LOS ANGELES, Dec. 16 (Xinhua) -- Coastal waters off California are acidifying twice as fast as the global ocean average, according to a new study published Monday in the journal Nature Geoscience.
To come to this conclusion, scientists from the U.S. National Oceanic and Atmospheric Administration examined nearly 2,000 shells from microscopic creatures called foraminifera, measuring how the shells have changed over a century.
Every day, the shells of dead foraminifera rain down on the ocean floor and are eventually covered by sediment. Layers of sediment containing shells form a vertical record of change.
"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, who used this novel technique to produce the most extensive record yet created of ocean acidification using directly measured marine species. Osborne measured shells that represented deposits dating back to 1895.
The fossil record also revealed an unexpected cyclical pattern: Though the waters have increased their overall acidity over time, the shells revealed decades-long changes in the rise and fall of acidity.
This pattern matched the Pacific Decadal Oscillation, a natural warming and cooling cycle, according to the study. Human-caused carbon dioxide emissions are driving ocean acidification, but this natural variation also plays an important role in alleviating or amplifying ocean acidification.
Scientists hope to build on the study by learning more about how changes in ocean acidification may be affecting other aspects of the marine ecosystem.