Mesoscale surface distribution of biogeochemical characteristics in the Crozet Basin frontal zones (South Indian Ocean)
| Type | Article | ||||||||
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| Date | 2003 | ||||||||
| Language | English | ||||||||
| Author(s) | Fiala M1, Delille B2, Dubreuil C3, Kopczynska E4, Leblanc K3, Morvan J5, Queguiner B3, Blain S6, Cailliau C6, Conan P1, Corvaisier R6, Denis M3, Frankignoulle M2, Oriol L1, Roy S3 | ||||||||
| Affiliation(s) | 1 : Univ Paris 06, UMR CNRS 7621, Lab Arago, F-66651 Banyuls sur Mer, France. 2 : Univ Liege, Inst Phys, Unite Oceanog Chim, B-4000 Sart Tilman Par Liege, Belgium. 3 : Univ Mediterranee, UMR CNRS 6535, Lab Oceanog & Biogeochim, F-13288 Marseille 9, France. 4 : Polish Acad Sci, Dept Antarctic Biol, PL-02141 Warsaw, Poland. 5 : Ecole Natl Super Chim Rennes, F-35700 Rennes, France. 6 : Univ Bretagne Occidentale, Inst Univ Europeen Mer, UMR CNRS 6539, Lab Sci Environm Marin, F-29280 Plouzane, France. |
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| Source | Marine Ecology Progress Series (0171-8630) (Inter-research), 2003 , Vol. 249 , P. 1-14 | ||||||||
| DOI | 10.3354/meps249001 | ||||||||
| WOS© Times Cited | 14 | ||||||||
| Keyword(s) | frontal zones, nutrients, biogenic silica, chlorophyll a, pCO(2), phytoplankton, bacteria | ||||||||
| Abstract | 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. | ||||||||
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