Key points:

  • Global climate-proxy data document that the Quaternary has been characterised by glacial/interglacial cycles with predominant 100-kyr cycles since at least ~ 700 kyr that influenced the formation of extensive ice covers in Northern Switzerland.
  • Past glacial climate conditions in Northern Switzerland are modelled to a regional level using a nested approach. Ice flow models using these modelled climate conditions reproduce the maximum ice cover extent for the last glaciation as known from proxies, such as moraines.
  • Coupled ice flow models allow estimation of the glacial erosion potential in Northern Switzerland during foreland glaciations. Key controlling factors are basal ice temperature, sliding speed and high subglacial water discharge.
  • Future glacial inception and severity of glaciations depend on anthropogenic CO2 emissions and may be significantly delayed, e.g. nearly 200 kyr for a present-day emission scenario.
  • Each glacial period is expected to be associated with permafrost conditions during the phases of coldest temperatures. Permafrost is expected to reach maximum depths of 100 –200 m.
  • Due to the different distance to the Alps and different topography, ice thicknesses and the duration of ice occupation at the sites varied during past glacial cycles (ZNO > NL > JO). The same pattern will most likely be seen during future glaciations with ice thicknesses between 200 and 400 m and durations of ice occupation between 1'000 and 3'000 years. 

 

The geology and geomorphology around the repository will be subject to erosional processes that are in turn influenced by climatic forcing. Large foreland glaciations may not only cause over­deepening of subglacial valleys but may also cause lithospheric depression and later isostatic rebound after deglaciation. These changes in mass may affect the local stress field as well as the hydrogeological system. Accordingly, this section provides the basis for climate as a driver of (deep glacial) erosion (Section 6.4.3.3). The coupling of climate to ice flow modelling allows derivation of a number of glacial parameters (e.g. ice thickness) which may be indicative for the evaluation of long-term hydrogeological changes (Section 6.5).

Section 6.3.1 starts with an overview of Quaternary climate evolution at a global scale (more regional aspects are summarised in Chapter 3). Past glacial cycles were important for the erosion history of Northern Switzerland, therefore the focus in Section 6.3.2 is on glacial conditions, including the occurrence of permafrost and knowledge about ice flow during extensive foreland glaciations. Based on the previous findings, changes in Earth’s orbital parameters and anthro­pogenic CO2 emissions, Section 6.3.3 provides model scenarios that were generated to better understand the onset of potential future glaciations. The main conclusions are provided in Section 6.3.4.

A more in depth discussion of climate evolution and ice flow is provided in Nagra (2024j).