Icy waters around the coast of Spitsbergen, Svalbard, in the Arctic Ocean
Stuart Melvin/Alamy
The western Arctic Ocean is experiencing acidification at a rate that is four times faster than other oceans due to the melting of ice at record speeds.
Ocean acidification occurs when seawater absorbs carbon dioxide from the atmosphere. The increase in atmospheric CO2 since the industrial revolution has led to oceans becoming 30 per cent more acidic on average, causing widespread consequences for marine ecosystems.
In most ocean basins, the rate of ocean acidification has closely followed the increase in atmospheric CO2 levels. However, the Arctic Ocean contrasts this trend due to its unique characteristics of being cold and covered in ice during winter.
To better understand the distinct behavior of the Arctic Ocean, researchers led by Wei-Jun Cai from the University of Delaware analyzed data collected on 47 different expeditions to the Arctic between 1994 and 2020. They examined pH levels and the saturation of the mineral aragonite, which affects the ability of organisms like coral and oysters to build shells. Lower levels of both measurements indicate greater acidification.
The study found that pH levels in the western Arctic decreased about four times faster on average compared to other oceans during the same period. Aragonite saturation also decreased three times faster. The area of the ocean with low pH and low aragonite grew from almost nothing in 1990 to approximately 7 per cent of the entire Arctic Ocean in 2020.
“This changing chemistry can impact numerous aspects of the ecosystem,” says Hongjie Wang from the University of Rhode Island. The effects of acidification, compared to other changes like warming, are still not entirely understood, but Arctic ecosystems are known to be particularly sensitive.
The study focused on the western Arctic and did not include the eastern Arctic, which is controlled by Russia and has limited available data, according to Jens Terhaar from the Woods Hole Oceanographic Institution in Massachusetts.
The rapid rate of acidification in the western Arctic is attributed to melting ice. Seawater that is newly exposed to air absorbs more CO2. Additionally, meltwater dilutes compounds that buffer absorbed CO2 and reduces the mixing between the surface and deep ocean. As long as there is summer ice melting, the boosted acidification is expected to continue.
Terhaar suggests that the disappearance of sea ice is also responsible for the higher rate of acidification, but acknowledges that other factors, such as the influence of rivers flowing into the eastern Arctic from Siberia, could also be involved.
