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| Titel |
Molecular and radiocarbon constraints on sources and degradation of terrestrial organic carbon along the Kolyma paleoriver transect, East Siberian Sea |
| VerfasserIn |
J. E. Vonk, L. Sánchez-García, I. Semiletov, O. Dudarev, T. Eglinton, 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 ; 7, no. 10 ; Nr. 7, no. 10 (2010-10-14), S.3153-3166 |
| Datensatznummer |
250005015
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| Publikation (Nr.) |
 copernicus.org/bg-7-3153-2010.pdf |
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| Zusammenfassung |
| Climate warming in northeastern Siberia may induce thaw-mobilization of
the organic carbon (OC) now held in permafrost. This study investigated the
composition of terrestrial OC exported to Arctic coastal waters to both
obtain a natural integration of terrestrial permafrost OC release and to
further understand the fate of released carbon in the extensive Siberian
Shelf Seas. Application of a variety of elemental, molecular and isotopic
(δ13C and Δ14C) analyses of both surface water
suspended particulate matter and underlying surface sediments along a 500 km
transect from Kolyma River mouth to the mid-shelf of the East Siberian Sea
yielded information on the sources, degradation status and transport
processes of thaw-mobilized soil OC. A three end-member
dual-carbon-isotopic mixing model was applied to deduce the relative
contributions from riverine, coastal erosion and marine sources. The mixing
model was solved numerically using Monte Carlo simulations to obtain a fair
representation of the uncertainties of both end-member composition and the
end results. Riverine OC contributions to sediment OC decrease with
increasing distance offshore (35±15 to 13±9%), whereas coastal
erosion OC exhibits a constantly high contribution (51±11 to 60±12%)
and marine OC increases offshore (9±7 to 36±10%). We
attribute the remarkably strong imprint of OC from coastal erosion,
extending up to ~500 km from the coast, to efficient offshoreward
transport in these shallow waters presumably through both the benthic
boundary layer and ice-rafting. There are also indications of simultaneous
selective preservation of erosion OC compared to riverine OC. Molecular
degradation proxies and radiocarbon contents indicated a degraded but young
(Δ14C ca. −60‰ or ca. 500 14C years) terrestrial OC pool
in surface water particulate matter, underlain by a less degraded but old
(Δ14C ca. −500‰ or ca. 5500 14C years) terrestrial OC pool
in bottom sediments. We suggest that the terrestrial OC fraction in surface
water particulate matter is mainly derived from surface soil and recent
vegetation fluvially released as buoyant organic-rich aggregates (e.g.,
humics), which are subjected to extensive processing during coastal
transport. In contrast, terrestrial OC in the underlying sediments is
postulated to originate predominantly from erosion of mineral-rich
Pleistocene coasts (i.e., yedoma) and inland mineral soils. Sorptive
association of this organic matter with mineral particles protects the OC
from remineralization and also promotes rapid settling (ballasting) of the
OC. Our findings corroborate recent studies by indicating that different
Arctic surface soil OC pools exhibit distinguishing susceptibilities to
degradation in coastal waters. Consequently, the general postulation of a
positive feedback to global warming from degradation of permafrost carbon
may be both attenuated (by reburial of one portion) and geographically
displaced (degradation of released terrestrial permafrost OC far out over
the Arctic shelf seas). |
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