Location: Borkum (Island) – Hull/England, 53° 30’ North, distance ca. 400 kilometres,

Average depth ca. 15 m; maximum depth ca 35 m; 

 Due to the shallowness and tidal forces, temperature structure of the water body is homogeneous (from surface to the bottom) with small variations, as the average temperatures indicate; Dec (8.5°); Jan (6.5-7°); Feb (5.5°); Mar (5°), Apr (6.5°), suggesting that water very close to the coasts has lower temperatures during the winter season. The variations are negligible and can be ignored.

 

From May to August temperatures increase from 8.5° to 14.5°/17°C and decrease as follows: 

Depth	August	September	October	November
Surface, West-East	14.5-17 °C	14-16 °C	12-13.5 °C	09°- (mid) 11.5°-10°
20 m, West-East	14-16 °C	15-16.5 °C	13.5-14 °C	9.5-11 °C

 Fairly homogeneous figures for the water body with 15°/16° at peak time and the lowest in March (5°), indicate that the water body experiences anaverage decrease in temperatureof about two degrees per month.

 The annualapproximate temperaturevariation datain the three sectionsof the North Sea  isas follows: (Source: Tomezaqk & Goedecke) 

	Area in the North Sea
	Southern section West/East	Middle section West/East	Northern section West/East
Water depth	Temperature °C
Surface	10/12.5 °C	8/15 °C	6/10 °C
7.5 m	11/13 °C	8/15 °C	5.5/10 °C
20 m	11/13 °C	7/13 °C	5.5/8.5 °C
30 m	11 °C	6.5/12 °C	5/7.5 °C
40 m	-	6/11 °C	4.5/6 °C
60 m	-	4.4 °C	4.5/3.5 °C
80 m	-	3.5°C	4.5/1.5°C
100 m	-	-	4/1.5°C

Water Temperatures recorded at Helgoland Station in autumn 1939

It is well recorded that a positive seawater temperature series in the Helgoland Bight from 1930-39 at the Helgolandstation with WWII commencing suddenly came to an end. Goedecke dates this end at 1940-1942[3]. Nearby light vessel “Elbe 4” on the mouth of the river Elbe records the annual anomalies as: 1939 (+0.9); 1940 (-0.7); 1941 (-0.7); and 1942 (-0.2). At bothstations seawater temperatures increased again after 1942. Goedecke attributed thisincrease in temperatures until 1940 and after 1942 to “the secular climatic changes inthe Northern Hemisphere”[4], resulting “primarily from the warming of the polar and sub polar atmosphere”[5].

 This paper’s next step is to look in detail at the figures available for 1939, showing an averageannual seawater temperature increaseof 0.9°C. The starting line will be August 1939 to prove that the war at sea, during its initial months, i.e. September to December 1939 made its clear contribution in ushering inthe arctic winter of1939/40 in Europe.

 Figures from Helgoland station showing deviations from average temperaturesduring the autumn season of1939:

Average temperature 1901-30	August 16.34°	September 15.60°	October 13.15°	Nov. 9.68°	Dec. 6.48°
Deviation: 1930-37	+1.05	+0.85	+0.55	+0.3	+0.5
Deviation: 1938	+1.6	+1.0	+0.6	+1.7	+0.6
Deviation: 1939	+1.7	+2.6	-0.6	-0.4	-0.3

Source:Goedecke, Verhalten, p.7 

Deviations of seawater temperatures from the mean (1901-30) at Helgoland Station in early 1940 are: 

                                                      Diff.: 1940

	January	February	March	April
	-1.6	-3.5	-3.0	-2.3

Source:Goedecke, Verhalten; p.7 

Even if one is fully aware that the water masses of the German Bight (Helgoland Station) donot representthe North Sea as a whole, the differences are remarkable. The first hard fact is that August 1939 figuresofwater conditions had been in the normal range. A highfigure for a corresponding period as inSeptember 1939 had been recorded only once before, i.e. in September1875. The September 1939 figure is most likely so high because ofextraordinary naval ship movements and military activities thattook place, ‘shovelling’ lower and warmer water up to the surface. Once warmer water reached the surface, evaporation increased and subsequently seawater cooled more quickly.

 This becomes evident in two ways; firstly by the difference in temperaturebetween September and October, and secondly by the high deviation in temperaturefrom the previous decade by one degree in each of the months of October, November and December 1939, showing a very spontaneous and significant deviationfrom the sea climatology of the Helgoland Bight.

 If one can rely on the figures given by Goedecke, it can be fairly assumed thatmilitary activities were a key contributor inthe arrival of the arctic winter of 1939/40. ‘Normal’ monthly seawater temperature decrease recorded at Helgoland Station is 2.5°C from September to October, with a minor deviation (<0.4°C) over the decade since 1930. In 1939 water temperature decreasedwithin a period of onemonth from September-October by 5.7°C (normal 2.5°C; plus 3.2°C in 1939). Therefore thisbig drop requires an explanation. Further, the negative figures observed for the period October –December wouldcertainly have contributed to the surprising arrival of the cold winter. These events of‘temperature changes’ at a place where the German navy was very active, by laying thousands of minesin close by areas and the bombardment byBritish aeroplanes cannot beignored by climate watchers.  Links of these eventsto ensuing winter conditions are quite obvious. 

Early, severe and long lasting icing conditions 

Icingalong the Danish, German and Dutch coasts started early (see below: Events), and sea ice conditions lasted longer thanin dozens of previous years. On the other hand, the main features of the 1939/40 icing are not ‘completely’ out of question. For example, in December 1938, ice formation started early due to a sudden cold spell, but it lasted only for two to three weeks. The winter of1938/39 is listed as a quite moderate one, in fact, the warmest for decades. Also the post war winter of1946/47 could, in some respects, be regarded as an even icier winter than the first war winter of 1939-40, at least with regard to the North Sea, but the winter of 1946/47 was of a totally different nature than the winter of 1939/40. (A) 

Further details: (A) Late winter 1946-47, 4_21.

 The importanceof the winter of1939/40 as proof of the impact created bywar at sea onclimatic changes since 1939 remains valid in every respect. Circumstantial evidences throwing light tothe war winter of1939/40 are manifold and include following facts concerning sea ice:

·         seawater temperature data at Helgoland in autumn of1939;

·         suddenness with which icing started;

·         early start and longer stay of ice;

·         severity of icing;

·         long duration of the icyperiod caused by two cold waves, one in January and anotherin February 1940. 

Changed factors
Interchange air - water

During the first four months ofwar no quadrant of the North Sea would have seen the same war activities as any other location might have. Considering the very basic factors, it seems reasonable to concentrate on the southern plateau section, south of the line Hanstholm/Jutland – Dogger Bank  - Hull/England and the section north of this line. The southern part with its low depth and nearly homogeneous water body conditionroundthe year, saw, by far the most aggressive military activities during the early days of the war, such as 20-50,000 mines along the “Westwall” in the middle of the North Sea over a length of1,000 kms, 10,000 mines along the Dutch and English coast, hundreds ofnaval ship movements, depth charging and bombing, etc. every day. (A)However, thenorthern part saw certainly less activity, but due to the temperature structure depending onwater depths, the water body wouldoften react quite differently than in the southern part section andwith a long-term effect. 

Further details: (A) Sea mines, 2_14; and Depth charges, 2_15. 

A few words concerning the dynamics of seawater evaporation and seawater cooling: Watervapour escapes into the atmosphere only from water surfaces. The intensity of thisprocess depends on the temperature difference between the media, and also whether a certain amount of water vapour is in equilibrium with the water surface. If it is less, seawater will vaporise; if it is higher, the vapour in the air will condense and transform into clouds, rain, fog etc. In each system (water – atmosphere) the level of temperature is important. A rise in air temperature from 0°C to 10°C doubles the amount of water in the atmosphere at equilibrium. 

Evaporation cools a water surface by removing heat from it. As water cools, the equilibrium decreasesand the evaporation rate will decrease. Cold and salty water increasesvertical convection (water movements by sinking); warm and low salty water tends to sink less. 

However, in this investigation only two rules will be considered: 

The warmerthe water, the more evaporation;

The moreevaporation, the more the water cools. 

For the atmosphere this means: Adding water vapour to the atmosphere makes it less dense and causes vertical airmovements. In thecase of the North Sea, when air rises from a surface water layer, air thuslifted upwardsmust be replaced by air that is surrounding the location of evaporation, whereby dry air, presumably continental air, may try hardest to fill this space. Back in 1939 the German weather analyst wondered, when the usual wind from South-West turned to North-East. (A) 

Further details: (A) Lost west wind drift, 2_12, see: “End of October 1939”, or  Seewarte, 02 November 1939. 

Climatic conditions in Northern Europe had been regarded as ‘normal’ during the first eight months of 1939 until the end of August. Based on this assumption, the chain of causes in forcing a deviation in meanconditions during the winter of1939/40 could have worked as follows:

·         stirring of sea waters increased evaporation;

·         this blocked the west-wind, caused continental air to move in (N-E winds) and increase the barrier;

·         coldercontinental wind and high evaporation rate cooled seawater;

·         while the cooling effect was not very pronounced early, due to the fact that ‘stirring’ of the sea continued bringing warmer water to the surface thus delaying the ‘typical’ winter effect (e.g. icing);

·         this is clearly reflected by strong temperature deviation from January – April 1940, and particularly by a long duration of the ice period (see below: Events).  

 Southern North Sea: Due to low water depth (max 40 m) and tidal forces, the ‘mixing’, whether by natural dynamics or military activities,will occur fairly quickly throughout the whole water body. Correspondingly, the chain reaction affecting evaporation, change of wind direction and cooling, etc will set in motion:

·         if, at the peak time of high surface temperature, this water is mixed with colder water atdeeper levels, the total heat capacity will rise and the evaporation process will be reduced at the surface for some time;

·         if the stirring process continues or even increases, warm water from lower levels is exposed to the evaporation process at a higher frequency, thus accelerating the cooling of the surface and forcing wind to replacerising vapour;

·         the emergence of the first visible sign of cooled down seawater (icing) can be delayed by the continuation of the ‘mixing’ of water. 

All these criteria are clearly reflected in the sea surface data from Helgoland for the winter period of 1939/40. These main results can be fully applied for all of the southern part of the North Sea, south of the Hanstholm/Jutland –Dogger Bank - Hull/England line, even taking into account, that the Helgoland Bight particularlyhad been highly exposed to naval activities.

 Northern North Sea:  The forced ‘stirring and mixing’ situation of the water body in the northern part is much more diverse and intensethan in the southern part during autumn. A naval activity that may force the cooling of the sea surface layer in September may, by similar activity increase evaporation in December, or may bedoing both actions at the same time. On the other hand, a stirring and mixing within the upper water layer down to 10 or 20 metres in early autumn will, just as it does in the southern section, actively support an accelerated evaporation process in September and October. But speaking in general terms, a military activity-forced mixing in autumn will move warm water to agreater depth, thereby extending the retention ofthe amount of stored heat by weeks or even months. It should not be regarded as too big a surprise, if the northern section of the North Sea may have even contributed with a release of more heat into the air during the later partof the winter of 1939/40than during other years.

Heat matters

 Since the day the Second World War had started naval activities moved and turned the water in the North Sea at surface and lower levels at 5, 10, 20 or 30 metres or deeper on a scale that was possibly dozens of times higher than any comparable other external activity over a similar time period before. Presumably only World War One could be named in comparison.  The combatants arrived on the scene when the volume of heat from the sun had reached its annual peak. Impacts on temperatures and icing are listed in the last section: ‘Events’ (see below).  The following circumstantial evidences help conclude with a high degree of certainty that the North Sea contributed to the arctic war winter of1939/40. 

Meteorological ‘West Wall’– Wind Drift blocked

 Excessive evaporation from the first day of September until November 1939 could be evidenced by a decrease inwater temperature at Helgoland Station, Rising air (vapour) instead of attractingAtlantic cyclones to move into the North Sea area to travel east, in factassisted in blocking their movement. Presumably, this aspect alone would not have changed the situation very much. But the rising air certainly forced inflow of continental air from East and North. This air, flowing almost in the opposite direction to the West drift, necessarily prevented or reduced the  movement of Atlantic cyclone systems to travel oncommon routes. Daily weather analysis of the Seewarte wondered a number of times where the West Drift had gone. Excessive heat release as illustratedin previous paragraphs was the most likely cause forblocking Atlantic cyclones fromreaching and passing Western Europe as wasusually expected. In December, high pressure took full controlin Europe and the North Sea, leaving cyclones theonly opportunity to storm east either via the Barents Sea, or crash through the Iberian Peninsula into the Mediterranean Sea. (A) Others turned north and passed the battlefields inthe Arctic Circle in the Russian – Finnish war. (B)

     Further details: (A) Violent weather, 2_52; (B) Russian-Finnish war (2_41.

More Evaporation –  more wind, rain, cooling

 Water, among all solids and liquids, has the highest heat capacity except liquid ammonia. If water within a water body remained stationary and did not move (which is what it does abundantly and often forcefully for a number of reasons), the upper most water surface layer would, to a very high percentage, almost stop the transfer of any heat from a water body to theatmosphere.

However, temperature and salt are the biggest internal dynamic factors and they make the water move permanently. The question as to how much the ocean can transfer heat to the surface depends on how warm the surface water is relative to atmosphericair. Of no lesser importance is the question, as to how quickly and by what quantities cooled-down surface water is replaced by warmer water from sub-surface level. Atmospheric factors responsible for exposing quickly new water masses at the sea surface arewind, cyclones and hurricanes. Another ‘effective’ way to replace surface water is to stir the water body itself. Navalactivities are just doing this.

 On the basis of sea surface temperature record at Helgoland Station and subsequent air temperature, developments provide strong indication that the evaporation rate was high. This is confirmed by the following impacts observed: 

 More wind: As the rate of evaporation over the North Sea hasnot been measured and recorded, it seems there is little chance to prove thatmore vapour moved upwards during autumn 1939 than usual. What can be provedis that the direction of the inflow of wind had changed from the usually most prevailing SW winds, to winds from the N to E, predominantly from the East.  At Kew Observatory (London) general wind direction recordedwas north-easterly only three times during 155 winter years; i.e. in 1814, 1841 and 1940[6]. This continental wind couldhave significantly contributed to the following phenomena of 1939: ‘The Western Front rain’ (next paragraph).

 More rain: One of the most immediate indicators of evaporation is the excessive rain in an area stretching from Southern England to Saxony, Silesia and Switzerland. Southern Baltic Sea together with Poland and Northern Germany were clearly separated from the generally wet weather conditions only three to four hundred kilometres further south. A demonstration of the dominant weather situation occurred in late October, when a rain section (supplied from Libya) south of the line Middle Germany, Hungary and Rumania was completely separated from the rain section at Hamburg – Southern Baltic[7]. Plentifulrain from England to Silesia/Germany and to Switzerland may have been caused by military activities as follows:

 A north-easterly wind pushes humid air (partly generated by naval war in North Sea and Baltic Sea) southwards, while the coldness of the pushing air and abundantsupply of condensation nuclei, by shelling, bombing etc., intensify cloud formationand condensation further, thus forcing and sustainingrain over a longer period of time.  (A)

Further details: (A) Rain-Making, 2_ 31.

 More cooling: Further, coolingobserved fromDecember 1939 onwards can be linked to war activities in two ways. The most immediate effect, as has been explained (above), is the direct result from any excessive evaporation process. The second (at least for the establishment of global conditions in the first war winter) is the deprivation of the Northern atmosphere of its usual amount of water masses, circulating the globe as humidity. The less moist air is circulating the globe south of the Arctic, the more easily cold polar air can travel south. A good piece of evidence is the record lack of rain in the USA from October – December 1939 (A), followed by a colder than average January 1940, a long period of low water temperatures in the North Sea from October-March (see above) and the ‘sudden’ fall of air temperatures to record low in Northern Europe.

 Climatic conditions in the North Sea in autumn 1939, together with those ofthe Baltic Sea (B), played a key contributoryrole in sustaining the coldest winter in Northern Europe for more than 100 years.  

 Further details: (A) USA dried out, 2_32; (B) Baltic Sea cooling, 2_17.

 Events: Temperatures or Serious Icing in the North Sea Winter of1939/40

 The following listdoes not give a full picture of events but only points to some major events, places and impacts reported. 

 11 December 1939; Helgoland reported frost on December 11 and December 13-19 (from December 14-18 meantemperature of -1,6°C; December 15, mean temp. -3,6°C; lowest December 16, – 4,5°C; and frost from December 26-31[8].

 16 December 1939; Ice on river Elbe, (e.g. Glückstadt, Hamburg), remained continuouslyfor more than 90 days until mid March, 1940[9].

 17 December 1939; Tönning (near Husum) reportedfirst ice, which remainedfor 100 days[10]. Note: Before icing commences along the German North Sea coast, the air temperature needs to be below zero for about 4 to 5 days[11].

 17-21 December 1939; Almost all observation stationsalong the German coast from Nordstrand (island south of Sylt and Amrum) to Borkum report the emergence of sea ice,itsstay in the south ca. for 60 to 70 days, and further north ofCuxhaven for 70 to 102 days12. North of Husum (Amrum, Sylt) ice remained from early January for approx. 60 days.

 29-30 December 1939; During the night of29/30 a strong southwest storm swept through Helgoland Bight (Helgoland up to 11 Beaufort)13. At the same time in far East Germany (East Prussia) very cold air ofmore than -20°C, had been blowingfrom the North and pushing further south14.

 1 January 1940; Monthly meanair temperatures for January 1940 for Westerland,  Helgoland, Emden15 : 

Location	Month	Mean air temp.		Deviation from average			Lowest/day
Westerland	January 1940		- 4.2°C		- 5.3°C	-13.5°C/Jan.19
Helgoland	January 1940		- 3.2°C		- 5.1°C	-12.4°C/Jan.31
Emden	January 1940		- 7.0°C		- 8.1°C	-17.9°C/Jan.10

2 January 1940; Esbjerg – soft or new ice, navigation not hindered, Danish light buoys werewithdrawn over the next 10 days16. 

6 January 1940; Drift ice in the East Scheldt. Ameland temporarily cut off from the mainland by ice. river Maas is frozen over from Woudrichem to Heusden17.

 14 January 1940; Drift ice on river Scheldt reported to have torn buoys from their mooring18. Frankcom made the following comment justa few dayslater: “in these nine days conditions have deteriorated very rapidly and one sees the first real indication of somewhat abnormal conditions, most particular isfreezing of rivers Scheldt and Maas”. 

17 January 1940; Ice reported in the North Sea off Jutland for the first time in many years, up to 2 miles from the coast. Fjord in Jutland frozen over. Ice three metres thickreported from western end of Limfjord. Minus 23° F reported during the night in Denmark19

 20 January 1940; Difficulties due to icereported in the river Scheldt20.

 21 January 1940; Heavy ice drift reported on thewest Scheldt 21. 

23 January 1940; More difficulties due to icereported on river Scheldt. Many small vessels bound for Antwerp wereput into Flushing because of ice. Navigation to Brussels wasclosed by ice. Fast ice reported at Lobith, on the river Rhine22. Frankcom concludes inhis report datedJanuary 23, 1940, noting: “…the spread of ice out into the North Sea itself is a definite indication of unusually severe weather. It is particularlyunusual for shipping to be held up in the river Scheldt.” 23

27 January 1940; Helgoland hadice for 10 days between January 27 and February 2324; duration of ice formation inHelgoland is11 days25.

 28 January 1940; In the close vicinity of London river Thames hadbeen frozen for the first time since 1814. (Neue Zürcher Zeitung, 29 January 1940).

 1 February 1940; Given below are monthly meanair temperatures for February 1940 in respect of Westerland,  Helgoland and Emden26: 

Location	Month	Mean air temp.	Deviation from average	Lowest/day
Westerland	Feb. 1940	- 6.1°C	- 6.9°C	-13.5°C/Jan.19
Helgoland	Feb. 1940	- 4.1°C	- 5.7°C	-12.4°C/Jan.31
Emden	Feb. 1940	- 3.7°C	- 5.3°C	-17.9°C/Jan.10

 Remark: It should be noted that January was colder in Emden than in Westerland, which ranks first in February, a fact that could support the thesis that war activities in the northern section of the North Sea, delayed cooling of the sea (see previous chapter).

 From February until March 1940general winter conditions remained very severe. While investigating causes for the harsh winter, weather conditions observed inthe month of February are considered important as a second cold spell pushed the winter torecord low level. (A)               

Further details: (A) Winter 1939/40, 2_11. 

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