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Silicon Pool Dynamics and Biogenic Silica Export in the Southern Ocean, Inferred from Si-isotopes : Volume 8, Issue 2 (30/03/2011)

By Fripiat, F.

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Book Id: WPLBN0003987897
Format Type: PDF Article :
File Size: Pages 36
Reproduction Date: 2015

Title: Silicon Pool Dynamics and Biogenic Silica Export in the Southern Ocean, Inferred from Si-isotopes : Volume 8, Issue 2 (30/03/2011)  
Author: Fripiat, F.
Volume: Vol. 8, Issue 2
Language: English
Subject: Science, Ocean, Science
Collections: Periodicals: Journal and Magazine Collection, Copernicus GmbH
Publication Date:
Publisher: Copernicus Gmbh, Göttingen, Germany
Member Page: Copernicus Publications


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André, L., Fripiat, F., Dehairs, F., Cardinal, D., Cavagna, A., & Speich, S. (2011). Silicon Pool Dynamics and Biogenic Silica Export in the Southern Ocean, Inferred from Si-isotopes : Volume 8, Issue 2 (30/03/2011). Retrieved from

Description: Section of Mineralogy and Petrography, Royal Museum for Central Africa, Tervuren, Belgium. Water column silicon isotopic signatures (Δ30Si) of silicic acid (Si(OH)4) in the Southern Ocean were measured along a meridional transect from South Africa (Subtropical Zone) down to 57° S (northern Weddell Gyre). These data are the first reported for a summer transect across the whole Antarctic Circumpolar Current (ACC). Δ30Si variations are large in the upper 1000 m, reflecting the effect of the silica pump superimposed upon meridional transfer across the ACC: the transport of Antarctic surface waters northward by a net Ekman drift and their convergence and mixing with warmer upper-ocean Si-depleted waters to the north. Using Si isotopic signatures, we determined different mixing interfaces between ACC water masses: the Antarctic Surface Water (AASW), the Antarctic Intermediate Water (AAIW), and the thermoclines in the low latitude areas. The residual silicic acid concentrations of end-members control the Δ30Si alteration of the mixing products. With the exception of AASW, all mixing interfaces have a highly Si-depleted mixed layer end-member. These processes deplete the silicic acid AASW concentration across the different interfaces northward without significantly changing the AASW Δ30Si. By comparing our new results with a previous study in the Australian sector we show that during the circumpolar transport of the ACC eastward, there is a slight but significant Si-isotopic lightening of the silicic acid pools from the Atlantic to the Australian sectors. This results either from the dissolution of biogenic silica in the deeper layers and/or from an isopycnal mixing with the deep water masses in the different oceanic basins: North Atlantic Deep Water in the Atlantic, and Indian Ocean deep water in the Indo-Australian sector. This eastward lightening is further transmitted to the subsurface waters, representing mixing interfaces between the surface and deeper layers.

Using the Si-isotopic constraint, we estimate for the Greenwich Meridian a net biogenic silica production which should be representative of the annual export, at 4.5 ± 1.1 and 1.5 ± 0.4 mol Si m−2 for the Antarctic Zone and Polar Front Zone, respectively, in agreement with previous estimations. The summertime Si-supply into the mixed layer via vertical mixing was also assessed at 1.5 ± 0.4 and 0.1 ± 0.5 mol Si m−2, respectively.

Silicon pool dynamics and biogenic silica export in the Southern Ocean, inferred from Si-isotopes

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