California coastal waters rising in acidity at alarming rate, study finds
LOS ANGELES – Waters off the California coast are acidifying twice as fast as the global average, scientists found, threatening major fisheries and sounding the alarm that the ocean can absorb only so much more of the world’s carbon emissions.
A new study led by the National Oceanic and Atmospheric Administration also made an unexpected connection between acidification and a climate cycle known as the Pacific Decadal Oscillation – the same shifting forces that other scientists say have a played a big role in the higher and faster rates of sea level rise hitting California in recent years.
El Nino and La Nina cycles, researchers found, also add stress to these extreme changes in the ocean’s chemistry.
These findings come at a time when record amounts of emissions have already exacerbated the stress on the marine environment. When carbon dioxide mixes with seawater, it undergoes chemical reactions that increase the water’s acidity.
Across the globe, coral reefs are dying, oysters and clams are struggling to build their shells, and fish seem to be losing their sense of smell and direction. Harmful algal blooms are getting more toxic _ and occurring more frequently. Researchers are barely keeping up with these new issues while still trying to understand what’s happening under the sea.
Scientists call it the other major, but less talked about, CO2 problem.
The ocean covers more than 70% of the Earth’s surface and has long been the unsung hero of climate change. It has absorbed more than a quarter of the carbon dioxide released by humans since the Industrial Revolution, and about 90% of the resulting heat – helping the air we breathe at the expense of a souring sea.
Here in California’s coastal backyard, some of the nation’s most economically valuable fisheries are also the most vulnerable. Scientists for years have worried that the West Coast would face some of the earliest, most severe changes in ocean carbon chemistry.
Many have noted how West Coast waters seemed to acidify faster, but there was little historical data to turn to. Ocean acidification has become a field of research only in recent decades, so information has been limited to what scientists have since started monitoring and discovering.
This study, published Monday in the journal Nature Geoscience, came up with a creative way to confirm these greater rates of acidification. Researchers collected and analyzed a specific type of shell on the seafloor – and used these data to reconstruct a 100-year history of acidification along the West Coast.
“This is the first time that we have any sort of record that takes it back to the beginning of the (last) century,” said Emily Osborne, a NOAA researcher and lead author of the study. “Prior to this, we didn’t have a time series that was long enough to really reveal the relationship between ocean acidification” and these climate cycles.
The study analyzed almost 2,000 shells of a tiny animal called foraminifera. Every day, these shells – about the size of a grain of sand – rain down onto the seafloor and are eventually covered by sediment.
Scientists took core samples from the Santa Barbara basin – where the seafloor is relatively undisturbed by worms and bottom-feeding fish – and used the pristine layers of sediment to create a vertical snapshot of the ocean’s history.
The more acidic the ocean, the more difficult it is for shellfish to build their shells. So using a microscope and other tools, researchers measured the changes in thickness of these shells and were able to estimate the ocean’s acidity level during the years that the foraminifera were alive.
“We can read the deposits like pages in a book,” said Osborne, a scientist for NOAA’S Ocean Acidification Program. “In Santa Barbara, there are just beautifully preserved laminated records of the seafloor that allow us to generate these high-resolution reconstructions.”