New scientific study suggests ocean acidification rate ‘unparalleled’ over last 300m years
- 02 Mar 2012, 10:57
- Verity Payne
The world's oceans might be acidifying 10 times faster than at
any time during the last 300m years according to new research. And
if geological history is anything to go by, this is bad news for
Oceans can soak up excess carbon dioxide from the atmosphere.
One side effect is that the sea water, which is naturally slightly
alkaline, becomes less alkaline and more acidic - a process called
Scientists are concerned about even quite small shifts in ocean
acidity, as it can
affect how marine creatures grow their shells, which can be
crucial to their survival.
new study, published in the journal Science, researchers looked
for evidence of ocean acidification in the past, going back through
hundreds of existing studies of oceans throughout geological
They found that over the last 300m years ocean acidification has
never happened faster than it is happening now.
The only period that comes close to present acidification rates
is the Palaeo-Eocene Thermal Maximum (PETM), a
turbulent period of climate history around 56 million years ago
when large amounts of carbon were naturally released into the
atmosphere over a few tens of thousands of years. At the time, the
changes in the climate and ocean were accompanied by the extinction
of many marine species.
Over the past century carbon dioxide levels in the atmosphere
have risen by almost a third. Oceans currently take in about a quarter
of the carbon dioxide currently released from human activity.
This has led seawater pH (a measure of acidity - lower pH means
more acidic) to decrease by 0.1. This is around 10 times faster
than acidification during the PETM.
Scientists also suggest
that we are releasing carbon much faster than carbon was released
during the PETM. Study co-author Professor Andy Ridgwell,
University of Bristol,
"The geological record suggests that the
current acidification is potentially unparalleled in at least the
last 300 million years of Earth history, and raises the possibility
that we are entering an unknown territory of marine ecosystem
Since climate model projections
suggest ocean acidification could become more severe by the end
of the century, it is unlikely that any past change in
acidification can match what we might see in the future. Ridgewell
"Although similarities exist, nothing in
the last 300 million years parallels rates of future projections in
terms of the disrupting of ocean carbonate chemistry - a
consequence of the unprecedented rapidity of CO2 release currently
Such an unprecedented rate of change in seawater chemistry could
affect some important marine species. Professor Bärbel Hönisch,
paleoceanographer at Columbia University's Lamont-Doherty Earth
Observatory and lead author of the study
"What we're doing today really stands
out. We know that life during past ocean acidification events was
not wiped out-new species evolved to replace those that died off.
But if industrial carbon emissions continue at the current pace, we
may lose organisms we care about-coral reefs, oysters, salmon."
The conclusions reached in this research echo the findings of a
recent study combining observations with computer modelling
that also labelled man-made ocean acidity changes as
The video below shows how ocean acidity has changed since the
industrial revolution, and how it is projected to change in the
The animation shows how aragonite saturation (a measure of
ocean acidity) at the ocean's surface is projected to decrease
towards the end of the 21st century as man-made carbon dioxide
accumulation in the atmosphere continues to rise. Source:
Tobias Friedrich, SOEST Hawaii.