Sea Levels: Den Helder

The 150 year sea level record is tied to the dutch ordnance survey level.
The linear trend is 14.4 cm/century (relative sea level change).

The Netherlands ordnance survey datum is tied to underground benchmarks.
A recent study shows that these underground benchmarks have a subsidence
in the Den Helder area of approximately 5 cm/century. Fitting well with the subsidence models:

Henk Kooi et al,
Geological causes of Recent (~100 yr) vertical land movement in the Netherlands,
Tectonophysics 299 (1998) 297-316

Here is a subsidence map.
see also:

http://www.ncg.knaw.nl/SubBZ/BeginSubBZ.htm 
 

This gives for the eustatic sea level change a value of 9 cm/century.


Comparison with New York

In the course of the observed time series in Den Helder some deviations of the linear trend are observed.

The deviations can be attributed to the varying strength of the westerly winds 
due to the North Atlantic Oscillation. It is clear that a stronger westerly 
raises the level in Den Helder and lowers at the same time the level in New York 
on the opposite side of the Atlantic.



Finally:
Is the rise unprecedented?
Here is a paleosealevel graph for Holland 


Hans Erren

 


this page:
http://members.lycos.nl/ErrenWijlens/co2/denhelder.html

homepage:
http://members.lycos.nl/ErrenWijlens