https://www.theweathernetwork.com/ca/news/article/dino-killing-asteroid-ocean-acidification-caused-mass-extinctions
[images in online article]
Ancient marine extinctions reveal dangers of current ocean acidification
Scott Sutherland
Meteorologist/Science Writer
Wednesday, October 23rd 2019, 4:00 pm - How an ancient asteroid impact
affected our oceans is highlighting the dangerous path we are on due to
carbon emissions
Sixty-six million years ago, a massive asteroid smashed into the Gulf of
Mexico, touching off a global extinction event. Scientists estimate that
up to 75 per cent of all species on Earth quickly died out following
this impact, including all species of non-avian dinosaur.
A new study, led by Michael Henehan at the GFZ German Research Centre
for Geosciences, shows how the acidification of the oceans that followed
the Chicxulub impact played a large part in this die-off.
This discovery provides insights into exactly what caused this mass
extinction event. Previous research has suggested that there was a
gradual degradation of Earth's ecosystems and gradual acidification of
ocean waters due to extensive volcanic activity leading up to the
impact. This new study, on the other hand, shows that rapid ocean
acidification only occurred directly after the meteorite strike.
"For years, people suggested there would have been a decrease in ocean
pH because the meteor impact hit sulphur-rich rocks and caused the
raining-out of sulphuric acid, but until now, no one had any direct
evidence to show this happened," Henehan said in a Yale University press
release.
Henehan and an international team of researchers found this evidence by
looking for tiny plankton fossils in sediments laid down before and
after the impact -- in cores drilled from the ocean floors and from
rocks formed at the time. The type of plankton they were looking for,
known as foraminifera, are known to grow calcium-carbonate shells, which
makes them very sensitive to ocean acidity levels.
When ocean waters have a higher pH level (more basic), growing these
shells is easy. When pH levels drop (become more acidic), their shells
are thinner or even non-existent.
One site they collected samples from, Geulhemmerberg Cave in The
Netherlands, was found to have sediments that were laid down during the
100-1000 years directly following the Chicxulub impact. In samples from
these layers, they discovered a change in the number of foraminifera
fossils that suggests a period of rapid ocean acidification that lowered
ocean pH levels by around 0.25, or more, during that time period.
"The ocean acidification we observe could easily have been the trigger
for mass extinction in the marine realm," Pincelli Hull, a senior author
of the study from Yale University, said in a statement.
With the die-off of these tiny creatures at the base of the food chain,
this contributed to the mass extinction of ocean life farther up the
food chain.
A WARNING FROM THE PAST?
With rapid ocean acidification linked to the mass extinction of life on
Earth comes a stark warning about what could happen to the planet now,
if we do not quickly end our dependence on fossil fuels.
For reference, pure, distilled water has a pH of 7.0, while in
pre-industrial times, ocean water had a pH level of around 8.1.
Since the widespread burning of fossil fuels began in the mid-1800s, the
oceans have been absorbing more and more carbon dioxide, and now take up
at least a quarter of all carbon dioxide from fossil fuel emissions.
Since carbon dioxide dissolved into ocean water produces carbonic acid,
this has resulted in a lowering of ocean pH levels to around 8.0. Much
of that acidification has taken place in just the past 70 years.
According to the latest IPCC special report The Ocean and Cryosphere in
a Changing Climate, if we continue to emit greenhouse gases at an
increasing rate, ocean pH levels are expected to drop further, reaching
around 7.75 by the end of this century. That represents a total drop in
pH of 0.35 since pre-industrial times.
"If 0.25 was enough to precipitate a mass extinction, we should be
worried," Henehan said, according to a report by The Guardian.
While ocean and atmospheric conditions were different during the time of
the Chicxulub impact, it is the overall magnitude of the changes, over
such a short amount of time, that is most important.
Life can adapt to many adverse conditions if given sufficient time. It
is the rapid time frame that these changes are taking place over that
makes them so worrying.
If a change in ocean pH of 0.25 over a few hundred to a few thousand
years following the Chicxulub impact caused such a dramatic die-off of
marine life, the projected ocean acidification we could see by 2100
could lead to a similar mass extinction.
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