Britannica
Sources used in this answer
Why can changes in ocean-basin volume alter sea level even when the total amount of ocean water stays nearly the same?
Created from Britannica articles
using AI.
AI can make mistakes, so verify using Britannica articles.
paleogeography
Watch a time-lapse of Earth changing through geologic time, from the Cambrian Era to the projected period of Pangea Proxima.
In the context of paleogeography, changes in sea level are often driven by fluctuations in the volume of ocean basins rather than changes in the total amount of water on Earth, which has remained relatively stable since the early Precambrian.1
As plate tectonics and seafloor spreading alter the shape and volume of these basins, the capacity of the ocean to hold water changes. Several mechanisms drive this:21
- Ocean Ridges: The formation of new oceanic crust at mid-ocean ridges creates buoyant, elevated features that displace seawater, forcing it to rise and flood continental margins.2
- Crustal Age and Subsidence: As oceanic crust moves away from ridges, it cools, becomes denser, and subsides. This increases the volume of the ocean basin, causing sea level to drop.2
- Subduction: When subduction consumes older, denser crust, the average age of the remaining seafloor decreases. Because younger crust is more buoyant and sits at a higher elevation, it reduces basin volume and causes sea level to rise.2