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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