Oceanic CDRs were created to address the need for Climate Variables, especially Essential Climate Variables (ECVs) as identified by the Global Climate Observing System (GCOS). The Oceanic surface ECVs are: Sea-surface temperature, Sea-surface salinity, Sea level, Sea state, Sea ice, Surface current, Ocean colour, Carbon dioxide partial pressure, Ocean acidity, Phytoplankton. The Oceanic sub-surface ECVs are: Temperature, Salinity, Current, Nutrients, Carbon dioxide partial pressure, Ocean acidity, Oxygen, Tracers. CDRs are often generated by blending satellite observations, in-situ data, and/or model output.