Full scale applications
Full scale simulations were conducted for the Gorleben reference site. An overview of the geology and hydrogeology is given in (Noseck et al., 2012). Possible future climate transitions are a seawater trans- and regression and the freezing and thawing of permafrost, amongst others. Model simulations were only conducted for a seawater trans- and regression (in the following denoted as “seawater transgression”).
Possible future climate transitions can be derived from the geological past. The Quaternary period is characterized by extreme climate changes, i. e. the repeated advance and retreat of inland ice sheets, and the transgression of the North Sea in Northern Germany due to a global sea level rise (Benda, 1995). With the knowledge about past climate and its driving forces, possible future climate states can be simulated.
Several studies investigate the possibility of a future sea level rise due to global warming. Some authors assume a sea level rise of 20 m to 30 m within the next 50,000 a. Taking the thermal expansion and density changes of seawater into account, the melting of the global ice volume can be calculated. Therefore, a sea level rise of up to 80 m is possible (Williams & Hall, 1993), but is mostly not regarded as a realistic scenario.
All in all, a repetition of past interglacial and glacial cycles is most probable on a time scale of one million years, so that a future cold stage or a sea level rise have to be considered for the long-term future. In this project, the Holstein Warm Stage is used as a reference for warm stage model simulations.
Quaternary sea level oscillations can be regarded as a result of the Milankovitch cycles and hence are dependent on the global ice volume (Imbrie et al., 1984). In Northern Germany, the sea level variations amounted to several dekameters up to ca. 120 m in the course of the last 18,000 a (Streif, 2004). Several Quaternary North Sea transgressions are recorded for Northern Germany. In the geological past, periods of seawater inundation in Northern Germany persisted for about a few thousand years only (Streif, 2004). The maximum extension of the Quaternary marine transgressions occurred during the Holstein Warm Stage (Fig. 1), which lasted from 335,000 until 330,000 a before present (BP). The marine transgression occurred in form of a single, uninterrupted sea-level rise with an average rising rate of 1 m per 100 a (Streif, 2004). This led to a local sea level rise of more than 50 m (Streif, 2004) up to ca. 65 m (Linke et al.,1985), while the global sea-level rise amounted to more than 100 m (Rohling et al., 1998). The sea-level high stand persisted for the time of ca. 5,000 a.
Fig. 1: Global sea level record of the past 500,000 a (figure after Rohling et al, 1998).
Solid lines are based on different climate proxies. The dashed line shows schematic sea-level fluctuations sketched through the control points following the main trends in the oxygen isotope record. Cross-hatched ovals show ranges of interglacial sea-level highstands. Error bars represent ranges of glacial sea-level lowstands according to the model presented in (Rohling et al., 1998). The red oval shows the Holstein interglacial.
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