In 1915 C. J. H. Speerschneider from DMI compiled alot of evidence regarding past ice conditions in Danish waters. My colleague J.P. Steffensen found it in a pile of books being thrown out and saved it. I’ve scanned it to a pdf to make it more accesible. There is a summary in english on page 124.
The vinter conditions for individual years is carefully summarized with good references. Often additional evidence from other European countries is also cited. For example the harsh ice conditions in the 1785 winter for Rotterdam and Haag is cited.
In the period from 690-1763 AD there is unfortunately only sporadic anecdotal evidence. Still, extremely harsh winters may be related to large tropical volcanic eruptions and could possibly be used as a supporting evidence for the dating of these events.
I’ve typed in some of the Speerschneider tables and compared it to another long Baltic sea ice record (Seinä et al. 2001). The agreement is very good. I note that it is also an excellent source of references for winter conditions in Europe.
Seinä, A., Grönvall, H., Kalliosaari, S., and Vainio, J.: Ice seasons 1996–2000 in Finnish sea areas / Jäätalvet 1996–2000 Suomen merialueilla, Meri, Report Series of the Finnish Institute of Marine Research, 43, 2001.
Icebreakers Danbjørn and Thorbjørn in Frederikshavn.