In early May, the 273-foot research vessel Roger Revelle docked in Cabo Verde with an international team of scientists after 53 days at sea, crossing the open Atlantic along a cruise path known as A16S.
With scientists at NOAA’s Atlantic Oceanographic and Meteorological Laboratory (AOML) and the Cooperative Institute for Marine and Atmospheric Studies (CIMAS) and Woods Hole Oceanographic Institute (WHOI) acting as Chief Scientists onboard, this cruise marks the fourth reoccupation of A16S over four decades under the Global Ocean Ship-based Hydrographic Investigation Program (GO-SHIP), collecting invaluable data to assess long-term changes across an entire ocean basin.
“We could not have done this without the help of our partnering institutions at the National Science Foundation and UNOLS and the resilience of our crew,” says Leticia Barbero, Ph.D., a CIMAS Associate Scientist with AOML’s Ocean Carbon Cycling group and Chief-Scientist on the cruise.
GO-SHIP is an international effort to examine changes in the chemical, physical and biological parameters that fuel ecosystems across the global ocean. As scientists across institutions repeat these cruises every decade along a series of predetermined paths, they analyze these parameters from the surface to the seabed, enabling a global effort to track long-term changes in our ocean.
GO-SHIP cross sections (lines) to monitor long-term changes in ocean chemistry, currents and the cycling of key elements driving ecosystems on a global scale. Scientists repeat each cross section on weekslong cruises every decade. The A16 cross section runs roughly through the center of the Atlantic with A16S (A16-South) extending from the southern end of Chile to Cabo Verde and A16N (A16-North) from Natal, Brazil to Reykjavik, Iceland.
With the completion of the A16-North line in 2023 and now the A16-South, an international team of scientists have successfully sampled a transect that stretches from the convergence of the Southern Ocean and South Atlantic all the way to Reykjavik, Iceland.
Casting a CTD-Rosette at 96 stations along the A16S transect, scientists collected seawater samples at various depths from the surface to the seafloor – as deep as 6,000 meters – to analyze dissolved oxygen, nutrient concentrations, carbonate chemistry, salinity, temperature, and other chemical and physical parameters. However, crossing the South Atlantic brought unexpected challenges for the team.
CTD-Rossette (which stands for “Conductivity, Temperature and Density/Depth”) being deployed on the Revelle. This instrument is deployed as deep as 6,000 meters, collecting seawater samples throughout the water column for scientists to analyze biological and chemical parameters once it returns to the surface.
In the 1980’s, the largest iceberg ever recorded detached from Antarctica, and a mass of ice the size of Rhode Island floated freely across the Southern Ocean for decades. In 2025, it crashed against the island of South Georgia and began disintegrating, producing a field of icebergs that by February 2026 blanketed the South Atlantic – just as the Revelle began venturing northward.
(left) South Georgia, Photo Credit: Clara Gramazio, University of Miami (right) Satellite image along the path of A16S. The dots in the image show icebergs large enough to be captured via satellite. Source: https://zoom.earth/
The team navigated the masses of ice and the rough waters that plague the South Atlantic with swells in some regions reaching 18 feet – where these degrees of latitude south of the equator were aptly named the “Roaring Forties,” “Furious Fifties” and “Screaming Sixties” by sailors dating back to the 15th century. Through these natural barriers, they continued their work around the clock.
At specific stations, a variety of deep and core Argo floats were deployed to capture oceanographic data that enable scientists to assess changes in ocean currents, temperature and salinity – and ultimately changes in climate patterns and the global volume of sea ice. Global drifters deployed at the surface collected oceanographic data that was transmitted in near-real time via satellite, aiding forecasters’ ability to more accurately predict weather and ocean conditions.
The ending of the A16S cruise is a feat that brings the completion of the entire A16 cross section for the fourth time since the first iterations of the GO-SHIP program in the 1990’s (when it was called the World Ocean Circulation Experiment, or WOCE). With 34 Argo floats deployed and over 20,000 individual seawater samples taken across the 96 stations of the A16S cruise, this international collaboration has collected four decades of oceanographic data in the most remote regions of the Atlantic.
“What we’ve learned from this global effort from its first iteration as the WOCE to GO-SHIP today has changed the way we understand the global ocean and changes that impact the natural resources we depend on so essentially,” says Leticia Barbero, Ph.D. “The completion of the A16S cruise is a milestone in this ongoing collaboration.”
GO-SHIP is the gold standard in investigating vital changes across the global ocean. With the data from this cruise, scientists can now examine the impacts of environmental stressors such as ocean acidification, changes in major ocean circulation and the cycling of key elements that drive ecosystems.
The A16S cruise would not have been possible without the continued efforts and support of the National Science Foundation (NSF), NOAA’s Global Ocean Monitoring and Observation Program (GOMO), the University-National Oceanographic System (UNOLS), Scripps Institution of Oceanography and collaborating organizations
Explore More About The Cruise:
Life as a CTD watch stander onboard the cruise: https://www.go-bgc.org/expedition/atlantic-2026/heavy-doors
From an Argentinian observer:
https://www.go-bgc.org/expedition/atlantic-2026/transitando-los-azules
https://www.go-bgc.org/expedition/atlantic-2026/the-data-ocean
A16S Crew enjoy the sunset