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Carbon isotopes and lipid biomarker investigation of sources, transport and degradation of terrestrial organic matter in the Buor-Khaya Bay, SE Laptev Sea
Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
Vise andre og tillknytning
2011 (engelsk)Inngår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 8, nr 7, s. 1865-1879Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

The world's largest continental shelf, the East Siberian Shelf Sea, receives substantial input of terrestrial organic carbon (terr-OC) from both large rivers and erosion of its coastline. Degradation of organic matter from thawing permafrost in the Arctic is likely to increase, potentially creating a positive feedback mechanism to climate warming. This study focuses on the Buor-Khaya Bay (SE Laptev Sea), an area with strong terr-OC input from both coastal erosion and the Lena river. To better understand the fate of this terr-OC, molecular (acyl lipid biomarkers) and isotopic tools (stable carbon and radiocarbon isotopes) have been applied to both particulate organic carbon (POC) in surface water and sedimentary organic carbon (SOC) collected from the underlying surface sediments. Clear gradients in both extent of degradation and differences in source contributions were observed both between surface water POC and surface sediment SOC as well as over the 100 s km investigation scale (about 20 stations). Depleted delta(13)C-OC and high HMW/LMW n-alkane ratios signaled that terr-OC was dominating over marine/planktonic sources. Despite a shallow water column (10-40 m), the isotopic shift between SOC and POC varied systematically from +2 to +5 per mil for delta(13)C and from +300 to +450 for Delta(14)C from the Lena prodelta to the Buor-Khaya Cape. At the same time, the ratio of HMW n-alkanoic acids to HMW n-alkanes as well as HMW n-alkane CPI, both indicative of degradation, were 5-6 times greater in SOC than in POC. This suggests that terr-OC was substantially older yet less degraded in the surface sediment than in the surface waters. This unusual vertical degradation trend was only recently found also for the central East Siberian Sea. Numerical modeling (Monte Carlo simulations) with delta(13)C and Delta(14)C in both POC and SOC was applied to deduce the relative contribution of - plankton OC, surface soil layer OC and yedoma/mineral soil OC. This three end-member dual-carbon-isotopic mixing model suggests quite different scenarios for the POC vs SOC. Surface soil is dominating (63 +/- 10 %) the suspended organic matter in the surface water of SE Laptev Sea. In contrast, the yedoma/mineral soil OC is accounting for 60 +/- 9% of the SOC. We hypothesize that yedoma-OC, associated with mineral-rich matter from coastal erosion is ballasted and thus quickly settles to the bottom. The mineral association may also explain the greater resistance to degradation of this terr-OC component. In contrast, more amorphous humic-like and low-density terr-OC from surface soil and recent vegetation represents a younger but more bioavailable and thus degraded terr-OC component held buoyant in surface water. Hence, these two terr-OC components may represent different propensities to contribute to a positive feedback to climate warming by converting OC from coastal and inland permafrost into CO(2).

sted, utgiver, år, opplag, sider
2011. Vol. 8, nr 7, s. 1865-1879
HSV kategori
Forskningsprogram
tillämpad miljövetenskap
Identifikatorer
URN: urn:nbn:se:su:diva-66878DOI: 10.5194/bg-8-1865-2011ISI: 000294153700009OAI: oai:DiVA.org:su-66878DiVA, id: diva2:468947
Forskningsfinansiär
EU, FP7, Seventh Framework Programme, 220424
Merknad

authorCount :8

Tilgjengelig fra: 2011-12-22 Laget: 2011-12-21 Sist oppdatert: 2017-12-08bibliografisk kontrollert
Inngår i avhandling
1. Organic geochemical investigation of sources, transport and fate of terrestrial organic matter in the southeast Laptev Sea
Åpne denne publikasjonen i ny fane eller vindu >>Organic geochemical investigation of sources, transport and fate of terrestrial organic matter in the southeast Laptev Sea
2012 (engelsk)Licentiatavhandling, med artikler (Annet vitenskapelig)
Abstract [en]

Permafrost carbon stores have been suggested to react to warming trends with increased terrestrial loading to its coastal waters. Presently, the warming has been seen to be especially high in the East Siberian Arctic and the fate of the major release of terrestrial matter to these coasts is yet to be detailed.

Our work is focused on the East Siberian Shelf (ESS) – which is the largest continental shelf in the world. It receives substantial inputs of terrestrial organic matter both from the large Russian rivers and from eroding coastlines. The largest of its rivers, the Lena, discharges in Buor-Khaya Bay, which is also a hot spot for coastal erosion.

Previous studies of molecular and δ¹3C and Δ¹⁴C composition of terrestrial organic matter received by Arctic coastal waters have suggested a different propensity of different terrestrial source materials towards bacterial degradation. This detailed isotopic and molecular marker survey which is the basis for this thesis reveals clearly distinguished source patterns both between surface water (POC) and sea floor (SOC) as well as with distance away from the sources. The heavy terrestrial dominance over marine/planktonic sources are clearly detected in gradients of high POC and SOC levels, as well as depleted δ13C -OC and high HMW/LMW n-alkane ratios. Furthermore, data suggests that terr-OC was substantially older yet less degraded in the surface sediment than in the surface waters. This unusual vertical degradation trend was only recently found also for the coastal and central East Siberian Sea. It seems that the riverine terr-OC component comprising mainly annual thaw layer surface soil dominates the buoyant surface water POC and is readily degraded. This is in contrast to the coastline-erosion terr-OC which is associated with minerals and therefore ballasted to the sediments where it makes up the key OC component and seems relatively protected from degradation.

The study area of this work is a region with strong terrestrial influence hosting many of the important carbon cycling processes, and data reveal two important OC contributors of different origin, mineral associated coastal erosion matter and riverine borne surface soil matter. These two components may well represent different propensities to contribute to a positive feedback to climate warming by converting OC from coastal and inland permafrost into CO₂.

sted, utgiver, år, opplag, sider
Frescati, Stockholm: Stockholm University, 2012. s. 23
HSV kategori
Forskningsprogram
biogeokemi; marin geovetenskap; tillämpad miljövetenskap
Identifikatorer
urn:nbn:se:su:diva-82863 (URN)
Presentation
2012-05-25, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 15:00 (engelsk)
Opponent
Veileder
Tilgjengelig fra: 2013-01-22 Laget: 2012-11-28 Sist oppdatert: 2013-01-22bibliografisk kontrollert
2. Compositional clues to sources and sinks of terrestrial organic matter transported to the Eurasian Arctic shelf
Åpne denne publikasjonen i ny fane eller vindu >>Compositional clues to sources and sinks of terrestrial organic matter transported to the Eurasian Arctic shelf
2015 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
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.

sted, utgiver, år, opplag, sider
Stockholm: Department of Environmental Science and Analytical Chemistry, Stockholm University, 2015. s. 40
Emneord
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
HSV kategori
Forskningsprogram
tillämpad miljövetenskap
Identifikatorer
urn:nbn:se:su:diva-116876 (URN)978-91-7649-195-9 (ISBN)
Disputas
2015-06-11, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 13:00 (engelsk)
Opponent
Veileder
Merknad

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

Tilgjengelig fra: 2015-05-20 Laget: 2015-05-01 Sist oppdatert: 2015-05-29bibliografisk kontrollert

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