Kategorie: News
When Waste Becomes Climate Protection
Since September 8, 2026, twelve mesocosms - sealed, floating experimental tanks that will serve as an open-air laboratory for seven weeks - have been floating in the harbor of the small town of Taliarte on the east coast of Gran Canaria.
An international research team led by the GEOMAR Helmholtz Center for Ocean Research Kiel is conducting the first systematic test there to determine whether finely ground concrete rubble is suitable for increasing the alkalinity of seawater. The researchers aim to understand the consequences this has for the marine ecosystem.
The process known as Ocean Alkalinity Enhancement (OAE) mimics a natural process: the weathering of rock, during which minerals are released into the water, making it more alkaline. A more alkaline ocean can absorb more CO₂ from the atmosphere while simultaneously buffering the ongoing ocean acidification. Globally, approximately five billion metric tons of concrete rubble are generated annually - for the researchers, it makes sense to utilize a portion of this waste stream for precisely this purpose.
In the current experiment, some mesocosms are receiving ground concrete rubble in varying amounts, others are receiving sodium hydroxide (NaOH) as a comparison substance, and still others remain untreated as a control group. “This year, the goal is to compare a liquid source of alkalinity with ground concrete rubble and to test how well both substances are tolerated by the marine environment,” explains Ulf Riebesell, professor emeritus of biological oceanography at GEOMAR and scientific director of the experiment. The experiment is being led on-site by marine biogeochemist Kai Schulz from Southern Cross University in Australia.
Why Concrete Rubble Is Not a Simple Solution
Unlike sodium hydroxide, which allows alkalinity to be modified in a highly targeted and controlled manner, concrete rubble is a highly heterogeneous material: Its composition depends on the cement used, the aggregates, the age of the concrete, and the stresses it has been subjected to. In addition, ground material physically clouds the water - an effect that dissolved substances like NaOH do not cause in the first place.
Earlier experiments in the equatorial Pacific demonstrate just how significant such differences can be: there, phytoplankton reacted with varying degrees of intensity depending on the material used. Sodium hydroxide had only a minor effect, while olivine particles, for example, caused significantly more pronounced changes. This very question is therefore at the heart of the current experiment: “With this experiment, we want to find out whether it is the particles themselves that have an additional effect on the ecosystem - or whether the observed effects are due solely to the increased alkalinity of the water,” says Kai Schulz.
Understanding Risks and Side Effects
Riebesell emphasizes the far-reaching implications of potential side effects: “Effects on zooplankton would also impact animals higher up in the food chain. Only by thoroughly understanding these mechanisms can we realistically assess the potential and possible risks of ocean alkalinization.”
The experiment is part of the international research project OceanAlkAlign, which aims to standardize measurement and evaluation methods for OAE processes and thus make them comparable - a prerequisite for creating a reliable basis for future decision-making.
The researchers themselves emphasize that such methods can by no means replace the urgently needed, rapid reduction of greenhouse gas emissions. Instead, they are being discussed as a potential supplement to offset unavoidable residual emissions in the long term. But one thing is also clear: The experiment off the coast of Gran Canaria marks the beginning, to some extent, of genuine geoengineering in the open ocean system - still within the controlled framework of mesocosms, but using a source material whose composition has not yet been standardized by anyone.
Further information:
GEOMAR Helmholtz Center for Ocean Research Kiel