Axis 1 : Sea level and Vertical coastal movements
Vertical land movements at the coast are present in the sea level variations recorded by tide gauges. They may be of epirogenic origin (tectonics, volcanism, postglacial rebound, sedimentation processes) or anthropogenic (subsidence related to the pumping of underground fluids, hydrocarbons or groundwater). A few examples opposite show their importance over long periods of time spanning several decades or even centuries (Figure adapted from PSMSL).
These are therefore signals of non-climatic origin that need to be carefully determined in order to separate them from the climatic contributions, namely the thermal expansion of the oceans and the melting of continental ice (polar ice caps or alpine glaciers), but also to better understand them and take them into account in projections of sea level evolution at the coast and the associated impact studies. The ultimate challenge is to better anticipate and better adapt to coming changes, whether of epirogenic or climatic origin.
– The first action of this research axis is to determine these vertical movements through observation, more precisely by space geodesy and absolute gravimetry methods. Among space geodesy techniques, GPS quickly established itself due to the quality of its results, its practical use and the relatively reasonable cost of the equipment. An example of the potential of this technique is given below, illustrating the presence of vertical land movements in long tide gauge time series and how detailed analyses of GPS measurements can separate (reduce) them in order to better isolate the climatic contributions (action 1).
– The second action is to understand and model the processes responsible for vertical movements. Within the wide range of epirogenic processes, postglacial rebound is an important large-scale phenomenon for which relatively precise models exist (so-called glacio-isostatic adjustment or GIA models). However, the accuracy of their predictions is limited by our knowledge of the deglaciation history and of the parameters of the Earth model, such as lithosphere thickness or the viscosity profiles of the upper and lower mantle (action 2).
Precise sea level measurements, complementary to and independent of tide gauging, have been provided by satellite radar altimetry since 1992 (for example, the Topex/Poseidon satellite). Furthermore, historical archives are also an important source of sea level data, all the more so as the French heritage proves very significant, in terms of both stations and data volume, and it bears witness to a bygone past that can no longer be revisited (to measure), but which is interesting to study in order to understand present-day sea level fluctuations. these ancillary aspects of actions 1 and 2 are important in research axis 1, and we remain on the lookout for resource opportunities to explore them.
Action 1 : Determination of relative and absolute sea level variations ; separation of climatic contributions from epirogenic contributions
Action 2 : Understanding vertical movement processes related to postglacial rebound
Parallel action : Development of an observation Service infrastructure called SONEL (www.sonel.org), labelled by the INSU (CNRS) in 2011
