This is a pretty extraordinary claim and it may well be a primary
climate driver. The waxing and waning of the density factor is on
the time scales that appears to be rapid enough to explain the long
cycle changes that can be seen in the climatic record.
I was looking for a switch able to produce a thousand year cycle.
This is actually a good candidate. It certainly appears up to the
forty year cycle that we see in the hurricane record.
It certainly not a marginal effect that is dragooned into explaining
some pet theory.
What we do know for certain in relation to climate change is that a
major volcano or a cascade of volcanoes can have a devastating impact
on the global climate and bring temperatures down sharply.
So far there is little in global warming to get alarmed about except
to note that we are presently lucky.
Latest Southern
Ocean research shows continuing deep ocean change
by Staff Writers
Canberra, Australia (SPX) May 25, 2012
Deploying a mooring
carrying a suite of monitoring sensors into the sea ice. Credit:
Steve Rintoul.
Comparing detailed
measurements taken during the Australian Antarctic program's
2012 SouthernOcean marine science voyage to historical data
dating back to 1970, scientists estimate there has been as much
as a 60 per cent reduction in the volume of Antarctic Bottom Water,
the cold dense water that drives global ocean currents.
In an intensive and
arduous 25-day observing program, temperature and salinity samples
were collected at 77 sites between Antarctica and Fremantle. Such
ship transects provide the only means to detect changes in the deep
ocean.
The new measurements,
which have not yet been published, suggest the densest waters in the
world ocean are gradually disappearing and being replaced by less
dense waters.
"The amount of
dense Antarctic Bottom Water has contracted each time we've measured
it since the 1970s," said Dr Steve Rintoul, of CSIRO and
the Antarctic Climate and Ecosystems CRC. "There
is now only about 40 per cent as much dense water present as observed
in 1970."
The ocean profiles
also show that the dense water formed around Antarctica has become
less saline since 1970.
"It's a clear
signal to us that the oceans are responding rapidly to variations in
climate in polar regions. The sinking of dense water around
Antarctica is part of a global pattern of ocean currents that has a
strong influence on climate, so evidence that these waters are
changing is important," Dr Rintoul said.
The research was
carried out by more than 50 scientists on
the AustralianAntarctic Division's research and
resupply vessel Aurora Australis, which sailed to Commonwealth Bay,
west along the Antarctic coast, and returned into Fremantle.
The Australian
Antarctic Division's Chief Scientist, Dr Nick Gales, said the
findings of the oceanographic study are profoundly important.
"Not only will
this research improve our understanding of ocean currents, but will
also feed into our knowledge of how the Southern Ocean and the
Antarctic continent drives the world's climate processes," Dr
Gales said.
Dr Rintoul was Chief
Scientist on the recent voyage and has made a dozen voyages to the
Southern Ocean. "When we speak of global warming, we really
mean ocean warming: more than 90 per cent of the extra heat
energy stored by the earth over the last 50 years has gone into
warming up the ocean.
The Southern Ocean is
particularly important because it stores more heat and carbon dioxide
released by human activities than any other region, and so helps to
slow the rate of climate change" Dr Rintoul said. "A key
goal of our work is to determine if the Southern Ocean will continue
to play this role in the future."
The causes of the
observed changes in the Southern Ocean are not yet fully understood.
Changes in winds, sea ice, precipitation, or melt of floating glacial
ice around the edge of Antarctica may be responsible. Data collected
on the latest voyage will help unravel this mystery.
A major challenge is
the lack of observations at high latitude, where much of the ocean is
covered by sea ice in winter. During the voyage scientists deployed
nine drifting profilers, called Argo floats, which will transmit
profiles of temperature and salinity every 10 days for the next five
years. These ice-capable floats in the seasonal ice zone in the
Australian sector of the Southern Ocean are funded through
Australia's Integrated Marine Observing System.
"The Argo floats
have revolutionised our ability to measure the ocean, particularly in
winter when ship observations are very rare," said Dr Rintoul.
"On this voyage, we deployed a new kind of float designed to
survive encounters with the sea ice. These floats will allow us to
see how dense water forms in winter for the first time."
The Aurora Australis
visited Commonwealth Bay as part of a celebration of the centenary of
Sir Douglas Mawson's Australian Antarctic Expedition. Dr Rintoul's
team had the opportunity to repeat oceanographic measurements made by
Mawson's team 100 years ago, obtaining one of the few century-long
records obtained anywhere in the ocean.
"Our measurements
collected in 2012 are quite different to those collected by Mawson in
1912," Dr Rintoul said. "This is an indication of
a change inthe ocean currents that may be related
to a reduction in the amount of dense water formed near Antarctica."
"Mawson's
expedition really marked the transition from the "Heroic Age"
of Antarctic exploration to a period where science was the primary
motivation for Antarctic expeditions. I think he would have gotten a
real kick out of the idea that measurements made by his team a
century ago are still useful and that Australian scientists are
continuing his legacy by studying Antarctica and its connection to
the rest of the globe."
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