This summer made Europe’s water problem hard to ignore. From April to June, large parts of the continent, from Portugal to southern Finland, received well below average rainfall, and the heat that followed pushed rivers, reservoirs and soils into serious deficit.
The impacts were concrete and widespread. France recorded its lowest maize harvest in 50 years. Romania lost more than one million hectares of maize. Wildfires burned over 116,000 hectares in Spain and 42,000 hectares in France, and several countries introduced restrictions on non essential water use as river levels fell and hydropower output came under strain.
These are not isolated events. The same study points to a clear pattern: as the atmosphere warms, the conditions that drive drought in Europe are becoming both more likely and more severe. Water resilience, the ability of a region to keep providing clean and reliable water even under this kind of pressure, needs to be treated as a core part of European climate policy, not an afterthought.
HOW OCEAN IS LINKED TO EUROPE’S WATER RESILIENCE?
Most of the rain that falls in Europe begins as ocean evaporation. The North Atlantic acts as both the source of moisture and the heat engine that makes northern Europe habitable. Two critical disruptions are threatening this balance:
- Circulation instability: Alongside this, the strength of the Atlantic Meridional Overturning Circulation (AMOC) is a critical scientific question, and a weakening would directly reorganise European rainfall and temperature patterns.
- Thermal and chemical stress: The ocean has absorbed more than 90% of the excess heat trapped by greenhouse gases, and it is taking up CO2 at a rate that is measurably acidifying surface water.
THE ESSENTIAL ROLE OF PLANKTON
Half of all oxygen in the Earth’s atmosphere is produced in the ocean. It is done by phytoplankton, tiny organisms too small to see with bare eyes. Through photosynthesis, they drive the biological carbon pump, the process that moves carbon from the surface into the deep ocean. This process explains to a large extent why the ocean holds more carbon than the atmosphere and every terrestrial plant combined.
The ways by which oceans sustain life on land reach well beyond carbon. Every oceanic fish stock in Europe is dependent on healthy oceans through balanced marine food webs and plankton serve as the base of the marine food web.
Oceans also play a critical role on how clouds form. Water vapour needs tiny particles to condense on – called cloud condensation nuclei. Without such particles there are no droplets to form clouds. Clouds not only provide steady rain but also effectively reflect sunlight back to space owing to their white color, thus providing a cooling effect compared to sunlight hitting the darker ocean surface.
Above the open ocean, there are intrinsically few particles, and consequently, droplets. Over terrestrial areas there are plenty of particles of dust, pollen, smoke and pollution, all of which can act as cloud condensation nuclei to form clouds. Above the open ocean, cloud formation relies substantially on plankton. As plankton are grazed and broken down, they release gases that feed into cloud formation.
In order for plankton to thrive, they need what any plant needs: light, carbon dioxide, and nutrients such as nitrogen and phosphorus. They also need iron, in trace amounts, as iron is part of the machinery that photosynthesis runs on.
Human activity has been removing iron from the natural system. Commercial fishing alone removes up to 30,000 tonnes of iron per year in the fish catch (Moreno and Haffa 2014). This is roughly the mass of four Eiffel Towers annually. In essence, iron that stays in the ocean circulates through predation, through excretion, and through the sinking of dead organisms. Iron that gets removed due to fishing decreases the amount of iron in circulation by leaving the system.
The solution: restoring plankton through Ocean Iron Replenishment
Ocean Iron Replenishment (OIR) biomimicks something that already happens in nature. Dust storms and volcanic ash all carry iron into the open ocean. OIR does the same thing deliberately, and on a scale that can be measured. Trace amounts of natural iron-rich mineral dust are released into iron-limited open water, more than 200 km from any coast, at concentrations of parts per trillion. The aim is to return a crucial nutrient back into circulation that human activity has been taking out. Iron replenishment is neither a substitute for cutting emissions, but provides an additional, nature-based method to remove carbon dioxide from the atmosphere.
More than a dozen controlled trials since 1993 have shown that very small additions of iron increase phytoplankton growth in iron limited water. In the most successful trials, at least half of the resulting bloom sank below 1,000 metres, allowing carbon to stay out of contact with the atmosphere for centuries (Smetacek et al., Nature, 2012). Location and timing are the most significant factors determining the success of the method.
There are still research gaps, including:
- How large a fraction of the fixed carbon sinks into the deep ocean, and how long does it stay there?
- Which plankton species are favoured and which are displaced, and how the possible community shifts cascade through the food web?
- How does iron replenishment affect oxygen and nutrient concentrations in the treated and surrounding marine areas?
- How large is the contribution of plankton to the release of cloud-forming nuclei?
- How to define and monitor success in OIR trials?
ExOIS, a U.S-based international coalition is planning the next generation trials and has set out to answer several of these questions. Oceanry supports the ExOIS governance framework and advocates for active European leadership in it.
Key policy asks for the European leaders
The paper sets out three concrete policy asks for European climate leaders:
- Fund priority ecological research through controlled mesocosm trials. Resolving the current knowledge gaps around ocean iron replenishment requires answering fundamental ecological questions about species response, downstream nutrient dynamics, and marine cloud formation. When properly managed, ocean iron replenishment provides a highly scalable, nature-positive restoration and carbon removal pathway. CarbonGap recommends €2.6 billion for early-stage carbon removal by ring-fencing dedicated funding within FP10 and the European Competitiveness Fund. This would enable safe, controlled mesocosm studies as the essential bridge from laboratory research to ocean trials.
- Integrate ocean water resilience to mCDR certification under the CRCF. European water security begins at sea, where marine biological systems drive the moisture and weather patterns that sustain the continent. Integrating ocean restoration into the European Water Resilience Strategy ensures a comprehensive approach to climate stability. To support this vision, the EU must establish dedicated, high-integrity monitoring, reporting, and verification (MRV) methodologies for mCDR within the Carbon Removal Certification Framework (CRCF). Standardized baselines and independent scientific guardrails are essential to guarantee ecological safety, maintain public trust, and certify durable ocean carbon removal.
- Modernise EU ocean restoration and enable coordinated mCDR governance. Existing EU policy, including the Nature Restoration Law and Biodiversity Strategy 2030, focuses on habitats and species rather than functional nutrient cycles. Establishing a clear regulatory framework for ocean iron replenishment fills this critical gap, modernising EU marine restoration. Integrating mCDR across biodiversity, climate and marine legislation alongside the upcoming Ocean Act will establish predictable permitting pathways, robust environmental safeguards, and essential links to European monitoring infrastructure like OceanEye.
