 |
| Titel |
Aminopentol, a possible novel biomarker tracer for methane hydrate stability in sedimentary records |
| VerfasserIn |
L. Handley, H. M. Talbot, M. P. Cooke, T. Wagner |
| Konferenz |
EGU General Assembly 2009
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250023904
|
|
|
|
|
|
| Zusammenfassung |
| The Congo Fan is a region of important methane (CH4) storage and seepage: large gas
hydrate reservoirs at and just below the sediment surface occur alongside deeply-buried
reservoirs of thermogenic methane linked with hydrocarbon source rocks. Methane
release from both reservoirs has the potential to drive or respond to changes in local
and global climate, thus causing changes in ocean chemical properties and biotic
responses. Understanding these mechanisms of methane emission and reconstructing the
history of past emissions in the Congo Fan (ODP Site 1075) is the main focus of this
study.
Bacteriohopanepolyols (BHPs) are lipid membrane constituents of bacteria and occur
with a wide range of structural and functional variability. Amino-BHPs are produced by
methane-oxidising bacteria and the 35-aminobacteriohopane-30,31,32,33,34-pentol
(aminopentol) is a highly specific biomarker for aerobic methane oxidation.
Aminopentol abundance varies significantly throughout the studied section with a
suspected precession-driven cyclical variability superimposed on longer-term short
eccentricity cycles. Compound-specific stable carbon isotope analyses confirm
that the amino-BHPs are of methanotrophic origin. A period of sustained greater
concentrations and inferred emissions occurs from ca. 500 and 600 ka during which soil
organic matter input, as recorded by soil BHP concentrations and the BIT index, is
consistently low. Unsaturated Î6-bacteriohopanetetrol cyclitol ether, which is interpreted
as a biomarker for nitrogen-fixing marine Tricodesmium cyanobacteria, was also
found in this interval and is absent from the remainder of the section. This interval
could therefore reflect a period of low terrigenous organic matter and associated
nutrient input during which nitrogen-fixing bacteria may have flourished in the
resultant nutrient-, in particular nitrate, poor water. Ongoing sea surface temperature
reconstruction, using the TEX86 proxy, seeks to investigate potential perturbations in
local climate with relation to these previously unrecognized methane emission
events.
The aerobic oxidation of methane is thought to be intrinsically linked with methane gas
hydrate dissolution. Thus, the variability in amino-BHP abundance could provide an
indicator for past methane emission events, directly linking key aspects of structural
geology with gas hydrate stability, deep ocean processes, and methane cycling. |
|
|
|
|
|
|