The BOxHy Project – Preparing a Pilot Site Study to Remediate Low Oxygen Conditions in Coastal Seas

Low oxygen conditions increasingly threaten marine ecosystems by reducing habitat and biodiversity. Low oxygen also influences biogeochemical processes in water and sediment, greenhouse gas emissions, and contributes to toxic algae blooms by increased phosphorus recycling. As a result, this can have significant impact on regional economies, affecting thousands of jobs and billions of dollars. Deoxygenation of marine environments has been linked to human activities since the 1950s. Low-oxygen zones exist in the open ocean, over continental shelves, and in coastal seas, and are expected to expand especially in the coastal marine space in the future due to warming and increasing nutrient pollution.

Despite these on-going threats, current conservation measures do not effectively address the impacts of reduced oxygen or feature large time lags in implementation or projected outcomes.

While small-scale artificial oxygen injection (AO) has been used in lakes and marine aquaculture, larger-scale efforts are rare. The use of marine renewable energy for green hydrogen production presents a new, exciting opportunity for sea-based mitigation through anthropogenic oxygenation. The oxygen produced during hydrogen generation (e.g., 0.5 GW electrolyzer: ~210 t H₂ d^-1; ~1700 t O₂ d^-1) could be used to mitigate anoxia, restore benthic habitat, reduce phosphorus loading, and suppress algal blooms. Constant AO could also help combat increasing hypoxia caused by circulation shifts, decreased deep mixing in autumn and winter and climate change.

AO technologies that can scale up to marine applications are now common in USA reservoirs. The largest is 350 tonnes O₂/d. Although there is evident potential, AO for the marine environment has received little attention, likely due to the current cost of oxygen and/or lack of infrastructure and awareness. Here, we want to present the BOxHy project, funded by the BSAP fund; this innovative project focuses on preparing a pilot study site for AO in the Baltic Sea environment with the perspective of upscaling the technology and science to basin wide scales. Offshore wind farms are planned in the Baltic Sea as the decarbonization of energy systems is advancing. Cost-efficient green hydrogen production strengthens the bankability of the concept, combining CO₂ reductions through the hydrogen economy and a decrease in anoxia. Coupled to the production of offshore hydrogen, the injection of the electrolysis by-product oxygen is a novel innovative technique that could be adapted to other anoxia-prone coastal environments with similar environmental challenges after successful research and demonstration, closing major knowledge gaps and exploring the risks for unintended consequences.

With the BOxHy project we contribute to challenges 1 and 2 and 4 of the UN Decade of Ocean Science and Sustainable Development. Given the current threats to coastal marine ecosystems, exploring AO as a mitigation measure directly aligns with the principles of "prevention of harm” and the “precautionary approach” outlined in the “Declaration of Ethical Principles in Relation to Climate Change”.