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PL
W artykule przedstawiono zmienność czasu trwania pokrywy lodowej na 17 dużych rzekach Arktyki. W drugiej połowie XX wieku czas trwania pokrywy lodowej uległ wyraźnemu skróceniu o 21-28 dni na 100 lat. Na czterech rzekach (MacKenzie, Pieczenga, Peczora, Titowka i Taz) czas trwania pokrywy lodowej uległ wydłużeniu nawet o 33 dni na 100 lat. Skrócenie czasu trwania związane jest z późniejszym formowaniem się pokrywy lodowej oraz z jej wcześniejszym rozpadem. Należy przypuszczać, że zmienność czasu trwania zjawisk lodowych jest dobrym wskaźnikiem zachodzących w Arktyce zmian klimatu. Ze skróceniem czasu trwa-nia zjawisk lodowych wiąże się wydłużenie okresu nawigacyjnego.
EN
Trends and fluctuations in the dates of ice cover formation and breakup on selected rivers in the Arctic worked out based on databases: Benson B., Magnuson J., 2000, Global lake and river ice phenology database; Vuglinsky V., 2000, Russian river ice thickness and duration; National Snow and Ice Data Center, 1998, Nenana Ice Classic: Tanana River ice annual breakup dates. Most of the Arctic rivers are frozen for 7-8 months. Dissimilarity of flow conditions during ice cover period, ice jams and dams allow to state that it is the most important part of the Arctic rivers hydrological regime. The main problem in comparison of ice events and determine its trends are heterogeneously data series. Data are selected to be the most similar. In this study are used homogeneous and comparable series for period 1958-1990. For analysis have chosen 17 rivers situated in different Arctic areas. 3 are in Europe, 10 on Siberia and the others 4 in Canadian Arctic and on Alaska. For all of them was calculated average time of ice cover duration, dates of freezing and breakup and trends of this parameters. Difference between ice cover duration on the Arctic rivers is 64 days. The longest time of ice cover duration is on Anabar – 248 days. The shortest, 184 days, on Yukon in Dawson. Average time of ice cover duration on most part of the rivers is more than 200 days. The earliest date of freeze-up is on Anabar river, average 2 October. To the end of the month ice cover is on most of the rivers. At the beginning of November come out on MacKenzie, Yukon and Pechenga rivers. Breakup starts 5 May (Tanana river). To the end of May ice cover vanish on most of the rivers. Exceptions are rivers in Eastern Siberia and Coppermine river, where spring ice drift starts latest, average 18 June. Differences between freeze-up dates amount 40 days, while between breakup on various rivers 44 days. Ice cover duration trends are diverse but generally on most of the rivers trends are negative (for 11 of 16 rivers). The biggest trend was on Yukon river in Dawson in 1970-90 (–24.2 days/100 years). A little bit smaller trend (–23.7 days/100 years) was on Ob (1958-90) and Anabar (–21.8 days/100 years). Positive values characterized rivers: MacKenzie, Pechenga, Pechora and Taz, which had a biggest value (33.2 days/100 years). Freeze-up on the Arctic rivers occurs later and later. It is described by positive value of this parameter. It fluctuates within 0.9 days/100 years on Anabar to 18.9 days/100 years on Coppermine. However in two stations in the Canadian Arctic, 3 in European Arctic and on Lena ice cover freeze-up more and more early. Only two rivers: Yndigirka and Pechora freeze-up later and later (it is 2.7 days/100 years on Yndigirka and 15.7 days/100 years on Pechora). On the others rivers trends are negatives and fluctuates within 0.2 days/100 years (Coppermine) to 47 days/ 100 years (MacKenzie in Fort Good Hope). Presented trend’s values are different from this presented by Magnuson et al. (2000), who compared freezing dates for lakes and rivers together for all the northern hemisphere.
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