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Acidity in the atmosphere is transforming the ocean

Rising levels of atmospheric acidity are transforming the ocean by altering the nutrient supply, according to a new study from the University of East Anglia. The experts report that increasing acidity is disrupting the ecological balance of marine ecosystems.

The researchers explain that the way nutrients are delivered to the ocean not only affects its productivity, but also its ability to absorb CO2 from the atmosphere.

“Human emissions of pollutants have caused significant changes to the acidity of the atmosphere, leading to well-known environmental impacts such as acid rain,” said study lead author Professor Alex Baker.

“Atmospheric acidity affects the quantity and distribution of nutrients (nitrogen, phosphorus and iron) delivered to the ocean.”

“Acids attack the surface of desert dust particles as they are transported through the atmosphere, increasing the proportion of the phosphorus and iron contained in those particles that will dissolve when the dust falls into the ocean.”

“Our work suggests that increasing acidity since the Industrial Revolution increased the proportions of phosphorus and iron that are soluble by 14 percent and 16 percent respectively. These increases will have had a direct fertilizing effect on marine phytoplankton.”

During the same time frame, the amount of nitrogen delivered to the oceans through the atmosphere has at least doubled as a result of emissions.

Professor Maria Kanakidou of the University of Crete used an atmospheric chemistry transport deposition model to contribute to the research.

“Acidity controls the distribution of nitrogen between particles and gases in the atmosphere, so that changes in acidity alter the length of time that nitrogen remains in the atmosphere and hence where in the ocean it will be deposited,” said Professor Kanakidou.

Beyond fertilization, these changes in the amount and distribution of nutrients have an impact on the ecological balance of the ocean.

“Phytoplankton communities are sensitive to the proportions of nutrients available to them. The changes in nutrient deposition that we have identified will likely have led to ecological shifts as the atmospheric input alters the nutrient balance of surface waters,” said Professor Kanakidou.

“These changes can promote certain phytoplankton types over others, depending on the organisms’ adaptation to the relative levels of nutrients present in the water.”

Study co-author Professor Athanasios Nenes is an expert at the Ecole Polytechnique Fédérale de Lausanne, Switzerland, and the Center for the Study of Air Quality and Climate Change of the Foundation for Research and Technology Hellas.

“Fine aerosol particles tend to remain strongly acidic, despite considerable reductions in pollutants. Understanding this counterintuitive behavior and its impact on nutrient supply to the ocean has only become possible thanks to advances in theory and modeling,” said Professor Nenes.

“Anthropogenic emissions will continue to change the acidity of the atmosphere into the future. Emissions controls implemented to address acid rain will reduce aerosol acidity in many regions of the world, while continued economic development is likely to see further increases in acidity in other regions.”

According to the researchers, the system is unlikely to return to its pre-Industrial condition due to an increasing frequency of wildfires, which influence both nutrient supply and acidity, and their uncertain impacts. 

“Knowledge of the complex interactions between nutrient supply and marine microbial communities is limited,” said Professor Baker. “Predictions of the consequences of long-term changes in atmospheric acidity on marine ecosystems will need to be considered alongside other stressors on the system, such as ocean acidification, warming and deoxygenation.”

The study is published in the journal Science Advances.

By Chrissy Sexton, Staff Writer

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