If you happen to be skeptical of climate modeling, this makes it a
rout. A powerful nonlinear effect is dynamically responsible for
injecting 40 % of the oceanic CO2 into the deep. Ignoring this is
akin to ignoring tornadoes and we have just discovered it. The real
problem is that we need a really good three dimensional dynamic model
of the Ocean. From that it becomes plausible to model the overlying
atmosphere. Perhaps one day we will be able to track and follow the
heat.
Otherwise we naturally fall into the error of assuming the atmosphere
is the dominant driver. A little like describing cooking and
forgetting the role of the heat source. On Earth we have two heat
sources. One is the sun and the other is the Ocean and to a far
lesser degree the land surface.
That is the principle reason that I suspect that the key driver for
the abrupt appearance of a little ice age happens to be an oceanic
current flow transition of some sort. It would only need an inversion
of cold water over the Gulf Stream for even a few years to wreak
Europe and drop the average temperature by a couple of degrees. I
can imagine it and we do not know if it is possible. More likely the
real scenario will be a complete surprise.
Giant
carbon-capturing funnels discovered in Southern Ocean
Aug 1, 2012
A team of scientists
from the UK and Australia has shed new light on the mysterious
mechanism by which the Southern Ocean sequesters carbon from the
atmosphere. Winds, vast whirlpools and ocean currents interact to
produce localized funnels up to 1000 km across, which plunge
dissolved carbon into the deep ocean and lock it away for centuries.
Critically, these processes themselves – and the Southern
Ocean's ability to affect global warming caused by human activities –
could be sensitive to climate variability in as-yet-unknown ways.
Oceans represent an
important global carbon sink, absorbing 25% of annual man-made
CO2 emissions and helping to slow the rate of climate change.
The Southern Ocean in particular is known to be a significant
oceanic sink, and accounts for 40% of all carbon entering the deep
oceans. And yet, until now, no-one could quite work out how the
carbon gets there from the surface waters.
"We thought wind
was the major player," says lead author of the new study,
Jean-Baptiste Sallée of the British Antarctic Survey. "The
ocean is like an onion – in layers – and there is very little
connection between the surface and deep layers," he explains.
When strong winds displace a large slab of surface water and cause it
to accumulate in a specific region, the localized bloat in the
surface layer gets injected downwards into the ocean's interior. But
this kind of wind action alone should have a fairly uniform effect
over vast swathes of ocean – which is not what the scientists
measured.
Subduction hotspots
Scrutinizing 10 years
of temperature, salinity and pressure data from a fleet of 80 small
robotic probes dotted around the remote Southern Ocean, the
researchers discovered that surface waters are drawn down – or
subducted – at a number of specific locations. This occurs due to
the interplay between winds, dominant currents and circular currents
known as "eddies". "You end up with a very particular
regional structure for the injection of carbon," says Sallée,
describing 1000 km-wide funnels that export carbon to the
depths.
The team pinpointed
five such zones in the Southern Ocean, including one off the southern
tip of Chile and another to the south-west of New Zealand.
Elsewhere, currents return carbon to the surface in a process known
as "reventilation", but overall, the Southern Ocean is a
net carbon sink.
Carbon bottleneck
The mechanisms
governing atmosphere-to-ocean carbon transfer – the mechanical
mixing action of wind and waves, and biological uptake by
micro-organisms in the sunlit top layer of water – are already well
understood. The step that determines the rate of the oceanic uptake
of carbon, according to co-author of the study, Richard Matear of
Australia's Commonwealth Scientific and Industrial Research
Organization, is the physical transport of this dissolved carbon from
the surface waters into the ocean interior. "Our study
identifies these pathways for the first time," he says.
Understanding these
subduction pathways fully is key to predicting how climate change
might alter the Southern Ocean's carbon sequestering capabilities.
Both global warming and the Antarctic ozone hole increase the
temperature gradient between the equator and the pole, which
intensifies the southern hemisphere winds. Climate models predict
that stronger winds could stir up deep waters, especially in violent
seas such as the Southern Ocean, and result in a net release of
carbon back into the atmosphere.
"What we don't
know yet is the impact of climate change on eddy formation,"
says Sallée. Eddies arise from oceanic instabilities caused by
extreme gusts of wind, intense surface heating or cooling, or strong
currents meeting uneven bottom topography, but tend to escape the
granularity of even the most detailed climate models. "We can
speculate that if wind increases, there will also be more eddies to
counterbalance its effects," considers Sallée. "But it's a
question we don't know how to answer yet. And it's a big incentive
for climate models to refine their grid."
Improving climate
models
Ocean-carbon-cycle
expert Corinne Le Quéré, director of the Tyndall Centre for Climate
Change Research, UK, who was not involved in the study, echoes
Sallée's call for improved understanding of wind-eddy interplay.
"Southern Ocean winds have increased in the past 15 years in
response to the depletion of stratospheric ozone," she explains,
adding "There's a lot of discussion right now about how
[wind-induced changes] are then counterbalanced by changes in
eddies."
Because of this,
today's climate models diverge when it comes to predicting the future
carbon sequestration response of the Southern Ocean. "I think
this [paper] is really the first time that we have such small-scale
resolution in the exchange of carbon in the ocean from observation
directly," says Le Quéré. "The natural next step will be
to take climate models and see how well they're performing spatially
and [temporally]...this study can really help constrain which are the
good models."
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