives a strong relationship between the net balance(b ) and the ELA (z ). This has been shown on different temperate glaciers6 elswhere e.g. on Storbreen in Norway (Liestol, 1967), Storglaciàren in Sweden (Schytt, 1981) and Peyto Glacier in Canada (Young, 1981). Kuhn (1981) stated that, for a given glacier, climatic fluctuations can best be traced from observations of variations in the equilibrium line altitude. A simple regression analysis gave the linear equation for Braggerbreen:

b = 0.649 - 0.002637 z with r = 0.961 (3) n e 1 a v '

and for Lovénbreen:

b = 0.9158 - 0.003223 z with r = 0.953 (4) n e 1 a K '

Both lines are shown in Fig. 3. The measurements have shown that during the twenty

years of observations the mean ELA is 417 m a.s.l. on Breggerbreen and 399 m a.s.l. on Lovénbreen.

The equations (3) and (4) give equilibrium lines for zero net balance at 246 and 284 m a.s.l. respectively

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(Fig. 3). This balance could be obtained if the mean melting degree-day sum (MDD) was lowered from 390 to 290, which correspond to a lowering of the mean summer temperature by about 1°C. The same balance could be obtained by about 50% higher winter precipitation.

BR0GGERBREEN 1967-88 LOVENBREEN 1967-88

an 1 3 6 7 - 3 3

1,0 -1 .0 0,5 1.0

Specific net mass baiar.ee (b„) rn water eq

Specific net mass balance (b„) m water eq

FIG. 3 The relation between the equilibrium line altitude and the specific net mass balance on Broggerbreen and Lovénbreen.

When the snow pack is melting away, the superimposed ice is visible in the zone below the transient snow-line. The altitude of the transient snow line may be far above the actual ELA and the altitude difference varies as the amount of superimposed ice vary. Thus we need stake readings to find the elevation of the equilibrium line. When this elevation is found, the net balance of the glacier can be calculated from the regression equations (3) and (4) .

Both the Norwegian and the Soviet mass balance measurements, except on Finsterwalderbreen (233.8 km), have been carried out on relatively small (6 km ) glaciers close to the coast. The main part of these glaciers are below 500 m a.s.l. On large glaciers and ice caps only sporadic measurements have been carried out for single years. Recent investigations on Kongsvegen (Hagen, 1988) indicate that these glaciers covering higher areas are

baiar.ee

J. O. Hagen et al. 322

closer to steady state balance than the small ones. In the balance year 1987-1988 the net balance on Kongsvegen was -0.05 m while it was -0.50 m on Br0ggerbreen. The equilibrium line altitude was at 520 m on Kongsvegen and at 450 m on Br0ggerbreen. The mean altitude on Br0ggerbreen is 310 m a.s.l. and on Kongsvegen 560 m a.s.l.. The area distribution is thus very important.

Correlation

The result of multiple correlation between Broggerbreen net mass balance and climatic parameters is presented in Table 4 with several correlation coefficients. It is interesting to determine a useful simple model with the smallest number of parameters possible and a complex model utilizing all influential variables. We have data série of 20 years (1969-1988). The best multiple correlation coefficient is R = 0.88, in the simple but useful relation (I) or R = 0.90 in (II) in the more complete one. These coefficients explain respectively 77 and 81% of the variance.

Regression

We used the coefficients from (II) in Table 4. Thus the linear regression equation is :

b = -0.0014 T - 0.0053 T - 0.0067 T -n 6 7 8

- 0.0023 T + 0.0019 P + 1.009 (5) 9-10 10-5

and from (IV):

b = -0.0065 T - 0.0756 LW + 0.0016 P + n 7-8 7-8 10-5

+ 1.009 (6)

where b is the estimated net balance, T is the melting degree "days (MDD) in June(T ), July(T ), August(T ), September and October (T _ ) July and August (T ), Pio the precipitation from October to May, LW ~ the long wave radiation in July and August.

Fig. 4 shows that observed and estimated Broggerbreen net mass balances are fairly close. The analysis indicate that "melting degree days" for every month from the beginning to the end of the ablation season are the best parameter.

Radiation

In view of the limited number of observations, we have introduced the fewest explanatory variables possible. The


TABLE 4 Correlation coefficients. "MDD" is the temperature in positive degree days, precipitation is in mm water equivalent, LW is the long-wave radiation in kcal irf . Temp. in July, August and September in Longyearbyen is the monthly mean temperature. For relations I, II, III, for relation V, P<0.1%

P<0.03%; for relation IV, P<0.3%;

Number of years

Correlation coefficients

Explanatory variables

Multiple Partial Total

A. Correlation between Broggerbreen net balance and climatic parameters from Ny-Âlesund:

[I) 19 O.i

;il) 19 0.90

(III) 20 0.79

(IV) 8 0.9Ï

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MDD in July and August (T _ ) Precipitation from October to May MDD in June ( MDD in July ( MDD in August ( MDD in Septembe October (T )

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1 0 - 5

MDD in July and August (T _ ) MDD in September and October (T )

9-10

MDD in July and August (T _ ) Longwave radiation in July and August (LW _ ) Precipitation from October to May (P ) * 10-5 '

B. Correlation between Broggerbreen net balance temperature in Longyearbyen:

and

(V) 22 0.72 -0.55

-0.31

-0.68 Temp, in July and August (T?_8)

-0.56 Temp, in September (T ) \ 9 '


best correlation coefficient is obtained with the use of just one more parameter, the long-wave radiation from the atmosphere in July and August (IV in Table 4). Introduction of June radiation decreased the correlation and in September data are missing. This analysis agrees with Braithwaite & Olesen (1985) who found in West Greenland little relationship between ablation and global radiation and suggested that the best parameter would be the long waves radiation.

(m water eq)

1967 1970 1975 1980 1985 1988

FIG. 4 Br0ggerbreen net balance for the period 1967-1988. (a) - b observed; (b) - b estimated from summer and autumn temperatures "and winter precipitation in Ny-Alesund, (see equation 5) ; (c) - b estimated from summer and autumn temperatures in Longyearbyen, (see equation 7); (d) - trend of the observed net balance.

Broggerbreen mass balances since 1912

There is a good correlation between Broggerbreen annual net mass balance and temperature in Ny-Alesund (Table 4). A similar evolution of summer temperatures is known at every station in Svalbard including Bjornoya and Jan Mayen (Steffensen, 1982) . The most complete series of observations are for Isfjord Radio and Longyearbyen situated almost 100 km from Ny-Alesund. We reconstructed


temperatures in Longyearbyen for the missing periods. For the period 1976-1988 we used data from Ny- Alesund because we had a good correlation and also corroboration from the Svalbard Lufthavn record, 5 km of Longyearbyen. Thus we have summer and autumn temperatures in Longyearbyen from 1912 to 1988 (Fig. 6). The multiple correlation coefficient between Broggerbreen mass balance and these temperatures is R = 0.72 with 22 years of data, explaining 52% of the variance. The equation of the linear regression is :

b = -0.35 t - 0.05 t + 1.603 (7) n 7-8 9

where b is the estimated mass balance, t _ the mean temperatures in July and August, t the mean temperature in September.

A comparison between observed and estimated mass balance is shown in Fig. 4. There are some gaps, year to year, but the observed and estimated mean and cumulative mass balances are equal, the annual average is -0.43 m and the total -9.53 m of water equivalent. The standard deviation is 5 = 0.28 for observed and only S = 0.20 for the estimated data. Summer temperatures in Longyearbyen explain only half of the annual variation of the mass balance but give a good estimation of the cumulative values.

The evolution of the cumulative net mass balance for the Brogger glacier since 1912 is shown in Fig. 5. The total mass of ice lost is 34.35 m of water equivalent, with a mean of -0.45 m per year.

We have shown that the shrinkage of the Brogger glacier started around 1918. In 1907 Isachsen (1912) observed and took pictures of small cirque glaciers on the Br0gger peninsula. He noticed that Broggerbreen and Lovénbreen were at their maximum for the time. Their fronts were domed with an associated frontal moraine and there were no other frontal moraines down stream. Later, aerial photography from 1936, 1948, 1966 and 1977 indicate that the decrease of these glacier was continuous. Thus there is an agreement between the estimated balance and historic observations.

The climate

Temperature recordings in Svalbard started in 1912. The most striking in this series is the rapid increase of winter temperature from 1912-1920. This is in good agreement with recordings in northern Scandinavia and the Northern Hemisphere. The summer temperature increase in 1912-1920 however was less pronounced, but still significant. Fig. 6 shows the five-year running mean summer temperature (July, August, and September) in Longyearbyen. It has been fairly stable, but with a slight decrease since 1920, and fluctuated between 4 and 4.5 C.


The slight decrease means that the summer balance is less negative and thus, specially with the observed indication of a slight increase in winter accumulation, the annual deficit is slightly decreasing too.

- 3 4 , 3 5 -

cumuiated b„ A a Cm water eq) A b

FIG. 5 Cumulative net balance of Breggerbreen for 1912-1988 estimated from temperature in July, August, and September in Longyearbyen. (a) - estimated net balance; (b) - observed net balance.

°c

6 -

1912 1930 1948 1966 1984 1916 1934 1952 1970 1988

FIG. 6 Five-year running mean temperatures of July, August, and September in Longyearbyen for the période 1912-1988. Recorded data for twelve years between 1916 and 1946 and for the period 1957-1976. Estimated data for other years before 1957 and for the period 1976- 1988.

In polar regions, the greenhouse climate effect is expected to be largest and possibly first observable. Different models all conclude with a temperature increase


of 6 to 8 C in polar regions within 40 years. Even with the lowest expected increase this means +0.15°C per year.

Increased temperature results in higher evaporation and thus higher precipitation. On a global scale some models predict this effect to cause 7 to 11% higher annual precipitation within the next forty years, mainly in the tropics. However, an increase of about 5% of the winter precipitation in the Svalbard area will compensate only a mean increase of the summer temperature of about 0.1°C.

Increased glacier melting is one of the easiest measurable effects of temperature rise. However, many climate models predict annual temperature increase and less seasonal temperature differences. An increase in the winter temperature has a minor effect on the summer ablation. The main effect of a temperature increase on the glaciers is thus the increase in the summer temperature, or the total sum of "melting degree days".

As far as we can see from twenty years of mass balance measurements, in north-west Spitsbergen there is no indication of increased mass loss/melting rate on the glaciers. The glaciers have had a steady decrease in volume with negative net balance nearly in all years. The only trend is a slightly less negative net balance due to a small increase of the winter accumulation.

REFERENCES

Braithwaite, R.J. & Olesen, O.B. (1985) Ice ablation in West Greenland in relation to air temperature and global radiation. !_,_ Gletscherkd. Glazialgeol. 20 (1984), 155-158.

Gus'kov, A.S. (1983) Water-ice balance of glaciers of Spitsbergen in the 1979/80 balance year (in Russian). Materialy Glyatsioloqicheskikh Issledovaniv 46. 136-139.

Hagen, J.O. (1988) Glacier mass balance investigations in the balance year 1986-87. Polar Research 6., 205-209.

Hagen, J.O. & Liest0l, 0. (1990) Long term glacier mass balance investigations in Svalbard 1950-88. Ann. Glaciol.l4f 102-106.

IAHS/UNEP/UNESCO (1988) Fluctuations of qxaciers 1980 -1985. Volume V. Zurich: World Glacier Monitoring Service.

Isachsen, G. (1912) Exploration du Nord-Ouest du Spitsberq Entreprise sous les Auspices de S.A.S. le Prince de Monaco. Résultats des campagnes scientifiques accomplies sur son yacth par Albert 1er, Prince Souverain de Monaco 40.

Kuhn, M. (1981) Climate and glaciers. Symposium on Sea Level, Ice and Climatic Change, Canberra 1979. IAHS Publication 131. 3-20.

Lefauconnier, B. & Hagen, J.O. (1990) Glaciers and climate in Svalbard, statistical analysis and reconstruction of the Br0gger Glacier mass balance for the last 77


years. Ann. Glaciol. 14. 148-152. Liestol, 0. (1975) Glaciological work in 1973. Norsk

Polarinstitutt Brbok 1973, 181-192. Liest0l/ 0. (1977) Pingos, springs and permafrost in

Spitsbergen. Norsk Polarinstitutt flrbok 1975, 7-29. Liestol, 0. (1967) Storbreen glacier in Jotunheimen,

Norway. Norsk Polarinstitutt Skrifter 141. Schytt, V. (1981) The net mass balance of Storglaciâren,

Kebnekaise, Sweden, related to the height of the equilibrium line and to the height of the 500 mb surface. Geoarafiska Annaler 63(A). 219-223.

Steffensen, E.L. (1982) The Climate at Norwegian Arctic Stations. Klima, The Norwegian Meteorological Institute, 5.

Wold, B. (1976) En Glasiologisk unders0kelse av Austre Br0ggerbre, Spitsbergen. Unpubl.thesis, Dept. of Geography, University of Oslo.

Young, G.J. (1981) The mass balance of Peyto Glacier, Alberta, Canada, 1965 to 1978. Arctic and Alpine Research 13 (3), 307-318.

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