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Ice boat details ozone collapse
The
dramatic springtime collapse of surface ozone in the Arctic has been
documented by scientists.Observations from a boat that drifted with the
ice across the North Pole show the gas can disappear in just days.Dr
Jan Bottenheim told a US conference that the precise chemical reactions
involved were not fully understood.However, he said any changes to
these processes as the Arctic warmed might limit the region’s ability
to deal with pollutants in the atmosphere.”Ozone is the source for the
‘vacuum cleaner of the atmosphere’ – the molecule OH. So if we don’t
have as much ozone, we can’t make as much hydroxide. If we then pump
pollutants from mid-latitudes into the Arctic, they may just stay
there,” explained Dr Bottenheim.”But a lot of this is speculation at
the moment because so much of this information is new and we are not
sure what to make of it.”Spring sunshine
The ozone studied
by Dr Bottenheim and colleagues at Environment Canada is distinct from
the gas high up in the stratosphere that has been damaged through the
release of reactive chlorine compounds by industrial society. The
group’s ozone exists at ground level – or, in the case of the Arctic,
at ice level – in the first 100-200m of air.In the winter, the
concentration of the three-atom oxygen-molecule in this still air is at
normal levels; but as the sunlight returns to the polar north in the
spring, chemical reactions are set in train that reduce the ozone in
dramatic fashion.Dr Bottenheim told BBC News: “In a city, in the
evening the ozone will react with exhausts from cars and can go down
from, say, 40 to five or even one [units of ozone]; but in the Arctic
we’ve seen it go to 100 times less than one, which is an incredibly low
level that I don’t think has been seen anywhere else.”And once it goes,
it can go very fast. It can go in almost a day.”Ice changes
The
ozone instrument on the Tara schooner observed one period in late April
of this year when there was virtually no ozone for a period of more
than 15 days.Whereas stratospheric ozone is depleted though an
unnatural process involving chlorine; the ice-level ozone falls victim
to reactive bromine atoms released quite naturally from briny Arctic
waters. In perfect conditions, the chemistry produces an explosion of
bromine oxide (BrO), which is detectable by over-flying
satellites.Scientists are now trying to determine how the ozone
behaviour might change in a rapidly warming Arctic.Conditions that lead
to more slushy ice, which could assist the release of bromine, might
result in more extensive periods of ozone loss.”It’s a possibility, but
as I say this is still speculative,” stressed Dr Bottenheim.The
consequences of any change needed to be understood, he added. It is
known from observations, for example, that the depletion of ozone at
the same time also causes a depletion of gaseous mercury, a major toxic
chemical.The ozone study is just one of a number of fascinating
outcomes from the Tara expedition. The boat was originally owned by a
private French company but was donated to the European research
community.
TARA ARCTIC DRIFT EXPEDITION
The 36m, 130-tonne boat is currently locked in ice
The schooner provides habitation for about 10 people
Scientists deploy and monitor a number of instruments
Experiments study air, ice and ocean behaviour
It
is a key project in Damocles (Developing Arctic Modelling and Observing
Capabilities for Long-term Environmental Studies), a European-led
effort to gather much needed new information on the changing Arctic.The
two-masted vessel was sailed into the pack-ice in September 2006 and
allowed to drift with the ocean currents and wind – but it has moved
further, faster than anyone expected.”The boat is full of sensors to
monitor the ocean, the atmosphere and the ice. It also serves as a
logistics platform for Damocles to put observational beacons all around
the Arctic,” explained Christian de Marliave, Tara’s scientific
director.”When you are on a boat at least you are floating. This is a
big security. More and more I think, it will be a ship that will be
used as an ice camp. It’s become very dangerous. This year, the
Russians were unable to find ice thick enough to place their camps.”Quick release
Tara
is approaching the edge of the pack-ice and is likely to emerge into
the open ocean between Greenland and Svalbard in the next few
weeks.With just over half of International Polar Year (IPY) still left
to run, Tara is likely to be sent to the Bering Strait to study how
warm waters from the Pacific are entering the Arctic Ocean and
contributing to ice shrinkage.Dr Dave Carlson, the director of IPY,
said the Tara platform had provided many remarkable insights during its
15-month drift.He has been taken by its observations of “frazil
ice”.”We think of ice as forming at the interface of ocean and
atmosphere, but Tara has seen a lot of this ice that foams 20m down and
then floats up to the surface.”You can think of it as a reverse
snowfall – crystals that form at depth and then make their way to the
surface because of their density. It tells us the layers in the ocean
don’t work in quite the way we thought they did.”
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