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Iodine distribution in the Australian sector of the Southern Ocean and its relation to new production and water masses

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Brandão, Ana Cláudia(Ana Cláudia Moreira) (2001) Iodine distribution in the Australian sector of the Southern Ocean and its relation to new production and water masses. PhD thesis, University of Tasmania.

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Abstract

The distribution of iodate and iodide was studied in seawaters from the Australian
sector of the Southern Ocean and Antarctic coastal waters. Most samples were
collected along the WOCE repeat section SR3, from Tasmania to Antarctica, during
one winter and two summer cruises. Two other transects were also sampled, the
WOCE S4 (Australian sector) and the Princess Elizabeth Trough. Iodide was
determined directly by matrix-elimination ion chromatography with post-column
reaction detection using a new method developed for this work. The detection limit
of the method was about 6 nM, with a relative standard deviation better than 4 % at
40 nM (n=5).
Iodate concentration in surface waters increased from Tasmania to Antarctica, with
the most dramatic increase occurring along the Subtropical Front, which separates
Subtropical from Subantarctic waters at approximately 46°S. Iodide concentration in
surface waters showed the opposite trend. Iodide concentration in Antarctic surface
waters during summer was below 40 nM, with the lowest measured surface
concentration of 15 nM, one of the lowest ever recorded for the region. This was the
first iodine study ever conducted in the Australian Sector of the Southern Ocean that
included samples from Subtropical, Subantarctic and Antarctic regions.
Along the SR3 transect, iodate concentration in surface waters decreased from winter
(July) to summer (January), presumably due to biological uptake. Differences in
iodide concentration during the same period were not observed. Depth-integrated
average iodate depletion in surface waters from winter to summer varied from
0.08 mmol m-2 in the Antarctic Zone north of the 64°S to 2.5 mmol m-2 in the
Subtropical Zone. Annual differences were also noticed. As iodate showed good
correlation with nitrate in surface waters, depth-integrated iodate depletion was
related to carbon production and used, for the first time, to estimate seasonal primary
production in different zones within the Southern Ocean. Average estimated seasonal
production values estimated from iodate depletion from July to January were:
3,684 mmol C m-2 for the Subantarctic Zone, 696 mmol C m-2 for the Polar Frontal
Zone, 496 mmol C m-2 for the Antarctic Zone north of 64°S, and 2,659 mmol C m-2
for the Antarctic Zone south of 64°S. These values are within ranges found in the
literature.
Iodate concentration generally increased from the surface to deep waters. South of
60°S, however, a decrease in iodate concentration below 1000-m depth was also
observed. This decrease is reported here for the first time and was related to the
presence of Antarctic Bottom Water (AABW). Iodate concentration in AABW
appeared to be significantly smaller than iodate concentration in the Circumpolar
Deep Water above and it is suggested that iodate could perhaps be used as an
independent tracer of AABW inside the Australian Antarctic Basin.

Item Type: Thesis (PhD)
Keywords: Iodine compounds, Seawater, Seawater, Ocean circulation
Copyright Holders: The Author
Copyright Information:

Copyright 2001 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 2001. Includes bibliographical references

Date Deposited: 25 Nov 2014 00:50
Last Modified: 21 Jun 2016 01:21
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