Among the world’s oceans, the waters off California are acidifying twice faster, according to a study published Monday. This suggests worsening chemical changes in the ocean due to climate change that could pose a threat to seafood and fisheries.
The role of oceans is very vital in the delicate carbon cycle of the planet. These act as a crucial reservoir that not only absorbs carbon dioxide from the atmosphere but also stores it. The new research finds that oceans can withstand some natural variations in climate. Still, global warming may be adding to the stress on those ecosystems and overwhelming their ability to cope up with the changes.
“The system is adapted to experience and be able to thrive in a variable environment, but when you add extra stress, these changes become more extreme,” said Emily Osborne, a researcher at the National Oceanic and Atmospheric Administration, or NOAA, the lead author of the study, which was published in the journal Nature Geoscience.
Almost 2,000 fossil shells of a tiny organism known as planktonic foraminifera were analyzed by Osborne and her colleagues to create a 100-year history of ocean acidification along the California coast. The organisms live for only about a month and build their shells using calcium carbonate, meaning they leave behind clues about their environment.
“We can see how they’ve grown and how they’re influenced by the ambient carbon chemistry of the seawater around them,” Osborne said. “They capture the chemistry in their shell that is the chemistry of the ocean, too.”
According to NOAA study published in the journal Science in March, the estimated amount of carbon dioxide emissions that oceans around the world have absorbed is up to 31 percent from 1994 to 2007, equivalent to 34 billion metric tons of carbon. When carbon dioxide mixes with ocean water, it activates chemical reactions in the ocean water, making the water more acidic.
The sea creatures struggle to build up hardier shells as oceans become more acidic. According to Osborne, this allowed her and her colleagues to study the thickness of foraminifera shells and trace ocean acidity levels back through time. The shells of the organisms were thinning as oceans become more acidic, they found.
“We saw a clear, long-term declining trend with shell thickness that aligns with the signature of carbon that comes from the atmosphere,” she said.
The researchers were able to separate out variations in natural climate by zeroing in on specific signatures of carbon that result in chemical fluctuations along the West Coast, such as El Niño and La Niña cycles.
“That variability has its own chemical signature associated with it, so while they do overlap, we were able to disentangle natural variations that way,” Osborne said.
Since the Industrial Revolution in 1750, previous studies have shown that oceans have faced a decline of 0.1 in pH. The pH scale ranges from 0 to 14, and lower values denote more acidic and higher values more basic state.
California’s coastal waters lack similar data for that entire period, but Osborne and her colleagues found that California’s coastal waters have experienced a 0.21 decline in pH in just the past century, which is twice the global average over more than 2½ centuries.
Osborne said more research is required; the consequences could be negative because of chemical changes for the vibrant fisheries off California and elsewhere worldwide.
“There are different stressors like warmer temperatures, decreased oxygen concentration and multiple other things happening in concert to affect these species,” she said. “There’s a vast amount of research that has happened and continues to happen to get at what the responses will be and what it means broadly in terms of how ecosystems will respond.”