Eustasy and Geoid Changes

Abstract

The real ocean surface-the equipotential surface of the geoid or the geodetic sea level-is rough and uneven and characterized by humps and depressions of several meters. The present geoid configuration cannot have remained stationary back in time. The main question is over what time units geoid changes may have played a significant role. The instability of the geoid configuration has not been considered previously. The geoid may change both horizontally (geographical dislocation of the geoid relief) and vertically (magnitudinal changes in relief). There are numerous variables (during different geological time units) that must have affected the geoid. Geoid changes must certainly have occurred during the Phanerozoic and the Late Quaternary. Holocene "eustatic" data also yield indication of geoid changes. Tide gauge data and Holocene eustatic short-period fluctuations seem to indicate geoid changes even during short-period time units. Geoid changes are related to fundamental geophysical-astronomical problems. Late Quaternary data suggest a cyclic pattern of the geoid changes that resembles the precession cycle. Holocene geoid changes-like correlated magnetic, climatic, and volcanic fluctuations-seem to be caused by changes at the core/mantle interface (bumps and eddies) and coupling. Because of geoid changes, eustasy is not globally valid.