How will climate change impact the oceans? 02:10
(CNN)Climate
change is extending far beyond the threat of melting polar ice caps --
it's putting a dangerous stranglehold on life in oceans, too.
A new study published in the science journal Nature Wednesday found that the ocean's worldwide oxygen content declined by more than 2% between 1960 and 2010.
Scientists
have long warned about the potentially deadly consequences of the
ocean's declining oxygen levels on marine life, and its resulting impact
on humans.
The study came from the GEOMAR Helmholtz Centre for Ocean Research
in Kiel, Germany, where the three co-authors -- Sunke Schmidtko, Lothar
Stramma and Martin Visbeck -- pulled data dating back to 1960.
Using
information on oxygen, temperature and other factors relating to the
world's oceans, they mapped it around the globe and estimated the
overall oxygen loss.
"We
were able to document the oxygen distribution and its changes for the
entire ocean for the first time. These numbers are an essential
prerequisite for improving forecasts for the ocean of the future," wrote
Schmidtko.
Where bacteria thrives
While
2% may sound like only a small change, it doesn't take much of a drop
to threaten the state of oceans. The only organism in the ocean that
thrives with little-to-no oxygen is bacteria.
"Just
a little loss of oxygen in coastal waters can lead to a complete change
in ecosystems -- a small decrease in oxygen like this can transform
from something desirable to very undesirable," said David Baker,
Assistant Professor at the University of Hong Kong's Swire Institute of
Marine Sciences.
Oxygen in the
world's oceans is not evenly distributed, and the 2% drop represents
just an average of all the globe's oceans together.
In
some parts of the world, there has been a much steeper decline of
oxygen levels over the past five decades -- for example, in the North
Pacific, where the largest volume of oxygen was lost. The largest
percentage was lost in the Arctic Ocean.
"The
oxygen losses in the ocean can have far-reaching consequences because
of the uneven distribution. For fisheries and coastal economies this
process may have detrimental consequences," wrote Stramma.
Chinese residents collect seaweed by the coastline in Qingdao after a break-out of algae bloom, May 27, 2012.
Climate change
The ocean's oxygen depletion, the study shows, is mostly a result of climate change.
One
driving factor, the authors found, is as simple as warming temperatures
-- like a warm can of Coke that can't hold fizz, warm ocean water has
difficulty holding oxygen. But this only accounts for 15% of the oxygen
depletion.
What also causes oxygen
depletion, again driven by climate change, is that the ocean is becoming
more stratified. This is a result of changing temperature gradients in
the Arctic, and the reduction of sea ice.
Oxygen
enters the water at the surface, but as that surface layer gets warmer,
it's less likely to sink to the oxygen-starved layers below.
"It's
almost like the oceans are getting ready for a heart attack," said
Baker. "You're essentially slowing the heartbeat of the ocean, and
you're getting less oxygen to the ocean."
The
study finds that the reduction of sea ice has led to more plankton
growth -- and with more plankton growth comes more plankton
decomposition. Decomposition decreases oxygen levels even further.
So-called
"dead zones" -- low-oxygen areas in the ocean's shallow waters -- are
also multiplying along the shore, the study finds.
Fish
can't thrive there -- a dangerous threat to both the ecosystem and the
economy -- but that's not the only problem. These areas are pumping out a
harmful greenhouse gas called nitrous oxide -- "the evil counterpart to
carbon dioxide," as Baker puts it.
'Far-reaching implications'
Nitrous
oxide is potent. It lasts in the atmosphere a long time and contributes
to global warming -- meaning that the effects of climate change on the
world's oceans causes more global warming, in turn.
The
study's authors end their report on a pessimistic note, writing that
"far-reaching implications for marine ecosystems and fisheries can be
expected."
While Baker said that
the world is edging closer to solving the carbon dioxide problem, it's
barely scratched the surface when it comes to the issue of nitrous
oxide.
He said that there's little
hope in addressing this in a timely way unless people commit to
addressing problems that are quickly becoming cliché, like consuming
less and recycling more.
"The
oceans are really a mirror of human health -- if they're sick and dying,
then that's the future of humanity as well," said Baker.
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