The World Ocean Atlas (WOA) contains objectively analyzed climatological fields of in situ temperature, salinity, oxygen, and other measured variables at standard depth levels for various compositing periods for the world ocean. Regional climatologies were created from the Atlas, providing a set of high resolution mean fields for temperature and salinity. The World Ocean Atlas 2018 (WOA18) release September 30, 2018 updates previous versions of the World Ocean Atlas to include approximately 3 million new oceanographic casts added to the World Ocean Database (WOD) and renewed and updated quality control. The WOA18 temperature and salinity fields are being released as preliminary in order to take advantage of community-wide quality assurance. WOA follows the World Ocean Database – WOD periodic major releases and quarterly updates to those releases.