British
and Australia scientists discover how carbon is stored in the
Southern Ocean
A
team of British and Australian scientists has discovered how carbon
is drawn down from the surface of the Southern Ocean to the deep
waters beneath.
30 July, 2012
30
July 2012 (CSIRO) – The Southern Ocean is an important carbon sink
in the world – around 40 per cent of the annual global CO2
emissions absorbed by the world’s oceans enter through this region.
Reporting
this week in the journal Nature Geoscience, scientists from British
Antarctic Survey (BAS) and Australia’s national research agency,
the Commonwealth Scientific and Industrial Research Organisation
(CSIRO), reveal that rather than carbon being absorbed uniformly into
the deep ocean in vast areas, it is drawn down and locked away from
the atmosphere by plunging currents a thousand kilometres wide.
Winds,
currents, and massive whirlpools that carry warm and cold water
around the ocean – known as eddies – create localised pathways or
funnels for carbon to be stored.
Lead
author, Dr Jean-Baptiste Sallée from British Antarctic Survey says,
“The Southern Ocean is a large window by which the atmosphere
connects to the interior of the ocean below. Until now we didn’t
know exactly the physical processes of how carbon ends up being
stored deep in the ocean. It’s the combination of winds, currents,
and eddies that create these carbon-capturing pathways drawing waters
down into the deep ocean from the ocean surface.”
“Now
that we have an improved understanding of the mechanisms for carbon
draw-down we are better placed to understand the effects of changing
climate and future carbon absorption by the ocean.”
CSIRO
co-author, Dr Richard Matear says the rate-limiting step in the
anthropogenic carbon uptake by the ocean is the physical transport
from the surface into the ocean interior.
“Our
study identifies these pathways for the first time and this matches
well with observationally–derived estimates of carbon storage in
the ocean interior,” Dr Matear says.
Due
to the size and remote location of the Southern Ocean, scientists
have only recently been able to explore the workings of the ocean
with the help of small robotic probes – known as Argo floats. In
2002, 80 floats were deployed in the Southern Ocean to collect
information on the temperature and salinity. This unique set of
observations spanning 10 years has enabled scientists to investigate
this remote region of the world for the first time.
The
floats are just over a metre in length and dive to depths of 2km.
Today, there are over 3,000 floats in the oceans worldwide providing
detailed information used in oceanic climate models.
The
team also analysed temperature, salinity and pressure data collected
from ship-based observations since the 1990s. The instrument used for
this is called a CTD profiler which is a cluster of sensors taking
measurements as it’s lowered deep down into the ocean to depths of
more than 7km.
The
work was supported through the Wealth from Oceans and Australian
Climate Change Science Programs, and the Australian Government’s
Cooperative Research Centre program.
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