Is Ocean Acidification Causing the Arctic To Melt?

Melting Ice Arctic Antarctic Concept

A new study has found a link between fast-melting Arctic ice and ocean acidification

The discovery highlights a dual danger to the survival of plants, shellfish, coral reefs, other marine species, and the climate.

After finding that the western Arctic Ocean’s acidity levels are rising three to four times faster than other ocean waters, an international team of scientists has sounded new alarm bells about the changing chemistry of the ocean.

The team, which includes Wei-Jun Cai of the University of Delaware, found a strong correlation between the rate of ocean acidification and the accelerated rate of ice melting in the region. This is a dangerous combination that puts the survival of plants, shellfish, coral reefs, other marine life, and other biological processes throughout the planet’s ecosystem at risk.

The new study, published in the prestigious journal Science, is the first to analyze Arctic acidification data covering more than two decades, from 1994 to 2020.

The Icebreaker RV Xue Long

Researchers, including the University of Delaware’s Zhangxian Ouyang, traveled aboard the icebreaker R/V Xue Long into an active melting zone in the Arctic Ocean to get samples for analysis. Credit: Zhangxian Ouyang, Wei-Jun Cai, and Liza Wright-Fairbanks/ University of Delaware

Arctic sea ice in this region is expected to disappear by 2050, if not sooner due to the region’s increasingly warm summers. Without a persistent ice cover to slow or otherwise mitigate the advance, the ocean’s chemistry will become more acidic as a consequence of this sea-ice retreat each summer.

This poses serious risks to the extremely diversified population of marine animals, plants, and other living things that rely on a healthy ocean for existence. Crabs, for example, live in a crusty shell made of calcium carbonate, which is abundant in ocean water. Polar bears depend on healthy fish populations for food, fish and sea birds rely on plankton and plants, and seafood is an important part of many people’s diets.

That makes the acidification of these distant waters a big deal for many of the planet’s inhabitants.

Collecting Ice Samples in the Arctic

Scientists collect samples on the ice in the Arctic. Credit: Zhangxian Ouyang, Wei-Jun Cai, and Liza Wright-Fairbanks/ University of Delaware

First, a quick refresher course on pH levels, which indicates how acidic or alkaline a given liquid is. Any liquid that contains water can be characterized by its pH level, which ranges from 0 to 14, with pure water considered neutral with a pH of 7. All levels lower than 7 are acidic, and all levels greater than 7 are basic or alkaline, with each full step representing a tenfold difference in the hydrogen ion concentration. Examples on the acidic side include battery acid, which checks in at 0 pH, gastric acid (1), black coffee (5), and milk (6.5). Tilting toward basic are blood (7.4), baking soda (9.5), ammonia (11), and drain cleaner (14). Seawater is normally alkaline, with a pH value of around 8.1.

Cai, the Mary A.S. Lighthipe Professor in the School of Marine Science and Policy in UD’s College of Earth, Ocean, and Environment, has published significant research on the changing chemistry of the planet’s oceans and this month completed a cruise from Nova Scotia to Florida, serving as the chief scientist among 27 aboard the research vessel. The work, supported by the National Oceanic and Atmospheric Administration (NOAA), includes four areas of study: The East Coast, the Gulf of Mexico, the Pacific Coast, and the Alaska/Arctic region.

The new study in Science included UD postdoctoral researcher Zhangxian Ouyang, who participated in a recent voyage to collect data in the Chukchi Sea and Canada Basin in the Arctic Ocean.

The first author of the publication was Di Qi, who works with Chinese research institutes in Xiamen and Qingdao. Also collaborating on this publication were scientists from Seattle, Sweden, Russia, and six other Chinese research sites.

“You can’t just go by yourself,” 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 accessing the Arctic water was even harder in the past three years due to COVID-19. And we always have European scientists participating.”

Cai said he and Qi both were baffled when they first reviewed the Arctic data together during a conference in Shanghai. The acidity of the water was increasing three to four times faster than in ocean waters elsewhere.

That was stunning indeed. But why was it happening?

Cai soon identified a prime suspect: the increased melt of sea ice during the Arctic’s summer season.

Historically, the Arctic’s sea ice has melted in shallow marginal regions during the summer seasons. That started to change in the 1980s, Cai said, but waxed and waned periodically. In the past 15 years, the ice melt has accelerated, advancing into the deep basin in the north.

For a while, scientists thought the melting ice could provide a promising “carbon sink,” where carbon dioxide from the atmosphere would be sucked into the cold, carbon-hungry waters that had been hidden under the ice. That cold water would hold more carbon dioxide than warmer waters could and might help to 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 northwest corner of the region, all the way to the Canada Basin — far beyond its typical range. He and his collaborators found that the fresh meltwater did not mix into deeper waters, which would have diluted the carbon dioxide. Instead, the surface water soaked up the carbon dioxide until it reached about the same levels 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 level of the Arctic waters, they knew, reducing the alkaline levels of the seawater and reducing its ability to resist acidification. But how much? And how soon? It took them another decade to collect enough data to derive a sound conclusion on the long-term acidification trend.

Analyzing data gathered 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 melt as the key mechanism to explain this rapid pH decrease because it changes the physics and chemistry of the surface water in three primary ways:

  • The water under the sea ice, which had a deficit of carbon dioxide, now is exposed to atmospheric carbon dioxide and can take up carbon dioxide freely.
  • The seawater mixed with meltwater is light and cannot mix easily into deeper waters, which means the carbon dioxide taken from the atmosphere is concentrated at the surface.
  • The meltwater dilutes the carbonate ion concentration in the seawater, weakening its ability to neutralize the carbon dioxide into bicarbonate and rapidly decreasing ocean pH.

Cai said more research is required to further refine the above mechanism and better predict future changes, but the data so far show again the far-reaching ripple effects of climate change.

“If all of the multiple-year ice is replaced by first-year ice, then there will be lower alkalinity and lower buffer capacity and acidification continues,” he said. “By 2050, we think all of the ice will be gone in the summer. Some papers predict that will happen by 2030. And if we follow the current trend for 20 more years, the summer acidification will be really, really strong.”

No one knows exactly what that will do to the creatures and plants and other living things that depend on healthy ocean waters.

“How will this affect the biology there?” Cai asked. “That is why this is important.”

Reference: “Climate change drives rapid decadal acidification in the Arctic Ocean from 1994 to 2020” by Di Qi, Zhangxian Ouyang, Liqi Chen, Yingxu Wu, Ruibo Lei, Baoshan Chen, Richard A. Feely, Leif G. Anderson, Wenli Zhong, Hongmei Lin, Alexander Polukhin, Yixing Zhang, Yongli Zhang, Haibo Bi, Xinyu Lin, Yiming Luo, Yanpei Zhuang, Jianfeng He, Jianfang Chen and Wei-Jun Cai, 29 September 2022, Science.
DOI: 10.1126/science.abo0383

12 Comments on "Is Ocean Acidification Causing the Arctic To Melt?"

  1. The article provides us with a refresher on pH, where they state, “All levels lower than 7 are acidic, and all levels greater than 7 are basic or alkaline, … Seawater is normally alkaline, with a pH value of around 8.1.” They then claim, “The acidity of the water was increasing three to four times faster than in ocean waters elsewhere.” How can the acidity be increasing if it isn’t acidic? That is like claiming ice become more liquid as it warms. The meaning of words matters, and I expect better from those who call themselves scientists.

    If the melting ice is such a threat to the pH of the Arctic, why don’t the tropics have serious problems ecological problems resulting from a lack of an ice barrier and frequent lowering of the surface salinity when tropical thunderstorms deluge the area?

    The change in salinity of the sea water from dilution with melting ice is probably a greater threat to the ecosystem than the speculated pH change. However, in all cases, being a surface phenomenon, organisms that are sensitive to the changes in salinity or pH can swim or sink to deeper levels to avoid the problem.

    • The statement that the acidity is increasing is correct. Acidity is the measure of the concentration of hydrogen ions (H+) in an aqueous solution. pH is the negative of the logarithm of that concentration: pH = -log(H+). When the H+ concentration of a solution increases, its acidity increases and pH decreases. This is an accurate description of the process no matter the absolute value of the pH. When gaseous CO2 dissolves in seawater, the acidity increases because of the reaction: CO2 + H2O = H+ + HCO3-.

      • No! Acidity is NOT the measure of the concentration of hydronium ions (H+) in an aqueous solution. Acidity does not span the range of pH from 0 to 14. Acidity is the chemical behavior of a water solution with an excess of hydronium ions. What is important is the ratio of hydronium ions to hydroxyl ions. When they are equal (1:1) the solution is neutral. A pH of 7 is the boundary between acidic and alkaline solutions, by definition. The chemical behavior of solutions with a pH less than 7 is different from solutions with a pH greater than 7. It is the excess of hydronium ions that allows chemical reactions that won’t take place in solutions with a deficiency of hydronium ions. Your claim is a sophist rationalization for using a chemistry term inappropriately.

        • If, by definition, acid solutions have pH 10^-7 mol/kg. Thus, acidity is a measure of the hydrogen ion concentration a solution. When the hydrogen ion concentration goes up, the solution becomes more acidic than it had been previously. Simple. And BTW, providing a link to a climate change denier website doesn’t help your argument. Quite the contrary in fact.

          • The first part of my response was scrambled by my use of greater than and less than symbols. It was to have read: If, by definition, acid solutions have pH less than 7 and, by definition, pH = -log(H+), then, by definition, those solutions have hydrogen ion concentrations (H+) greater than 10^-7 mol/kg.

          • Clyde Spencer | November 4, 2022 at 11:11 am |

            I see that you are confused about more than just chemistry. In science, an argument should be able to stand on its own merit and not depend on who authored it or where it was published. In case you didn’t notice, I am the author of the paper at the link I provided. You should be providing objections to what I wrote, not where it was published. It says a lot about you that you are more concerned about where something is published than what is written.

            For the record, there are few, if any, authors or commenters that deny that climate changes, to be found on that website. What is at issue is the quantitative impact of humans, which is the heart of scientific inquiry.

            You apparently don’t know how to program computers. If you did, I would expect that you would be familiar with the IF…THEN…ELSE logic flow-control syntax. That is, pH 7 is a critical point describing the behavior of a solution.

            The pH of a solution is no more than the -log of the hydrogen ion concentration [H3O]+, which varies inversely with the hydroxyl concentration. However, the behavior of the solution with respect to other materials is determined by the relative abundance of the two species [H3O]+ and [OH]-. It is the chemical behavior that determines whether something is acidic or alkaline. You imply that something that is alkaline can be specified by its ‘acidity.’ That is an awkward and not very useful definition. The only redeeming feature of your position is that it is politically ‘correct.’

          • Clyde, thanks for taking the bait. You have revealed your true agenda. Nick Stokes provided an excellent response to your silly objections to the term “ocean acidification” both in the comments to your 2015 guest post on Anthony Watts’ climate change denial blog and here:

    • An informed discussion of ocean acidification terminology:

      • “Clyde, thanks for taking the bait.”
        So, is this some kind of a game for you that you are trolling for ‘bites?’ Just what do you suppose my “true agenda” is?

        I would like to think that my motivation is to call out sophistry that attempts to support alarmism with regard to anthropogenic CO2. I have told Stokes many times that I think he is a sophist because I have never known him to admit to being wrong, and one can depend on him to come up with some obscure ‘fact’ taken out of context to support his position. Nobody is so good that they are never wrong.

        The essence of the debate is whether it is appropriate to call ANY decrease in pH, “acidification,” from a grammatical and chemical viewpoint. To do so, creates some very practical problems in doing chemistry, where a procedure may (as is often the case) require one to neutralize, and then slightly acidify, a solution to keep a precipitate in solution. It ignores the fundamental definition of acids and bases, wherein an acid is DEFINED as having a pH less then 7, and by virtue of an excess of hydronium ions, has physical properties different from an alkaline solution. As examples, most metals can be dissolved by an acid, but not a base; saponification cannot take place in an acid solution. These are important, practical distinctions not only in chemistry, but in everyday life.

        In your appeal to ‘Stokian Authority,’ you link to something he has written wherein he says, “But in any case, the structure once formed has to resist solution, at all times, when conditions are fluctuating.” I have provided you with an explanation of how organisms accomplish this. Why is it that you give more credence to what he writes than what I write? Is it because you feel his position is more in line with your belief system? You might want to take the time to read the comments to Stokes. I suspect that some of these are better chemists than Stokes.

        One last thing that you might want to think about: If the carbonate ion is so much more important to calcite/aragonite shell production than the bicarbonate ion, why are calcifiers so successful in a pH environment that is near the peak of the bicarbonate concentration on the Bjerrum Diagram, where the carbonate ions are scarce and are approaching zero concentration asymptotically?

  2. Whatever you call it, this is very important stuff. When ocean pH drops from 8.2 to 8.1, the hydrogen ion concentration increases by 25% (from 6.3 to 7.9 x 10^-9 mol/kg). Those are extraordinarily small numbers and mean very little on their own. However, seawater contains much more than just H20, H+ and OH-. It contains a suite of carbonate ions: H2CO3, HCO3-, and CO3= whose concentrations are much greater. It is the balance amongst these that largely determines the chemical behavior of seawater. Under a range of near neutral pH, HCO3- is most abundant, but it is the concentration of CO3= that controls the ability of organisms to precipitate calcium carbonate (CaCO3) shells and body parts. Less CO3= is bad. The concentration of CO3= drops 44% (from 19.0 to 10.6 x 10^-4 mol/kg) when the pH drops from 8.2 to 8.1 by dissolution of increased CO2 from the atmosphere. That’s a huge change that messes with the carbon cycle of the oceans. Those organisms are absolutely critical to the ocean’s capacity for moderating atmospheric CO2 levels because, when they die, they take carbon to bottom of the ocean where it gets buried. This is why the issue of ocean acidification is of such importance.

    • “…, when they die, they take carbon to bottom of the ocean where it gets buried.”
      Most alarmists would be pleased to hear that CO2 is being sequestered as a result of decreasing pH.

      However, I think that the real concern is with dissolution of the shells of calcifiers, particularly juveniles. This is primarily a problem in coastal waters that experience upwelling from the cold, deep ocean, which is saturated with CO2 and can approach a pH of 7.

      “Under a range of near neutral pH, HCO3- is most abundant, but it is the concentration of CO3= that controls the ability of organisms to precipitate calcium carbonate (CaCO3) shells and body parts.”
      Actually, if you examine the Bjerrum Diagram at you will see that the maximum bicarbonate concentration in sea water is reached at a pH just under 8, not near neutrality. Currently, sea water is typically on the high side of the bicarbonate peak, meaning that a slight lowering of pH will increase the availability of bicarbonate. Actually, seasonal and even diurnal changes in surface pH are greater than the claimed historical 0.1 change in pH. Calcifiers are able to manipulate the pH at the growth-edge of their shells, and most actually use bicarbonate rather than free carbonate. Different species of calcifiers have different optimal ranges of pH, probably determined by what the ocean pH was when they first evolved. Once grown, the shells are typically protected by chitin and/or mucous, while the organism is alive.

      I think that your 44% claim is disingenuous. It may well be 44% from a pH of 8.2 to 8.1, but you should probably be using the percentage change of the total range for proper context if you want to use the “huge” claim.

      It is not clear that ocean pH was formerly 8.2. Those researchers working in the field have ignored the historical measurements and built a model to estimate pre-industrial pH. How can they validate their model if they reject historical measurements? If they don’t reject historical measurements, then why not just use them?

  3. Carbonate-precipitating organisms can only bury carbon if they were once alive and then die At reduced CO3=, they never form in the first place. But you are correct about the danger to juveniles.

    If you actually look at the Bjerrum Diagram, you’ll see what the problem is. Between pH 6 and 10, bicarbonate (HCO3-) is the most abundant dissolved form of CO2. However, carbonate (CO3=) is also present and, as pH decreases, its concentration decreases with severe negative consequences for carbonate-precipitating organisms. I used Nick Stokes handy calculator to determine how much the decrease would be for a drop in pH from 8.2 to 8.1. I think most folks would agree that a 44% reduction in a parameter is huge.

    You are increasingly grasping at strawmen as this exchange has gone on. I’ll leave it here.

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