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| Titel |
Silicon stable isotope distribution traces Southern Ocean export of Si to the eastern South Pacific thermocline |
| VerfasserIn |
G. F. Souza, B. C. Reynolds, G. C. Johnson, J. L. Bullister, B. Bourdon |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 9, no. 11 ; Nr. 9, no. 11 (2012-11-01), S.4199-4213 |
| Datensatznummer |
250007370
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| Publikation (Nr.) |
 copernicus.org/bg-9-4199-2012.pdf |
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| Zusammenfassung |
| The cycling and transport of dissolved silicon (Si) in the ocean may
be traced by its stable isotope composition, δ30Si. We
present a dataset of δ30Si values along 103° W
in the eastern South Pacific Ocean, ranging from the Antarctic Zone of
the Southern Ocean (62° S) to the equatorial Pacific
(12° S). At high southern latitudes, the uptake and
associated isotope fractionation of Si by diatoms results in highly
elevated δ30Si values (up to +3.2‰) in
the summer mixed layer. High δ30Si values (+2‰)
are also preserved in the high-latitude fossil winter mixed layer,
documenting the efficient export of diatom opal beyond the maximum
depth of winter convection. This elevated winter mixed layer δ30Si
signature is introduced into the ocean interior by the subduction of
Subantarctic Mode Water (SAMW) and Antarctic Intermediate Water
(AAIW), whose northward spreading results in a strong isopycnal
control on lower-thermocline and intermediate δ30Si
values in the well-ventilated eastern South Pacific. Values of
δ30Si are strongly conserved along SAMW and AAIW
density levels as far north as 26° S, documenting the
importance of the export of preformed Si from the surface Southern
Ocean to lower latitudes. In contrast, in the equatorial Pacific,
depressed δ30Si values in the mesopelagic ocean are
observed, most likely documenting the combined influence of a North
Pacific Si source as well as the accumulation of remineralized Si
within the eastern equatorial Pacific shadow zone. At depth,
δ30Si values in the South Pacific remain
indistinguishable from deep Southern Ocean values of
+1.25‰, even within Si-rich and oxygen-poor deep
waters returning from the North Pacific. This homogeneity implies that
the dissolution of opal plays a negligible role in altering the
δ30Si value of deep waters as they traverse the deep
Pacific Ocean. |
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