# PRAGUE CENTRE OF
MATHEMATICAL
GEOPHYSICS,
METEOROLOGY, AND THEIR
APPLICATIONS

(MAGMA)

### Reduction of the influence of pleistocene ice-sheet evolution
on a global tide-gauge data set

Jan Hagedoorn, GeoForschungsZentrum, Potsdam, Germany

Prague, Nov 3, 2004
A consistent model for the calculation of the influence of pleistocene
ice-sheet evolution on recent sea-level rise is presented, which
consists of three components, the glacial isostatic adjustment (GIA),
the variation of earth's rotation (ER) and the sea-level equation (SLE).
The solution of the SLE describing the redistribution of glacial melt
water in the oceans is implemented in conjunction with the
spectral-finite element method of modeling GIA in the time domain.
The additional contribution to sea-level caused by the ER due to the
ice-water mass redistribution is determined by means of the
Liouville-equation.

For the calculation of the influence of the pleistocene ice-sheet
evolution on sea-level change, three different global models of the
pleistocene deglaciation and four different viscosity stratifications
are used.

To evaluate the prescribed models a method is developed independent
from tide-gauge data using so-called sea-level indicators (SLI). This are
geological samples, which gives an indication about relative sea-level
change and which can be dated. The comparison of the predicted
postglacial sea-level change induced by the pleistocene ice-sheet
evolution with a set of globally distributed SLI is the basis to
evaluate the acceptability of the underlying earth and ice models.

The PSMSL archived monthly mean values recorded by a globally
distributed net of tide-gauge stations. From this data base time
series are selected with at least 45 a of data and additional criteria
are applied, to choose only time series minimally affected by other
processes than the pleistocene ice-sheet evolution (e.g. tectonic or
anthropogenic induced vertical displacements or sediment compaction).

The best-fitting models are employed to remove the influence of the
pleistocene ice-sheet evolution on recent sea-level change recorded by
the set of selected tide-gauge stations. The reduced global mean sea-level
rise observed by this set of tide-gauge stations is 1.46 +/- 0.2
mm/a. Still the question remains, what this global mean value means
and how it is interpreted in the context of ongoing discussion about
recent sea-level rise.

Last edited Nov 18, 2004