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Molecular and isotopic characterization of terrestrial organic carbon released to (sub-)Arctic coastal waters
Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM). (Gustafsson)
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Stockholm: Department of Applied Environmental Science (ITM), Stockholm University , 2010. , 51 p.
Keyword [en]
organic carbon, terrestrial biomarkers, radiocarbon, particulate organic carbon, sediments, sphagnum, Arctic, Bothnian Bay, East Siberian Sea, Kalix River, Kolyma River
Research subject
Applied Environmental Science
Identifiers
URN: urn:nbn:se:su:diva-38589ISBN: 978-91-7447-057-4 (print)OAI: oai:DiVA.org:su-38589DiVA: diva2:311042
Public defence
2010-05-21, Nordenskiöldsalen, Geovetenskapens Hus, Svante Arrheniusväg 12, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 3: Accepted. Paper 4: Manuscript. Available from: 2010-04-28 Created: 2010-04-19 Last updated: 2010-04-20Bibliographically approved
List of papers
1. Lipid biomarker investigation of the origin and diagenetic state of sub-arctic terrestrial organic matter presently exported into the northern Bothnian Bay
Open this publication in new window or tab >>Lipid biomarker investigation of the origin and diagenetic state of sub-arctic terrestrial organic matter presently exported into the northern Bothnian Bay
2008 (English)In: Mar. Chem., Vol. 112, 1-10 p.Article in journal (Refereed) Published
Keyword
Environmental science
Identifiers
urn:nbn:se:su:diva-18949 (URN)doi:10.1016/j.marchem.2008.07.001 (DOI)000261824000001 ()
Available from: 2009-02-17 Created: 2009-02-17 Last updated: 2011-01-10Bibliographically approved
2. Calibrating n-alkane Sphagnum proxies in sub-Arctic Scandinavia
Open this publication in new window or tab >>Calibrating n-alkane Sphagnum proxies in sub-Arctic Scandinavia
2009 (English)In: Organic Geochemistry, ISSN 0146-6380, E-ISSN 1873-5290, Vol. 40, no 10, 1085-1090 p.Article in journal (Refereed) Published
Abstract [en]

Moss covered, high latitude wetlands hold large amounts of terrestrial organic matter (OM), which may be vulnerable to expected climate warming. Molecular analysis of fluvially transported material from these regions can distinguish between different sources of terrestrial OM. Sphagnum moss may represent one of the major sources. This study aimed to quantitatively establish a molecular proxy for identifying Sphagnum-derived OM from high latitude peatlands in the sub-Arctic coastal ocean. We collected and analyzed Sphagnum species throughout northern Sweden and Finland. Results show that the C25/(C25 + C29) n-alkane ratio is most suitable for terrestrial OM source apportionment in these coastal regions since, compared to other n-alkane Sphagnum proxies, it shows (i) the least variation between species, (ii) the most constant values for different latitudinal regimes and (iii) the largest dynamic range to the higher plant end member in two-source mixing models. Application of the proxy to surface sediments and suspended particulate matter in the sub-Arctic northern Baltic Sea shows that 68–103% of the terrestrial OM fraction is derived from Sphagnum-rich peatland. We recommend that future studies on terrestrial OM fluxes into (sub-)Arctic regions should apply the C25/(C25 + C29) proxy to improve insight into the contribution of Sphagnum-derived terrestrial OM from climate-vulnerable, high latitude wetlands.

National Category
Earth and Related Environmental Sciences Natural Sciences
Identifiers
urn:nbn:se:su:diva-36967 (URN)10.1016/j.orggeochem.2009.07.002 (DOI)000275197600005 ()
Available from: 2010-02-01 Created: 2010-02-01 Last updated: 2017-12-12Bibliographically approved
3. Selective preservation of old organic carbon fluvially released from sub-arctic soils
Open this publication in new window or tab >>Selective preservation of old organic carbon fluvially released from sub-arctic soils
2010 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 37, L11605- p.Article in journal (Refereed) Published
Abstract [en]

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.

National Category
Natural Sciences
Identifiers
urn:nbn:se:su:diva-38600 (URN)10.1029/2010GL042909 (DOI)000278732400001 ()
Available from: 2010-04-20 Created: 2010-04-20 Last updated: 2017-12-12Bibliographically approved
4. Molecular and radiocarbon constraints on sources and degradation of terrestrial organic carbon along the Kolyma paleoriver transect, East Siberian Sea.
Open this publication in new window or tab >>Molecular and radiocarbon constraints on sources and degradation of terrestrial organic carbon along the Kolyma paleoriver transect, East Siberian Sea.
Show others...
(English)Manuscript (preprint) (Other academic)
Identifiers
urn:nbn:se:su:diva-38601 (URN)
Available from: 2010-04-20 Created: 2010-04-20 Last updated: 2010-04-20Bibliographically approved

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