Iodine distribution in the Australian sector of the Southern Ocean and its relation to new production and water masses
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...
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| Format: | Thesis |
| Language: | English |
| Published: |
2001
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| Online Access: | https://eprints.utas.edu.au/19126/ https://eprints.utas.edu.au/19126/1/whole_BrandaoAnaClaudia2001_thesis.pdf |
| Summary: | 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. |
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