MEPS 435:47-61 (2011)  -  DOI:

Efficient silicon recycling in summer in both the Polar Frontal and Subantarctic Zones of the Southern Ocean

François Fripiat1,2,*, Karine Leblanc3, Marc Elskens4, Anne-Julie Cavagna4, Leanne Armand5, Luc André1, Frank Dehairs4, Damien Cardinal1,6

1Geology and Mineralogy, Section of Mineralogy and Petrography, Royal Museum for Central Africa, 3080 Tervuren, Belgium
2Department of Earth and Environmental Sciences, Université Libre de Bruxelles, 1050 Brussels, Belgium
3Aix-Marseille Université (CNRS – LOPB), UMR 6535, Laboratoire d’Océanographie Physique et Biogéochimique, OSU/Centre d’Océanologie de Marseille, 13288 Marseille Cedex 09, France
4Earth System Sciences & Analytical and Environmental Chemistry, Vrije Universiteit Brussel, 1050 Brussels, Belgium
5Department of Biological Sciences, Faculty of Science, Macquarie University, New South Wales 2109, Australia
6Present address: Laboratoire d’Océanographie et du Climat: Expérimentations et Approches Numériques, Université Pierre & Marie Curie, 75252 Paris Cedex 05, France

ABSTRACT: We measured biogenic silica (bSiO2) dissolution and production rates at 3 Southern Ocean sites with contrasting biogeochemical regimes (SAZ-Sense cruise, January to February 2007). Two sites were located in the Subantarctic Zone (SAZ) southeast and southwest of Tasmania, and 1 site was in the Polar Frontal Zone (PFZ). The measurements were repeated 3 times within a time frame of 4 to 7 d. In the PFZ and the western SAZ, the release of silicon from dissolving bSiO2, following a productive period, appeared sufficient to entirely sustain Si demand in surface waters. Biogenic silica dissolution was more efficient in the SAZ, likely owing to stronger microzooplankton grazing and bacterial activity. The degree of iron co-limitation correlated to bSiO2 growth rates (VSi, d–1). Highest rates were observed in the SAZ, southeast of Tasmania, a region influenced by iron-enriched East Australian Current water advecting through the Subtropical Front. The diatom communities appeared differently adapted and conditioned, in terms of uptake ability, for growth under low Si(OH)4 availability. Combining our results with existing bSiO2 dissolution and production data, we estimate a spring to summer net bSiO2 production for the circumpolar SAZ and PFZ regions of 7.4 and 3.6 Tmol yr–1, respectively, representing 4.3 and 2.1% of the global net bSiO2 production for each region. Furthermore, a clear seasonal pattern emerges with (1) higher bSiO2 production in spring (0.9 to 12.7 and 6.8 to 60.7 mmol Si m–2 d–1 for the SAZ and PFZ, respectively) compared to summer (0.1 to 6.6 and 0.3 to 9.1 mmol Si m–2 d–1 for the SAZ and PFZ, respectively) and (2) a bSiO2 dissolution to production ratio of <1 in spring (~0.4) and generally >1 in summer (~1.7).

KEY WORDS: Diatoms · Biogenic silica · Silicon cycle · Dissolution · Production · Southern Ocean

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Cite this article as: Fripiat F, Leblanc K, Elskens M, Cavagna AJ and others (2011) Efficient silicon recycling in summer in both the Polar Frontal and Subantarctic Zones of the Southern Ocean. Mar Ecol Prog Ser 435:47-61.

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