The following contribution was presented at the poster session of the INQUA-SEQS/NITG-TNO Eemian symposium (The Netherlands, 1998):

A readjusted sea level curve of the Eemian in the Netherlands

Hein de Wolf, Piet Cleveringa & Tom Meijer [NITG-TNO]

Introduction
In an article with the title "Sea level changes in the Netherlands during the Eemian" (1983) Zagwijn published a curve of the high tide sealevels. With the help of the pollen-analysis the time span of the Eemian was subdivided into zones and subzones. The duration of the Eemian was at that time estimated to be about 10,000 years and on the basis of the counts of annually layered sediments by Müller (1974), a time-scale for the pollen-zones E1 to E4b was established.

New data
As a result of the geological mapping, 1: 50,000 during the last decade, new data on the marine and non-marine Eemian became available. Last year [1998] a new core (Amsterdam-Terminal), in the interglacial basin of Amsterdam, was investigated with the help of biotic and a-biotic specialists. The fruitful discussions about the environmental changes yielded a new insight into the rise and fall of the sea level during the Eemian
Because of the new data on the Amsterdam-Terminal boring, it was necessary to re-interpret the data of previous investigations of Eemian deposits. Some of Zagwijn's older data are still useful. The first and preliminary results of a reconstruction of a curve based on fresh - marine contacts obtained from different sites in the Netherlands and the adjacent North Sea area are presented. All data are from cores investigated for their diatom, foram and/or shell contents. With the help of pollen-analysis the clastic and/or organic deposits have been (relatively) dated. The duration of the entire interglacial is estimated to be about 22,000 years (Winograd, 1997).

Validation
An example of how the diatom data of the Amsterdam-Terminal core is used for the reconstruction of the sea level curve.
The sediments of the Late Saalian (pollenzone LS) were deposited in a fresh water environment under cold conditions in a periglacial landscape without trees. The treeline had not yet passed this location (De Wolf, et al., 1995). Navicula jaernefeltii is the dominant species in the lower assemblage at the base of the infill. At the time the treeline passed, a fresh water lake with an Aulacoseira italica flora is present (pollenzones E1 and E2). At an early moment during the Eemian interglacial (pollenzone E3) the first 'whiff' of a marine influence in the fresh water environment is shown by the Fragilaria bloom.
The following marine phase (pollenzones E4a, E4b, and E5) is characterized by three diatom floras, from bottom to top:

  • a flora with Hyalodiscus scoticus indicating clear marine-brackish waters without tidal influence.
  • a flora characterized by allochtonous Stephanopyxus turris and Chaetoceros spores, indicative of cold oceanic waters, and Cocconeis disculoides which is autochtonous and characteristic for marine-brackish, warmer and southerly waters. There is still no evidence of a clear tidal influence in the basin.
  • a flora characterized by Cymatosira belgica showing a marked similarity to the Holocene North Sea flora. In this phase the tidal influence is clearly present.


We are aware that reconstruction of true rates of rise and fall in the sea level during the Eemian is still not possible, as Zagwijn already mentioned in 1983. Nevertheless, the data now available may be useful in understanding phenomena like differences in local and regional subsidence.
In follow-up investigations the preliminary findings will be elaborated. Additional data from either our own archives or from our national geological database will result in a more reliable curve and better validation of the facies of the marine and terrestrial Eemian.
For model-builders this is necessary to improve predictions and cost calculations. This is the case for climatologists as well as engeneers involved in subsoil infrastructures.
 
 
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