An international team of researchers has set off new alarm bells about the changing chemistry of the western Arctic Ocean region after discovering that acidity increased three to four times faster than ocean waters elsewhere.
The team, which includes University of Delaware marine chemistry expert Wei-Jun Cai, also identified a strong correlation between the accelerated rate of melting ice in the region and the rate of ocean acidification, a dangerous combination that the survival of plants, crustaceans, coral reefs and other marine life and biological processes throughout the planet’s ecosystem.
The new study, published Thursday, September 30 in Scienceis the first analysis of Arctic acidification to include data from more than two decades, spanning the period from 1994 to 2020.
Scientists have predicted that by 2050, if not sooner, Arctic sea ice in this region will no longer survive the increasingly hot summer seasons. As a result of this sea ice retreat each summer, the ocean’s chemistry will become more acidic, with no continued ice cover to slow or otherwise diminish the advance.
That creates life-threatening problems for the wildly diverse population of marine animals, plants and other living things that depend on a healthy ocean for their survival. For example, crabs live in a crusty shell made up of the calcium carbonate found in ocean water. Polar bears depend on healthy fish populations for their food, fish and seabirds depend on plankton and plants, and seafood is an important part of many people’s diets.
That makes acidification of these distant waters a major problem for many of the planet’s inhabitants.
First, a quick refresher on pH values, which indicate how acidic or alkaline a particular liquid is. Any liquid containing water can be characterized by its pH value, which ranges from 0 to 14, with pure water being considered neutral with a pH of 7. All levels below 7 are acidic, all levels above 7 are basic or alkaline, with each complete step represents a tenfold difference in the hydrogen ion concentration. Examples on the acidic side are battery acid, which checks in at 0 pH, stomach acid (1), black coffee (5) and milk (6.5). Tilting towards alkaline are blood (7.4), baking soda (9.5), ammonia (11) and drain cleaner (14). Seawater is normally alkaline, with a pH level of about 8.1.
Cai, the Mary AS Lighthipe Professor in the School of Marine Science and Policy in UD’s College of Earth, Ocean and Environment, has published important research on the changing chemistry of the planet’s oceans, completing a cruise from Nova Scotia to Florida this month. , serving as chief scientist under 27 aboard the research vessel. The work spans four areas of study: the East Coast, the Gulf of Mexico, the Pacific Coast, and the Alaska/Arctic.
The new study in Science including UD postdoctoral researcher Zhangxian Ouyang, who took part in a recent data collection trip in the Chukchi Sea and the Canada Basin in the Arctic Ocean.
The first author of the publication was Di Qi, who collaborates with Chinese research institutes in Xiamen and Qingdao. Scientists from Seattle, Sweden, Russia and six other Chinese research sites also contributed to this publication.
“You can’t go alone,” Cai said. “This international collaboration is very important for collecting long-term data over a large area in the remote ocean. In recent years, we have also collaborated with Japanese scientists as access to Arctic waters has been even more difficult over the past three years due to COVID-19. And we always have European scientists participating.”
Cai said he and Qi were both stunned when they first looked at the Arctic data together at a conference in Shanghai. The acidity of the water increased three to four times faster than the ocean water elsewhere.
That was indeed astonishing. But why did it happen?
Cai quickly identified a prime suspect: the increased melting of sea ice during the Arctic’s summer season.
Historically, the Arctic sea ice has melted in shallow marginal areas during the summer seasons. That started to change in the 1980s, Cai said, but increased and decreased periodically. Over the past 15 years, the ice melt has accelerated and has moved into the deep basin in the north.
For a while, scientists thought the melting ice could form a promising “carbon sink,” where carbon dioxide would be sucked from the atmosphere into the cold, carbon-hungry waters hidden beneath the ice. That cold water would contain more carbon dioxide than warmer waters could and could help offset the effects of increased carbon dioxide elsewhere in the atmosphere.
When Cai first studied the Arctic Ocean in 2008, he saw that the ice had melted beyond the Chukchi Sea in the region’s northwest corner, all the way to the Canada Basin — well beyond its typical range. He and his collaborators found that the fresh meltwater did not mix with deeper waters, which would have diluted the carbon dioxide. Instead, the surface water took up the carbon dioxide until it reached about the same level as in the atmosphere and then stopped collecting it. They reported this result in a paper in Science in 2010.
That would also change the pH of Arctic waters, they knew, lowering seawater’s alkaline levels and reducing its ability to resist acidification. But how much? And how fast? It took them another decade to collect enough data to draw a solid conclusion about the long-term trend of acidification.
Analyzing data collected from 1994 to 2020 — the first time such a long-term perspective was possible — Cai, Qi and their collaborators found an extraordinary increase in acidification and a strong correlation with the increasing rate of melting ice.
They point to sea ice melting as the main mechanism to explain this rapid drop in pH, as it changes the physics and chemistry of surface waters in three main ways:
- The water under the sea ice, which was deficient in carbon dioxide, is now exposed to the atmospheric carbon dioxide and can freely absorb carbon dioxide.
- The meltwater mixed seawater is light and does not mix easily in deeper waters, meaning the carbon dioxide taken from the atmosphere is concentrated at the surface.
- The meltwater dilutes the carbonate ion concentration in the seawater, making it less able to neutralize the carbon dioxide to bicarbonate and rapidly lowering the ocean pH.
Cai said more research is needed to further refine the above mechanism and better predict future changes, but the data so far once again show the far-reaching ripple effects of climate change.
“If all the multi-year ice is replaced with freshman ice, there will be lower alkalinity and lower buffering capacity and acidification continues,” he said. “By 2050, we think all the ice will be gone by the summer. Some newspapers predict that will happen by 2030. And if we follow the current trend for another 20 years, the summer acidification will be really, really strong.”
No one knows exactly what that will do to the creatures, plants and other living things that depend on healthy ocean water.
“How will this affect the biology there?” asked Cai. “That’s why this is important.”
International team reports ocean acidification is spreading rapidly in the Arctic Ocean
Di Qi et al, Climate change causes rapid ten-year acidification in the Arctic Ocean from 1994 to 2020, Science (2022). DOI: 10.1126/science.abo0383
Quote: Scientists find link between rapidly melting Arctic ice and ocean acidification (2022, Sept. 29) retrieved Sept. 29, 2022 at https://phys.org/news/2022-09-scientists-link-fast-melting-arctic-ice . html
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