Ice winter 2007/2008 was short and very mild
The October month was warmer than usual with the temperature of the seawater at the end of the month being above the average by one to two and a half degrees Celsius.
In the northern Bay of Bothnia and in the Gulf of Finland off St. Petersburg the freezing begun in mid November two weeks later than normal. In terms of thermal conditions, November was normal but owing to the warm October the temperature of the seawater was high with no notable ice-formation.
In the beginning of December, the sea was frozen only in the inner archipelago of the northern Bay of Bothnia and in the Gulf of Finland off St. Petersburg and Vyborg. December month was exceptionally warm with no notable increase in the amount of ice. At the end of the year the northern Bay of Bothnia and places in the inner archipelago were covered with ice. The Gulf of Finland had a slight ice cover only off Vyborg and St. Petersburg.
In early January the weather got colder with ice forming in coastal regions of the Bay of Bothnia, the Vaasa archipelago and the inner archipelago of the Sea of Bothnia. In the open Bay of Bothnia south-westerly winds formed a brash barrier at the ice edge. In the Gulf of Finland the amount of ice off Vyborg and St. Petersburg increased with thin ice forming in the archipelago of the Kotka–Hamina area.
Following a cold spell of about a week the temperature in Finland remained five to ten degrees Celsius above the average until the end of the month with no new ice formation. At the end of January the inner archipelago of the Bay of Bothnia, the Vaasa archipelago and the inner archipelago of the northern Sea of Bothnia had an ice cover. In the open seas of the Bay of Bothnia the ice edge ran approximately along the line of Raahe lighthouse –Malören–Nygrån. In the Gulf of Finland only areas off St. Petersburg, the Bay of Vyborg and in the inner archipelago of the Kotka–Hamina area were covered in ice.
In mid-February there was a cold spell with the amount of ice increasing. The Bay of Bothnia north of the line Marjaniemi–Falkensgrund–Piteå and the coastal regions had ice cover. The Vaasa Archipelago and the inner archipelago of Sea of Bothnia were frozen. In places the Archipelago Sea was covered with thin ice between the islands. The inner archipelago of the Gulf of Finland had thin ice cover. Off St. Petersburg and Vyborg the new ice came up to island Seskar.
February ended mild and at the turn of the month only the ice cover in the Bay of Bothnia had increased a little with the open sea areas frozen to the north of the line Raahe–Skellefteå.
In the beginning of March the weather became colder with ice forming in the Quark on the fifth day of the month. On the following day new ice in the open Gulf of Finland reached island Seskar and thin ice occurred in the Finnish coastal regions. The middle part of the Bay of Bothnia south of the line Raahe–Skellefteå remained free from ice. The ice field was drifting towards northwest with a lead opening up on the Finnish coast. For a couple of days the temperature remained below freezing with new ice forming in the Bay of Bothnia lead. Round about the tenth day the weather got milder.
Towards the end of the month the weather became colder one more time and in terms of areal extent the ice cover reached the winter's maximum on 24th of March with 49 000 km². At that time the Bay of Bothnia and the Quark were frozen. In the northern part of the Sea of Bothnia the ice edge ran from Strömmingsbådan to Sydostbrotten and from there on to Skagsudde. The coastal regions of Sea of Bothnia and Gulf of Finland had a very thin ice cover in places in the inner archipelago. The eastern Gulf of Finland had a thin ice cover in the Bay of Vyborg and off St. Petersburg.
At the end of March the weather got milder and the thin ice melted quickly away in the first days of April. By the end of the first week of April the ice had become rotten in the Gulf of Finland and the Bay of Bothnia up to the latitude of Kokkola. The Gulf of Finland and the Sea of Bothnia were ice-free on 9th of April and the last ice of the Gulf of Finland, in the Bay of Vyborg, melted away on 19th of April. At the same time the open areas of the Bay of Bothnia were free from ice with the exception of the Swedish northern archipelago. The remaining coastal ice in the Bay of Bothnia disappeared in the beginning of May so that the Bay of Bothnia was ice-free on 15th of May.
The ice winter in the northern Bay of Bothnia was almost five weeks shorter than average. In the southern Bay of Bothnia the ice season was almost seven weeks, in the Quark more than five weeks and in the Sea of Bothnia almost six weeks shorter than average. In the Archipelago Sea and the Gulf of Finland no ice winter can be considered having existed with the exception of the Russian sea areas.
The maximum fast ice thickness in the Bay of Bothnia was 40 to 60 cm, Sea of Bothnia 5 to 30 cm, Archipelago Sea 1 to 10 cm and in the western and middle Gulf of Finland 1 to 10 cm and in the eastern Gulf of Finland 15 to 30 cm. In the open sea areas of the Bay of Bothnia the ice thickness for the northern parts was 20 to 40 cm and for the southern parts 5 to 30 cm. The open areas of the Sea of Bothnia remained ice-free similarly to those in the Gulf of Finland apart from its easternmost part, where the maximum ice thickness of the open sea areas was 10 to 15 cm.
Patrick Eriksson and Jouni Vainio