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Historical records of organic matter supply and degradation status in the East Siberian Sea
Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. CNR-National Research Council of Italy, ISMAR-Marine Sciences Institute, Italy.
Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
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Number of Authors: 8
2016 (English)In: Organic Geochemistry, ISSN 0146-6380, E-ISSN 1873-5290, Vol. 91, 16-30 p.Article in journal (Refereed) Published
Abstract [en]

Destabilization and degradation of permafrost carbon in the Arctic regions could constitute a positive feedback to climate change. A better understanding of its fate upon discharge to the Arctic shelf is therefore needed. In this study, bulk carbon isotopes as well as terrigenous and marine biomarkers were used to construct two centennial records in the East Siberian Sea. Differences in topsoil and Pleistocene Ice Complex Deposit permafrost concentrations, modeled using delta C-13 and Delta C-14, were larger between inner and outer shelf than the changes over time. Similarly, lignin-derived phenol and cutin acid concentrations differed by a factor of ten between the two stations, but did not change significantly over time, consistent with the dual-carbon isotope model. High molecular weight (HMW) n-alkane and n-alkanoic acid concentrations displayed a smaller difference between the two stations (factor of 3-6). By contrast, the fraction for marine OC drastically decreased during burial with a half-life of 19-27 years. Vegetation and degradation proxies suggested supply of highly degraded gymnosperm wood tissues. Lipid Carbon Preference Index (CPI) values indicated more extensively degraded HMW n-alkanes on the outer shelf with no change over time, whereas n-alkanoic acids appeared to be less degraded toward the core top with no large differences between the stations. Taken together, our results show larger across-shelf changes than down-core trends. Further investigation is required to establish whether the observed spatial differences are due to different sources for the two depositional settings or, alternatively, a consequence of hydrodynamic sorting combined with selective degradation during cross-shelf transport.

Place, publisher, year, edition, pages
2016. Vol. 91, 16-30 p.
Keyword [en]
Arctic, East Siberian Arctic Shelf, Pb-210, Monte Carlo, delta C-13, Delta C-14, Lignin, HMW wax lipids
National Category
Earth and Related Environmental Sciences
Research subject
Applied Environmental Science
Identifiers
URN: urn:nbn:se:su:diva-126195DOI: 10.1016/j.orggeochem.2015.10.008ISI: 000366706100003OAI: oai:DiVA.org:su-126195DiVA: diva2:898536
Available from: 2016-01-28 Created: 2016-01-26 Last updated: 2016-12-22Bibliographically approved
In thesis
1. Transport, degradation and burial of organic matter released from permafrost to the East Siberian Arctic Shelf
Open this publication in new window or tab >>Transport, degradation and burial of organic matter released from permafrost to the East Siberian Arctic Shelf
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Permafrost soils in the Arctic store large quantities of organic matter, roughly twice the amount of carbon that was present in the atmosphere before the industrial revolution. This freeze-locked carbon pool is susceptible to thawing caused by amplified global warming at high latitudes. The remobilization of old permafrost carbon facilitates its degradation to carbon dioxide and methane, thereby providing a positive feedback to climate change.

Accelerating coastal erosion in addition to projected rising river discharge with enhancing sediment loads are anticipated to transport increasing amounts of land-derived organic carbon (OC) to the Arctic Ocean. On its shallow continental shelves, this material may be remineralized in the water column or in the sediments, transported without being altered off shelf towards the deep sea of the Arctic Interior or buried in marine sediments and hence sequestered from the contemporary carbon cycle. The fate of terrigenous material in the marine environment, though offering potentially important mechanisms to either strengthen or attenuate the permafrost-carbon climate feedback, is so far insufficiently understood.

In this doctoral thesis, sediments from the wide East Siberian Arctic Shelf, the world’s largest shelf-sea system, were used to investigate some of the key processes for OC cycling. A range of bulk sediment properties, carbon isotopes and molecular markers were employed to elucidate the relative importance of different organic matter sources, the role of cross-shelf transport and the relevance of degradation during transport and after burial.

Overall, OC released from thawing permafrost constitutes a significant proportion of the sedimentary organic matter on the East Siberian Arctic Shelf. Two sediment cores from the inner and outer East Siberian Sea recorded no substantial changes in source material or clear trends in degradation status for the last century. With increasing distance from the coast, however, strong gradients were detected towards lower concentrations of increasingly reworked land-derived OC. The time spent during cross-shelf transport was consequently found to exert first-order control on degradation. Compound-specific radiocarbon dating on terrigenous biomarkers revealed a net transport time of ~4 000 years across the 600 km wide Laptev Sea shelf, yielding degradation rate constants for bulk terrigenous OC and specific biomarkers on the order of 2-4 kyr-1.

From these results, the carbon flux released by degradation of terrigenous OC in surface sediments was estimated to be ~1.7 Gg yr-1, several orders of magnitude lower than what had been quantified earlier for dissolved and particulate OC in the water column. Lower oxygen availability and close associations with the mineral matrix may protect sedimentary OC from remineralization and thereby weaken the permafrost-carbon feedback to present climate change.

Place, publisher, year, edition, pages
Stockholm: Department of Environmental Science and Analytical Chemistry, Stockholm University, 2016
Keyword
organic carbon, marine sediments, East Siberian Sea, Laptev Sea, cross-shelf transport, degradation rate constants, carbon isotopes, terrestrial biomarkers, HMW wax lipids, lignin phenols, compound-specific radiocarbon analysis
National Category
Environmental Sciences
Research subject
Applied Environmental Science
Identifiers
urn:nbn:se:su:diva-136380 (URN)978-91-7649-571-1 (ISBN)978-91-7649-572-8 (ISBN)
Public defence
2017-02-03, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Submitted. Paper 4: Manuscript.

Available from: 2017-01-11 Created: 2016-12-05 Last updated: 2017-03-14Bibliographically approved

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