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| Titel |
Organic matter accumulation and degradation in subsurface coastal sediments: a model-based comparison of rapid sedimentation and aquifer transport |
| VerfasserIn |
J. M. Holstein, K. W. Wirtz |
| 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 ; 7, no. 11 ; Nr. 7, no. 11 (2010-11-22), S.3741-3753 |
| Datensatznummer |
250005067
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| Publikation (Nr.) |
 copernicus.org/bg-7-3741-2010.pdf |
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| Zusammenfassung |
The redox succession in shallow marine sediments generally exhibits a
predictable pattern. Pore water profiles from a back barrier tidal flat in
the German Wadden Sea depart from the expected redox zoning. Instead, a
sulfate minimum zone associated with a sulfate-methane-sulfate double
interface and a distinct ammonium peak at 1.5 m below sea floor (mbsf) is
displayed. Such evidence for significant degradation of organic matter (OM)
in subsurface layers is challenging our understanding of tidal flat
biogeochemistry as little is known about processes that relocate reactive OM
into layers far distant from the sediment-water interface. The objectives of
our model study were to identify possible mechanisms for the rapid transport
of organic matter to subsurface layers that cause the reversed redox
succession and to constrain several important biogeochemical control
parameters. We compared two scenarios for OM transfer: rapid sedimentation
and burial of OM as well as lateral advection of suspended POM. Using a
diagenetic model, uncertain process parameters, in particular those connected
to OM degradation and (vertical or lateral) transport, are systematically
calibrated using field data.
We found that both scenarios, advection and sedimentation, had solutions
consistent with the observed pore water profiles. For this specific site,
however, advective transport of particulate material had to be rejected since
the reconstructed boundary conditions were rather improbable. In the
alternative deposition set-up, model simulations suggested the deposition of
the source OM about 60 yrs before cores were taken. A mean sedimentation
rate of approximately 2 cm yr−1 indicates substantial changes in near coast
tidal flat morphology, since sea level rise is at a much lower pace. High
sedimentation rates most probably reflect the progradation of flats within
the study area. These or similar morphodynamic features also occur in other
coastal areas so that inverted redox succession by horizontal or vertical
transport may be more common than previously thought. Consequently, regional
values for OM remineralization rates may be higher than predicted from
surface biogeochemistry. |
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