Eustatic and Relative Sea Level Changes

Sea level changes can be driven by either variations in the masses or volume of the oceans, or by changes of the land with respect to the sea surface. In the first case, a sea level change is defined ‘eustatic’; otherwise, it is defined ‘relative’. Several techniques can be used to observe changes in sea level, from satellite data to tide gauges to geological or archeological proxies. Regardless of the technique used, ‘eustasy’ cannot be measured directly, but only calculated after perturbing factors of different origins are taken into account. In this paper, we review the meaning and main processes that contribute to eustatic and relative sea level changes, and we give an overview of the different techniques used to observe them.