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| Titel |
Molecular and isotopic investigation of eroding reliefs of the East Siberian Arctic Coastal-Ice complex |
| VerfasserIn |
L. Sánchez-García, J. Vonk, V. Alling, S. Pugach, B. van Dongen, 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 |
250041365
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| Zusammenfassung |
| The Eurasian Arctic represents contains a vast stock of carbon in form of frozen loess
deposits formed during the Last Glacial Maximum (~40,000 years ago): the so-called
Yedoma or Ice Complex. The current global warming with particular influence on this area
[1] is causing the thawing of the so far freeze-locked carbon deposits, remobilizing and
releasing large amounts of carbon mainly as particulate organic carbon (POC) [2]. A
combination of thermal collapse, sea-level rise and enhanced wave fetch from loss of coastal
sea-ice cover, is causing accelerated coastal erosion of the Pleistocene Ice Complex [3].
Utilization of this old carbon, remobilized during the Ice Complex erosion by the microbial
community present, would mean reintroduction of fossil forms of carbon in the short-term
carbon cycle and potentially cause the release of greenhouse forms which, in turn, would
trigger further warming. Our knowledge on the magnitude of the climatically-forced coastal
erosion and the fate of the terrestrial OC once it enters the Arctic Ocean is still very
limited.
This study aims to approach these questions, studying a well known case of coastal
erosion (retreat rate up to 20 m/y over last decade) in the Eurasian Arctic Shelf
(EAS): The island of Muostakh (SE Laptev Sea). Soil samples (n=11) were collected
from Muostakh in 2006 along 4 “erosion transects”, in order to characterize the
eroded material in terms of organic carbon (OC) content, bulk 14C-based age and
lipid biomarkers composition (n-alkanes, n-alkanoic acids, n-alkanols, sterols).
On-site CO2 measurements were carried out on similar surface, to detect degradation
signals. To elucidate what happens with the eroded OC once it enters the shelf,
seawater samples (n=218) were collected at different depths from 94 sites on the EAS
samples, as part of the ISSS-08 (International Siberian Shelf Study, 2008) sampling
program. The distribution and composition of POC was studied in relation with
other water column parameters (salinity, turbidity, aromatic moieties, DOC, humic
substances).
The ratio of high-molecular weight (HMW) n-alkanoic acids over n-alkanes showed
lower values for the older soil samples collected from the lower reliefs of Muostakh. This,
together with larger CO2 fluxes and higher abundance of short-chain n-alkanes (C27Â ), illustrate the
higher extent of degradation at the low part of the island. The higher exposure of the low
reliefs to wave impact and coastal erosion facilitates the OC remobilization and makes it
potentially available for biodegradation.
Once in the water column, larger contents of POC and aromatic moietieswere observed
close to land, showing a rapid decrease with distance from the coast. The coupling between
both parameters suggesting similar terrestrial sources related with coastal erosion.
The higher POC values observed in erosion affected sites, in contrast to higher
DOC values derived from river origin, make the POC/DOC ratio a useful tool to
distinguish between river (ratios < 0.2) and coastal erosion sources (ratios -¥ 0.2).
The highest POC/DOC ratios (up to 0.5) and largest content of aromatic moieties
were measured nearby Muostakh, manifesting the intensity of erosion affecting the
island.
References
[1] NOAA (National Oceanic and Atmospheric Administration), 2006. State of the Arctic
Report.
[2] Guo, L. and MacDonald, R.W., 2006. Global Biogeochem. Cycles 20,
GB2011, doi:10.1029/2005GB002593.
[3] Stein, R. and MacDonald, R.W., 2004. The organic carbon cycle in the Arctic Ocean
363 pp, Springer, Berlin. |
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