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Contrasting regimes for organic matter degradation in the East Siberian Sea and the Laptev Sea assessed through microbial incubations and molecular markers
Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
Stockholm University, Faculty of Science, Department of Geological Sciences.
Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
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2015 (English)In: Marine Chemistry, ISSN 0304-4203, E-ISSN 1872-7581, Vol. 170, 11-22 p.Article in journal (Refereed) Published
Abstract [en]

Compositional studies of organic matter on the East Siberian Arctic Shelf (ESAS) suggest that different terrestrial carbon pools have different propensities for transport and/or degradation. The current study combined laboratory-based microbial degradation experiments with earlier published degradation-diagnostic composition of several classes of terrestrial biomarkers on the same sediments to investigate differences and driving forces of terrestrial organic matter (TerrOM) degradation in two biogeochemically-contrasting regimes of the ESAS. The incubation-based anaerobic degradation rates were consistently higher (by average factor of 6) in the East Siberian Sea Kolyma Paleoriver Channel (ESS-KPC) (15 mu mol CO2 g OC-1 day(-1)) compared to the Laptev Sea Buor-Khaya Bay (LS-BKB) (2.4 mu mol CO2 g OC-1 day(-1)). The reported molecular markers show similarities between the terrestrial carbon pools in the two systems, but impose contrasting degradation regimes in combination with the incubation results. For the LS-BKB, there was a strong relationship between the degradation rates and the three lignin phenol-based degradation proxies (r(2) = 0.93-0.96, p < 0.01, linear regression) and two wax lipid-based degradation proxies (r(2) = 0.71 and 0.66, p < 0.05, linear regression). In contrast, for the ESS-KPC system, there was no relationship between incubation-based degradation rates and molecular marker-based degradation status of TerrOM. A principal component analysis indicated that short-chain fatty acids and dicarboxylic acids from CuO oxidation are mainly of terrestrial origin in the LS-BKB, but mainly of marine origin in the ESS-KPC. Hence, the microbial degradation in the western (LS-BKB) system appears to be fueled by TerrOM whereas the eastern (ESS-KPC) system degradation appears to be driven by MarOM. By combining molecular fingerprinting of TerrOM degradation state with laboratory-based degradation studies on the same ESAS sediments, a picture evolves of two distinctly different modes of TerrOM degradation in different parts of the ESAS system.

Place, publisher, year, edition, pages
2015. Vol. 170, 11-22 p.
Keyword [en]
Organic matter lability, Reactivity, Decomposition, Remineralization, Terrestrial organic carbon, Incubations, Arctic Ocean, Coastal shelf, Continental margin, Permafrost, Wax lipids, Lignin, CuO oxidation, Organic geochemistry, Sediment
National Category
Chemical Sciences Oceanography, Hydrology, Water Resources
Research subject
Applied Environmental Science
Identifiers
URN: urn:nbn:se:su:diva-116604DOI: 10.1016/j.marchem.2014.12.005ISI: 000350938900002OAI: oai:DiVA.org:su-116604DiVA: diva2:809541
Note

AuthorCount:7;

Available from: 2015-05-04 Created: 2015-04-22 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Compositional clues to sources and sinks of terrestrial organic matter transported to the Eurasian Arctic shelf
Open this publication in new window or tab >>Compositional clues to sources and sinks of terrestrial organic matter transported to the Eurasian Arctic shelf
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The amount of organic carbon (OC) present in Siberian Arctic permafrost soils is estimated at twice the amount of carbon currently in the atmosphere. The shelf seas of the Arctic Ocean receive large amounts of this terrestrial OC from Eurasian Arctic rivers and from coastal erosion. Degradation of this land-derived material in the sea would result in the production of dissolved carbon dioxide and may then add to the atmospheric carbon dioxide reservoir. Observations from the Siberian Arctic suggest that transfer of carbon from land to the marine environment is accelerating. However, it is not clear how much of the transported OC is degraded and oxidized, nor how much is removed from the active carbon cycle by burial in marine sediment.

Using bulk geochemical parameters, total OC, d13C and D14C isotope composition, and specific molecular markers of plant wax lipids and lignin phenols, the abundance and composition of OC was determined in both dissolved and particulate carrier phases: the colloidal OC (COC; part of the dissolved OC), particulate OC (POC), and sedimentary OC (SOC). Statistical modelling was used to quantify the relative contribution of OC sources to these phases. Terrestrial OC is derived from the seasonally thawing top layer of permafrost soil (topsoil OC) and frozen OC derived from beneath the active layer eroded at the coast, commonly identified as yedoma ice complex deposit OC (yedoma ICD-OC). These carbon pools are transported differently in the aquatic conduits. Topsoil OC was found in young DOC and POC, in the river water, and the shelf water column, suggesting long-distance transport of this fraction. The yedoma ICD-OC was found as old particulate OC that settles out rapidly to the underlying sediment and is laterally transported across the shelf, likely dispersed by bottom nepheloid layer transport or via ice rafting.

These two modes of OC transport resulted in different degradation states of topsoil OC and yedoma ICD-OC. Terrestrial CuO oxidation derived biomarkers indicated a highly degraded component in the COC. In contrast, the terrestrial component of the SOC was much less degraded. In line with earlier suggestions the mineral component in yedoma ICD functions as weight and surface protection of the associated OC, which led to burial in the sediment, and limited OC degradation. The degradability of the terrestrial OC in shelf sediment was also addressed in direct incubation studies. Molecular markers indicate marine OC (from primary production) was more readily degraded than terrestrial OC. Degradation was also faster in sediment from the East Siberian Sea, where the marine contribution was higher compared to the Laptev Sea. Although terrestrial carbon in the sediment was degraded slower, the terrestrial component also contributed to carbon dioxide formation in the incubations of marine sediment.

These results contribute to our understanding of the marine fate of land-derived OC from the Siberian Arctic. The mobilization of topsoil OC is expected to grow in magnitude with climate warming and associated active layer deepening. This translocated topsoil OC component was found to be highly degraded, which suggests degradation during transport and a possible contribution to atmospheric carbon dioxide. Similarly, the yedoma ICD-OC (and or old mineral soil carbon) may become a stronger source with accelerated warming, but slow degradation may limit its impact on active carbon cycling in the Siberian Shelf Seas.

Place, publisher, year, edition, pages
Stockholm: Department of Environmental Science and Analytical Chemistry, Stockholm University, 2015. 40 p.
Keyword
organic carbon, degradation, microcosm, incubation, terrestrial biomarkers, acyl lipids, lignin phenols, radiocarbon, Eurasian Arctic shelf, East Siberian Sea, Laptev Sea, Lena River, colloidal matter, particulate matter, sedimentary matter
National Category
Earth and Related Environmental Sciences
Research subject
Applied Environmental Science
Identifiers
urn:nbn:se:su:diva-116876 (URN)978-91-7649-195-9 (ISBN)
Public defence
2015-06-11, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 13:00 (English)
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Note

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

Available from: 2015-05-20 Created: 2015-05-01 Last updated: 2015-05-29Bibliographically approved

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Karlsson, Emma S.Bruchert, VolkerTesi, TommasoGustafsson, Örjan
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