Volcanic ash fertilizes seas

Increase in algae growth through nutrient release

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What do volcanic eruptions on land have to do with the growth of plants in the sea? Perhaps more than previously thought, as now Kiel researchers found out. The ashes apparently supply the algae with the nutrients that limit their growth.


It is known that the growth of unicellular algae in large parts of the seas can be limited by a lack of certain nutrients, in particular iron. However, it has hardly been investigated yet whether volcanic ash can increase the content of nutrients such as iron in the surface ocean and thus boost the growth of unicellular algae. The fertility of volcanoes on land has long been known. Kiel oceanographers now went to the question of whether volcanoes also contribute to the fertility of the oceans.

Ash releases nutrients

Researchers at the Leibniz Institute for Marine Sciences, IFM-GEOMAR, in Kiel have published new findings in the journal Geophysical Research Letters. In laboratory experiments, they were able to show that volcanic ash quickly releases a number of nutrients when in contact with seawater, including iron, phosphate, ammonium, silica, copper and zinc. Just as for plants on land, these nutrients are building blocks for the algae in the sea.

"With chemical experiments, we were able to demonstrate for the first time that volcanic ash immediately starts to release this combination of nutrients when it comes into contact with seawater." Svend Duggen. His colleague Peter Croot adds: "What surprised us most was the fact that most of the process took place within minutes." display

Active in top layer

Volcanic eruptions can cause massive amounts of ash to be scattered into the oceans. The Kiel study shows for the first time how quickly volcanic ash can actually fertilize the surface layer of the ocean. "Namely, where the phytoplankton grows, because in the dark below about 100 meters depth, the nutrients would not help the algae growth, " adds Ulrike Schacht. That volcanic ash in the sea can also quickly provoke a biological reaction, showed further experiments with seawater and representatives of an important group of phytoplankton, the diatoms.

"In our experiments, we were able to show for the first time that unicellular algae can use the iron from volcanic ash to build biomass, " explains the newly graduated biologist Linn Hoffmann. Volcanic ash thus proves to be a natural and fast-acting combi fertilizer for the oceans.

"It's as if the volcanic god Vulcanus and the fertility goddess Freya have made an agreement with Neptune about which we are only now learning something, " says Svend Duggen.

Important role for CO2 cycle

The findings are important because increased growth of phytoplankton in the ocean would accelerate the uptake of CO2 from the atmosphere, thereby reducing man-made greenhouse effect. The role of volcanic material entry into the sea in the global CO2 cycle is not well known at the moment.

The IFM-GEOMAR is now supporting the continuation of the new research direction in the marine sciences with the interdisciplinary junior project group NOVUM 1 (Nutrients Originating in Volcanoes and their Effect on the eUphotic Zone of the Marine ecosystem). In this first part, the young researchers from Kiel want to quantify for the first time, with further chemical experiments and computer models, what significance the fertilization of the oceans with volcanic ash can have for the global CO2 cycle.

(Leibniz Institute of Marine Sciences, 20.02.2007 - NPO)