» Wahrscheinlich bildeten die Friesischen Inseln in alten Zeiten 

 eine zusammenhangende Diinenkette nur durchflossen von den gros- 

 seren Fliissen. Der ganzen Bodengestaltung bei den friesischen In- 

 seln und im ausgedehnten Wassergebiet ist nach Kriimmel erst dureh 

 die Gezeitenstromung der charakteristische Typ aufgedriickt wor- 

 den. (Peterm. Mitt. 1889 s. 129 ff). Die sakulare Senkung von der 

 die Dargschikten unter der Marsch und die submarinen Walder und 



Moore Zeugniss ablegen, so wie der, nach Browne an der Schwelle 

 der historischen Zeit, nach Walther vor 6,000 bis 8000 Jahren, erfolg- 

 te Durchbruch des anglo-franzosischen Isthmus, ferner der starkere 

 Flutwechsel der ja erst nach diesem Ereigniss besonders in die Erschei- 

 nung tritt, machten ihre verheerenden Einwirkungen auf die Diinen- 

 kette geltend» — ■ — — ■ — 



V. 



The freezing in certain winters of the Baltic and Cattegat and the growth of the Hanseatic 



herringsfishery during the Middle=ages. 



Both these phenomena are important when studying the cause of 

 climatic variations in historic time. In the first place it is neccessary 

 to prove their reality by carefully sifting and comparing available 

 data which are numerous but often contradicting as to the time and 

 extent of freezing a. s. f. We have come to look upon climatic vari- 

 ations as quite irregular and incomprehensible and because of this there 

 is now a tendency to discredit the statements of the chronicles regar- 

 ding the severe winters and occasional abnormally hot summers of 

 the 13th and 14th centuries, the shifting in the climatic seasons, the 

 variation between drought and extreme precipitation, a. s. f. The 

 old writers are supposed to have exaggerated, because in their time 

 humanity was less able to protect itself against the influences of such 

 variations and it is assumed that, as navigation was generally suspen- 

 ded during winter, the ice-conditions of the sea were judged from what 

 could be seen from the shore. As to the abundant herringfishery of 

 the Oresund, it is argued that in certain years even now a tolerably 

 abundant fishery is carried on off the coast of Scania and that the 

 astounding records of the old Hanseatic fishery are due to an 

 enormous exaggeration of the ancient returns of the yield. 



In my opinion the state of the Baltic during the Middle-ages, 

 when known, will furnish the key to the mystery of the climatic vari- 

 ations. The statements relating to this subject are so numerous and 

 distributed over so many ancient chronicles and later summaries 

 of chronicles that the collection and sifting of this material will re- 

 quire a special study. 



In France the interest for historic climatology was awakened 

 by Arago, in Sweden by Ehrenheim in his celebrated presidential add- 

 ress to the Academy of Sciences of Stockholm in 1824. The scientific 

 scrutiny of the Swedish material was begun by R. Rubenson and con- 

 tinued by N. Ekholm, x ) who in the 5th chapter of his paper »Om 

 klimatets andringar och dess orsaker» gives the most complete sum- 

 mary of the subject known hitherto. The name of the chapter is: 

 » Klimatvaxlingar under historisk tid, sarskildt i nordvastra Europa. » 

 Ekholm commences his discourse thus; 



»It remains to consider the climate-variations in historic time. 

 The observation-material is certainly very comprehensive but there 

 is such a want of order and regularity in it that it seems almost imposs- 

 ible at present to get a clear view of the different kinds of phenomena 

 and the connection between them». 



The material from which such deductions can be drawn consists, 

 according to Ekholm, partly of historic records, numerous but unre- 

 liable and irregular, and partly in actual observations of the weather 

 which however do not date further back than 150 years. Our know- 

 ledge of climatic variations during the Middle-ages must thus be ba- 

 sed chiefly on historic records. As their authenticity has been questio- 

 ned, because in some cases the writers have taken down their acco- 

 unts from hearsay or copied one another, I have tried to collect new 

 documents and concentrate my research upon one problem, viz., the 

 state of the Baltic. For, if it is possible to show that the records regarding 

 the freezing of this sea and the herringfishery therein are based on 

 actual facts, it is absolutely certain that hydrographic changes have 

 occurred in the circulation of the waters of our seas and we have 

 obtained a basis for our endeavour to discover their causes. In the 

 Icelandic, the Swedish and particulary in the Danish historic litera- 

 ture I have found material wherewith to compare and criticise these 

 records. This chapter contains a collection of such statements which 

 I have obtained partly directly, partly from information given by Swe- 

 dish authorities on Mediaeval historic literature. Captain C. J. Speer- 

 schneider of the DanishMet.Inst.has collected a great deal of inform ation 

 regarding the ice-years of the Baltic. I have been able to compare my 

 historic data with those of Captain S. and I have found that several 

 of the old records have been wrongly copied and suffer from confusion 

 of geographical names. Captain S. has particulary pointed out that 



1) Quarterly Journ. of the R. Meteorol. Soc. 1901 January. 



the statements regarding the freezing of the Skagerak in reality concern 

 the Cattegat, as in old times no proper distinction was made between 

 the two seas. Thus when the Icelandic records state that in one win- 

 ter packs of wolves went across the ice from Norway to Denmark, or 

 when the Diarium Minoritorum Wisbyensium relates of the year 1296: 

 »congelatum est mare tanto rigore ut eqvitari poterat de Opslo ad 

 Jutiam » , it probably does not mean that communication was kept upon 

 the ice directly between Christiania (Oslo) and Skagen, but probably 

 between some place on the coast of Bohuslan and Jutland. But even 

 if the freezing of the North Sea or the Skagerak should not be taken 

 literally, that of the Baltic, which occurred so frequently in Mediaeval 

 time, is a fact that cannot be doubted or explained otherwise. As 

 the large material collected by Captain Speerschneider is soon to be 

 published I will here only consider a few years, which may be regar- 

 ded as typical for a mediaeval ice-winter. 



1306. The freezing of the Baltic during the winter 1306 — 1307 is a wellknown 

 historic fact which cannot be doubted. So severe a winter had not occurred for 

 many years. The entire Baltic was frozen over from Livonia and the Gulf of Fin- 

 land to the Sound. There the ice is said to have measured 15 ells in thickness and 

 for 14 weeks to have formed a solid bridge between Sweden and the Danish Islands. 

 The war between Sven Estridsson and the Dukes was stopped by the cold. 



In Diarium Minoritorum Visbyensium we find: »fuit hiemps maximus ita quod 

 mare inter Olandiam et Estoniam exstitit congelatum ». 



In the Icelandic records (Annales regii) and in the Skalholt Annals a. v. I have 

 fcund the following description of the ice winter 1306 — 1307, which was felt in Icelan- 

 dic seas as well as in the Baltic. 



»1306. Haffis fyrir Nordanland um allt sumar 15 alna harr. Frost sva mikit i j)y- 

 versku landi ok i Franz sem pa er stera lagi eru i Noregi ok gengv af Ravdstock til 

 Danmerkr yfir Eyrassvnnd». 



1323. 



From 1322 — 1323 we have the greatest number of notes regarding a mediae- 

 val ice-winter in the Baltic. Captain Speerschneider has permitted me to quote from 

 his collection of historic meteorological data, drawn from Danish and German records, 

 everything that concerns this particular winter. 



»We are told in the history of Olaus Magnus, that the frost was so hard that 

 it became possible to cross the ice from the coast of Lybeck to Denmark, and that 

 hostelries were put up on the ice. 



Both Hennig (Katalog bemerkenswerther Witterungsereignisse, Berlin 1904) 

 and Mansa (Folkesygdomme og Sundhetspleiens Historie i Danmark, Kopenhamn 

 1873) relate that the winter began on the 30 of Nov. 1322 and lasted to the half 

 of Lent 1323 had passed. Peter Olsen says that the cold culminated in March. Hvid- 

 feldt (Seriptores rer. Dan. II.' 528) tells us that there was general traffic across the 

 frozen Belt from Candlemass 2/2 for 6 weeks and that the Drost, Herr Lauritz rode 

 across from Taarborg with the troops. Pfaff (liber den strengen Wintern etc. Kiel 

 1809) speaks of the severe winter and that it was possible to ride and drive from 

 Germany to Denmark and from Liibeck to Dantzic over the Baltic, so late as 28/2 

 Arago (iEuvres completes) repeats after him that one could ride from Denmark 

 to Dantzic. 



Mansa says that the entire Baltic was frozen between Denmark, Venden and 

 Fehmern. Strelow (Cronica Guthilandorum Kobhvn. 1633) says that one could drive 

 across the ice between Sweden and Gulland. 



Quotations: 



A. De frigoribus autem illius Germanise seu Gothicis maris plura meminit Alber- 

 tus Crantzius, diligentissimus omnium regionum scriptor. Ait enim: anno 1323 gelidis- 

 simo frigore constringebatur mare ut pedestri itinere per glaciem de littore Lubicensi 

 in Daniam & in Prussiam mare transiretur dispositis per loca opportuna in glacie 

 hospiciis (Olaus Magnus' historie 1555). 



B. Erat autem 1323 qvum gelidissimo frigore mare constringeretur ut pedestri per 

 glaciem itinere de littore nostro in Daniam inqve Prussiam mare transiretur disposi- 

 tis per opportuna loca in glacie hospitiis, si quid commentibus intervenisset (Albertus 

 Krantzius Francof, 1580). 



C. Via communis erat ambulantibus et eqvitantibus in multitudine super glaciem 

 per passagium maris Baltici eundo et redeundo qvasiper continuum sex septimanarum 

 spatium circa purificationis Marias virginis similiter per passagia inter Seelandiam 

 et proximos partes Slavise (Appendix ad incerti annales Danarum). 



D. Between Norway, England and the Flanders (from the harbour Leven in the 

 latter country) the ships were frozen in on the open sea so that the merchants went 

 visiting one another over the ice. When the ice broke up most of the ships frozen in 

 the south were saved but few remained of these frozen in the north. (Suhrn a 

 St. 11.61). 



Captain Speerschneider summarizes his impressions of the icewinter 1322 — 1323 

 in this manner: 



— 16 — 



