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Biogeosciences An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/bg-2018-149
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
15 May 2018
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).
Silicon cycle in the Tropical South Pacific: evidence for an active pico-sized siliceous plankton
Karine Leblanc1, Véronique Cornet1, Peggy Rimmelin-Maury2, Olivier Grosso1, Sandra Hélias-Nunige1, Camille Brunet1, Hervé Claustre3, Joséphine Ras3, Nathalie Leblond3, and Bernard Quéguiner1 1Aix-Marseille Univ., Université de Toulon, CNRS, IRD, MIO, UM110, Marseille, F-13288, France
2UMR 6539 LEMAR and UMS OSU IUEM - UBO, Université Européenne de Bretagne, Brest, France
3UPMC Univ Paris 06, UMR 7093, LOV, 06230 Villefranche-sur-mer, France
Abstract. This article presents data regarding the Si biogeochemical cycle during two oceanographic cruises conducted in the Southern Tropical Pacific (BIOSOPE and OUTPACE cruises) in 2005 and 2015. It involves the first Si stock measurements in this understudied region, encompassing various oceanic systems from New Caledonia to the Chilean upwelling between 8 and 34° S. Some of the lowest levels of biogenic silica standing stocks ever measured were found in this area, notably in the Southern Pacific Gyre, where Chlorophyll a concentrations are most depleted worldwide. Integrated biogenic silica stocks are as low as 1.08 ± 0.95 mmol m−2, and are the lowest stocks measured in the Southern Pacific. Size-fractionated biogenic silica concentrations revealed a non-negligible contribution of the pico-sized fraction (< 2–3 µm) to biogenic silica standing stocks, representing 26 ± 12 % of total biogenic silica during the OUTPACE cruise and 11 ± 9 % during the BIOSOPE cruise. These results indicate significant accumulation in this size-class, which was undocumented for in 2005, but has since then been related to Si uptake by Synechococcus cells. Our Si kinetic uptake experiments carried out during BIOSOPE confirmed biological Si uptake by this size-fraction. We further present diatoms community structure associated with the stock measurements for a global overview of the Si cycle in the Southern Tropical Pacific.
Citation: Leblanc, K., Cornet, V., Rimmelin-Maury, P., Grosso, O., Hélias-Nunige, S., Brunet, C., Claustre, H., Ras, J., Leblond, N., and Quéguiner, B.: Silicon cycle in the Tropical South Pacific: evidence for an active pico-sized siliceous plankton, Biogeosciences Discuss., https://doi.org/10.5194/bg-2018-149, in review, 2018.
Karine Leblanc et al.
Karine Leblanc et al.
Karine Leblanc et al.

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The Si biogeochemical cycle was studied during two oceanographic cruises in the Southern Tropical Pacific in 2005 and 2015, between New Caledonia and the Chilean upwelling (8–34° S). Some of the lowest levels of biogenic silica stocks were found in the Southern Pacific Gyre, where Chlorophyll a concentrations are most depleted worldwide. Size-fractionated biogenic silica concentrations as well as Si kinetic uptake experiments revealed biological Si uptake by the picoplanktonic size-fraction.
The Si biogeochemical cycle was studied during two oceanographic cruises in the Southern...
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