In hydrology, an oceanic basin (or ocean basin) is anywhere on Earth that is covered by seawater. Geologically, most of the ocean basins are large geologic basins that are below sea level.
This figure shows the main ocean basins as they are defined in "Limits of Oceans and Seas". The boundaries are based on geography of continents and the equator.
Movements of tectonic plates and the formation of oceanic ridges and trenches.
Mean sea level is an average surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datum – a standardised geodetic datum – that is used, for example, as a chart datum in cartography and marine navigation, or, in aviation, as the standard sea level at which atmospheric pressure is measured to calibrate altitude and, consequently, aircraft flight levels. A common and relatively straightforward mean sea-level standard is instead a long-term average of tide gauge readings at a particular reference location.
This marker indicating sea level is situated between Jerusalem and the Dead Sea.
Sea level sign seen on cliff (circled in red) at Badwater Basin, Death Valley National Park
The Last Glacial Period caused a much lower global sea level.
Warming temperatures and melting glaciers are currently raising the sea level.
