The waters bordering North America could soon be inhospitable to critical marine creatures if the Northeastern Pacific Ocean continues to acidify at the current rate, a new study shows.

Earth’s oceans have become since the industrial revolution began more than 200 years ago. Acidification changes marine chemistry and that calcifying organisms, such as corals and clams, need to build their skeletons and shells. The Northeastern Pacific is naturally more acidic than other oceans, fueling debate about how much its chemistry will change in the coming decades.

The study, , shows that high baseline acidity makes the water more sensitive to additional carbon dioxide from human activities. Analyses of coral skeletons from the past century revealed that CO2 has been accumulating in North American waters faster than in the atmosphere, driving rapid acidification.

“This fits into a class of really important records that show how the world has changed over the human era,” said senior author a 91̽�� associate professor of oceanography.

“The findings implicate not only marine ecosystems, but all of the people who depend on them as well,” added lead author , a 91̽��doctoral student of oceanography.

The ocean becomes more acidified when carbon dioxide dissolves to form an acid that releases hydrogen and bicarbonate ions, lowering the water’s pH level. In North America, a powerful current system — the California Current — transports cool water south along the coast. The combination of current flow and wind creates optimal conditions for upwelling, a process that cycles deep water to the surface.

Organic matter — dead plants and animals — sinks to the bottom of the ocean, where it decomposes and releases carbon dioxide back into the water. Upwelling surfaces this CO2 rich water, increasing the acidity of subsurface and surface zones. These natural fluctuations complicate researchers’ efforts to predict how much acidification will occur from human activities.

This study helps resolve these questions with records kept by centuries old corals.

Coral incorporates elements and minerals from seawater as it grows, leaving behind a valuable record of environmental conditions in its skeleton. The Pacific Ocean is home to a small vibrant species called orange cup corals. Gagnon’s lab was already studying orange cup corals when the researchers became interested in historic samples.

In 2020, the researchers began collecting samples— first from the Smithsonian Museum, and then from labs and museums all over the U.S. and Canada. They procured a total of 54 samples collected between 1888 and 1932 from the , the body of water connecting Washington state and Canada, and North American coastal waters.

Using handwritten records in logbooks, the researchers then navigated back to the original collection sites. They took orange cup corals from the same spots, sometimes more than a century later.

To plot CO2 and acidity over time, the researchers analyzed boron levels in the coral skeletons. In seawater, boron exists in several chemical forms that vary with acidity. Corals incorporate one of these forms into their skeletons as they grow, so the boron ratio in coral skeletons reflects the acidity of the seawater in which they formed.

Between 1888 and 2020, coral skeletons indicate that CO2 in seawater increased at a rate that outpaced the addition of greenhouse gases to the atmosphere. The magnitude of acidification was also higher 100 to 200 meters below the surface, even though ocean acidification is typically characterized as a surface process.

“No one has acidity measurements older than a few decades,” Gagnon said. “We had to go back in time and do some detective work to pull some kind of chemical signal out of the world and show this unfortunate amplification effect.”

The amplification effect will likely strengthen as atmospheric CO2 levels continue to climb. In the study, the researchers modeled worst case scenarios to see what could happen to species if acidification continues unchecked.

“The changes in ocean chemistry were really dramatic,” Stoll said. “The Salish Sea is a region with a lot of cultural, commercial and recreational ties to marine organisms that are all rooted in the health of these ecosystems.”

Despite the tenor of their results, the researchers say there is still time to course correct.

“This is no time for nihilism. The ocean is not destroyed,” Gagnon said. “As very large emitters per capita, we have the power to change our emissions and influence outcomes for the oceans.”

Studying regions where ocean acidification is happening faster than elsewhere can also provide key insights and warning signs.

“This is a uniquely important area to study,” Stoll said. “It is at the leading edge of ocean acidification impacts and provides a window into conditions predicted for the rest of the ocean in the coming decades.”

For more information, contact Stoll at mmstoll@uw.edu or Gagnon at gagnon@uw.edu

Co-authors include at Princeton; and at the University of St. Andrews; and at NOAA’s Pacific Marine Environmental Laboratory and at St. Olaf College.

This study was funded by the Washington Ocean Acidification Center, the 91̽�� Program on Climate Change, the Northwest Straits Foundation Caroline Gibson Scholarship, the National Science Foundation, the National Oceanic and Atmospheric Administration, and the Gordon and Betty Moore Foundation, the Leverhulme Trust Early Career Fellowship, and a European Research Council Horizon 2020 research and innovation program grant.

An oceanographer at the 91̽�� is part of a new project to study how glacial particles, created as glaciers grind the rock beneath them into a powder, reacts with seawater to remove carbon dioxide from the atmosphere.

, an associate professor of oceanography at the UW, is one of the investigators on a newly funded project that involves field and lab studies of a natural setting that could help understand the ocean’s role in carbon removal, which many experts believed will need to be combined with emissions reductions to address climate change.

, a nonprofit based in San Francisco, and , a research consortium, on Oct. 28 two 18-month grants to evaluate the environmental impacts of through the study of natural environments.

Ocean-based carbon dioxide removal analogues are defined as natural marine settings that remove carbon dioxide from the atmosphere via processes that could theoretically be replicated, sped up or done at larger scales.

The team’s $220,000 grant will fund a study near the edge of glaciers that contact the ocean at high tides in Alaska’s Prince William Sound. Researchers will measure the rate of addition of alkaline material from rocks surrounding the fjords, where glaciers naturally pulverize rocks and discharge fine-grained particles into the ocean. The study will measure CO₂ uptake at various water depths and in the sediments to test the link between adding alkaline powder and atmospheric CO₂ removal. The team will also determine how trace metals released by the rocks, such as zinc and iron, affect marine ecosystems.

The project partners are , a 91̽��affiliate associate professor of oceanography and research scientist at the U.S. Geological Survey’s Alaska Science Center; , a biological oceanographer and chief science officer at the Prince William Sound Science Center; and , a 91̽��graduate student in oceanography.

The team will use the science center’s research vessel, the R/V New Wave, to collect samples, and then analyze them in a 91̽��lab.

The other grant was awarded to a team at Woods Hole Oceanographic Institution that will study seasonal changes in the Mississippi River’s discharge to the Gulf of Mexico.

For more information, contact Gagnon at gagnon@uw.edu.

Oceanographers at the 91̽��, the University of California, Davis and the Pacific Northwest National Laboratory have used modern tools to provide an atomic-scale look at how that shell first forms. Results could help answer fundamental questions about how these creatures grow under different ocean conditions, in the past and in the future. The study is published this week in the .

“There’s this debate among scientists about whether shelled organisms are slaves to the chemistry of the ocean, or whether they have the physiological capacity to adapt to changing environmental conditions,” said co-lead author , a 91̽��assistant professor of oceanography.

The new work shows, he said, that they do exert some biologically-based control over shell formation.

“I think it’s just incredible that we were able to peer into the intricate details of those first moments that set how a seashell forms,” Gagnon said. “And that’s what sets how much of the rest of the skeleton will grow.”

The results could eventually help understand how organisms at the base of the marine food chain will respond to more acidic waters. And while the study looked at one organism, Orbulina universa, which is important for understanding past climate, the same method could be used for other plankton, corals and shellfish.

The study used tools developed for materials science and semiconductor research to view the shell formation in the most detail yet to see how the organisms turn seawater into solid mineral.

“We’re interested more broadly in the question ‘How do organisms make shells?'” said first author , a former postdoctoral researcher at the University of California, Davis who is now at Australian National University in Canberra. “We’ve focused on a key stage in mineral formation — the interaction between biological template materials and the initiation of shell growth by an organism.”

These tiny single-celled animals, called , can’t reproduce anywhere but in their natural surroundings, which prevents breeding them in captivity. The researchers caught juvenile foraminifera by diving in deep water off Southern California. Then they then raised them in the lab, using tiny pipettes to feed them brine shrimp during their weeklong lives.

Marine shells are made from calcium carbonate, drawing the calcium and carbon from surrounding seawater. But the animal first grows a soft template for the mineral to grow over. Because this template is trapped within the growing skeleton, it acts as a snapshot of the chemical conditions during the first part of skeletal growth.

To see this chemical picture, the authors analyzed tiny sections of foraminifera template with a technique called at the Pacific Northwest National Laboratory. This tool creates an atom-by-atom picture of the organic template, which was located using a chemical tag.

Results show that the template contains more magnesium and sodium atoms than expected, and that this could influence how the mineral in the shell begins to grow around it.

“One of the key stages in growing a skeleton is when you make that first bit, when you build that first bit of structure. Anything that changes that process is a key control point,” Gagnon said.

The clumping suggests that magnesium and sodium play a role in the first stages of shell growth. If their availability changes for any reason, that could influence how the shell grows beyond what simple chemistry would predict.

“We can say who the players are — further experiments will have to tell us exactly how important each of them is,” Gagnon said.

Follow-up work will try to grow the shells and create models of their formation to see how the template affects growth under different conditions, such as more acidic water.

“Translating that into, ‘Can these forams survive ocean acidification?’ is still many steps down the line,” Gagnon cautioned. “But you can’t do that until you have a picture of what that surface actually looks like.”

The researchers also hope that by better understanding the exact mechanism of shell growth they could tease apart different aspects of seafloor remains so the shells can be used to reconstruct more than just the ocean’s past temperature. In the study, they showed that the template was responsible for causing fine lines in the shells — one example of the rich chemical information encoded in fossil shells.

“There are ways that you could separate the effects of temperature from other things and learn much more about the past ocean,” Gagnon said.

Other co-authors are 91̽��doctoral student ; Howard Spero, Ann Russell and Jennifer Fehrenbacher at the University of California, Davis; Daniel Perea, Zihua Zhu and Maria Winters at the Pacific Northwest National Laboratory; and Bӓrbel Hönisch at Columbia University.

The research was funded by the National Science Foundation and the Department of Energy.

###

For more information, contact Gagnon at 206-543-5627 or gagnon@uw.edu and Branson at obranson@ucdavis.edu.