Hobart

Seminar Abstract

Wednesday 18 November 2009, 11.30am (Tas time)
CSIRO Auditorium, Hobart

Nicolas Cassar
CSIRO Frohlich Fellow
Geosciences, Princeton University, and
Earth and Ocean Sciences, Duke University

Net community productivity during the SAZ Sense campaign: Controls on carbon export production in the Australian Subantarctic zone

We present data on gross primary production and net community production in the Subantarctic Zone south of Australia, determined as a collaboration with the SAZ-SENSE program (Austral summer of 2007 on Aurora Australis). Gross O2 production in the mixed layer was determined by measuring the triple isotope composition of dissolved O2, which gives an index of the fraction of dissolved O2 derived in situ from photosynthesis. Net community production was calculated from continuous measurements of the mixed layer O2/Ar ratio, which gives an index of biological O2 supersaturation. As carbon is not stored in the summertime mixed layer, NCP mostly sinks out, and NCP approximates carbon export. Ratios of NCP/GPP scattered about a value of 0.2 (corresponding to a carbon f-ratio of 0.4), similar to other regions of the Southern Ocean. NCP was highest just south of the subtropical front, likely due to the mixing of iron-rich subtropical waters with N- and P-replete subpolar waters. Productivities decreased to the south, presumably reflecting increasing iron limitation going away from aerosol and shelf sources. Controls on production were investigated by comparing GPP and NCP with extensive measurements of complementary physical and biogeochemical properties. Evidence for light limitation comes from the fact that productivities were much higher when mixed layer depths were shallower than 50 m than when they were deeper. Evidence for a link between iron and production comes from the fact that NCP increases with increasing variable fluorescence when comparing these properties for samples with MLD shallower than 50 m. Pigments were measured and used to deduce the abundance of phytoplankton groups by Chemtax analysis. The results show that there is no relationship between the abundance of diatoms and regions of high export production.

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Location:
CSIRO = Marine Laboratories Auditorium, Castray Esplanade, Hobart

For further information, or to schedule a seminar, contact:
To schedule a seminar, contact:
Clothilde Langlais, (Oceanographic seminars) CSIRO Marine and Atmospheric Research (03) 6232 5399
Natalie Kelly, (Biology/Modelling seminars) CSIRO Marine and Atmospheric Research 0438 452 483
Jillian Enraght-Moony, (seminar administrator) CSIRO Marine and Atmospheric Research (03) 6232 5320
Communications Manager, Antarctic Climate and Ecosystems CRC (03) 6226 2265
Margaret Hazelwood, Institute of Antarctic and Southern Ocean Studies (IASOS) University of Tasmania (03) 6226 2971

Last updated 24/11/09