Corals reveal alarming changes unfolding along the Pacific coast

From the shore, the Pacific Ocean looks endless and calm. Beneath the surface, the chemistry is shifting fast. A new study warns that ocean acidity is rising dangerously along North America’s west coast.

The California Current and the Salish Sea are changing faster than scientists expected, and that change could upend marine life and the people who rely on it.

Ocean acidity changing rapidly

Oceans absorb nearly a third of the carbon dioxide released into the air. Globally, this has made seawater about 30 percent more acidic since the industrial revolution.

But coastal zones like the California Current tell a sharper story. These waters already hold a lot of natural carbon dioxide. When human emissions mix in, the ocean’s chemistry reacts more strongly.

“This fits into a class of really important records that show how the world has changed over the human era,” said Alex Gagnon, a professor of oceanography University of Washington (UW).

According to the study, seawater in the Salish Sea and the California Current has acidified faster than the atmosphere.

The reason is a thermodynamic effect. As the ocean absorbs more carbon, it loses its ability to buffer against further acidity. Each new molecule of carbon dioxide has a stronger impact than the last.

Corals reveal history

To understand how this has unfolded, scientists used corals as natural archives. They studied the cold-water species Balanophyllia elegans, or orange cup coral, which records ocean chemistry in its skeleton.

Samples taken between 1888 and 1932 were compared with new ones collected from the same sites in 2020.

The results were clear. Seawater carbon dioxide rose by about 172 microatmospheres, even though the atmosphere increased by only 120 parts per million. That means the ocean’s chemistry changed faster than the air above it.

“The findings implicate not only marine ecosystems, but all of the people who depend on them as well,” said study lead author Mary Margaret Stoll, a UW doctoral student.

Acidity in the deep ocean

The deeper layers of the ocean showed the biggest changes. Below 100 meters, carbon dioxide levels increased up to 50 percent more than in the air.

These depths, where upwelled water rises toward the surface, now carry more acidity and less buffering strength.

Upwelling itself has barely changed in a century. The current’s speed and season have shifted only slightly. The problem lies elsewhere – in the ocean’s chemistry.

Once carbon-heavy water forms, it keeps amplifying the effect of every new emission. This feedback leaves less time for adaptation.

“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.”

Oceans facing major change

Model projections paint a bleak future if emissions remain high. By 2100, acidity in the California Current could outpace atmospheric carbon by as much as 60 percent at depths between 100 and 150 meters.

According to the study, pH levels may drop by 0.3, and the minerals that marine creatures need to build shells could dissolve faster than they can form.

Dungeness crab, the Pacific’s most profitable fishery, could see slower growth and higher mortality in its early life stages. Other species vital to the coastal food web will also struggle as conditions worsen.

“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.”

Choices still matter

Despite the grim data, Gagnon refuses to surrender hope. “This is no time for nihilism. The ocean is not destroyed,” he said.

“As very large emitters per capita, we have the power to change our emissions and influence outcomes for the oceans.”

Cutting emissions now can slow the pace of acidification. Protecting coastal ecosystems can buy time for adaptation. The California Current, with its rapid changes, offers a glimpse into the global ocean’s future – a preview humanity can still act on.

“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.”

The ocean is still fighting to keep its balance. Whether it succeeds depends on how quickly we act to protect it.

The study is published in the journal Nature Communications.

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