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| Titel |
Patterns of microbial nitrogen incorporation and retention in oxygen minimum zone sediments: An in situ 13C:15N labelling approach. |
| VerfasserIn |
William Ross Hunter, Bart Veuger, Ursula Witte |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250046059
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| Zusammenfassung |
| At present, approximately 6 % of the continental margins (1.5 million km2 of seafloor)
experience permanent dysoxic conditions within oxygen minimum zones (OMZs). These
areas are predicted to grow as a consequence of climate changes with major implications for
both localized ecosystem function and global biogeochemical cycles. The Arabian Sea
OMZ impinges upon the western Indian continental margin at bathyal depths (150
- 1500m) producing a strong depth dependent oxygen gradient at the sea floor.
Between October and November 2008, a multi-national expedition led by Prof
Hiroshi Kitazato (JAMSTEC) studied the role of benthic ecosystem zonation, oxygen
availability and organic matter (OM) availability and characteristics upon carbon
and nitrogen cycling. Within this research program, microbial processing of OM
was investigated by in situ stable isotope pulse chase experiments. Semi-enclosed
experimental meso-cosms (Spreaders) were used to deploy doses of 13C:15N labeled
Thalassiosira weissflogii, equivalent to 650 mg C. m-2, onto the sediment surface
at four stations from the OMZ core across its lower boundary (water depth 540
– 1100 m; [O2] = 0.35 - 15 μM). 13C and 15N labels were traced into sediment,
bacteria, meio- and macrofauna and in the case of 13C into porewater DIC and
DOC.
Here we present the results of incorporation and retention of 13C and 15N labels into the
hydrolysable amino acids (HAAs) and the bacterial biomarker D-alanine (D-ala), in the upper
0-1 and 1-2 cm sediment layers. In addition, the 13C label was traced into the bacterial
phospholipid fatty acids (PLFAs). Results showed clear differences in phytodetrital N
incorporation between the lower boundary versus the core of the OMZ. At the lower
boundary stations (800m and 1100m) relatively little of the phytodetrital N label was
recovered from the sediment, with the HAAs recovered derived primarily from unaltered
phytodetritus. In contrast, high concentrations of the labelled N were recovered from
sediment in the core of the OMZ (540m). Biomarker data (D-Ala & PLFA) revealed
substantial bacterial incorporation of both phytodetrital-C and –N, at 540m, with a strong
preference for N. These results indicate that the microbial pathways for carbon and nitrogen
cycling vary across an OMZ impacted continental margin, with demand for nitrogen
driving microbial uptake of both carbon and nitrogen from an organic matter source. |
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