The World Ocean Atlas (WOA) is a set of climatological mean, gridded fields of oceanographic variables based on in-situ measurements from a wide variety of sources.  Global, decadal averages of temperature, salinity, oxygen and nutrients are provided at monthly, seasonal and annual averaging periods on 102 standard depth levels from 0 to 5500m, and at 0.25° (temperature, salinity) and 1 ° (all variables) horizontal resolutions.   These fields are widely used for ocean model initialization and validation, climate studies, and operational forecasting.  Regional climatologies of temperature and salinity are available at 1/10 ° for select regions of the global ocean with good data coverage.  The WOA is often referred to simply as "Levitus" or the "Levitus Climatology" after its pioneering creator, Sydney Levitus.  The WOA generally represents large-scale features of the global ocean quite well but coverage can be inadequate for meaningful gradient and trend calculations in some regions and depths.