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| Titel |
Indications for near-surface fluid circulation cells at bacterial mats |
| VerfasserIn |
S. Gubsch, M. Haeckel, K. Wallmann |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250026527
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| Zusammenfassung |
| At submarine cold vents off Costa Rica detailed sediment sampling along transects across
bacterial mats was conducted during expedition M66/2 with RV METEOR deploying a
remotely operated vehicle (ROV). Bacterial mats occurred in patches of several m2 in size
covering the sediment surface. Porewater analyses of the pushcore sediments revealed rapid
sulfate consumption due to anaerobic methane oxidation (AMO) below the bacterial mats.
SO4 was depleted at ~5 cm sediment depth in the center of the mat and penetrating
deeper into the sediment towards the rim of the mat. Pushcores taken in the center
of these mats, however, showed a subsequent increase of sulfate concentrations
below a sediment depth of ~10 cm. Other dissolved compounds, such as Cl, Br,
H2S, TA, NH4, PO4, and SiO4, showed a similar behaviour with concentrations
returning towards bottomwater values. Since this trend is common to all of the solutes,
it is most likely explained by a physical process. We assume that focussed fluid
outflow near the center of the bacterial mat creates a convective flow cell with bottom
waters penetrating into the adjacent sediment area and directed towards the flow
channel.
A set of different 2-D and 3-D transport-reaction models were developed to test
this hypothesis. Fluid flow in the central channel turned out to be homogeneous
and thus, could be resembled as boundary condition of the surrounding sediment
domain. The model also includes AMO as the most important reaction of a cold vent
system. Model results indicate that the observed porewater sulfate and chloride
profiles can be reproduced fairly well, for example, when applying an advection
velocity of 100 cm/a in the central fluid channel and a mean background advection of
3 cm/a in the sediment domain. A detailed sensitivity study has been performed
determining the parameters dominating the establishment of the near-surface flow
cell. |
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