Rate of Ocean Acidification Unprecedented in 65 Million Years: Study
Rate of ocean acidification the fastest in 65 million years
Physorg.com, Feb, 16, 2010
(PhysOrg.com)
-- A new model, capable of assessing the rate at which the oceans are
acidifying, suggests that changes in the carbonate chemistry of the
deep ocean may exceed anything seen in the past 65 million years.
The
model also predicts much higher rates of environmental change at the
ocean’s surface in the future than have occurred in the past,
potentially exceeding the rate at which plankton can adapt.
The research, from the University of Bristol, is reported in this week's issue of Nature Geoscience.
The
team applied a model that compared current rates of ocean acidification
with the greenhouse event at the Paleocene-Eocene boundary, about 55
million years ago when surface ocean temperatures rose by around 5-6°C
over a few thousand years. During this event, no catastrophe is seen in
surface ecosystems, such as plankton, yet bottom-dwelling organisms in
the deep ocean experienced a major extinction.
Dr
Andy Ridgwell, lead author on the paper, said: “Unlike surface plankton
dwelling in a variable habitat, organisms living deep down on the ocean
floor are adapted to much more stable conditions. A rapid and severe
geochemical change in their environment would make their survival
precarious.
“The
widespread extinction of these ocean floor organisms during the
Paleocene-Eocene greenhouse warming and acidification event tells us
that similar extinctions in the future are possible.”
The
oceans are currently absorbing about a quarter of the CO2 released into
the atmosphere, forcing the pH of the surface ocean lower in a process
called ‘ocean acidification’.
Laboratory
experiments suggest that if the pH continues to fall, we may start to
see impacts such as the dissolution of carbonate shells of marine
organisms, slower growth, muscle wastage, dwarfism or reduced activity,
with knock-on effects throughout the ecosystem.
Dr
Daniela Schmidt, also an author on the paper, explained: “Laboratory
experiments can tell us about how marine organisms react, but
experiments cannot tell us whether marine organisms will be able to
adapt to ocean acidification via migration or evolution.
“Therefore,
a lot of attention has recently focussed on looking at known ocean
acidification and biotic reactions in the geological record. Various
types of geological evidence - the spread of warm water organisms
towards the poles and the dissolution of carbonate sediments on the
sea-floor tell us there was simultaneously both extreme warming and
acidification at this time - the hallmark of a massive greenhouse gas
release.”
On
the basis of their approach of comparing model simulations of past and
future marine geochemical changes, the authors infer a future rate of
surface-ocean acidification and environmental pressure on marine
calcifiers, such as corals, unprecedented in the past 65 million years,
and one that challenges the potential for plankton to adapt.
They
also argue that for organisms which live on the sea floor, rapid and
extreme acidification of the deep ocean would make their situation
uncertain. The occurrence of widespread extinction of these organisms
during the Paleocene-Eocenegreenhouse warming and acidification event
raises the possibility of a similar extinction in the future.
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