Washington, May 23 : An international team of scientists surveying the waters of the continental shelf off the West Coast of North America has discovered that the Pacific coast is turning more acidic.
These scientists, aboard the Wecoma, an Oregon State University (OSU) research vessel, discovered for the first time high levels of acidified ocean water within 20 miles of the shoreline, raising concern for marine ecosystems from Canada to Mexico.
They also discovered that this corrosive, acidified water that is being "upwelled" seasonally from the deeper ocean is probably 50 years old, suggesting that future ocean acidification levels will increase since atmospheric levels of carbon dioxide have increased rapidly over the past half century.
"When the upwelled water was last at the surface, it was exposed to an atmosphere with much lower CO2 (carbon dioxide) levels than today's," pointed out Burke Hales, an associate professor in the College of Oceanic and Atmospheric Sciences at Oregon State University.
"The water that will upwell off the coast in future years already is making its undersea trek toward us, with ever-increasing levels of carbon dioxide and acidity," he added.
Scientists have become increasingly concerned about ocean acidification in recent years, as the world's oceans absorb growing levels of carbon dioxide from the atmosphere.
When that CO2 mixes into the ocean water, it forms carbonic acid that has a corrosive effect on aragonite - the calcium carbonate mineral that forms the shells of many marine creatures.
Certain species of phytoplankton and zooplankton, which are critical to the marine food web, may also be susceptible, although other species of open-ocean phytoplankton have calcite shells that are not as sensitive.
During the past 50 years, atmospheric CO2 levels have gradually increased to a level of about 380 parts per million. These atmospheric CO2 levels form the beginning baseline for carbon levels in ocean water.
As water moves away from the surface toward upwelling areas, respiration increases the CO2 and nutrient levels of the water. As that nutrient-rich water is upwelled, it triggers additional phytoplankton blooms that continue the process.
The research team used OSU's R/V Wecoma to sample water off the coast from British Columbia to Mexico.
They found that the 50-year-old upwelled water had CO2 levels of 900 to 1,000 parts per million, making it "right on the edge of solubility" for calcium carbonate-shelled aragonites.
According to Hales, "If we're right on the edge now based on a starting point of 310 parts per million, we may have to assume that CO2 levels will gradually increase through the next half century as the water that originally was exposed to increasing levels of atmospheric carbon dioxide is cycled through the system."