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- Vonk, Jorien Elisabeth, 1978-
(author)
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Molecular and isotopic characterization of terrestrial organic carbon released to (sub-)Arctic coastal waters
- 2010
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Doctoral thesis (other academic/artistic)abstract
- Arctic soils store half of the global soil organic carbon (OC) pool and twice as much C as is currently present in the atmosphere. A considerable part of these carbon pools are stored in permafrost. Amplified climate warming in the Arctic will thaw permafrost and remobilize some of these substantial carbon stocks into the active carbon cycle, potentially causing positive feedback to global warming. Despite the global importance of this mechanism, our understanding of the fate of these thawing organic carbon (OC) pools is still poor, particularly regarding its degradation potential. This makes good estimates on greenhouse gas emissions versus coastal reburial impossible. This doctoral thesis aims to improve our understanding on the fate of high-latitude terrestrial OC during fluvial and coastal transport. In two study regions, the Bothnian Bay and the East Siberian Sea, we apply a wide range of bulk, molecular and isotopic geochemical analyses to reveal information on sources, age, degradation and transport routes. Our results show that both study regions receive and store large amounts of terrestrial OC, largely derived from peatlands (paper I, II and IV). This terrestrial matter undergoes extensive degradation in both the water column and surface sediments (paper I, III and IV). Surface sediments in the East Siberian Sea show a offshore-decreasing input of riverine OC and a considerable and constant input of OC from coastal erosion. The strong imprint of rapidly settling coastal OC far out on the shelf may be explained by a strong benthic boundary layer transport in combination with offshore ice-transport and selective preservation of erosion OC compared to riverine OC (paper IV). Molecular radiocarbon data allowed us to distinguish between two (sub-)Arctic soil OC pools that show a remarkably different susceptibility to degradation upon arrival in the coastal system; a young and easily degradable pool originating in surface peatlands, and an old and recalcitrant pool originating in deep mineral soils and coastal mineral Pleistocene deposits (paper III and IV). Our first estimates suggest that, in the Bothnian Bay coastal system, mineral soil OC is at least 20 times less susceptible to degradation than peatland OC (paper III). Hence, a considerable part of the thaw-released mineral OC pool may simply be relocated to coastal sediments instead of being emitted to the atmosphere.
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| 3. |
- Vonk, Jorien Elisabeth, et al.
(author)
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Selective preservation of old organic carbon fluvially released from sub-arctic soils
- 2010
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In: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 37, s. L11605-
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Journal article (peer-reviewed)abstract
- Amplified climate warming in the Arctic may cause thaw-remobilization of its large soil organic carbon (SOC) pool. Here we assess the remobilization and preservation of old SOC by the watershed-integrated radiocarbon signature of molecular SOC markers released from northernmost Scandinavia. The radiocarbon analyses revealed a remarkable fractionation for identical vascular plant markers (∼420‰ or ∼6000 14C years) upon settling from surface water to the underlying sediments. From this, we infer fluvial export of two SOC pools; a young surface peat component, and an old deep mineral soil component. The young pool exists as an easily degradable humic suspension, while the old pool is matrix protected from degradation and ballasted for preferential settling. The two soil types with highest OC in Arctic permafrost evidently exhibit different susceptibilities to degradation. Hence, a significant part of the thaw-released OC may simply be fluvially relocated to sediments instead of being emitted to the atmosphere.
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