GiSeLE

The figure of the Earth results from the combination of dynamic internal processes that occur at different temporal and spatial scales. Progress in numerical modeling techniques allow the description of mantle convection processes and associated changes in the overall shape of the Earth. However, the resolution is restricted by uncertainties in rheological parameters and the understanding of the Earth’s dynamics is therefore non-unique. In fact, the shape of the Earth can be used as an independent constraint to evaluate its internal dynamics, just like other geophysical observables like gravity or seismic tomography. Meanwhile, long-term sea-level evolution is inferred from the geological record, but a large controversy persists on the spatial and temporal properties of the signal. It is becoming more and more obvious that a large bias is introduced into the characterization of sea level change because observations are made on the constantly evolving morphology of the Earth. Understanding both absolute and relative sea level fluctuations requires a better knowledge of the internal dynamic processes that are responsible for the present (transient) state of the Earth’s morphology. Relative sea level is the intersection between the geoid and the solid Earth. As such, it monitors the evolution of both such that the geological record documents it with a high resolution, provided that a reference datum is defined. The present-day morphology of the Earth is a transient stage and therefore cannot be used as a reference level for an Earth on which plates are drifting. Because of this lack of reference level, the paleogeographic evolution of the Earth cannot be analyzed properly and defining a reference Earth seems to be crucial. The first step of this project is to compile comprehensive compilations of world-scale datasets that document sea level variations at geological time scale from the sedimentary record; during the Quaternary from Quaternary geomorphology; and at present from tide gauges and spatial altimetry. In addition, new data will be acquired for key point locations. The comparison between Quaternary and instantaneous sea level fluctuations, confronted to previous glacio-isostatic adjustment models will allow a stationary reference morphology to be defined. The second objective is to take advantage of these different time-scales to filter the data in order to quantify the world-scale, long-term, global and non-uniform sea level change induced by the Earth’s internal dynamics and to extract the dynamic component of morphology through time. The effort will be oriented towards solving this component, as opposed to the uniform component, for which deciphering the paleoclimatic and tectono-eustatic causes is a broad topic by itself. The third aim of this project is to use these results to calibrate forward models of mantle convection by matching a set of parameters to observations of long-term sea level change. The period of interests (Toarcian, Cenomanian and Present-day) are key episodes in the Wilson Cycle. Links between absolute sea level, relative sea level, and the localization in the characteristic geodynamical framework of a given time of the cycle will be explored.