Geoscience Reference
In-Depth Information
oratory investigation by Justin Ries and
associates at Woods Hole Oceanographic
Institute observed shell growth in the
laboratory under conditions of varied CO
2
content. Most shells were thinner under
elevated CO
2
conditions, but seven of eigh-
teen shelled organisms grew
thicker
shells.
The researchers noted that soft clams and
oysters showed reduced calcification, but
at least in the laboratory some hard clams
and lobsters and one species of coral didn't
seem to care one way or the other about
high CO
2
.
A big ocean acidification warning came
in 2010. Larval shellfish in hatcheries along
the Oregon coast began to die, apparently
because they were unable to form shells.
Burk Hales, an oceanographer at Oregon
State University, was able to demonstrate
that the problem was the excessive acidity
of waters pumped into the hatcheries from
the open ocean. Here was proof that ocean
acidification was at our doorstep and here
to stay.
One of the main questions that must be
answered is how carbonate-secreting or-
ganisms survived higher CO
2
concentra-
tions in the atmosphere in the time of the
dinosaurs. In the geologic past, as in the
present, CO
2
existed in a natural equilib-
rium with a number of processes including
the weathering of rocks, burial of organic
matter in sediment, volcanic activity, and
absorption in the ocean. Changes in any
of those long-term parameters can affect
the CO
2
concentration and hence ocean
acidification. During the big jump in at-
mospheric temperatures about 55 million
years ago known as the Paleocene/Eocene
thermal maximum (petm, discussed in
chapter 1), a huge amount of carbon was
released into the atmosphere, most likely
from methane hydrates (frozen meth-
ane) from the deep sea floor. The result-
ing ocean acidification caused a huge mass
extinction of deep-sea organisms (partic-
ularly foraminifera) as well as many land
species. According to James Zachos and as-
sociates, the atmosphere and oceans took
100,000 years to recover from that change
in climate. Its impact on shallow water or-
ganisms is, however, much less clear. Many
species of shallow-water calcareous marine
organisms survived the petm, possibly be-
cause the weathering of rocks on land in a
high- CO
2
atmosphere produced low-acidity
river water that flowed into the broad, shal-
low seas of that time, counteracting the
acidification caused by high CO
2
in the
atmosphere.
The petm events of millions of years ago
(and others in the geologic past) played out
very slowly, and as a consequence it is diffi-
cult to draw helpful lessons for today's very
rapidly moving acidification crisis. It may
be that the current rate of CO
2
addition to
ocean waters will be a rare event in geologic
history. There is a significant chance that
this time acidification will affect the entire
ocean water column, not just deep water as
in the petm event.
