The acidity of the coastal waters of the Antarctica could double by the end of this centurythreatening the survival of whales, penguins and hundreds of other species that inhabit the Southern Ocean, according to research just published by the University of Colorado Boulder (USA).
Scientists predict that by 2100, the upper 200 meters of the ocean, where much of the marine life resides, could see a more than 100% increase in acidity compared to levels recorded in the 1990s. article has been published in the magazine Nature Communications.
“The findings are critical to our understanding of the future evolution of marine ecosystem health,” said Nicole Lovenduski, co-author of the paper and interim director of CU Boulder’s Institute for Arctic and Alpine Research (INSTAAR).
The oceans play an important role as a buffer against climate change by absorbing almost 30% of the CO2 emitted Worldwide. But as more CO2 dissolves into the oceans, seawater becomes more acidic.
“Human-caused CO2 emissions are at the heart of ocean acidification,” said Cara Nissen, first author of the paper and INSTAAR research scientist.
The Southern Ocean, which surrounds Antarctica, is particularly susceptible to acidification, partly because colder water tends to absorb more CO2. The area’s ocean currents also contribute to the relatively acidic water conditions.
Using a computer model, Nissen, Lovenduski and their team simulated how Southern Ocean seawater would change in the 21st century and found that it will become more acidic by 2100 and that the situation will be really dire if the world fails to reduce emissions.
Both the surface and the bottom of the ocean
“It’s not just the top layer of the ocean. The entire water column of the Southern Ocean coast, including at the bottomcould suffer serious acidification,” Nissen said.
The team then investigated the situation specifically in the marine protected areas (MPA) from Antarctica. Human activities, such as fishing, are restricted in these regions to protect biodiversity.
Currently, there are two MPAs in the Southern Ocean, covering approximately 12% of the region’s water.
In recent years, scientists have proposed designating three more MPAs, which would cover about 60% of the Southern Ocean.
The team’s model showed that both currently existing and proposed Marine Protected Areas will experience significant acidification by the end of the century.
For example, assuming higher emissions, the average acidity of water in the Ross Sea region (the world’s largest MPA off the northern tip of Antarctica) would increase by 104% compared to 1990 levels for the year 2100. In an intermediate emissions scenario, water would still become 43% more acidic.
“I’m surprised how severe ocean acidification would be in these coastal waters,” Nissen said.
Phytoplankton in danger
Previous studies have shown that the phytoplankton, a group of algae that form the base of the marine food web, it grows at a slower rate or dies when the water becomes too acidic.
Likewise, acidic water also weakens the shells of organisms such as snails and sea urchins.
These changes could alter the food web and ultimately affect top predators, such as whales and penguins.
The Weddell Sea is one of three proposed MPAs located off the coast of the Antarctic Peninsula. Nissen notes that scientists believe the region of the Weddell Sea could act as a climate change sanctuary for organismsmainly because this area has the highest levels of sea ice cover in Antarctica.
The ice protects the ocean from warming and prevents the seawater below from absorbing CO2 from the air, thereby reducing the rate of acidification. Additionally, the region has little human activity to date.
But the models and simulations carried out by experts reveal that, As the planet continues to warm, sea ice will melt and the Weddell Sea region will experience acidification like other Marine Protected Areas in intermediate to high emissions scenarios, but with a slightly more delayed progression.
“The result shows that establishing Weddell Sea region as a protected area should be given high priority“Nissen stated.
“As a scientist who typically studies the open ocean, I tend to think of Antarctic coastal areas as a conduit for climate signals to reach the global deep ocean. This study reminded me that these changing Antarctic coastal areas can lead to rapid changes,” Lovenduski said. .
The study suggests that the world will only be able to avoid severe acidification of the Southern Ocean in the lowest emissions scenario, in which society reduces CO2 emissions quickly and aggressively.
Reference study: https://www.nature.com/articles/s41467-023-44438-x
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