eXpendable BathyThermograph (XBT) NETWORK
Boundary currents are critical elements in the global circulation and heat budget. Boundary currents carry mass, heat, freshwater and biogeochemical properties along their paths and into the ocean interior. The strength and variability of boundary currents affect the intensity of air-sea exchange of heat, moisture, and carbon and influence storm-track evolution and other extreme weather events. The global High Density eXpendable BathyThermographs (XBT) Network is an international effort that produces unique and high quality upper ocean temperature data across fixed repeat transects that, in conjunction with observations from other tools such as Argo floats and underwater gliders, monitor the variability of key ocean currents. XBTs monitor the variability of boundary currents, surface and subsurface currents, and basin-wide upper-ocean heat transport.
The XBT network is presently the main component of the global ocean observing system to provide long-term (>30 years) temperature sections to 800 meters depth across boundary currents and across ocean basins. XBTs are typically deployed every 20-30 kilometers at least four times per year along repeating coast-to-coast transects that resolve mesoscale variability and the major ocean boundary currents. Annually, between 10,000 to 15,000 XBTs are deployed globally, and their data are transmitted in real-time to ocean and weather forecast centers and submitted to data distribution centers. These data contribute to assessments of the state of the ocean, particularly of long term ocean variability, monitor boundary currents, fronts and eddies, provide continuous monitoring of meridional heat transport across ocean basins. XBT data provide in situ data for assimilating into and evaluating ocean and ocean-atmosphere models, which have been used to find links between changes of ocean currents and transports with extreme weather events, sea level changes, ecosystems, and fisheries.