A century’s worth of microscopic shells has revealed that ocean acidification is occurring in California waters at twice the rate of the global average. Ocean acidification stems from the same problem as climate change—too much excess carbon dioxide in the atmosphere. According to the National Oceanic and Atmospheric Administration, the ocean—a natural carbon sink—is absorbing excess carbon dioxide, lowering the pH and increasing the acidity of ocean waters. This increase in acidity impacts entire ocean ecosystems.
A new study published this week in Nature Geoscience examined the calcification of foraminifera to track the progression of ocean acidification in the California Current System throughout the past century. Scientists examined the shells of about 2,000 microscopic foraminifera fossils found in core samples from the Santa Barbara seafloor. According to NOAA, foraminifera shells settle on the ocean floor and become trapped in layers of sediment. A core sample of the seafloor would contain layer upon layer of these shells, allowing scientists to see how they’ve changed over the past century.
Emily Osbourne, lead author and scientist with NOAA’s Ocean Acidification Program, told NOAA reporters that “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." By using this new technique, Osbourne created the longest measured record of ocean acidification yet, dating back to 1895.
The study’s measurements showed a 20% reduction in the calcification of the foraminifera shells. According to the study, this translates to about a 35% reduction in carbonate ion concentration—which is a biologically important component of the carbonate system. Osbourne told New York Times reporters, “I could just watch the shells literally getting thinner as I moved up through the record and got closer to present day.” A decline in the availability of carbonate ions would negatively impact the ability of calcium carbonate shell-building ocean animals.
Additionally, the study revealed a cyclical rise and fall of acidity that coincided with the Pacific Decadal Oscillation—a natural warming and cooling cycle. Although excess carbon dioxide emissions from human activities are causing ocean acidification, these natural cycles play essential roles as well. Natural climatic variations may amplify or alleviate human-induced ocean acidification in this region.
This new information may help local fisheries prepare for the impact of acidification on economically important species such as salmon, crabs, and shellfish. It will also help scientists create a broader picture of how acidification impacts are altering entire ecosystems.