Surprising discoveries in the Atlantic: Researchers clarify freshwater rivers!

Surprising discoveries in the Atlantic: Researchers clarify freshwater rivers!

A research team led by marine researcher Oliver Wurl is traveling in the Atlantic with the research ship Meteor. This scientific expedition, which reached its peak so far on July 16, 2025, began in Nice in June. After a stay in the Mediterranean and passage through the Strait of Gibraltar, where the team was accompanied by dolphins, the ship is now southwest of the Canary Islands. The research focus is on the salinity in the top layer of the ocean.

Salinity is a crucial factor that influences the exchange processes between the atmosphere and the ocean. Evaporation increases salinity, while rain decreases it. The challenge is to precisely measure freshwater flows. The goal of the “Processes and Sensors of Marine Interfaces” working group is to use salinity as an indicator of freshwater fluxes to improve understanding of the global water cycle and climate models. Measurements are carried out both in the surface layer and to a depth of one meter.

Objectives and methodology of the expedition

The current “FRESH ATLANTIC” measurement campaign has so far successfully completed six of a total of 41 planned days. The starting point was Nice, the destination is Ponta Delgada in the Azores. This expedition aims to collect data to better understand the exchange of freshwater between the ocean and the atmosphere. Freshwater exchange is defined as the ratio of evaporation minus precipitation. A particular focus is on the “Sea-Surface Microlayer” (SML), a marine surface film less than 1 mm thick that strongly influences the exchange processes between the ocean and the atmosphere.

In order to close the knowledge gaps in the observation of freshwater flows, the salinity of the SML is used as an indicator. Three focus regions are defined: the western Mediterranean, the eastern subtropical Atlantic and the tropical Atlantic. These regions were selected to compare evaporation patterns. Data collection is also carried out through the use of autonomous surface vehicles, including two research catamarans, drifters, drones and weather balloons, which are supported in an international cooperation by scientists from Germany, France and the USA.

Scientists like Prof. Meinhard Simon from the ICBM have the task of microbiologically characterizing the samples from the SML and the water underneath. The expedition is also supported by Rüdiger Röttgers from the Helmholtz Center HEREON, who measures backscattering, chlorophyll and turbidity down to a depth of 200 meters. Colorado State University and the University of Alabama Huntsville use specialized drones for meteorological data and aerosol surveys. The German Weather Service is helping with weather balloons, while researchers like Prof. Härter from the University of Potsdam are carrying out numerical simulations of sea surface temperature and wind shear.

The current phase of the expedition includes transit to the North Atlantic, where sightings of rays, whales and dolphins can be observed. Meanwhile, preparations for the next measuring stations are underway, and the crew occasionally finds time to play table tennis while a television team originally hired for a documentary series has already left the ship.

Research contexts and institutional environment

The Institute of Oceanography (IfM) is part of the Center for Earth System Research and Sustainability (CEN), which was founded in June 2011. The aim of this center is to advance research in the area of ​​earth systems and sustainability and to promote interdisciplinary collaboration. The IfM is actively involved in national, European and international research projects and is also part of the KlimaCampus Hamburg, which is supported by the DFG Excellence Cluster “Integrated Climate System Analysis and Prediction” (CliSAP). The overarching research topics of the IfM include the ocean in climate, climate-relevant processes in the ocean and the dynamics and ecology of shelf sea systems.

Using innovative methods and a strong interdisciplinary approach, the IfM team strives to further deepen the understanding of the complex interactions within the climate system and the influence of freshwater rivers on the world's oceans. The expedition highlights not only the importance of salinity for water exchange, but also the need for increased global scientific dialogue in times of climate change.