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Acid Sea Change
After years of concern over what so-called greenhouse gasses might be doing to warm our atmosphere, researchers studying our oceans are now starting to find that one of those gasses, carbon dioxide, has made the ocean about 30 percent more acidic in the last 200 years.
In addition, that same research is projecting that without major changes, it could become a 150 percent increase by the end of this century. “This is a larger change in the acidity of the ocean than has been observed through geological time, for at least 20 million years,” says Richard Feely, supervisory oceanographer at the National Oceanic & Atmospheric Administration’s Pacific Marine Environmental Laboratory.” He adds, “We’re changing the acidity of the oceans faster than the organisms have ever experienced.”
Beyond that, research recently published is describing a phenomenon where the ocean is working to make waters in some coastal areas that are important to fishing even more acidic than elsewhere in the ocean.
Feely and fellow NOAA oceanographer Christopher Sabine started measuring carbon dioxide (CO2) in the ocean starting in the 1990s. Sabine says, “We had approached all of this (research) with the idea that the oceans are performing a service for mankind.” They thought the ocean taking up carbon dioxide might be a good thing that could dampen the impact of global warming.
Their research has shown that since the start of the Industrial Revolution, around 1800, the ocean has taken up 118 billion metric tons of carbon dioxide. Sabine likens a metric ton to a small car. He says, “We put the equivalent of 118 billion VW bugs worth of carbon into the oceans.” That’s about one-third of the CO2 produced by industry.
A major reason they thought the oceans could absorb CO2 without harm was that about 90 percent of the earth’s carbon is already in the ocean. So, while 118 billion metric tons of carbon dioxide is a very large amount, the original scientific assumption was that the ocean was big enough to take it.
However, with further research Sabine says they discovered that “half of all the CO2 that’s accumulated in the oceans has actually remained in the upper 400 meters (the upper 1300 feet), those upper layers of the ocean.” And that, says Sabine, is “where (nearly) all the organisms live.”
Their latest research has added yet another dimension and potentially more issues for those who fish along the west coast of North America. They’ve found that naturally acidic deep ocean water is coming up to the surface in some areas, especially along the Continental Shelf. That’s making the water there even more acidic than elsewhere; a double whammy of sorts.
The water is coming up through a process called “upwelling.” In their research they found that in the summer, the winds shift and pull surface water away from shore. The deeper water rises up to replace the surface water.
Says Sabine, “What we found was we were getting levels of acidification up onto the shelf in these upwelling regions that were much more dramatic than we expected to see.” The change is not uniform as their measurements showed the most acidic seawater to be near the California-Oregon border.
The lower portions of the sea have much more carbon dioxide. That’s the result of thousands of years worth of plant and animal matter falling to the lower depths of the ocean and decaying, where bacteria act upon it. According to Feely, “Eventually it ends up back as CO2.” As a result that water is naturally more acidic than the water at the top.
The impact of the increase in acidity on sea life is now being studied. Feely notes that lab studies on some shelled marine snails called pteropods showed that their shells would start to dissolve within 48 hours after being placed into the water with acid levels near that of what is expected to be found at the turn of the century. He says, “There’s a real question of whether or not they can continue to survive.”
Feely says these pterapods are “the primary food source for the first year class of salmon and herring and mackerel and many of the pollock, many of the fish that we depend on for food.” He doubts these fish would survive that first year without having pterapods to eat.
Another area of concern, says Feely, is the impact of this water on coral reefs, which serve as home for many fish, at least during some periods of their lives.
So, while it’s a comparably new area of study and concern for scientists, this change in ocean acidity is an issue that will need more study in the future.
This research was published in the journal Science for July 13, 2008 and was supported by grants from the National Oceanographic and Atmospheric Administration (NOAA) and the National Aeronautics and Space Administration (NASA).
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