A group of European scientists, in collaboration with two innovative startups, are embarking on a groundbreaking experiment to address one of the most pressing threats to marine life: ocean deoxygenation. 

This critical issue, which is contributing to the decline of fish populations and biodiversity, is also a key topic on the agenda at the upcoming United Nations Biodiversity Conference (COP16) in Columbia.

Researchers from Stockholm University, the French industrial company Lhyfe and the Finnish startup Flexens are working together on the Baltic Sea Oxygenation and the Super-Green Hydrogen Economy (BOxHy) project. Their goal is to reoxygenate the Baltic Sea by producing hydrogen at sea. 

This innovative approach offers a potential solution to the asphyxiation that threatens the marine ecosystem of this vital sea, which borders nine northern European countries.

Oxygen is essential for the survival of underwater organisms. "But for more than 50 years, its concentrations have been decreasing," said Christophe Rabouille, a scientist at France's National Centre for Scientific Research.

The loss of oxygen has two main causes, according to the International Union for Conservation of Nature.

The warming of oceans due to climate change is one. Warmer oceans contain less oxygen, while organisms require more oxygen in hotter waters.

The other is eutrophication, the process in which fertilizer runoff, sewage, animal waste, aqua culture and the deposits of nitrogen from burning fossil fuels creates excessive algae blooms. When this seaweed decomposes it produces vast amounts of CO2, removing oxygen from the water.

The central Baltic, a semi-enclosed sea bordered by agricultural and industrial countries, "is one of the largest dead spots in the world... basically an ecological desert," Alf Norkko from the University of Helsinki said. 

The aim of BOxHy, which has received support from the UN as part of a 10-year program on sustainable ocean development, is to study the feasibility of injecting gaseous oxygen at depth, a technique used in certain freshwater lakes in North America. 

"Restoring oxygen conditions in deep waters through long-term additions would have many positive effects on the Baltic Sea ecosystem," such as expanding the habitat for cod breeding, said Jakob Walve from Stockholm University and associated with the project. 

The project is still in its early stages, with researchers working to determine how the injection would be done, how much, and at what rate all need to be decided, as well as how to measure the subsequent impact on fauna and flora. 

The second phase of BOxHy involves running a pilot project, expected to last five to six years and is scheduled to start in 2025, according to Szilvia Haide of Flexens who is coordinating it. The aim of the pilot is to work out the method of injecting oxygen and to study the impact on the environment and biodiversity. 

While the project offers a promising approach to combating ocean deoxygenation, it's important to recognize that it's a long-term endeavor. 

According to calculations by Lhyfe CEO Matthieu Guesne, around 30 offshore platforms on the Baltic would be necessary to completely reoxygenate it, and it is estimated to take 20 to 30 years. It will also depend on the agricultural industry and its use of fertilizers.

(With input from AFP)