Reference : Mesoscale surface distribution of biogeochemical characteristics in the Crozet Basin fro...
Scientific journals : Article
Life sciences : Aquatic sciences & oceanology
Life sciences : Environmental sciences & ecology
Physical, chemical, mathematical & earth Sciences : Earth sciences & physical geography
Mesoscale surface distribution of biogeochemical characteristics in the Crozet Basin frontal zones (South Indian Ocean)
Fiala, M. [> > > >]
Delille, Bruno mailto [Université de Liège - ULg > Département d'astrophys., géophysique et océanographie (AGO) > Océanographie chimique >]
Dubreuil, C. [> > > >]
Kopczynska, E. [> > > >]
Leblanc, K. [> > > >]
Morvan, J. [> > > >]
Queguiner, B. [> > > >]
Blain, S. [> > > >]
Cailliau, C. [> > > >]
Conan, P. [> > > >]
Corvaisier, R. [> > > >]
Denis, M. [> > > >]
Frankignoulle, M. [> > > >]
Oriol, L. [> > > >]
Roy, S. [> > > >]
Marine Ecology. Progress Series
Oldendorf Luhe
[en] frontal zones ; nutrients ; biogenic silica ; chlorophyll a ; pCO(2) ; phytoplankton ; bacteria
[en] A mesoscale study was conducted in January and February 1999 in the Crozet Basin frontal zones (43degrees50' to 45degrees20'S, 61degrees00' to 64degrees30'E) within the southernmost and easternmost convergence area of the Antarctic Circumpolar Current (ACC) and the Agulhas Return Current (ARC). Distribution of biogeochemical parameters was strongly linked to the merged Subtropical (STF) and Subantarctic (SAF) Fronts which mark the border between the cold and less saline subantarctic waters and the warm and more saline subtropical waters. This survey took place during a post-bloom period. Chlorophyll a concentrations were low throughout the study area ranging from 0.2 mug l(-1) in the Polar Frontal Zone (PFZ) to 0.4 mug l(-1) in the Subtropical Zone (STZ). Maximum chlorophyll a values (0.8 mug l(-1)) associated with an increase in biogenic silica concentration (from 0.03 to 0.34 muM) and a diatom peak (1.2 x 10(5) cells l(-1)) were encountered in the northeastern part of the STF edge. Despite northwardly decreasing concentrations of nitrates from 14 muM in the PFZ to 6 PM in the STZ, they were not the main factor limiting phytoplankton growth. Low silicic acid (mean = 0.6 muM) could have limited diatom development in the PFZ and the STZ where diatom numbers were low. In STZ waters, where average diatom numbers were highest, various species of Nitzschia and Thalassiothrix were common, but Pseudonitzschia spp. were dominant. Throughout the survey area, pico- and nano-sized cells dominated the phytoplankton assemblage, and their number was the highest in the STZ. Cyanobacteria, only present in subtropical waters >12.5degreesC, were the major component of the picoplankton size-fraction. While dinoflagellate numbers were low in the Subantarctic Zone (SAZ), their abundance and species numbers increased in the STZ, where Oxytoxum laticeps became dominant and several further large-size species of Prorocentrum, Ceratium and Gymnodinium appeared in addition to those at the STF. The distribution of different biogeochemical parameters suggests that the Crozet Basin frontal region is a non-exporting system at the end of summer. During this post-bloom period, biological activity is low and phytoplankton growth severely limited. This is evidenced by the weak dependence of the partial pressure of carbon dioxide (pCO(2)) on biological activity and the importance of the air-sea exchange in maintaining pCO(2) close to saturation.
Unité d'Océanographie Chimique
Politique Scientifique Fédérale (Belgique) = Belgian Federal Science Policy
This work is a French contribution to the
SO-JGOFS program. It was supported by the French Polar
Institute (IPEV) and the INSU-CNRS. This research was
partly financed by the Polonium Program of scientific cooperation
between Poland and France. It was also partly conducted
under grants A4/DD/B14 and EV/12/7E within the
Scientific Research on the Antarctic supported by the Belgian
Office for Scientific, Technical and Cultural Affairs.

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