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| Titel |
Modelling the effect of boundary scavenging on Thorium and Protactinium profiles in the ocean |
| VerfasserIn |
M. Roy-Barman |
| 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 ; 6, no. 12 ; Nr. 6, no. 12 (2009-12-18), S.3091-3107 |
| Datensatznummer |
250004233
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| Publikation (Nr.) |
 copernicus.org/bg-6-3091-2009.pdf |
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| Zusammenfassung |
| The "boundary scavenging" box model is a cornerstone of our understanding
of the particle-reactive radionuclide fluxes between the open ocean and the
ocean margins. However, it does not describe the radionuclide profiles in
the water column. Here, I present the transport-reaction equations for
radionuclides transported vertically by reversible scavenging on settling
particles and laterally by horizontal currents between the margin and the
open ocean. Analytical solutions of these equations are compared with
existing data. In the Pacific Ocean, the model produces "almost" linear
230Th profiles (as observed in the data) despite lateral transport.
However, omitting lateral transport biaises the 230Th based particle
flux estimates by as much as 50%. 231Pa profiles are well reproduced
in the whole water column of the Pacific Margin and from the surface down to
3000 m in the Pacific subtropical gyre. Enhanced bottom scavenging or inflow
of 231Pa-poor equatorial water may account for the model-data
discrepancy below 3000 m. The lithogenic 232Th is modelled using the
same transport parameters as 230Th but a different source function. The
main source of the 232Th scavenged in the open Pacific is advection from
the ocean margin, whereas a net flux of 230Th produced in the open
Pacific is advected and scavenged at the margin, illustrating boundary
exchange. In the Arctic Ocean, the model reproduces 230Th measured
profiles that the uni-dimensional scavenging model or the
scavenging-ventilation model failed to explain. Moreover, if lateral
transport is ignored, the 230Th based particle settling speed may by
underestimated by a factor 4 at the Arctic Ocean margin. The very low
scavenging rate in the open Arctic Ocean combined with the enhanced
scavenging at the margin accounts for the lack of high 231Pa/230Th
ratio in arctic sediments. |
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