The Earth's oceans are constantly changing due to surface currents, deep ocean currents, changes in sea level, and tides. All changes of this type are generally accompanied by a redistribution of the mass within the oceans. To determine whether the sea level is changing due to heat (thermal expansion) or water redistribution, we will combine our present knowledge of sea level height with gravity measurements from the GRACE satellite.

We cannot presently observe deep ocean currents from the surface but we may be able to detect them with GRACE because of their effects on mass distribution within the oceans. The balance between long-term ice-sheet changes and thermal expansion of the oceans contributes to the study of sea-level rise, with its obvious impact on society.