On August 19, 2025, the research vessel Elisabeth Mann Borgese set out on the two-week expedition EMB373 to the western Baltic Sea. On board was an IOW research team from various scientific disciplines, whose joint aim was to take samples from shallow coastal waters that are heavily impacted by human activity and oxygen depletion.

The expedition was the first ship-based research cruise conducted as part of the IOW's research into shallow water processes and their relevance for the entire Baltic Sea (Shore to Basin, S2B). The results will contribute to a better understanding of coastal oxygen depletion (hypoxia). The expedition was led by IOW scientist Jacob Geersen, an expert in marine geological processes and their interaction with climatic and human stressors.

The shallow coastal zone is very difficult to sample due to ist limited depth. For this reason, the IOW first spent several years developing new methods and equipment for this purpose. The Elisabeth Mann Borgese has very well-equipped laboratories and served as a working platform during the expedition. Divers launched their diving operations from another small boat, during which they carefully sampled seagrass beds and took undisturbed sediment and water samples. The samples were then immediately analyzed and processed on board the research vessel. In addition, so-called landers and other state-of-the-art measuring systems were used to measure climate-relevant trace gases, nutrients, and turnover processes on the seabed from on board. A lander is a platform that combines several autonomous measuring and sampling devices and is placed on the seabed for 24 to 48 hours. The scientist Allison Schaap from the National Oceanography Centre (Southampton, UK) joined the IOW research team to perform highly accurate measurements of nutrient concentrations using autonomous nutrient analyzers.

During their very first dive, the team observed many small flake-like remnants of previous plankton blooms floating in the water. These flakes consist of dead or excreted organic material that transports nutrients and carbon to deeper layers of water as it sinks. Once there, they become food for microorganisms, which consume oxygen as they break down the flakes, contributing to oxygen-depleted water masses near the seabed. IOW scientist Maren Voss, who initiated the trip and is an expert on the marine nitrogen cycle, emphasizes the importance of interdisciplinary collaboration: “The fact that these flake-like aggregates are so numerous in shallow water is a surprise. This observation is only possible thanks to the combined measurement strategy of landers with photo systems and divers.”

The trip will now be followed by meetings to evaluate the data and plan further research. This trip was only the first in a series of trips to explore shallow water areas, as they offer far more unknown interrelations than the research team had previously expected.