1
October 2008 Dissolved iron distributions
in the full-water column along the SR3 transect
between Tasmania and Antarctica (Bowie et
al., unpublished data). The surface waters
of the vast Southern Ocean are suffering
from 'marine anaemia' – a serious deficiency
in the micronutrient iron. Just as iron
deficiency negatively affects the health
and productivity of humans and other land-based
creatures, so it affects the phytoplankton
(microscopic marine plants) existing in
the oceanic realm.
The environmental consequences
of this condition restrict primary production
(photosynthesis) in the surface waters of
the ocean. This means that less carbon dioxide
is taken up from the atmosphere to fuel
phytoplankton growth. The smaller the transfer
of this greenhouse gas is from air to sea,
the greater are the consequences for Earth's
climate. It is the sequestering of carbon
dioxide in the deeper ocean and deep-sea
sediments that provides a natural contribution
to solving the problem.
During the International
Polar Year (IPY), teams of international
scientists on several research ships are
investigating iron and other trace element
micronutrients (such as zinc, cobalt, aluminium,
copper and manganese) in cold, high-latitude
waters around both poles. The research aims
to understand the distribution and cycling
of these important micronutrients, how they
are supplied to the ocean, and how they
affect the different phytoplankton communities
in polar waters of both Hemispheres.
This cooperative program
– the IPY-GEOTRACES Bipolar project – is
supported by GEOTRACES, a new decade-long
global science program focusing on trace
elements in the oceans.
Southern Ocean transects
occupied during the International Polar
Year – GEOTRACES Bipolar project by Australian
(SR3), French (Bonus-Good Hope), German
(Zero & Drake) and United States (I6S)
research vessels.
Under IPY-GEOTRACES,
research voyages are being run along key
transects in the Southern Ocean – the 'choke
points' for the Antarctic Circumpolar Current,
where land masses impinge on this massive
radial circulation. German and Dutch scientists
on Polarstern recently surveyed along the
'Zero Meridian' (0º longitude), then
back northward across the Strait of Magellan,
through the Drake Passage and along the
South American coast ('Zero & Drake').
French and Belgian scientists on Marion
Dufresne made a voyage ('Bonus-Good Hope')
out of Cape Town, South Africa, which ran
diagonally across to the Zero Meridian,
then overlapped the track of Polarstern
to the coast of Antarctica and returned
to Durban. Concurrently, US scientists followed
a transect line south of Africa ('I6S'),
at approximately 30oE.
In March-April this
year, an Australian-led voyage aboard Aurora
Australis, organised by the Antarctic Climate
and Ecosystems Cooperative Research Centre,
followed the 'SR3' transect along approximately
140°E, between Tasmania and the coast
of Antarctica. This transect has been well
characterised oceanographically in the past
two decades (Australian Antarctic Magazine
8: 4). Scientists gathered samples with
great care, to prevent contamination from
the water column, at each degree of latitude
along this north-south transect. Some trace
elements (such as iron and mercury) were
measured directly using ship-board instrumentation.
Others, in their various forms, will be
analysed in laboratories later. A high volume
aerosol sampler was also deployed to measure
the concentration of dust in the atmosphere,
since dust blown from continental land masses
is likely to be the main source of iron
in the remote ocean south of Australia.
The results of this
work will yield the first synoptic, circumpolar
measurements of micronutrient trace elements
in the Southern Ocean. Dissolved iron data
along the SR3 transect represent an order
of magnitude improvement in sampling resolution
and show widespread iron limitation in upper
ocean waters along the transect. These and
related observations promise to reveal important
information concerning primary production
in this region, phytoplankton community
structure, and ultimately, a better understanding
of the important regulators of climate change.
Through this and similar projects, scientists
are beginning to learn how the functioning
of Southern Ocean ecosystems is constrained
by the small 'cogs and gears' of iron and
other trace element micronutrients.
