Antarctic coastal waters facing 100% increase in acidity: study

A recent study from the University of Colorado Boulder has raised concerns that the acidity levels in the coastal waters of Antarctica could increase twofold by the end of this century. This change could pose a threat to whales, penguins, and hundreds of other species living in the Southern Ocean.

Ocean acidity may double by 2100

The scientists predict that by the year 2100, the top 650 feet (200 meters) of the ocean, which is home to a significant amount of marine life, could experience an acidity increase of more than 100% compared to the levels recorded in the 1990s. This research was published on January 4 in the journal Nature Communications.

Nicole Lovenduski, the paper's co-author and the interim director of CU Boulder's Institute of Arctic and Alpine Research (INSTAAR) said, 'Our understanding of the future evolution of marine ecosystem health critically depends on the findings.'

Oceans are crucial in combating climate change as they soak up nearly 30% of global CO2 emissions. However, this leads to an increase in seawater acidity as more CO2 dissolves. Cara Nissen, the lead author of the study and a research scientist at INSTAAR, points out that human-induced CO2 emissions are the main cause of this ocean acidification.

The Southern Ocean, encircling Antarctica, is especially prone to acidification. This is partly due to the fact that colder water absorbs more CO2, and the ocean currents in this region also lead to more acidic water conditions.

A computer model was used by Nissen, Lovenduski, and their team to predict the changes in the Southern Ocean's seawater in the 21st century. They discovered that by 2100, the water would become significantly more acidic, and the situation could worsen if we do not reduce global emissions.

Nissen said, "It's not just the top layer of the ocean. Severe acidification could affect the entire water column of the coastal Southern Ocean, even at the bottom."

Scientists propose more Antarctic marine protections

The research team examined the conditions in Antarctica’s Marine Protected Areas (MPAs), where human activities like fishing are limited to preserve biodiversity. Currently, two MPAs cover about 12% of the Southern Ocean, and scientists have proposed three additional MPAs, which would protect around 60% of the Antarctic Ocean.

The team’s model predicted that both existing and proposed MPAs would face significant acidification by 2100. For instance, under a high-emission scenario with no emission reductions, the average acidity in the Ross Sea region, the world’s largest MPA, would increase by 104% compared to 1990s levels. Even under a moderate emission scenario, the water would become 43% more acidic.

Nissen expressed surprise at the severity of the projected ocean acidification in these coastal waters. Previous research has shown that increased acidity can slow the growth of phytoplankton, the foundation of the marine food web, or even cause them to die out. Acidic water can also weaken the shells of organisms like sea snails and sea urchins, disrupting the food web and potentially affecting top predators like whales and penguins.

Warming threatens Weddell Sea refuge

Scientists think that The Weddell Sea, one of the proposed MPAs, serves as a refuge for organisms in the face of climate change due to its high sea ice coverage, which shields the ocean from warming and reduces CO2 absorption, thereby slowing acidification. However, the model suggests that if global warming continues and sea ice melts, the Weddell Sea region could experience acidification similar to other MPAs, albeit with a slightly delayed timeline.

Nissen emphasized the importance of designating the Weddell Sea region as a protected area. Lovenduski, who usually studies the open ocean, noted that the study highlighted the potential for rapid change in the dynamic Antarctic coastal areas.

The study concluded that only the lowest emission scenario, which requires swift and aggressive cuts in CO2 emissions, could avoid severe ocean acidification in the Southern Ocean. Nissen warned that our time to choose our emission pathway is running out, even though there is still time left.

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