Abstract
The first eXpendable BathyThermographs (XBTs) were deployed in the 1960s in the North Atlantic Ocean. In 1967 XBTs were deployed in operational mode to provide a continuous record of temperature profile data along repeated transects, now known as the Global XBT Network. The current network is designed to monitor ocean circulation and boundary current variability, basin-wide and trans-basin ocean heat transport, and global and regional heat content. The ability of the XBT Network to systematically map the upper ocean thermal field in multiple basins with repeated trans-basin sections at eddy-resolving scales remains unmatched today and cannot be reproduced at present by any other observing platform. Some repeated XBT transects have now been continuously occupied for more than 30 years, providing an unprecedented long-term climate record of temperature and geostrophic velocity profiles that are used to understand variability in ocean heat content, sea level change, and meridional ocean heat transport. Here, we present key scientific advances in understanding the changing ocean and climate system supported by XBT observations. Improvement in XBT data quality and its impact on computations, particularly of ocean heat content, are presented. Technology development for probes, launchers, and transmission techniques are also discussed. Finally, we offer new perspectives for the future of the Global XBT Network.
Highlights
EXpendable BathyThermographs (XBTs) are instruments that provide the simplest and most cost-efficient solution for frequently obtaining temperature profiles along fixed transects of the upper thousand meters of the ocean
This review presents the current state of the Global XBT Network, major scientific advances resulting from the decadeslong XBT record, and synergy between the Global XBT Network and other components of the observing system
XBT operations are coordinated on a global scale by the Ship Of Opportunity Programme Implementation Panel (SOOPIP), a network of the Ship Observations Team (SOT) which operates under the framework of the Joint Technical Commission for Oceanography and Marine Meteorology (JCOMM) of the World Meteorological Organization (WMO) and UNESCO’s Intergovernmental Oceanographic Commission (IOC)
Summary
EXpendable BathyThermographs (XBTs) are instruments that provide the simplest and most cost-efficient solution for frequently obtaining temperature profiles along fixed transects of the upper thousand meters of the ocean. The current Global XBT Network collects observations at spatial and temporal scales that cannot feasibly be duplicated by other observational platforms While platforms such as profiling floats (Riser et al, 2016) and underwater gliders (Rudnick, 2016) provide temperature profiles, they cannot occupy repeated, mesoscale-resolving, trans-ocean basin transects across major currents on the time scales that are regularly sampled using XBTs from fast-moving ships. High Density or High Resolution (HD/HR): Usually four or more repetitions are conducted annually along a fixed transect with an average of one XBT deployment about every 10–50 km along the ship track (35 XBT deployments per day at a ship speed of 20 kts) This mode is aimed at obtaining high spatial resolution in a single realization to resolve the spatial structure of mesoscale eddies, fronts, and boundary currents. Monitoring the state of the ocean, with respect to the MOC, OHC, and sea level change, and extreme weather events, are highlighted
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