Archivi tag: seawater

World’s oceans turn acidic fastest in 300 mln years

CLIMATE-OCEANS/ACID
Oceans’ acidic shift may be fastest in 300 mln years
* Study finds prehistoric clues about climate change impact
* Acid waters could endanger oysters, mussels, salmon
* Few parallels seen in 300-million-year record

WASHINGTON, March 1 (Reuters) – The world’s oceans are
turning acidic at what could be the fastest pace of any time in
the past 300 million years, even more rapidly than during a
monster emission of planet-warming carbon 56 million years ago,
scientists said on Thursday.
Looking back at that bygone warm period in Earth’s history
could offer help in forecasting the impact of human-spurred
climate change, researchers said of a review of hundreds of
studies of ancient climate records published in the journal
Science.
Quickly acidifying seawater eats away at coral reefs, which
provide habitat for other animals and plants, and makes it
harder for mussels and oysters to form protective shells. It can
also interfere with small organisms that feed commercial fish
like salmon.
The phenomenon has been a top concern of Jane Lubchenco, the
head of the U.S. National Oceanic and Atmospheric
Administration, who has conducted demonstrations about
acidification during hearings in the U.S. Congress.
Oceans get more acidic when more carbon gets into the
atmosphere. In pre-industrial times, that occurred periodically
in natural pulses of carbon that also pushed up global
temperatures, the scientists wrote.
Human activities, including the burning of fossil fuels,
have increased the level of atmospheric carbon to 392 parts per
million from about 280 parts per million at the start of the
industrial revolution. Carbon dioxide is one of several
heat-trapping gases that contribute to global warming.
To figure out what ocean acidification might have done in
the prehistoric past, 21 researchers from the United States, the
United Kingdom, the Netherlands, Germany and Spain reviewed
studies of the geological record going back 300 million years,
looking for signs of climate disruption.
Those indications of climate change included mass extinction
events, where substantial percentages of living things on Earth
died off, such as the giant asteroid strike thought to have
killed the dinosaurs some 65 million years ago.
The events that seemed similar to what is happening now
included mass extinctions about 252 million and 201 million
years ago, as well as the warming period 56 million years in the
past.
The researchers reckoned the 5,000-year hot spell 56 million
years ago, likely due to factors like massive volcanism, was the
closest parallel to current conditions at any time in the 300
million years.
To detect that, they looked at a layer of brown mud buried
under the Southern Ocean off Antarctica. Sandwiched between
layers of white plankton fossils, the brown mud indicated an
ocean so acidic that the plankton fossils from that particular
5,000-year period dissolved into muck.
During that span, the amount of carbon in the atmosphere
doubled and average temperatures rose by 10.8 degrees F (6
degrees C), the researchers said. The oceans became more acidic
by about 0.4 unit on the 14-point pH scale over that 5,000-year
period, the researchers said.
That is a fast warm-up and a quick acidification, but it is
small compared with what has happened on Earth since the start
of the industrial revolution some 150 years ago, study author
Baerbel Hoenisch of Columbia University’s Lamont-Doherty Earth
Observatory said by telephone.

EXTINCTIONS ON THE SEAFLOOR
During the warming period 56 million years ago, known as the
Paleocene-Eocene Thermal Maximum, or PETM, and occurring about 9
million years after the extinction of the dinosaurs,
acidification for each century was about .008 unit on the pH
scale, Hoenisch said.
Back then, many corals went extinct, as did many types of
single-celled organisms that lived on the sea floor, which
suggests other plants and animals higher on the food chain died
out too, researchers said.
By contrast, in the 20th century, oceans acidified by .1
unit of pH, and are projected to get more acidic at the rate of
.2 or .3 pH by the year 2100, according to the study.
The U.N. Intergovernmental Panel on Climate Change projects
world temperatures could rise by 3.2 to 7 degrees F (1.8 to 4
degrees C) this century.
“Given that the rate of change was an order of magnitude
smaller (in the PETM) compared to what we’re doing today, and
still there were these big ecosystem changes, that gives us
concern for what is going to happen in the future,” Hoenisch
said.
Those skeptical of human-caused climate change often point
to past warming periods caused by natural events as evidence
that the current warming trend is not a result of human
activities. Hoenisch noted that natural causes such as massive
volcanism were probably responsible for the PETM.
She said, however, that the rate of warming and
acidification was much more gradual then, over the course of
five millennia compared with one century.
Richard Feely, an oceanographer at the U.S. National Oceanic
and Atmospheric Administration who was not involved in the
study, said looking at that distant past was a good way to
foresee the future.
“These studies give you a sense of the timing involved in
past ocean acidification events – they did not happen quickly,”
Feely said in a statement. “The decisions we make over the next
few decades could have significant implications on a geologic
timescale.”

(Editing by Peter Cooney)
REUTERS


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