Seasonal variations in sea level induced by continental water mass: first results from GRACE

Variations in the Earth's water cycle are commonly quantified by their effect on global mean sea-level. However, the interaction between passive adjustment of the ocean to changes in gravitational attraction due to mass redistribution, the related deformation of the solid Earth and disturbances in the Earth's rotation vector will yield a distribution that is more complicated than a uniform rise or fall of the ocean's surface.

In this study, we present the first estimates of seasonal changes in passive sea-level (which we define as the height difference between the sea surface at rest and ocean floor, excluding steric and dynamical effects) based on direct observations of surface mass redistribution, made by the Gravity Recovery and Climate Experiment (GRACE) between 2003 and 2010. We show that this 'selfgravitation-effect' causes seasonal variations of the sea-level with of up to 1 cm -- comparable to the amplitude of the long-period tides -- and that inclusion in numerical ocean models results in a better agreement between observed and modelled ocean bottom pressure variations, particularly in coastal zones.