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| Titel |
Carbon isotopes and lipid biomarker investigation of sources, transport and degradation of terrestrial organic matter in the Buor-Khaya Bay, SE Laptev Sea |
| VerfasserIn |
E. S. Karlsson, A. Charkin, O. Dudarev, I. Semiletov, J. E. Vonk, L. Sánchez-García, A. Andersson, Ö. Gustafsson |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 8, no. 7 ; Nr. 8, no. 7 (2011-07-13), S.1865-1879 |
| Datensatznummer |
250006048
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| Publikation (Nr.) |
 copernicus.org/bg-8-1865-2011.pdf |
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| Zusammenfassung |
The world's largest continental shelf, the East Siberian Shelf Sea, receives
substantial input of terrestrial organic carbon (terr-OC) from both large
rivers and erosion of its coastline. Degradation of organic matter from
thawing permafrost in the Arctic is likely to increase, potentially creating
a positive feedback mechanism to climate warming. This study focuses on the
Buor-Khaya Bay (SE Laptev Sea), an area with strong terr-OC input from both
coastal erosion and the Lena river. To better understand the fate of this
terr-OC, molecular (acyl lipid biomarkers) and isotopic tools (stable carbon
and radiocarbon isotopes) have been applied to both particulate organic
carbon (POC) in surface water and sedimentary organic carbon (SOC) collected
from the underlying surface sediments.
Clear gradients in both extent of degradation and differences in source
contributions were observed both between surface water POC and surface
sediment SOC as well as over the 100 s km investigation scale (about 20 stations).
Depleted δ13C-OC and high HMW/LMW n-alkane ratios
signaled that terr-OC was dominating over marine/planktonic sources.
Despite a shallow water column (10–40 m), the isotopic shift between SOC and
POC varied systematically from +2 to +5 per mil for δ13C and
from +300 to +450 for Δ14C from the Lena prodelta to the
Buor-Khaya Cape. At the same time, the ratio of HMW n-alkanoic acids to HMW
n-alkanes as well as HMW n-alkane CPI, both indicative of degradation, were
5–6 times greater in SOC than in POC. This suggests that terr-OC was
substantially older yet less degraded in the surface sediment than in the
surface waters. This unusual vertical degradation trend was only recently
found also for the central East Siberian Sea.
Numerical modeling (Monte Carlo simulations) with δ13C and
Δ14C in both POC and SOC was applied to deduce the relative
contribution of – plankton OC, surface soil layer OC and yedoma/mineral
soil OC. This three end-member dual-carbon-isotopic mixing model suggests
quite different scenarios for the POC vs SOC. Surface soil is dominating
(63 ± 10 %) the suspended organic matter in the surface water of SE
Laptev Sea. In contrast, the yedoma/mineral soil OC is accounting for 60 ± 9 %
of the SOC. We hypothesize that yedoma-OC, associated with
mineral-rich matter from coastal erosion is ballasted and thus quickly
settles to the bottom. The mineral association may also explain the greater
resistance to degradation of this terr-OC component. In contrast, more
amorphous humic-like and low-density terr-OC from surface soil and recent
vegetation represents a younger but more bioavailable and thus degraded
terr-OC component held buoyant in surface water. Hence, these two terr-OC
components may represent different propensities to contribute to a positive
feedback to climate warming by converting OC from coastal and inland
permafrost into CO2. |
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