Friday, April 13, 2012
There was a strong suspicion that some strain of bacteria was to blame. And, in the initial research investigations, some elevated bacteria levels and some toxins were discovered. However, none was persistent nor strong enough to have caused a die-off in successive years.
One group looked at a particular possibility: the chemistry of the north eastern Pacific coastal waters. What they found was conclusive proof that increased acidity in the coastal waters of Pacific North America was preventing oyster larvae from properly forming coherent shells, killing them long before they could start to mature. (If you don't want to wade through a scientific oceanographic paper, you can get the gist from this Seattle Times report).
It is now documented that the world's surface oceans have suffered a 16% decrease in carbonate ion concentrations and the pH of global sea water has dropped by 0.1 of a unit from the pre-industrial era. It is likely colder northern waters are suffering even a greater loss of balance.
The reason is simple. The oceans are the largest carbon sink on the planet. They suck up 2 million tonnes of CO2 daily. The more that gets pumped into the atmosphere, the more the ocean sucks up. As the oceans absorb more CO2 from the atmosphere it adds to the CO2 that naturally rises due to coastal upwellings. The increased CO2 levels create a higher acidity level. The elevated acid (reduced pH) is corrosive to calcium carbonate minerals, the stuff that marine life uses to make critically protective shells.
Here is a short, simple, but informative video on how the process of shell formation is impaired by increased CO2.
Of course, there's more to it but, compared to climate physics and chemistry, the chemistry of the ocean, particularly where CO2 is having an effect, is relatively easy. And it's very obvious.
Upwellings occur as a result of ocean movement. Simply put, storms and high wind move the surface and draw up the deeper CO2 saturated water. Much of the CO2 from the deep is naturally occurring although a significant portion is the result of anthropogenic increases in the atmosphere.
What isn't natural is the elevated CO2 already at the surface. When the deeper ocean water rises it mixes with surface water. The resultant coastal water has a higher CO2 level than is usually found. That disturbs the formation of calcium carbonate, which weakens shell formation and ... oysters pay the price.
Yes it is. In fact it's very big. For one thing this is happening decades faster than anyone ever thought it could. But the worst is yet to come.
The upwelling water and the wide area surface waters take decades to move. The increased CO2 saturation in the water that has been arriving on the North American Pacific coast is from many decades ago when anthropogenic CO2 was, as the authors of the paper point out, substantially lower.
What's coming will be even more acid and even more corrosive.
Those baby oysters are the canary in the mine shaft.