The winter was severe and began early. From the 1 :st of Febr. to the middle of 

 March the ice lay in the Cattegat, the Belts and the western Baltic. The ice was 

 used for communication across the great Belt and the Fehmerbelt, probably also the 

 Sound. There must at least have been ice along the whole of the Baltic coast of Ger- 

 many extending far out into the sea and also between Sweden and Oulland. » 



Also in the southern countries the winter must have been ssvere. Hennig says, 

 that the Gulf of Venice was frozen over; Arago says, that the winter was severe 

 in France and Italy >>. 



This shows that the cold culminated between 1 Febr. and 15 March »as it 

 does now ». 



1394. 



»It was possible to walk across from the coast of Venden to Denmark and Swe- 

 den. » (Captain Speerschneiders notes.) 

 1407. 



»one of the coldest winters on record. The sea between Sweden and Den- 

 mark was frozen over. (Captain Speerschneiders notes.) 



Hennig's Katalog has the following note on the winter 1407 — 1408: 



Der grosse winter von 11 Nov. bis 27 Jan; in England v. 11 Dezember bis 2 

 Jan. Alle Fliisse tragen die schwersten Lastwagen, iiber den gefrorenen Skagerak 

 (Kattegat?) laufen die Wolfe von Norwegen nach Jutland. Seit 3 Jan. veranlasst plots- 

 lich starkes Tauwetter in England grosse Oberschwemmungen. 28 Jan. plotzliches 

 Tauwetter in ganz Mittel-Europa wodurch sehr grosse Uberschwemmungen hervor- 

 gerufen wurden. 



1418. 



According to Stavenow, Chronologia vetusta 1298 — 1473 contains this statement: 

 Anno MCCCCXVII!. Hiemps erat nimis aspera et mare salsum fuit congelatum ita 

 qvod homines transierunt intra Alemanniam et Daniam videlicet Gezor et Rotstock. ». 



1423. 



According to Stavenow the following statement is contained in an anonymous 

 record called »Remarkable occurrences in Sweden 1220 — 1552 >>. »In 1423 the winter 

 was so severe that the Baltic was covered with ice so that it was possible to travel 

 in sleighs along the route of the vessels from Dantzic to Liibeck and from Pom- 

 merania to Denmark. » 

 1460. 



From Hennig's Katalog; sAusserordentlich strenger winter bis 20 Martz. Die 

 Ostsee friert vollstandig zu so dass man zu Fuss iiber das Eis von Liibeck und Stral- 

 sundnach Norwegen (Danemark?), von Reval nach Schweden gehen kann. Die Donau 

 und andere Fliisse von 13 Jan. bis 11 Martz derart zugefroren dass sie die schwersten 

 Wagen tragen. » 



From the 16th century also there are records of the Baltic being 

 frozen in such a degree that the ice could be used for communication 

 between Germany and Denmark. But this happened more and more 

 seldom and the winter of 1636 is considered to be the last in which 

 the Baltic was frozen between Scania and Bornholm. In the above 

 quotations I have only made use of such notices which, as far as 

 I can find, have never before been published or compared before. 

 Hennig's Katalog contains several notices to the same effect, f. 

 inst. regarding the ice-winter 1318 — 1319, like this: »Strenger winter, 

 alle grosse Fliisse audi der Po zugefroren 20 Tage lang derart dass 

 sie Wagen trugen» etc. I do not however intend to enumerate 

 and examine all notices on ice-winters which occurred at that time. 

 The subject is of great interest and deserves a special study, which 

 will be undertaken sooner or later. I only wish to prove the 

 reality of the phenomenon and to obtain a general view of the of 

 time in which it occurred most frequently. To sum up, I find that 

 the freezing of the Baltic occurred most frequently during the last 

 centuries of the Middle ages. The period of cold winters appears 

 to have commenced about 1200 and to have culminated in the 

 14th century. The year 1322 — 1323 may be taken as typical. 

 After heavy floods of the Rhine, the Rhone a. o. rivers in June 

 and later months 1322 the cold set in at the end of November. 

 In the beginning of 1323 the Baltic and part of the North Sea were 

 frozen and the cold made itself felt over the greater part of Europe. 

 As a rule these cold winters were followed in spring by devasta- 

 ting inundations of the great rivers. No less than 55 such occur- 

 rences are mentioned by the chronicles of the 13th century. Some 

 other years, like 1304 and 1328, however, had exceedingly mild winters 

 and hot and dry summers. Such were the years 1387, 1393 a. o. 

 On the whole this century was noted for its extreme climatic 

 variations on the eastern shore of the Atlantic. As I have already 

 shown in this paper, corresponding phenomena occurred in Iceland 

 and on the coast of Greenland. Later on I will show the influence 

 which these variations exercised on the harvest yield and the econo- 

 mic conditions of Scandinavia. 



The freezing of the Baltic in severe winters appears to have 

 been most frequent in the last centuries of the Middle-ages. Then 

 gradually it occurred more rarely. In the last 3 centuries the Baltic 

 has never been frozen to. The intervals between the ice-winters 

 gradually lengthened till at last they ceased altogether. Yet the 

 recurrence of the old severe winters have been felt up to our time, 

 although mitigated, in the freezing of the water along the shores 

 of the Baltic, the crowding of ice in Oresund, driftice appearing 

 in the Cattegat etc. which has happened now and again in the 

 last decades. The phenomenon appears to be of a periodic 

 nature with a complex periodicity and to have culminated 6-7 

 centuries ago. Whether the freezing of the Baltic occurred before, 

 f. inst. during the Viking-age or the time of 800 — 900 a. G. 

 is not possible to tell, but it seems improbable that so could be 

 the case as the Sagas never mention it. Nor do the Icelandic 



records speak of ice having hindered navigation in the western At- 

 lantic. 



It should be observed that the culmination of the Baltic ice- 

 winters occurred simultaneously with the period of great storm- 

 floods and the absolute maximum in the tide-generating force of 

 the sun and moon at the beginning of the 14th century. Besides 

 this there is another phenomenon, viz. the annual immigration of 

 herrings into the Baltic and Oresund, the s. c. Hanseatic herring- 

 fishery, which culminated 1100 — 1500 and afterwards declined. 



Summing up all that the chronicles tell us of the ice-winters 

 of that time we find: 



That there was a period 6-7 centuries ago when the Baltic, the 

 Sounds and the Cattegat were frozen over and covered by a solid 

 sheet of ice which could be frequented by pedestrians and carriages 

 in certain winters. This happened most frequently in the 13th, 14th, 

 15th centuries but ceased in the 16th century. For the last 250 years 

 the Baltic has not been frozen over. 



It must not be concluded, however, that the average winter 

 climate for the last centuries has been less severe than during the 

 Middle-ages. It is possible and even probable that it is so; but this 

 »elimatic improvement* which would mean a transition from a 

 continental to a more maritime climate for the countries on the 

 Baltic must be proved in other ways to become a recognised me- 

 teorological fact. For the freezing of the Baltic depends not, as will 

 be shown, on meteorologic but on hydrographic causes, though the 

 phenomenon may very well have influenced the climate. 



The waters of the Baltic as well as of the Cattegat and Ska- 

 gerak are stratified. The surface layer in the Middle and South 

 Baltic has a comparatively even and uniform salinity varying from 

 7 °/ 00 to 9 °/ 00 . The freezing point is about — 0°.35 and the 

 maximum of density more than 1° above 0. Every particle of 

 water, which is cooled by contact with the atmosphere in winter, 

 sinks down to the lower border of the water-layer while other 

 particles, warmer and less heavy take its place at the surface and 

 are cooled in their turn. . In this manner the whole bulk of water 

 is cooled by convection down to 1° or 2° above during authumn 

 and winter. Because of the thickness of the layer (40-50 m. in 

 the Baltic proper) and the rapid interchange of water in the horizon- 

 tal direction in the western Baltic and the Belts the surface 

 layer has not time to cool to its freezingpoint in winter. In Febr. 

 and March the cooling reaches its maximum a little above +1° 

 in severe and a little above +2° in mild winters. 



Because of the thickness of the surfacelayer it is impossible 

 at present that the Belts or the southern Baltic should be covered 

 by a continuous ice-sheet. For this to happen (except of co- 

 urse near the shore and in shallow bights) it is neccessary 

 that the surface-layer gets thinner and the bottomlayer is swelled 

 by a stronger influx through the Belts and Sound, thus raising 

 its level. Under such conditions the Baltic would freeze, as easily 

 as would a shallow lake or one of the fjords of the Cattegat, 

 where a thin layer of fresh water is superposed over a deep layer 

 of salt and warm oceanic water. Whereas these fjords, f. inst. the 

 Gullmar and the inner Christiania fjord, freeze every winter 

 the Baltic has kept open now for 3 centuries even in very cold win- 

 ters. 



Knowing, as we do, that 600 years ago the Baltic froze frequ- 

 ently so that the ice could be used for communication between 

 Denmark and Germany and even for so vast a distance as that 

 between Sweden, Gothland and Esthland, we are forced to con- 

 clude that the oceanic current of salt water entering through the 

 Belts and the Suncl must have been more powerful at that time 

 and able to raise the level of the salt water which filled the depths 

 of the Baltic basins to a greater height than now. Under such con- 

 ditions the surface of the Baltic would freeze in cold winters. A 

 deepening by some meters of the channels in Oresund would do 

 the same and the explanation nearest at hand would be, that Oresund 

 and the Baltic were deeper during mediaeval time and gave wider 

 access to the undercurrent. 



I have carefully examined this alternative by taking the opi- 

 nion of the geologists who have made a special study of the level 

 of the Baltic, (Munthe, Sernander and de Geer) and by examining, 

 carefully the oldest sea charts existant of Oresund which are in keep- 

 ing of the Pilot-Office of the Royal Danish Marine. There are 

 none of these older than the 17th century and the soundings show 

 on the whole the same depths as our .modern charts between Scania 

 and Sjselland. 



The changes in the Baltic from mediaeval to modern time cannot 

 ;be attributed to geologic causes. They must be caused by the al- 

 tered hydrographic conditions and the only possible explanation 

 is that the salt undercurrent was more intense during the Middle- 

 ages than now, so that the bottom-layer of the Baltic then attained 

 a higher level and the surface-layer was thinner, which caused the 

 latter to freeze in cold winters. There is no other explanation possible. 



