Ocean Acidification May Disrupt Diatoms' Role in Carbon Capture

New research from Flinders University shows how ocean acidification could disrupt diatoms — microscopic, single-celled algae found in oceans, lakes, rivers and damp soil — undermining marine food webs and the ocean's ability to capture carbon. The study, published in Marine Ecology, used advanced methods to test microalgal species and see how stressors, including acidification from rising carbon dioxide (CO2) levels, affect their absorption of trace metals.

Diatoms produce a significant share of Earth's atmospheric oxygen and account for 40%-50% of primary production in the ocean, said senior author Sophie Leterme, director of the ARC Industry Transformation Training Centre for Biofilm Research and Innovation at Flinders University. They also help export organic carbon to the deep ocean by fixing CO2 from near-surface waters.

"We showed that changes in ocean pH can affect the growth, abundance and elemental composition of these diatoms," Leterme said, adding that researchers need to study how these changes interact with trace elements and could disrupt food webs, reduce carbon and silicon export, and increase microbial activity. Rising carbon emissions are changing seawater pH, altering how planktonic algae absorb trace elements such as iron, zinc and cadmium — essential for taking up inorganic carbon.

The dissolution of CO2 into the ocean has already dropped global seawater pH by 0.1 units since the end of the Industrial Revolution, with a further drop of 0.3 to 0.6 units expected by the end of this century. Using seawater from South Australia's Gulf St. Vincent and the CSIRO algae collection, researchers applied neutron activation analysis, with ANSTO support, to Thalassiosira pseudonana and Nitzschia navis-varingica.

"While higher abundance and growth of diatoms might help reduce carbon dioxide levels, the impact of lower concentrations of major and trace elements in the environment is not well understood," the researchers said. They added that the findings could also apply to other marine organisms, and that diatoms are already used as bioindicators of water quality.