Aboard the Hespérides, the scientific team has carried out a 26-day campaign from the Weddell Sea to the Scotia Sea.
Last March saw the successful conclusion of the oceanographic campaign SACO-SO 2025, conducted aboard the research vessel Hespérides by an international scientific team led by the Institute of Marine Sciences of Barcelona (ICM) and the Spanish Institute of Oceanography (IEO), both affiliated with the CSIC.
The expedition made it possible to study the outflow of Antarctic Bottom Water (AABW) from the Weddell Sea to the Scotia Sea, a key region for understanding the Southern Hemisphere's thermohaline circulation. It marks a milestone for Spanish oceanography, being the first campaign dedicated to physical oceanography in Antarctic waters in over 15 years.
During the expedition, a detailed bathymetric mapping of four submarine canyons on the South Scotia Ridge was carried out, enabling the identification of ideal points to deploy three oceanographic moorings equipped with temperature, salinity, current and oxygen sensors. These moorings will record data over the next two years, providing key information on the temporal variability of the water column from 400 metres deep to 1800.
“The installation of these three instrumented anchors will allow us to monitor the remote Phillips Passage, located in the southern Scotia Ridge, which is one of the exit routes for the Antarctic bottom waters formed in the Weddell Sea,” explains Josep Lluís Pelegrí, ICM researcher and project leader.
In addition, multiple CTD stations were carried out along the continental ridge and in the mapped canyons, complemented by the deployment of two Argo profiling buoys, as part of the Spanish contribution, Argo-Spain, to the global Argo observation system, specifically programmed to register the properties of the slope current.
The formation of these waters, estimated at between five and nine million cubic metres per second, is one of the factors that controls the strength of the global conveyor belt and, as a result, the Earth’s climate. “This initiative, led by two sister CSIC centres, represents a fundamental step in Spain’s contribution to international efforts to monitor climate change,” notes Pelegrí.
The importance of Antarctic Bottom Water
The AABW is the densest water mass in the global ocean and accounts for more than 35% of the planet’s water volume. Its formation occurs in the Antarctic polar regions due to intense interactions between air, sea and ice, especially in the Weddell Sea. These processes generate extremely dense waters that sink and flow northward along the ocean floor, feeding the lower branch of the global thermohaline circulation.
“The AABW plays a crucial role in regulating the global climate, as it acts as a sink for atmospheric carbon dioxide, helping to mitigate the effects of climate change,” explains Pedro Llanillo, researcher at the Canary Islands Oceanographic Centre of the IEO and chief scientist of the campaign. “It also transports oxygen and nutrients to the ocean depths, influencing marine ecosystems and ocean dynamics on a planetary scale,” adds the scientist.
International collaboration
The SACO-SO 2025 campaign has been an example of international scientific cooperation, involving the participation of the Institute of Marine Sciences (ICM), which leads the project, the Spanish Institute of Oceanography (IEO), which has led the campaign, the Scientific Research and Higher Education Centre of Ensenada (CICESE) of Mexico, the Centre National de la Recherche Scientifique (CNRS) of France, and the company Lobelia.
The success of the expedition was made possible thanks to the logistical support of the Spanish Navy and the Marine Technology Unit (UTM), who ensured the proper development of activities aboard the Hespérides. The SACO-SO 2025 oceanographic campaign is part of the South Atlantic Connections (SACO) Project, specifically the sub-project South Atlantic Connections: Southern Ocean (SACO-SO). This project has been funded by the Ministry of Science, Innovation and Universities through the National Plan for Scientific Research, Development and Technological Innovation.