Since its initiation in 1997, PIRATA (Prediction and Research Moored Array in the Tropical Atlantic) has evolved to become a cornerstone of sustained ocean–atmosphere observations in the tropical Atlantic. Organized around annual oceanographic cruises, PIRATA combines long-term maintenance of a unique buoy network with systematic hydrographic surveys and analyses and other complementary deployments, providing long-term time series for global climate research as well as physical, biogeochemical and marine ecosystem research in the tropical Atlantic. At the heart of PIRATA is the 17 equatorial mooring network, strategically deployed across the basin, including five French-maintained meteo-oceanic buoys and three equatorial current-meter moorings in the eastern Atlantic. These platforms deliver high-frequency measurements of meteorological variables (winds, air temperature, radiation, precipitation) and subsurface ocean variables (temperature, salinity, currents), forming a backbone for real-time climate monitoring. Thanks to robust engineering and dedicated maintenance, PIRATA has achieved excellent data return rates, with more than 77% of delayed-mode datasets recovered since 1997 and over 90% of real-time transmission sustained, even under challenging conditions.

The PIRATA cruises themselves play multiple roles. Hydrographic CTDO₂/LADCP profiles, conducted annually to at least 2000 m, provide reference data for sensor calibration, for the global Argo and Deep-Argo programs, and for physical process studies at interannual timescale. Since 2018, deeper profiles to 4000 m have been added, particularly during float deployments or at buoy positions, further extending vertical coverage. On average, 5 to 7 Argo floats, 15 drifting buoys, and 90 XBTs are deployed during each campaign, ensuring that these remote waters remain connected to global observing systems. PIRATA cruises enable numerous seawater samples to be carried out for the analysis of biogeochemical parameters (nutrients, pigments, pH, total alkalinity, particulate organic matter). They also provide access to the open ocean of the tropical Atlantic for opportunistic sampling (carbon parameters, isotopes, methane, sargassum, plankton, tuna) and continuous measurements throughout the campaign (Ship-mounted ADCP, acoustics, weather data). Finally, the network’s buoys are equipped with additional instruments (CO₂ sensors, turbulence probes, acoustic receivers), thereby maximizing scientific return.

Through more than 27 years of sustained activity, PIRATA has delivered breakthrough insights into tropical Atlantic variability. Long-term time series have clarified the dynamics of the Equatorial Undercurrent, the processes driving the Atlantic Cold Tongue, and the coupled ocean–atmosphere modes that influence rainfall variability in West Africa and South America. PIRATA observations have been central to identifying the role of turbulent mixing in seasonal SST cooling, tracking oxygen minimum zone dynamics, and quantifying variability in air–sea CO₂ fluxes. These results have fed directly into climate and ecosystem modeling, operational forecasting, and satellite validation, while supporting more than 400 scientific publications.

Equally important, PIRATA campaigns play a strong role in capacity building. They provide training opportunities for PhD students, postdocs, and master’s students, who participate in cruises, data analysis, and international collaborations. Beyond science and training, PIRATA contributes directly to global initiatives. It is an integral part of the Global Tropical Moored Buoy Array and provides essential inputs to GCOS, GOOS, the Data Buoy Cooperation Panel, and the Argo program. The program operates in the challenging equatorial region, deploying floats, drifters, and sensors in strong currents and divergent surface waters, thereby ensuring global coverage and strengthening international observing capacity. PIRATA is sustained by strong international collaboration, with French, Brazilian, and US teams working jointly under a shared MoU, alongside partners from Germany, Canada, and South Africa. The program stimulates a broad scientific community around research projects. Several major European initiatives (AMMA, PREFACE, AtlantOS, EuroSea, TriATLAS), as well as numerous national efforts (LEFE, TOSCA, ANR), have relied – and continue to rely – on the PIRATA network. The latter thus occupies a central place at the heart of scientific initiatives aimed at better understanding and predicting climate variability in the Atlantic.