Melting Antarctic Ice Sheet
Is a “Sleeping Giant”
Victoria University of Wellington scientist have warned of
massive sea level rises if carbon dioxide levels in the atmosphere
continue increasing, as predicted, causing the giant East Antarctic
ice sheet to melt.
“Our study shows that this ice sheet becomes unstable and
melts if carbon dioxide levels in the atmosphere reach 600 parts
per million – levels which may be reached by the end of the
century if emissions reductions targets agreed to recently in Paris
are not met,” says Prof Tim Naish. “If the Antarctic ice sheet
completely melted, global sea level would rise about 60 metres.
It’s a sleeping giant.”
The research, published inScience(tinyurl.com/ha69e5g),
is based on geological drill cores taken from the Ross Sea near New
Zealand’s Scott Base. “The drill cores show that the irst Antarctic
ice sheet was quite dynamic. It advanced and retreated many times
between 34–35 million years ago before inally stabilising at its
largest extent when atmospheric carbon dioxide levels dropped
below a threshold of 600 parts per million,” Nash says.
Carbon dioxide levels are currently 400 parts per million and
are predicted to increase. Last year alone they rose by more than
3 ppm.
“We know that parts of the ice sheet sitting below sea-level in
West Antarctica are already melting in response to current global
warming, but the much larger East Antarctic ice sheet, which sits
mostly on rock above sea level, was thought to be more stable,”
Naish says. “We found it is vulnerable, and was much smaller the
last time atmospheric carbon dioxide levels matched those predicted
before the end of the century.”
The research also provides the irst direct evidence that ice
expanded all the way to the coast and out into the ocean, causing
erosion of the seabed.
APRIL 2016|| 7
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The Silence of the Shrimp
The loudest invertebrates in the ocean, snapping shrimps, may be
silenced as the oceans become more acidic due to high levels of
CO 2 , a University of Adelaide study has found.
Ocean acidiication is expected to have profound consequences
for many species that rely on sound cues for information about
the location and quality of food, shelter, partners and potential
predators.
“Shrimp ‘choruses’ can be heard kilometres offshore, and are
important because they can aid the navigation of baby ish to their
homes,” says PhD candidate Tullio Ross. “Ocean acidiication is
jeopardising this process.”
The snapping shrimp are the most common and noisiest of the
sound-producing marine animals in coastal ecosystems
(tinyurl.com/hljjhgx). They can produce sounds of up to 210 dB
through the formation of bubbles created by rapidly closing their
snapping claw as a warning sign to scare off predators.
Rossi and supervisors A/Prof Ivan Nagelkerken and Prof Sean
Connell measured the sound produced by shrimp in ield record-
ings at natural CO 2 volcanic vents at three different ocean locations
and under laboratory conditions. They found substantial reductions
in both the levels of sound produced and in the frequency of snaps.
The results were published in the Proceedings of the Royal Society
B (tinyurl.com/jt8z8sv)
“Our results suggest that this is caused by a change of behaviour
rather than any physical impairment of the claw,” Nagelkerken
says. “This outcome is quite disturbing. Sound is one of the most
reliable directional cues in the ocean because it can carry up to
thousands of kilometres with little change, whereas visual cues and
scents are affected by light, water clarity and turbulence.
“If human carbon emissions continue unabated, the resulting
ocean acidiication will turn our currently lively, noisy reefs into
relatively silent habitats. And given the important role of natural
sounds for animals in marine ecosystems, that’s not good news for
the health of our oceans.”
Compiled by Guy Nolch
karenfoleyphoto/adobe
