(CN) – The ocean off the coast of California is acidifying at twice the normal rate, according to a study published Monday morning.
The federal study, published in Nature Geoscience by scientists with the National Oceanic and Atmospheric Administration, used a novel technique to measure acidification – by studying the 100-year record of microscopic shells scattered on the ocean floor just off the coast of California near Santa Barbara.
“By measuring the thickness of the shells, we can provide a very accurate estimate of the ocean’s acidity level when the foraminifera were alive,” said lead author Emily Osborne.
Osborne developed this novel method of measuring oceanic changes in acidification by accentuating the relationship between the shells and the acid levels in the ocean.
“This is actually something researchers have been developing for a while now, with researchers showing this relationship between shell wall thickness and sea water chemistry,” Osborne said.
But Osborne was the first to use the relationship in a novel way to show how acidification is worsening in a given area as most researchers have been interested in using the organisms and their fossilized remains to draw conclusions about global climate changes over vast time scales.
At a basic level, the more acidic oceanic waters the more difficult it is for the organisms to form their shells, meaning scientists can use the varying thickness of the foraminifera shells as an indicator for acid levels.
This is so valuable precisely because Osborne and other researchers were able to gather and analyze fossils buried under layers of ocean sediment to develop a record. The value is particularly acute as acidification is a relatively new area of study, with earth scientists only gaining awareness of the problem in recent decades.
One of the significant hurdles encountered by the researchers was proper calibration of the relationship between shell thickness and acidity. In other words, if a shell wall is 25% thinner, for instance, how much of a change in pH does that reflect?
Osborne used a set of well-developed data that specifically tracked changes in the ocean chemistry off the coast of Santa Barbara. She then collected samples of foraminifera shells from the same three-year period to establish the proper calibration.
Once this was done, Osborne was able to establish the rate at which the acidity of the ocean changed by using shell wall thickness using samples dating back to 1895. The results were startling.
A recent study by other oceanic researchers established the pH in surface waters had fallen by .1 pH units, representing an approximately 30% increase in acidity. But the record established by Osborne, while shorter by 100 years, still found the pH of surface waters had fallen by .21 pH units, mean the area was acidifying at twice the rate.
Ocean acidification correlates directly to carbon emissions on Earth, as the ocean absorbs much of the carbon dioxide emitted into the atmosphere. As much as 40% of the human-caused carbon dioxide emissions are absorbed into rivers, lakes and the ocean.
But human causes only tell part of the story of why the acidification of the ocean off California is particularly intense. The other major factor, according to Osborne, is the Pacific Decadal Oscillation, a natural process in California’s coastal waters that produces cooling and warming cycles.
Fluctuations in the foraminifera shell thickness indicate the natural process at work, but also must be properly understood if coastal managers are going to properly handle the acidification problem.
“During the cool phases of the Pacific Decadal Oscillation, strengthened winds across the ocean drive carbon dioxide-rich waters upward toward the surface along the West Coast of the U.S.,” Osborne said. “It’s like a double whammy, increasing ocean acidification in this region of the world.”
The ramifications of acidification in the coastal waters of California extend beyond the purely ecological, as California maintains one of the most productive fisheries – with salmon, crab and shellfish – in the nation and the world.
Recent statistics showed fishermen made about $200 million from selling seafood to customers, whether individuals or distributors. The industry supports about 120,000 jobs on and off the water, according to NOAA.
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