Thursday, January 12, 2012

Marine Chemistry a Study in Progress by Sue Pike

It felt like summer on that first beautiful Sunday of the new year out on the flats digging clams. The flats were littered with deposits of old clam and mussel shells, spiraled remnants of periwinkles and moon snails. Hard-shelled barnacles, still alive, encrusted the crumbling shells. Digging into the mud often involved working through thick layers of clam shells, layer upon layer, marking the passage of time.

The balmy temperatures and the shells got me thinking about one of the many changes to our world that is being driven by increased carbon dioxide emissions: ocean acidification.

Reports on ocean acidification have become fairly regular features in the science sections of newspapers lately, primarily because of new research into the intricacies of marine chemistry and the effects of increasing atmospheric carbon dioxide on marine life. We all have heard that atmospheric carbon dioxide has been increasing due to the burning of fossil fuels; a large part of this, almost one-third of the carbon dioxide emitted globally, is absorbed by the worlds' oceans.

Once it enters the ocean, the carbon dioxide reacts with water to produce carbonic acid. This is what causes ocean acidification. Organisms that live in the ocean and have shells or skeletons made out of calcium carbonate (barnacles, clams, a number of types of plankton and coral, for example) can have trouble getting enough carbonate for their shells if the water is too acidic. In fact, if the water becomes too acidic there can be so little carbonate that shells will start to dissolve.

This has happened before: 55 million years ago there was a period of global warming driven by increased atmospheric carbon dioxide. There are no fossils of microorganisms with calcium carbonate shells found in ocean sediments from that period, indicating that the sea water had become sufficiently acidic to keep these organisms from forming shells. (Nature March 2011).
It is quite worrisome that ocean acidification is believed to be progressing at least 10 times faster today than it did 55 million years ago.

While most studies point to the negative impacts of ocean acidification on marine life, the findings aren't all doom and gloom. One recent study out of Scripps Institute of Oceanography showed that pH (a measure of acidity) is highly variable throughout the world's oceans, and some places, like coral reefs, can become quite acidic as part of a daily cycle with no apparent ill effect on local residents. Other studies have found that different species differ in their ability to tolerate acidic, carbonate-deprived water.

In fact, two populations of the same species of spider crab were found to vary in their sensitivity to acidic waters. The more northern population was more sensitive; the southern population less so.

The take-home message from these studies is that the sea is one complicated kettle of fish; we currently don't fully understand marine chemistry, much less the impact of significantly changing that chemistry through our obsession with fossil fuels. The barnacles and clams and mussels must all hope that we stop what we are doing to the oceans soon enough to save them. I certainly do.
Sue Pike of York has worked as a researcher and a teacher in biology, marine biology and environmental science for years. 

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