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The Southern Ocean may become much less productive due to acidification

The Southern Ocean may become much less productive due to acidification. The oceans have absorbed more than 40 percent of the carbon dioxide emitted through human activities, and most of this CO2 has been captured by the Southern Ocean, which is one of the most important carbon sinks in the world. The acidification that results from carbon absorption, however, may have serious consequences for marine life.

A team of researchers led by the University of Technology Sydney has found that ocean acidification (OA) is transforming the structure of Antarctic phytoplankton communities.

Study lead author Dr. Katherina Petrou explained that while changes in ocean acidity have been shown to impact marine calcifying organisms, the effects on silicifying diatoms have remained largely unknown. 

“Previous studies reported a range of responses to OA (in phytoplankton) yet rarely considered how environmental pH shifts might affect silicification rates in diatoms,” said Dr. Petrou.

“Diatoms are unique phytoplankton in that they need silicic acid to produce silica cell walls. Under the microscope they look like beautiful glass jewellery boxes, but importantly, this dense, glass-like armor promotes sinking, which makes diatoms an important conduit for transport of carbon to the deep ocean where it can be stored for millennia.”

Diatoms contribute to around 40 percent of ocean productivity, playing a major role in supporting marine food webs and sustaining life.

In the current study, the team set out to investigate the impacts of predicted future changes in ocean acidity on the community structure of the Antarctic phytoplankton. At the Australian Antarctic base, the scientists conducted experiments using large tanks and temperature-controlled seawater 

“We were alarmed to find that diatoms were so negatively affected, with some species likely to have diminished silica production before the end of this century,” said Dr. Petrou.

In the context of global climate change, study co-author Kai Schulz said that these findings are important because they reveal that ocean acidification can not only alter phytoplankton community composition, but can also reduce the sinking ability of diatoms. 

This means that fewer diatoms will end up on the ocean floor, resulting in less atmospheric CO2 being removed from our atmosphere and transported for storage in the deep ocean. “The only genuine way to circumvent this outcome, is to cut our greenhouse gas emissions and limit the acidification of our oceans,” wrote the researchers.

The study is published in the journal Nature Climate Change.

By Chrissy Sexton, Staff Writer

Image Credit: Katherina Petrou

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