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| Titel |
Silicon pool dynamics and biogenic silica export in the Southern Ocean inferred from Si-isotopes |
| VerfasserIn |
F. Fripiat, A.-J. Cavagna, F. Dehairs, S. Speich, L. André, D. Cardinal |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1812-0784
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| Digitales Dokument |
URL |
| Erschienen |
In: Ocean Science ; 7, no. 5 ; Nr. 7, no. 5 (2011-09-06), S.533-547 |
| Datensatznummer |
250004797
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| Publikation (Nr.) |
 copernicus.org/os-7-533-2011.pdf |
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| Zusammenfassung |
Silicon isotopic signatures (δ30Si) of water column silicic
acid (Si(OH)4) were measured in the Southern Ocean, along a meridional
transect from South Africa (Subtropical Zone) down to 57° S (northern
Weddell Gyre). This provides the first reported data of 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 water 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 determine different mixing interfaces: the Antarctic Surface Water
(AASW), the Antarctic Intermediate Water (AAIW), and thermoclines in the low
latitude areas. The residual silicic acid concentrations of end-members
control the δ30Si alteration of the mixing products and 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 northward, across the different interfaces, without
significantly changing the AASW δ30Si composition. By comparing
our new results with a previous study in the Australian sector we show that
during the circumpolar transport of the ACC eastward, the δ30Si
composition of the silicic acid pools is getting slightly, but significantly
lighter 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 isotopic trend is further transmitted to
the subsurface waters, representing mixing interfaces between the surface
and deeper layers.
Through the use of δ30Si constraints, net biogenic silica
production (representative of annual export), at the Greenwich Meridian is
estimated to be 5.2 ± 1.3 and 1.1 ± 0.3 mol Si m−2 for the
Antarctic Zone and Polar Front Zone, respectively. This is in good agreement
with previous estimations. Furthermore, summertime Si-supply into the
mixed layer of both zones, via vertical mixing, is estimated to be 1.6 ±
0.4 and 0.1 ± 0.5 mol Si m−2, respectively. |
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