The Icing of the Baltic (3_24)

-Winter 1941/42-

Introduction

The ice coverage of the Baltic Sea during the winter 1941/42 was possibly one of the severest since observation had been taken. That was a long time ago, at least 200 years. The long observation series highlights the exceptionality of this winter and the two previous war winters. Did the war at sea ‘make’ these harsh winters, or at least contribute significantly for its arctic appearance?

The absolute speciality of the winter 1941/42 is, that it is the third in a row of three successive very strong ice winters within three years. This has never happened before. Even the comparable winters 1802/03 –1804/05 did not match the severity of the three war winters 1939/40, 1940/41, 1941/42 (Lit.: Liljequist, Isvintern 1941/42). The exceptionality of three successive heavy winters is discussed elsewhere, Three-years-package (3_31). Here the focus is laid on the unique features that on the one hand the Baltic had never been so much action ground for parties in combat over several months until the winter broke its ground, followed by the possibly most strangest winter sea ice conditions ever experienced in the region. As the impact of stirring and mixing the differently tempered water levels in a sea has been explained elsewhere, North Sea cooling (2_16), the following discussion will primarily identify those aspects, which indicate a military contribution to the deviation from common climatic terms.

Baltic Sea geographical features

For this investigation the Baltic Sea can be considered as a closed basin. The average depth is 56 metres, very few locations reach depths over 100 metres. Its shallow coastal areas freeze fairly quickly, even during cold spells of short duration, whereas the water masses of the open sea require much longer time to cool and permit ice formation. Only in rigorous winters, characterized by prolonged very cold spells, is ice formed in the open sea of the southern Central Baltic. The upper limit, 420,000 square kilometres, i.e. ice cover throughout the Baltic, is often reached considerably before the culmination point of the ice winter, the date from which the ice cover begins to diminish (Lit.: Palosuo, p.28).

Due to Leppäranta, et.al (Lit.), the extent and duration of the ice season is dependent, inter alias, on the following conditions. From October onwards the temperature of the Baltic Sea is clearly higher than the air temperature. Since the sea effectively loses heat, it finally brings about a change in the consistency (i.e. the water freezes). It is worth mentioning that, owing to the salinity, the freezing point in the sea areas bordering on Finland is 0.2 – 0.5 degrees below 0°C. At first only a thin layer at the surface is at freezing point. However, during the winter the water becomes mixed and a layer with uniform temperature is formed down to a depth of 30 – 80 metres.

Leppäranta also mentions the following ‘external’ conditions for the build-up and the break-up of the ice. Concerning the former they state: “Ice formation during the early winter depends to a great extent on the varying climatic condition.”

Concerning the latter condition it is said: “The external factor controlling the break-up of the ice is the factor that solar radiation increases rapidly as the spring advances. There are no great differences between the sea areas as regards radiation. …The heat of the sun is transferred much more effectively to the ice through the intermediation of water than directly, since ice absorbs approximately 20 –60% of the solar radiation concentrated upon it while the water surface absorbs 93%.”

They ( Leppäranta, et.al.) further point to the fact, that the exchange of heat between the sea and the atmosphere depends to a high degree on the ice concentration. The Baltic Sea loses heat to the atmosphere as much as ten times more effectively in the open areas than through the ice. Due to solar radiation in spring, the break-up process is far more fixed in time than the cooling of the sea in autumn (ditto, p.22). Out in the open sea the ice receives considerably more heat from the sea than close to the coast, and therefore the thickness of the ice level, as a rule, is much smaller in the drift ice fields. (Lit.: Leppäranta, et.al).

Comments to Leppäranta, et.al.’s analysis:

The given excerpts make very clear that the water of the Baltic Sea holds the key concerning the icing conditions and that from a climatic point of view it makes a big difference which of the seasons is concerned. After all, the absolute dominant climate factor is sun radiation, immediately followed by sea water if the sun is less or not available for heat infusion during the winter season.

Average commencement of icing in the Baltic Sea (based on means from 1930 to 1960)

Source: (Lit.: Dietrich)

Other points that illustrate some climatic parameters of the Baltic (Lit.: Magaard, p. 25-31):

--The annual amplitude between the mean air temperatures varies from 17°C in the Southwest of the sea to 27°C in the North.

--In January the mean temperature in the regions bordering the Baltic is very cold (-2°C to -10°C), while the air over the sea surface is considerably warmer (-4°C in the North, in the other areas 0 to +2°C). Only in April the air temperature is on an equal level over the land and the sea.

--The annual air temperature variations in the East Atlantic are 5°C to 6,5°C; in the North Sea 9,5°C to 11,5°C; and in the Baltic 13°C to 15°C; this indicates the difference between the influence of a maritime and an already continental climate.

--Extended fine weather periods are rare statistically the best chance have May and June.

Comment: One of the reasons may be attributable to the still cold seawater. Cold water does not force evaporation, no humidity – no clouds, no temperature difference in the atmosphere – no wind, and so on.

Icing in Finland’s waters

When icing started in December 1941 the military rush through the Baltic Sea had already lasted for five months. Many thousands of sea mines had been laid, swept and destroyed. By various attacks the Reichsmarine had forced the Baltic Fleet to abandon occupied ports and defence positions and to retreat to Leningrad under heavy losses. In early December the Russians were forced to leave the Finnish Island Hangoe at the entrance to the Gulf of Finland, that cost the Baltic Fleet a dozen of ships, many due to sea mines. The water body of the Baltic Sea was stirred and shaken day and night until sea ice prevented the use of ships and naval vessels. That was a ‘self-inflicted’ hindrance by the parties at war. A detailed description of the war at sea in the Baltics from June to December 1941 is given in the paper: ’Barbarossa’ – Naval and other activities in the Baltic Sea from June to December 1941 (3_21).

In the very northern part of the Gulf of Bothnia the freezing began earlier than usual. The open sea was only covered with thin ice on 15th December (Lit.: Jurva, p.36). Ice had appeared in the northern part of the Aland Sea by 9th January, and lighthouses reported fast ice by mid-January, ‘as far as it was possible to see’ (Lit.: Palosuo, p.36). The ice was measured at Maerket (Aland) on January 16th and proved to be 5 cm thick.

South of the Aland Sea, in the region of the Gulf of Finland the early freezing was quite exceptional. Ice formed in the coastal bays at the end of October already (Lit.: Palosuo, p.33). During a third frost period, which came in the middle of November, ice covered the inner archipelago of the Gulf of Finland.

It was also exceptional to have three periods of frost as early as this autumn (Lit.: Palosuo, p.33).

A hard period of frost came in early December. In the middle of December the open sea of the Gulf of Finland was iced over throughout the filed of view of the fixed observation stations about 30-40 km east of Helsinki (Pellinki). (Lit.: Palosuo, p.34)

Hard frost formed rapidly new ice from 23-27 December. Stations in the central part of the Gulf reported: the sea totally ice covered within the field of view. (Lit.: Palosuo, p.34).

In the Gulf of Finland (west of Hangoe – Osmussaar) snow-free ice was formed (Dec. 30-31) showing small openings 10-15 metres in diameter; these probably originated from the moving of the ice. However, in the region of the archipelago at least the formation of the openings appears to have been influenced by the basin bottom and currents it forms, and this can hardly be used to explain the origin of the openings in the sea ice (Lit.: Palosuo, p.35).

Remark: The areas had been considerably mined, including the Aland archipelago. Mines close under the surface could have come in ‘contact’ with the ice and exploded; as well as drifting mines. The ‘ice holes’ could also have been made by recently sunk vessels and boats, of which hundreds scattered the sea bottom.

Arctic air mass arrived January 6th , resulting in the formation of a ridge of stationary high air pressure over Scandinavia (Lit.: Palosuo, p.35). A reconnaissance flight over the eastern Gulf of Finland on January 7th found that the entire sea area was covered with fairly thick ice, but as a result of the wind the ice had been in motion, and a number of lanes had formed in the ice.

During early January ice moved from the western part of the Gulf of Finland to the northern Central Baltic, reaching the line Kökarsören (south of Aland) to Tahkuna (island at the west-end of Gulf) on January 16th. (Lit.: Palosuo, p.36)

Sweden

The information by Gösta H. Liljequist (Lit.) distinguishes between ‘’harbour’ and ‘water ways’. In the north the difference can make up to 14 days, in the south it may be one day or even nil. The following dates for the start of the icing are only those for the water ways.

Lulea (15/Nov); Holmsund (11/Dec); Stockholm-Sandhamm (6/Jan); Norrköping (5/Jan); Karlskrona (6/Jan); Malmö (13/Jan); Göteborg (13/Jan).

Liljequist summarizes the winter 1941/42 as follows (few excerpts):

• The winter 1941/42 was colder than the winters 1939/40 and 1940/41. At Stockholm it was one of the coldest winters since 1756.
• The formation and breaking up of the ice took place at a rather normal time in the Gulf and the Sea of Bothnia. The formation of ice in the Baltic and at the West coast started in the first part of January, generally one or two weeks earlier than normally. The ice conditions grew worse after a mighty invasion of cold air on January 24th, when temperatures between -25°C to -30°C were recorded in the whole country; at the same time the wind force was 6 on the Beaufort scale or more.
• The thickness of ice was about 100 cm in the Gulf of Bothnia, in the Baltic 50 –90 cm, and in the Sound and at the West coast 50-60 cm.
• The break-up of ice was very late in the whole Baltic, but especially late in the Sound and at the West coast, which was not ice-free before the end of April.
• Actually, drift ice was still observed off Malmo on May 12th, the latest date of ice melting since ice observations had been taken in 1870. (Lit.: Liljequist, p. 14)
• On June 6th 1942 all Swedish waters were ice-free.

In comparison to the two previous ice winters Liljequist concludes: that 1941/42 was worse in the Baltic and at the West coast, but that 1939/40 superseded the other two ice winters regarding the length of the ice period.

According to a map of the ice conditions in the Skagerrak on February 11th (Lit.: Liljequist, Isvintern 41/42, Fig.2) the whole area, from Oslo, Kristiansand, Skagen and Goteborg was almost fully covered with heavy fast ice and frozen over ice, except the sea area off Denmark’s north coast.

Liljequist (Lit.: p.5) mentions also the following observation: At the coast off Goteborg an interesting phenomenon was observed in the second half of January. Despite the strong cold the ice melted from beneath, and during daytime open holes emerged in areas that before had been solid and strong enough to drive on. The causation was a thin level of brackish water that covers the warmer and saltier ocean water. If wind drives the brackish water to the open sea, the warmer ocean water will soar. The rising warmer and saltier ocean water melts the coastal ice.

Denmark

The winter 1941-42 was extraordinary lasting and cold in spite of December having mean temperatures above normal. For the country January and February were about 6°C colder then normal. From January 7th on, a long and lasting frosty period fell in and dropped to a record low temperature of –31,0°C on January 26th. After a severe cold February (down to - 29°C), also March and April had been cold. (Lit.: Det Danske)

An extraordinary early ice on November 4th disappeared quickly and the second freezing did not start before the last days of December, and thereon developed forcefully. January 21, extended areas were covered with loose ice going to congeal into flats;

February 02, considerable portions of the fairways were covered with fast ice;

February 14, some days with westerly wind and rather high temperatures had broken up the ice in extended areas;

February 27, heavy ice, which was only partly joined through congealing, covered the main part of the fairways;

March 14, the ice in the Kattegat had now grown less heavy, at the same time as it had increased in the Baltic;

March 30, the ice had disintegrated in the Kattegat, but was still present in parts of the Baltic in a violently packed condition;

April 12, in the southern approach to the Sound was still obstructed by ice. (Lit.: Det Danske).

Germany

Although the Germans controlled the southern Baltic Sea, from Flensburg/Kiel to Koenigsberg (Kaliningrad), this investigation has only few data concerning the ice conditions. Nusser mentioned that the material from air reconnaissance flights on ice observations from 1939-1945 had been lost. (Lit.: Nusser, Gebiete).

In another paper Nusser (Lit.: Arctic Sea) wrote: “The part of the Baltic tending least to glaciations is the south-eastern area. Ice reconnaissance flights in 1941 and 1942 showed that in this area, unfavourable to ice, only loose ice can occur. In spite of the easterly position little ice occurs because of the depth of this great basin which, during summer, accumulates a great stock of heat”. Of particular significance are observations by Blüthgen (Lit.: Blüthgen) concerning the first ice observed in late 1941. Already by mid-November there were a number of locations along the Mecklenburg-Vorpommern coast having new and floating ice for 10 to 14 days. Since 1922 there had not been one single year where such events had been observed. This was in some cases more than 20 days earlier (e.g. Barhöft, Stralsund, Swinemünde, Stettiner Haff) than the next earliest date since 1922.

By the end of January the southern Central Baltic had an ice shield extending from the west at least as far as Bornholm in the east. Open water could only have existed further east in the Central Baltic around the Bight of Danzig (Gdansk) and northward from there. It was reported from Germany that by February 5th the entire Central Baltic was ice-covered (Lit.: Palosuo, p.46f).

On February 21st a Swedish air reconnaissance flight reported a narrow fast ice edge off Kolberg followed by a 40 km or 22 sea miles wide zone of drift ice and pressured ice, and finally unbroken snow covered ice as far as the Swedish coast (Lit.: Palosuo, p.60), see also: (Lit.: Liljequist, Isvintern 41/42, p.8.)

“A fast ice bridge” typical of severe winters was also formed in the Fehmarn Belt in the winter of 1942. How long it lasted this winter is not clear from the material available, especially as navigation in this area had come to a standstill because of the ice. (Lit.: Palosuo).

Some additional events

15 Nov.; Germany (Mecklenburg-Vorpommern); New and floating ice for up to 14 days at several locations. Second icing started late December or early January (as usual for strong ice winters), (Lit.: Blüthgen).

15 Dec.; The open Gulf of Bothnia is covered with thin ice.(Lit.:Jurva, p.36).

17 Dec.; Germany (East coast): First ice on the Schlei (Schleswig/Kappel) (Lit.:DHI-Eisb.).

21 Dec.; Germany (East coast): First ice Travemünde Hafen, Trave, Lübeck (Lit.:DHI-Eisb.)

08-16 Jan.42; Icing along the Germany Baltic East coast had started in fully. (Lit.:DHI-Eisb.)

17 Jan.; Ice has formed on the Swedish coast as far out as 30 sea miles from the coast (Lit.: Palosuo, p.36).

19 Jan.; In the Gulf of Finland the wind increases to 5-6 Beaufort, N-NE-wind. (Lit.: Palosuo, p.37).

20. Jan.; Southern Central - German coast; thin ice about 6 sea miles north of Arkona, and heavy drift ice closer to Swinemunde. (Lit.: Palosuo, p.42)

25 Jan.; A remarkable occurrence was observed in the Danish waters, the forming of an “ice bridge” across Oresund at Van. (Lit.: Palosuo, p.42)

31 Jan.; Southern Central - German coast; freezing in the southern Central Baltic had progressed so far that heavy unbroken ice was observable on the German coast (by a Swedish air plane flight report), and some 35 km further out thin ice. (Lit.: Palosuo, p.42)

02 Feb.; Southern Central - German coast; the sea was frozen from the German coast to at least level with Bornholm, as well as the sea from Bornholm to Sweden (Lit.: Palosuo, p. 46).

21 Feb.; Southern Central - German coast; ice conditions became difficulty off Pomeranian coast, due to a narrow fast ice edge off Kolberg followed by a 40 km (22 sea miles) wide zone of drift ice and pressured ice, and finally unbroken snow covered ice as far as the Swedish coast (Lit.: Palosuo, p.60).

03 March;’ Ice bridges’ between Oeland and Gotland (Sweden), and (presumably already on 17 Feb., between Sweden and Bornholm (Lit.: Palosuo, p.58)

mid-March; According to Palosuo the culmination of the ice winter (meaning the state of ice before withdrawal) occurred in northern Denmark waters (Kattegatt) on 14 March; at the German East coast (Schleswig-Holstein) 19 March; in the northern Central Baltic, March 20 (Lit.: Palosuo, p.66).

Summary

The presentation pointed to a number of relevant connections between the military force unleashed over wide sea areas in the Eastern Baltic and the development of the sea icing. There is the astonishing early ice off the German coast in mid November and the relative late icing e.g. in the Gulf of Finland. Nothing can demonstrate better the influence that military activities have on the seawater condition. In summer they force more heat into the depths and in autumn (winter) they force the heat out of the sea. The latter point is evidently demonstrated in the fact, that the Baltic Sea in the winter 1941/42 was quite obviously deprived of ‘any heat reserves’. The arctic winter could settle in without any resistance from the sea, which is too shallow to store more heat than for one winter. The explanation Liljequist gives for the ‘ice holes’ at the Swedish West coast (see above) illustrates the point. The same conclusion can be drawn from Nusser’s remark to the part of the “Baltic tending least to glaciations” in the southeastern sea area. The reason is simple, the depth is here up to 110 metres instead of the average 56 metres, which means more heat in storage. In addition to the intensity and expansion of the ice cover, the duration of ice is a strong indication for the impact the war activities had, by cooling the sea down to the bottom, which took the sun in spring an unusual long time to warm the sea so much, that the ice could melt. It took until June 6th 1942 that all Swedish waters were freed from winter ice. Even in South Sweden the ice did not get away before mid May, the latest date since observations had been recorded. The military impact is obvious.

LITERATURE

Blüthgen, Joachim; ‘Eisverhältnisse der Küstengewässer von Mecklenburg-Vorpommern’, Remagen 1954.

Det Danske Metorologiske Institut; ‘Is- og besejlingsforholdene I de danske Farvande in Vinteren 1939 40; 1940-41; 1941-42; Kobenhavn.

DHI-Eisbeobachtung; Deutsche Hydrographisches Institut, "Eisbeobachtungen’, Nr.17, Hamburg 1961);

Dietrich, Günter, and Schott, Friedrich; ‘Eisverhältnisse’, in: Magaard, L. und G.Rheinheimer, G. (ed); Meereskunde der Ostsee’, Berlin 1974, p. 65.

Leppäranta,M. et.al; see: Finnish Institute of Marine Research “Phases of the ice season in the Baltic Sea’ No. 254, Suppl.2; Helsinki 1988

Liljequist, Gösta H.; "Isvintern 1941/42’; in: Staten Meteorologisk – Hydrograiska Anstalt, No.4, 1942, pp.2-15.

Magaard, L. und G.Rheinheimer, G. (ed); Meereskunde der Ostsee’, Berlin 1974, (Friedrich Defant, Klima und Wetter, pp. 25-31.)

Nusser, Franz; "Gebiete gleicher Eisvorbereitungszeit an den deutschen Küsten’, in: Deutsche Hydrographische Zeitschrift, Bd.3, Heft 3/4, 1950, pp.220-227.

Nusser, Franz; ‘Distribution and character of sea ice in the European Arctic’; Reprint from: “Arctic Sea Ice”, National Academy of Science – National Research Council, Publication 598 (year ?, pp.?),

Jurva, Risto and Palosuo, Eric; ‘Die Eisverhältnisse in den Finnland umgebenden Meeren in den Wintern 1938 –45 und die Baltischen Eiswochen in den Wintern 1938 –39’, Meerentutkimuslaitoksen Julkaisu Havsforskningsinstitutets Skrift, No.188, Helsinki 1959.

Palosuo, Erkki; "A Treatise on severe ice conditions in the central Baltic’, Fennia 77 No.1, Helsinki 1953.