What is eustatic sea level?

The term "eustatic" refers to the global sea level. This is opposed to the isostatic sea level, which is a local measurement that is often a result of tides. Eustatic sea level changes are global, and they are often the result of major upheavals to the climate or ocean basin.

The eustatic sea level can change for a number of reasons, but the effect is always, by definition, global. An example of eustatic sea level change is the drop that occurs during an ice age. During an ice age, a large amount of water is locked up on land and unable to flow to the sea. Combined with a cooler, denser ocean, the result is a global drop in the eustatic sea level.