Story at a glance

  • The oceans have slowed climate change by absorbing 27 percent of the carbon dioxide that has been pumped into the atmosphere since 1959.
  • But being a carbon sponge comes at a cost: It makes the ocean more acidic, which is bad for creatures trying to form shells.
  • New research finds that this process called ocean acidification is moving twice as fast in the productive waters off the coast of California compared to the rest of the world’s oceans.

The Pacific Ocean off California’s coast accounts for around 10 percent of the United States’ haul of seafood. But these productive waters are acidifying twice as fast as the rest of the world’s oceans, according to new research, and that’s bad news for anything with a shell. 

As humans fill the atmosphere with more and more planet-warming carbon dioxide, not only is it heating up the planet — with devastating effects on the world’s oceans — the gas is also being absorbed by seawater in huge quantities. Roughly 27 percent of all carbon dioxide emitted since 1959 has gone into the oceans. 

As all that carbon dioxide mixes with seawater, it makes the entire ocean more acidic, an effect commonly referred to as ocean acidification. The oceans are now around 30 percent more acidic than they were before the industrial revolution.

A more acidic environment is damaging for many marine species, but it’s especially bad for the ones that form shells. The acidic waters make the chemical building blocks that sea creatures use to form shells in the first place less plentiful and corrode those that do manage to coalesce. 

The new research analyzed the shell weights of nearly 2,000 fossilized shells from the last 100 years. The researchers found a disturbing 20 percent reduction in the shells of a tiny group of organisms called foraminifera, or forams, the New York Times reports.

“I could just watch the shells literally getting thinner as I moved up through the record and got closer to the present day,” Emily Osborne, one of the study’s authors, told the Times.

Those thinner shells allowed the researchers to figure out what was going on with the chemistry of the ocean the forams inhabited. They found the California waters that hosted these tiny critters had acidified at a bit more than twice the speed of the rest of the world.

Researchers suggested the accelerated pace has to do with an oceanographic phenomenon called coastal upwelling in which wind sweeps deep waters up to the surface. Those deep waters tend to be more acidic, which exacerbates the acidification caused by humans flooding the atmosphere with carbon dioxide. 

Earlier research exposed immature shellfish to seawater containing the quantity of mixed-in carbon dioxide that is expected in 2100 and found their shells were “malformed and eroded.”

The new research raises worrying questions about how long California’s marine ecosystems will be able to cope with an increasingly acidic underwater world.

“We know that evolution works and every creature has some degree of plasticity in them,” marine biologist Gretchen Hofmann told the Times. But “the environment is changing so fast that we’re probably outstripping the role that it can play.”

Published on Dec 16, 2019