DArgo25: New insights into a changing ocean

Joint press release by the Federal Maritime and Hydrographic Agency (BSH), the Leibniz Institute for Baltic Sea Research Warnemünde (IOW), the Institute for Chemistry and Biology of the Sea (ICBM) at the University of Oldenburg and the GEOMAR Helmholtz Centre for Ocean Research Kiel

Two thirds of the Earth's surface are covered with water. While satellites now have a good view of the surface of the ocean, they are unable to look into its interior. This requires sophisticated sampling strategies and observation systems. However, automated drifting buoys, so-called Argo floats provide such insights.

After being deployed, Argo floats sink to a depth of 1000 metres and continue to drift there with the ocean currents. Every ten days, they descend further to a depth of 2000 metres and then slowly rise again towards the water surface. On their way up, they continuously measure parameters such as temperature and salinity. After surfacing, the collected data is transmitted via satellites and made available almost in real time. Afterwards, the Argo floats sink again to continue drifting.

The first generation of Argo floats has already helped to improve for example global climate models and regional weather forecasts. As part of the DArgo2025 project, a German research network has now been able to expand the focus of the Argo floats by successfully testing new sensors that can be used worldwide in the future. The Federal Ministry of Education and Research funded the project, which ended in December 2021.

Argo-Floats 2.0: Eutrophication, turbidity and ocean acidification

Under the leadership of the BSH, scientists from several German marine research institutions have deployed a total of 20 Argo floats to test and validate new sensors. This allows a look inside a changing ocean:

GEOMAR Helmholtz Centre for Ocean Research Kiel has tested Argo floats with sensors for the oxygen concentration and pH of the water in the North Atlantic. Data collected in this way provide information about the acidification and oxygen depletion of the ocean and the ocean’s ability to continue taking up carbon dioxide from the atmosphere.

The Leibniz Institute for Baltic Sea Research Warnemünde (IOW) tested Argo floats with sensors for nutrients in the Baltic Sea. On the one hand, this provides information about the eutrophication of the Baltic Sea. On the other hand, it extends the area of application of Argo-Floats to the Baltic Sea.

The Institute for Chemistry and Biology of the Sea (ICBM) at the University of Oldenburg has tested Argo floats with new sensors to measure the light field in the Baltic Sea and the North Atlantic. This provides information about microalgae and other contents of the sea water.

In addition, the BSH has designed Argo floats with two different sensor systems for measuring temperature and salinity in the North Atlantic. Scientists deployed a number of Argo floats in an ocean eddy to keep this swarm of drifting buoys together for several months. The new sensor system was thus successfully evaluated.

International cooperation – reaching as far as into the deep sea

The Argo floats are operated within the framework of the international observation programme Argo. As part of the Argo programme, almost 4000 Argo floats are currently drifting in the ocean. The BSH is significantly involved in the management and further development of EuroArgo, the European contribution to the Argo programme. The BSH also coordinates the German contribution to the Argo programme and ensures the permanent quality control of the data.

Within the framework of the United Nations Ocean Decade for Sustainable Development, the Argo floats are to be further developed to enable them to also survey the deep sea. Through international cooperation, the range of the Argo floats could be extended to a depth of 6000 metres. This could further transform knowledge about the ocean so that science can better support its protection and sustainable use.