Though satellites provide highly detailed analyses of the temperature of the ocean surface, they cannot measure temperatures below the first 1 mm of water. For that deeper understanding, NOAA relies on thousands of buoys, ships, undersea gliders and other devices to measure temperatures at depth. The measurements are consolidated every few years by the National Oceanographic Data Center into a product known as the World Ocean Atlas. The measurements shown here go as deep as 5,000 m — far deeper than many places in the ocean — which is why there is a lack of data (black areas) in some of the deeper imagery.
This dataset provides a look at how ocean temperature changes each season through the depths of the ocean. For each season (three month averages January - March, April - June, July - September, and October - December) there are six depths available: surface, 100m, 500m, 1,000m, 2,000m, and 5,000m. Ocean temperatures get colder with depth. Cold water has a higher density than warm water. Water gets colder with depth because cold, salty ocean water sinks to the bottom of the ocean basins below the less dense warmer water near the surface. The sinking and transport of cold, salty water at depth combined with the wind-driven flow of warm water at the surface creates a complex pattern of ocean circulation called the 'global conveyor belt.' Another trend to notice is that ocean temperatures at the surface vary dramatically from season to season, but that variation becomes less and less as the depth increases. In these frames, past a depth of 500m (1640ft), ocean temperatures are fairly consistent from season to season.