Ocean Tides And Related Phenomena

Tidal Phenomena

Volume 66 of the series Lecture Notes in Earth Sciences pp 145-171


Earth tides and ocean tidal loading

  • Gerhard JentzschAffiliated withInstitut für Geowissenschaften, Friedrich-Schiller-Universität Jena

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The tidal deformation of the solid earth is superimposed by the loading effect caused by the ocean tides. There are two contributions: the attraction of the moving water masses and the deformation of the crust due to the water load. Thus, the elasticity of the local crust-mantle structure controls the response. The distribution of the continents and the topography of the ocean bottom avoid a uniform response of the ocean to the tidal forces. Therefore, the tidal loading signal is generally not in phase with the body tides.

The different transfer functions for gravity, tilt, and strain result in different loading effects as well: The loading signal in gravity is close to the ocean mostly smaller than the body tide, but it can still be observed at great distances from the oceans. On the other hand, in tilt and strain the loading signal may surmount the body tide close to the coast, but it vanishes below the noise level far from the coast. Therefore, tidal gravity provides an independent tool to constrain ocean tidal models, whereas tidal tilt and strain can be used to determine local crustal structures.

The vertical displacement due to ocean tidal loading may reach values of more than a decimeter close to the coasts, and it must be taken into account for high precision earth monitoring. Models for the correction of the body tides exist, but since there is still no global ocean tidal model available that also fits all the shelf tides further gravity measurements are needed.