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| Titel |
Remobilization and degradation of Muostakh Island (Laptev Sea) as part of the collapsing Arctic coastal ice complex |
| VerfasserIn |
L. Sánchez-García, J. Vonk, A. Charkin, D. Kosmach, O. Dudarev, I. Semiletov, Ö. Gustafsson |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250041201
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| Zusammenfassung |
| East Siberian´s permafrost is thought to contain about 400 GtC (Giga = 109) [1] in form of
the so-called Yedoma or Ice Complex, a huge stock of carbon mainly as frozen loess deposits
formed during the Last Glacial Maximum (~40,000 years ago). The Pleistocene Ice
Complex has not undergone much alteration by soil microorganisms since deposited,
which makes it particularly sensitive to global warming effects on large-scale C
dynamics. Accelerated coastal erosion of the Ice Complexes is brought on by a
combination of thermal collapse, sea-level rise and enhanced wave fetch from loss of
coastal sea-ice cover [2, 3]. Despite coastal erosion is estimated to deliver as much
OC to the East Siberian Arctic Shelf (ESAS) as all the great Russian-Arctic rivers
combined [3], the process is poorly understood, in particular with regard to the
fate of the OM derived from coastal erosion. This study aims to alleviate the lack
of information on the remobilization of OM from massive coastal erosion in the
ESAS.
The erosion evolution of a significant example of this destructive geological process
(Muostakh Island, SE Laptev Sea), has been observed over the past decade and it has been
estimated a retreat rate up to 20 m during the summer months (from 2001 to 2009). In
summer 2006, soil samples were collected from Muostakh at 11 different locations along four
“erosion transects”, spanning reliefs with ranges of approximately 25 m from the top plateau
to the water boundary. On-site CO2measurements were carried out on the surface along five
different transects across the island. Quantification of the organic carbon (OC), bulk 14C
content and biomarker analysis (n-alkanes, n-alkanoic acids, n-alkanols, sterols) were
performed to elucidate whether the old carbon forms eroded from Muostakh Island are
subject to degradation.
Elemental and isotopic analyses showed a vertical trend of younger (~modern) and
C-enriched (OC~38%) material toward the plateau of the island, in contrast to
the older (~35Â 000 y) and C-depleted (OC~0.7%) components at the land-sea
boundary. Different biomarker ratios, indicative of microbial degradation or loss of
functional groups, suggested higher extent of degradation at the low part of the
island. The on-site measurements of CO2 registered the largest fluxes on the land-sea
boundary, supporting a more intense degradation signal at the low locations of the
sampling transects. The presence of older OC in the lower parts of the island, more
exposed to wave impact and coastal erosion, suggests that nearly fossil C forms
(>35,000 years) could be remobilized and are therewith bioavailable to be degraded to
CO2. The larger CO2fluxes of Muostakh (~5 μM m-2 sec-1), compared to those
measured on Sphagnum-dominated tundra at the continental coasts (0.1-1.1 μM m-2
sec-1), manifest the more intense biodegradation undergone by the eroding Muostakh
Island.
References
[1] Tarnocai et al, 2009. Global Biogechem. Cycles 23, doi:10.1029/2008GB003327.
[2] Intergovernmental Panel on Climate Change (IPCC), 2007. Pachauri, R.K. and
Reisinger, A., 104 pp. IPCC, Geneva, Suiza.
[3] Stein, R. and MacDonald, R.W., 2004. The organic carbon cycle in the Arctic Ocean
363 pp, Springer, Berlin. |
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