Solid Earth sea level change contributions

For quantitative projections of regional sea level change we have to quantify factors arising from the visco-elastic response of the solid Earth to ice/water mass redistributions (Glacial Isostatic Adjustment - GIA), ongoing land ice discharge, changes of land water storage and river runoff and the regional evolution of coastal morphology due to sedimentary transport processes. Corresponding deformations of ocean basins and gravitational changes due to these factors produce regional changes in sea level that fundamentally affect remote coastlines. However, in existing climate projections, only preliminary attempts have been made to account for those effects (Slangen et al., 2014), despite their expected reinforcement in their spatial pattern than those observed in present day internal sea level variability (see Figure c). It was only recently hypothesized that the effects of viscoelastic deformations of the Earth’s lithosphere on regional sea level could be of particular importance to the reconstruction of paleo-sea level distributions, but also for projections of future sea level change in response to natural and anthropogenic changes in the distribution of water between land and ocean.

In certain areas of the ocean, the steric nature of regional sea level change is superseded by mass-related effects. The separation between both effects is an important step in detecting anthropogenic effects on sea level. Apart from the steric adjustments associated with changes in the thermohaline circulation and atmospheric feedbacks (Stammer et al., 2011), redistributions of water mass between the cryosphere, continent and the ocean, may be associated with motions of the Earth’s surface and changes in the geoid and are formulated in the sea level equation (Farrell and Clark, 1976). Furthermore, they may affect the Earth’s inertia and rotation, which produces an additional sea level response (Milne and Mitrovica, 1998), both processes need to be quantified. In addition, basin-scale gravitational effects related to present-day mass redistributions external to the ocean (atmosphere, hydrological storage; e.g., Vinogradova et al., 2010; Jensen et al., 2013) may mask other effects in coastal oceans and require to be quantified as well. Currently, such a separation is not possible; however, larger effects related to mass redistributions are expected in response to future releases of freshwater from melting glaciers (Gardner et al., 2013) or polar ice sheets (Shepherd et al., 2012), thus this process is expected to become more important to the coastline in the future.