jerzy PEREYMA Institute of Geography Wrocław University PI. Uniwersytecki 1, 50-137 Wroclaw POLAND

POLISH POLAR STUDIES XXVI Polar Symposium

/ft вШШй! Lublin, June 1999

CONTEMPORARY TENDENCIES IN THE FORMATION OF POLAR GLACIER MASS BALANCE

WSPÓŁCZESNE TENDENCJE W KSZTAŁTOWANIU BILANSU MASY LODOWCÓW POLARNYCH

INTRODUCTION

Formation of glacier mass balance is an important problem in contemporary subjects of global environment changes. They are closely connected with climatic changes in a regional or global scale. The measurement series of some Arctic and Subarctic glaciers (Fluctuations of Glaciers 1967, 1973, 1977, 1985, 1988, 1993, 1998) existing for several scores of years allows to determine the tendencies in cli-matic and glacial changes. Finding regularities in these changes comes acrross by some difficulties connected with climatic anomalies, among others, with the in-crease of greenhouse gas content and disturbances in oceanic and atmospheric cir-culations. This paper is related to the earlier ones based on an earlier series of re-search (Pereyma 1992).

CHARACTERISTIC OF ARCTIC AND SUBARCTIC GLACIERS

The analysis was based on the studies of six glaciers of the zone above 60° N car-ried out in 1965-1995 using in two cases a little shorter series (Figs. 1-6). There are no long uniform research series for other glaciers of the polar zone. The chosen glaciers are situated in four regions of the northern polar zone. These are:

Devon Ice Cap, Canadian Arctic, 75°N, 83°W; Austre Broegger, Spitsbergen 79°N, 12°E; Wolverine Alaska, 63°N, 145°W; Enga, North Scandinavia (Norway), 66°N, 14°E; Stor, North Scandinavia (Sweden), 68°N, 18°E.

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The Arctic glaciers Devon and A. Broegger were characterized by a negative mass balance all the time (Fig. 1). That is particularly well seen on Spitsbergen where in the summer season a relatively warm cyclonic circulation from the S-SW sector is active. It causes an increase of ablation surface, annual negative balances (BN/BA) about 500 mm of water equivalent (w.e) and according to the current ob-servations of the glacier A.Bregger, a retention of only 20% of its accumulative sur-face. However, this is twice as large a surface as that before 1991 when there was

400

200

0

'l -200

-400

-600

-800

-1000

-1200

Fig. 1. Mass balance (BN/BA) of Arctic glaciers: Devon Ice Cap in 1965-1995 and Austre Broegger, Spi-tsbergen in 1975-1995 (mm w.e.)

a positive balance followed by small negative ones in successive years. This disad-vantageous relation between accumulative and ablation surfaces is the reason for a large absorption of radiation energy in the ablation zone causing progressive en-largement of this zone. Disproportions of the radiation balance in the hypsometric zones are greater on valley glaciers than on the glacial domes (Oerlemans 1993). Being thus independent of atmospheric circulation dissimilarity, the Canadian Glacier Devon Ice Cap was characterized with less negative mass balances of about 200 mm w.e. yearly in the whole research period. It maintained a relatively stable part of the accumulative surface of about 50%.

The total mass balance of the two Arctic glaciers under disscussion is entirely different. The Spitsbergen glacier had the total mass loss of about 9,000 mm w.e. during 20 years but a less known Canadian glacier only about 200 mm w.e. (Fig. 4).

BN\BA

year • DEVON ICE CAP. CANADA И AUSTRE BROEGGER, SPITSBERGEN |

Contemporary tendencies in the formation of polar glacier mass balance 189

BNVBA c - o > — « i n j ^ o i — <n 1Л г- <B »- <4

|И WOLVERINE, ALASKA 0GULKANA, ALASKA

Fig. 2. Mass balance (BN/BA) of the Alaska subarctic glaciers Wolverine and Gulkana in 1965-1995 (mm w.e.)

The subarctic mass balances of the Alaska glacier are quite different. The Wol-verine Glacier situated over the Atlantic was characterized by small possitive BN/BA in 1965-1976. In successive years the annual balance was as large as 3,000 mm w.e. In 1988-1995 all BN/BA were negative, reaching up to -2,500 mm w.e. in 1990 (Fig. 2). For 30 years the continental Gulkan Glacier had yearly negative mass balances whose size enlarged lately. It is possible that the negative BN/BA occurring lately was due to smaller rainfalls on both glaciers on Alaska as a result of the activity of the oceanic oscillation El Nino.

The image of total mass balance of both Alaska glaciers (Fig. 5) indicates the return of Wolverine Glacier to the initial stage after 30 years and the large (-10,000 mm w.e.) loss of Gulkan Glacier. The hypsometric situation of the equilibrium line and the relation of accumulative and ablation areas did not change much on these glaciers. On Wolverine Glacier the accumulation zone increase was about 10% and a similar loss was observed on Gulkan Glacier.

Subpolar glaciers of Northern Scandinavia were characterized by a similarity of mass balance formation for many years. Lately they have reacted differently, though contrary to Alaskan glaciers. The coastal Enga Glacier was characterized by a stable high mass increment. The annual value of mass balance was about 200 mm w.e. The years of 1977-1988 were an exception when BN/BA were smaller and even negative (Fig. 3). The favourable localization of the glacier enabling an influx

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BN\BA

3500

3000

2500

2000

1500

1000

500 ' 0

-500

-1000

-1500

-2000 year

&ENGA, NORTH NORWAY • STOR. NORTH SWEDEN I

Fig. 3. Mass balance (BN/BA) of the Scandinavian subarctic glaciers: Enga in 1970-1995 and Stor in 1965-1999 (mm, w.e.)

CUMMULAT1VE BN\BA

' О '"' " S: 'V' •„• Э 8; G"'

year I DEVON ICE CAP, CANADA AUSTRE BROEGGER. SPITSBERGEN |

Fig. 4. Cumulative balance in Arctic glacier masses (description as in Fig. 1)

Contemporary tendencies in the formation of polar glacier mass balance 191

CUMMULATIVE BN\BA

WOLVERINE, ALASKA -O—GULKANA, ALASKA

Fig. 5. Cumulative balance of Alaska subarctic glacier masses (description as in Fig. 2)

of marine air masses caused the relatively large mass movement increment -20,000 mm w.e. in the period 1970-1995 (Fig. 6). The accumulation zone of Enga Glacier is exceptionally high, covering 80% the total area, the equilibrium line is situated in its central part. The Stor Glacier situated in the Scandinavian mounta-ins has been explored since 1946. It showed large mass losses till the end of the sixties. The loss decrease took place in 1974-1988. Unexpectedly positive values of BN/BA were observed in the last two years (Fig. 3) contrary to the glaciers on Ala-ska. During 50 years of research the mass loss on Stor Glacier was 11,000 mm but in 1965-1995 the cumulative mass balance was about zero (Fig. 6). The accumula-tive part of the glacier is about 50% of the total area.

CONCLUSIONS

The analysis of mass balance of representative glaciers in the northern polar and subpolar zones confirms the dependence of mass balance on rain-bearing ma-rine air masses. The modifying factor is the local radiation balance on the glacier area, which is different on glaciers of a different type. In the coastal areas of Northern Scandinavia characterized by a positive trend of air temperature caused mainly by warm winters (Walsh, Chapman 1990), negative thermal trends of the

192 Jerzy Pereyma

CUMMULAT1VE BNVBA

u i u ) 0 > a ) 0 ) 0 ) 0 ) D ) C » C n C n c A 0 ) 0 ) 0 > O ) 25000

20000

15000

10000

5000

I 0

-5000

-10000

Fig. 6. Cumulative balance of Scandinavian subarctic glacier masses (description as in Fig. 3)

summer season can be observed lately (Przybylak 1996). All these factors cause at present positive mass balances even on Stor Glacier situated farther from the coast. These simple dependences are maintained in Alaska probably due to active interactions of El Nino oscillations. The glaciers in high Arctic have a larger mass loss on Spitsbergen as a result of greater accessibility of the western part of this archipelago to warmer, cyclonic circulations of polar marine air masses in the summer period. Warming up effects due to the increase of greenhouse gas con-tents, resulting in negative glacier mass balances, can be observed in the whole Arctic.

REFERENCES

Fluctuation of glaciers 1967, 1973, 1977, 1985, 1988, 1993, 1998: vol. II-VII, JAHS, UNESCO. OERLEMANS J. 1993: Modelling of glacier mass balance in the light of some climatic factors. Ice in the

Climatic System (ed. Peltier W. E.), Springer: 101-116. PEREYMA J. 1992: Polar glacier mass balance in the light of some climatic factors. Wyprawy Geograficz-

ne na Spitsbergen, UMCS Lublin: 23-29. PRZYBYLAK R. 1996: Zmienność temperatury powietrza i opadów atmosferycznych w okresie obserwacji

instrumentalnych w Arktyce. Wyd. UMK, Toruń: 279. WALSH J., CHAPMAN W. 1990: Short-term climatic variability of the Arctic. Journ. of Climate, 3: 237-250.

I ENGA, NORTH NORWAY -P -STOR, NORTH SWEDEN

Contemporary tendencies in the formation of polar glacier mass balance 193

STRESZCZENIE

Zagadnienia kształtowania bilansu masy lodowców są jednym z ważniejszych problemów współ-czesnej tematyki zmian globalnych środowiska. Są one związane ze zmianami klimatycznymi o skali regionalnej i globalnej. Istniejąca od kilkudziesięciu lat seria pomiarowa nielicznych lodowców arktycz-nych i subarktycznych (Fluctuations of Glaciers...) pozwala na charakterystykę tendencji klimatyczno-glacjalnych. Niniejsze opracowanie nawiązuje do poprzednich prac o tej tematyce, opartych na wcześ-niejszych seriach badań (Pereyma 1992).

Przeprowadzona analiza bilansu reprezentatywnych lodowców północnej strefy polarnej i subpolar -nej potwierdza zależność ich bilansu masy od napływu opadonośnych morskich mas powietrza. Czynni-kiem modyfikującym jest lokalny bilans radiacyjny. W obszarach nadmorskich północnej Skandynawii stwierdza się ostatnio bilans dodatni zaś lodowce wysokiej Arktyki, zwłaszcza Spitsbergenu, mają zde-cydowaną przewagę ubytków masy, co wynika z łatwej dostępności zachodniej części tego archipelagu dla cieplejszych, cyklonalnych cyrkulacji polarnomorskich mas powietrza w lecie. Negatywne bilanse masy lodowców w całej Arktyce wiążą się również ze wzrostem zawartości atmosferycznych gazów szklarniowych.