Autonomous Profiling Floats: Workhorse for Broad-scale Ocean Observations

The autonomous profiling float has been a revolutionary development in oceanography, enabling global broad-scale ocean observations of temperature, salinity, velocity, and additional variables. The Argo float array applies this new technology to provide unprecedented measurements of the global upper ocean in near real time, with no period of exclusive use. It builds on its predecessors, the upper ocean thermal networks of the 1970’s to 1990’s— extending the spatial domain and depth range, improving the accuracy, and adding salinity and velocity. Precision satellite measurements of sea surface height, as made by the Jason1 altimeter, combine with Argo data in a dynamically complementary description of sea level variability and its subsurface causes. The broad-scale Argo float array is a central element in the international infrastructure for ocean research. A comprehensive ocean observing system can be constructed from floats, together with satellite measurements, improved measurements of air-sea fluxes, moored time-series in the tropics and other special locations, shipboard hydrography, and high resolution measurements in fronts, eddies and boundary currents from autonomous gliders. One of the primary objectives of the observing system is to close the oceanic budgets of momentum, heat, and freshwater on seasonal and longer time-scales in order to understand the role of the ocean in the climate system. The rapid progress toward a global Argo array, and the high level of interest worldwide, are due to the broad utility and efficiency of profiling float technology and to its central role in a comprehensive ocean observing system. The following discussion begins by considering the concept of broadscale ocean sampling, then its application in the Argo array, and finally summarizes the present status and future directions of profiling float technology.