Re: What was the sea level in the 10th century?

villandra wrote: 
I read that the sea level in teh 10th century had risen a meter or
something - consistently with what we are currently led to expect of
Greenland loses its glacier.  In the 10th century either it had no
glacier, ro the glacier was much smaller than it is now.

What is actually known about the sea level in the 10th century, and how
do we know it?

How did the sea level in the 10th century impact European coastal
cities?

I doubt that very much. I live in the Netherlands and we do have archeological findings suggesting there was more drie land available before the 13th century than afterwards.

For example, I do know that my old hometown - which was built before the 1280 - was originally located somewhat more to the west of the current location. During the 10th century this was all drie land. Later on - basically in the 13th century - it was moved to the current location next to the IJsselmeer (previously known as Zuiderzee). If sealevels were higher in the 10th century (ONE meter higher than the current level) it is illogical to have a village built in a location which is lower than the current (although the difference in height is a to be expressed in decimeters) and to have it moved to a "higher" location when sealevels dropped.

Secondly there have been maps of the Low Countries from Roman time up to the current times. Before the 13th century there was a considerable smaller lake named the Flevomeer (or actually a collection of smaller lakes). During the 1200-1600's the Zuiderzee formed itself (possibly because of a series of floodings. The area was only marshlands so no big sealevel rise was required to transform the area in the lake it eventually became!). (Lenselink, G. en Koopstra, R., 1994, Ontwikkelingen in het Zuiderzeegebied, van Meer Flevo, via de Almere-lagune, tot Zuiderzee. In: Rappol, M. en Soonius, C.M. (redactie). In de bodem van Noord-Holland. Lingua Terrae, Amsterdam, pp. 129-140). Note that this date corresponds quite nicely to the relocation of my hometown!

Furthermore the whole of the Netherlands has experienced worse floodings when time went on (from the 10th century onward). If the 10th century had higher sealevels than present, it follows logic that sealevels have dropped afterwards. There is no data available that supports that view. From eyewitness reports though it is known that floodings did occur with increasing frequency during history. Up to the 17th century the country also tended to lose drie land instead of gaining. This supports the view of rising sealevels (possibly enhanced by more and/or increasing violent storms) from the 10th century onwards.

Measurements in Amsterdam suggest sealevel rise between 1700-1800 was practically nil. Between 1800 - 1995 however it was 23cm. The avg sealevel rise on the Dutch coast between 1880 - 1995 was determined to be 18cm/century (De keerzijde van ons klimaat, RIKZ-IMAU, 1998). Zagwijn states that the avg sealevel rise during the last 1000 yrs has been between 30 - 50cms (Zagwijn, W.H. (1991) Nederland in het Holoceen. Rijks Geologische Dienst Haarlem, Sdu uitgeverij, 's-Gravenhage, tweede druk, 46 pp. ISBN 90 12 05239 4). De Groot however calculates the avg sealevel rise (on the Frisian Islands) between 500 - 2000AD to be 1mtr (de Groot, Th.A.M., Westerhoff, W.E. en Bosch, J.H.A., 1996. Sea-level rise during the last 2000 years as recorded on the Frisian Islands (the Netherlands).

So, to conclude, it seems unlikely that during the 10th century the sealevel was 1mtr higher than the current. Schilstra (1974) even states a lower than current sealevel. He describes the lowwater level on avg. to be at -1.7mtr NAP and the highwater level -0.10mtr NAP. (Schilstra, J.J., 1974. In de ban van de dijk. De Westfriese Omringdijk. Uitgeversmaatschappij West-Friesland, Hoorn, 192 pp.).

Some links:
- http://www.atem.nl/CIV/NED/NH001.HTM (shows a "map" of the northern part of the Netherlands during Roman times. Since no real measurements were done in these times this "map" is based upon reports). (is in Dutch!)
- http://avn.geog.uu.nl/13geologie/73/73.html (shows a map from the geological atlas of the Netherlands during Roman times) (is in Dutch!)
- http://home.tiscali.nl/~wr2777/West-Friesland.htm#De%20ligging%20van%20het%20bodemoppervlak%20t.o.v.%20de%20zeespiegel
Gives some data about sealevel rise. (is in Dutch!)

- http://www.agu.org/revgeophys/dougla01/node4.html#SECTION00040000000000000000 (sea level rise during recent millenia)

--
Richard
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