Organic carbon characteristics in yedoma and thermokarst deposits on Baldwin Peninsula, West-Alaska

Abstract. As Arctic warming continues and permafrost thaws, more soil and sedimentary organic carbon (OC) will be decomposed in northern high latitudes. Still, uncertainties remain in the quantity and quality of OC stored in different deposit types of permafrost landscapes. This study presents OC data from deep permafrost and lake deposits on the Baldwin Peninsula which is located in the southern portion of the continuous permafrost zone in West Alaska. Sediment samples from yedoma and drained thermokarst lake basin (DTLB) deposits as well as thermokarst lake sediments were analyzed for cryostratigraphical and biogeochemical parameters and their lipid biomarker composition to identify the size and quality of belowground OC pools in ice-rich permafrost on Baldwin Peninsula. We provide the first detailed characterization of yedoma deposits on Baldwin Peninsula. We show that three quarters of soil organic carbon in the frozen deposits of the study region (total of 68 Mt) is stored in DTLB deposits (52 Mt) and one quarter in the frozen yedoma deposits (16 Mt). The lake sediments contain a relatively small OC pool (4 Mt), but have the highest volumetric OC content (93 kg/m3) compared to the DTLB (35 kg/m3) and yedoma deposits (8 kg/m3), largely due to differences in the ground ice content. The biomarker analysis indicates that the OC in both yedoma and DTLB deposits is mainly of terrestrial origin. Nevertheless, the relatively high carbon preference index of plant leaf waxes in combination with a lack of degradation trend with depth in the yedoma deposits indicates that OC stored in yedoma is less degraded than that stored in DTLB deposits. This suggests that OC in yedoma has a higher potential for decomposition upon thaw, despite the relatively small size of this pool. These findings highlight the importance of molecular OC analysis for determining the potential future greenhouse gas emissions from thawing permafrost, especially because this area close to the discontinuous permafrost boundary is projected to thaw substantially within the 21st century.

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Organic matter characteristics in yedoma and thermokarst deposits on Baldwin Peninsula, west Alaska

Biogeosciences ◽

10.5194/bg-15-6033-2018 ◽

2018 ◽

Vol 15 (20) ◽

pp. 6033-6048 ◽

Cited By ~ 11

Author(s):

Loeka L. Jongejans ◽

Jens Strauss ◽

Josefine Lenz ◽

Francien Peterse ◽

Kai Mangelsdorf ◽

...

Keyword(s):

Organic Matter ◽

Lake Sediments ◽

Lake Basin ◽

Study Region ◽

Thermokarst Lake ◽

Discontinuous Permafrost ◽

Lipid Biomarker ◽

Biomarker Analysis ◽

Thawing Permafrost

Abstract. As Arctic warming continues and permafrost thaws, more soil and sedimentary organic matter (OM) will be decomposed in northern high latitudes. Still, uncertainties remain in the quality of the OM and the size of the organic carbon (OC) pools stored in different deposit types of permafrost landscapes. This study presents OM data from deep permafrost and lake deposits on the Baldwin Peninsula which is located in the southern portion of the continuous permafrost zone in west Alaska. Sediment samples from yedoma and drained thermokarst lake basin (DTLB) deposits as well as thermokarst lake sediments were analyzed for cryostratigraphical and biogeochemical parameters and their lipid biomarker composition to identify the belowground OC pool size and OM quality of ice-rich permafrost on the Baldwin Peninsula. We provide the first detailed characterization of yedoma deposits on Baldwin Peninsula. We show that three-quarters of soil OC in the frozen deposits of the study region (total of 68 Mt) is stored in DTLB deposits (52 Mt) and one-quarter in the frozen yedoma deposits (16 Mt). The lake sediments contain a relatively small OC pool (4 Mt), but have the highest volumetric OC content (93 kg m−3) compared to the DTLB (35 kg m−3) and yedoma deposits (8 kg m−3), largely due to differences in the ground ice content. The biomarker analysis indicates that the OM in both yedoma and DTLB deposits is mainly of terrestrial origin. Nevertheless, the relatively high carbon preference index of plant leaf waxes in combination with a lack of a degradation trend with depth in the yedoma deposits indicates that OM stored in yedoma is less degraded than that stored in DTLB deposits. This suggests that OM in yedoma has a higher potential for decomposition upon thaw, despite the relatively small size of this pool. These findings show that the use of lipid biomarker analysis is valuable in the assessment of the potential future greenhouse gas emissions from thawing permafrost, especially because this area, close to the discontinuous permafrost boundary, is projected to thaw substantially within the 21st century.

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Organic matter mineralization and trace element post-depositional redistribution in Western Siberia thermokarst lake sediments

Biogeosciences ◽

10.5194/bg-8-3341-2011 ◽

2011 ◽

Vol 8 (11) ◽

pp. 3341-3358 ◽

Cited By ~ 48

Author(s):

S. Audry ◽

O. S. Pokrovsky ◽

L. S. Shirokova ◽

S. N. Kirpotin ◽

B. Dupré

Keyword(s):

Trace Elements ◽

Organic Matter ◽

Organic Carbon ◽

Lake Sediments ◽

Water Column ◽

Western Siberia ◽

Ecosystem Development ◽

Thermokarst Lake ◽

Fe And Mn ◽

The Impact

Abstract. This study reports the very first results on high-resolution sampling of sediments and their porewaters from three thermokarst (thaw) lakes representing different stages of ecosystem development located within the Nadym-Pur interfluve of the Western Siberia plain. Up to present time, the lake sediments of this and other permafrost-affected regions remain unexplored regarding their biogeochemical behavior. The aim of this study was to (i) document the early diagenesic processes in order to assess their impact on the organic carbon stored in the underlying permafrost, and (ii) characterize the post-depositional redistribution of trace elements and their impact on the water column. The estimated organic carbon (OC) stock in thermokarst lake sediments of 14 ± 2 kg m−2 is low compared to that reported for peat soils from the same region and denotes intense organic matter (OM) mineralization. Mineralization of OM in the thermokarst lake sediments proceeds under anoxic conditions in all the three lakes. In the course of the lake development, a shift in mineralization pathways from nitrate and sulfate to Fe- and Mn-oxyhydroxides as the main terminal electron acceptors in the early diagenetic reactions was suggested. This shift was likely promoted by the diagenetic consumption of nitrate and sulfate and their gradual depletion in the water column due to progressively decreasing frozen peat lixiviation occurring at the lake's borders. Trace elements were mobilized from host phases (OM and Fe- and Mn-oxyhydroxides) and partly sequestered in the sediment in the form of authigenic Fe-sulfides. Arsenic and Sb cycling was also closely linked to that of OM and Fe- and Mn-oxyhydroxides. Shallow diagenetic enrichment of particulate Sb was observed in the less mature stages. As a result of authigenic sulfide precipitation, the sediments of the early stage of ecosystem development were a sink for water column Cu, Zn, Cd, Pb and Sb. In contrast, at all stages of ecosystem development, the sediments were a source of dissolved Co, Ni and As to the water column. However, the concentrations of these trace elements remained low in the bottom waters, indicating that sorption processes on Fe-bounding particles and/or large-size organo-mineral colloids could mitigate the impact of post-depositional redistribution of toxic elements on the water column.

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Seasonal dynamics of organic carbon and metals in thermokarst lakes from the discontinuous permafrost zone of western Siberia

Biogeosciences Discussions ◽

10.5194/bgd-12-1975-2015 ◽

2015 ◽

Vol 12 (2) ◽

pp. 1975-2019

Author(s):

R. M. Manasypov ◽

S. N. Vorobyev ◽

S. V. Loiko ◽

I. V. Kritzkov ◽

L. S. Shirokova ◽

...

Keyword(s):

Organic Matter ◽

Organic Carbon ◽

Water Column ◽

Permafrost Zone ◽

Ice Formation ◽

Thermokarst Lakes ◽

Dissolved Carbon ◽

Thermokarst Lake ◽

Discontinuous Permafrost ◽

Lake Waters

Abstract. Western Siberia's thermokarst (thaw) lakes extend over a territory spanning over a million km2; they are highly dynamic hydrochemical systems that receive chemical elements from the atmosphere and surrounding peat soil and vegetation, and exchange greenhouse gases with the atmosphere, delivering dissolved carbon and metals to adjacent hydrological systems. This work describes the chemical composition of ~ 130 thermokarst lakes of the size range from a few m2 to several km2, located in the discontinuous permafrost zone. Lakes were sampled during spring floods, just after the ice break (early June), the end of summer (August), the beginning of ice formation (October) and during the full freezing season in winter (February). Dissolved organic carbon (DOC) and the major and trace elements do not appreciably change their concentration with the lake size increase above 1000 m2 during all seasons. On the annual scale, the majority of dissolved elements including organic carbon increase their concentration from 30 to 500%, with a statistically significant (p < 0.05) trend from spring to winter. The maximal increase in trace element (TE) concentration occurred between spring and summer and autumn and winter. The ice formation in October included several stages: first, surface layer freezing followed by crack (fissure) formation with unfrozen water from the deeper layers spreading over the ice surface. This water was subsequently frozen and formed layered ice rich in organic matter. As a result, the DOC and metal concentrations were the highest at the beginning of the ice column and decreased from the surface to the depth. A number of elements demonstrated the accumulation, by more than a factor of 2, in the surface (0–20 cm) of the ice column relative to the rest of the ice core: Mn, Fe, Ni, Cu, Zn, As, Ba and Pb. The main consequences of discovered freeze-driven solute concentrations in thermokarst lake waters are enhanced colloidal coagulation and the removal of dissolved organic matter and associated insoluble metals from the water column to the sediments. The measured distribution coefficient of TE between amorphous organo-ferric coagulates and lake water (< 0.45 μm) were similar to those reported earlier for Fe-rich colloids and low molecular weight (< 1 kDa) fractions of thermokarst lake waters, suggesting massive co-precipitation of TE with amorphous Fe oxy(hydr)oxide stabilized by organic matter. Although the concentration of most elements is lowest in spring, this period of maximal water coverage of land creates a significant reservoir of DOC and soluble metals in the water column that can be easily mobilized to the hydrological network. The highest DOC concentration observed in the smallest (< 100 m2) water bodies in spring suggests their strongly heterotrophic status and, therefore, elevated CO2 flux from the lake surface to the atmosphere.

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Thermokarst lake methanogenesis along a complete talik profile

Biogeosciences ◽

10.5194/bg-12-4317-2015 ◽

2015 ◽

Vol 12 (14) ◽

pp. 4317-4331 ◽

Cited By ~ 21

Author(s):

J. K. Heslop ◽

K. M. Walter Anthony ◽

A. Sepulveda-Jauregui ◽

K. Martinez-Cruz ◽

A. Bondurant ◽

...

Keyword(s):

Lake Sediments ◽

Relative Magnitude ◽

Thermokarst Lake ◽

Ch4 Production ◽

Lake Sediment Core ◽

Permafrost Soils ◽

Thawing Permafrost ◽

Top 40 ◽

Lake Systems

Abstract. Thermokarst (thaw) lakes emit methane (CH4) to the atmosphere formed from thawed permafrost organic matter (OM), but the relative magnitude of CH4 production in surface lake sediments vs. deeper thawed permafrost horizons is not well understood. We assessed anaerobic CH4 production potentials from various depths along a 590 cm long lake sediment core that captured the entire sediment package of the talik (thaw bulb) beneath the center of an interior Alaska thermokarst lake, Vault Lake, and the top 40 cm of thawing permafrost beneath the talik. We also studied the adjacent Vault Creek permafrost tunnel that extends through ice-rich yedoma permafrost soils surrounding the lake and into underlying gravel. Our results showed CH4 production potentials were highest in the organic-rich surface lake sediments, which were 151 cm thick (mean ± SD: 5.95 ± 1.67 μg C–CH4 g dw−1 d−1; 125.9 ± 36.2 μg C–CH4 g C−1org d−1). High CH4 production potentials were also observed in recently thawed permafrost (1.18 ± 0.61 μg C–CH4g dw−1 d−1; 59.60± 51.5 μg C–CH4 g C−1org d−1) at the bottom of the talik, but the narrow thicknesses (43 cm) of this horizon limited its overall contribution to total sediment column CH4 production in the core. Lower rates of CH4 production were observed in sediment horizons representing permafrost that has been thawing in the talik for a longer period of time. No CH4 production was observed in samples obtained from the permafrost tunnel, a non-lake environment. Our findings imply that CH4 production is highly variable in thermokarst lake systems and that both modern OM supplied to surface sediments and ancient OM supplied to both surface and deep lake sediments by in situ thaw and shore erosion of yedoma permafrost are important to lake CH4 production.

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Ice algae resource utilization by benthic macro- and megafaunal communities on the Pacific Arctic shelf determined through lipid biomarker analysis

Marine Ecology Progress Series ◽

10.3354/meps13476 ◽

2020 ◽

Vol 651 ◽

pp. 23-43 ◽

Cited By ~ 1

Author(s):

CW Koch ◽

LW Cooper ◽

JM Grebmeier ◽

K Frey ◽

TA Brown

Keyword(s):

Organic Carbon ◽

Sea Ice ◽

Feeding Strategy ◽

Food Sources ◽

Ice Algae ◽

Surface Deposit ◽

Suspension Feeders ◽

Deposit Feeders ◽

Lipid Biomarker ◽

Biomarker Analysis

We studied ice algae utilization by benthic fauna from the northern Bering and Chukchi Seas using highly branched isoprenoid (HBI) biomarkers. We assessed whether various food acquisition strategies influence the observed HBI signatures. The proportion of phytoplankton to ice algae-sourced HBIs was determined through the H-Print approach that is presumed to reflect the percentage of sea ice organic carbon (iPOC) incorporated into tissues, relative to phytoplankton organic carbon. Cluster analysis separated 3 groups based on location and feeding strategy that were significantly influenced by annual sea ice persistence. Ice algae utilization was most significant in the northeast Chukchi Sea, where seasonal sea ice was present the longest. General feeding strategy was determined to be a significant factor in the degree of ice algae utilization. Predominant deposit feeders (both surface and subsurface) used more ice algae relative to suspension feeders. Organic carbon incorporated by predominant suspension feeders was primarily phytoplankton-based. The vast majority of all organisms sampled (~90%) incorporated a measurable quantity of iPOC. Sipunculids and brittle stars had the highest relative dependence on ice algae, while other taxa displayed plastic dietary responses, including the suspension/surface deposit feeder Macoma calcarea. This study indicates that ice algae are widely utilized in Pacific Arctic benthic food webs, but most benthic organisms displayed flexibility in consuming the available food sources. The elevated utilization of ice algae by deposit feeders may prove to be a disadvantage for these organisms if they cannot adapt to the ongoing decline of iPOC as seasonal sea ice declines.

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Quantification of biomarkers as an estimation of soil organic matter turnover and sources under a crop rotation

10.5194/egusphere-egu21-14822 ◽

2021 ◽

Author(s):

Layla M. San-Emeterio ◽

Ian D. Bull ◽

Jens Holtvoeth ◽

Rafael López ◽

Francisco J. González-Vila ◽

...

Keyword(s):

Organic Matter ◽

Organic Carbon ◽

Soil Organic Carbon ◽

Crop Rotation ◽

Total Lipid ◽

C3 Plant ◽

Organic Matter Turnover ◽

Lipid Biomarker ◽

Biomarker Analysis ◽

The Impact

Lipid biomarker analysis is an efficient tool for tracing organic matter sources in diverse environments. The quantification of biomarkers facilitates the location of soil organic carbon (SOC) from different sources in a soil profile. According to their structure, biomarkers from total lipid extracts (TLE) would exhibit different degrees of susceptibility to degradation, affecting thus their preservation in soils. Hence, it is crucial to better identify these biomarkers according to diverse stability scales. The aim of this study is to assess SOC contributions from aboveground and to develop a wider approach based on the allocation of C to quantitatively assess the sources of organic matter in low SOM content, highly weathered Mediterranean soils, following a C3-C4 rotation experiment.Soil samples were taken from three depth intervals (0-5, 5-20, 20-40 cm) from a Mediterranean agricultural soil at &#8220;La Hampa&#8221; experimental station used for a crop rotation experiment with wheat (C3 plant) and maize (C4 plant). Lipids were extracted and quantified as described in [1].The total lipid extracts were dominated by a homologous series of n-alkanols (saturated alcohols), short-, mid- and long-chain fatty acid methyl ester (FAME), branched FAME, unsaturated (mono- and polyunsaturated) FAME and sterols. Short-chain FAME, monounsaturated FAME were the most abundant fractions of free lipids. Mono-unsaturated alkanoic acids (Cn:1 FA) were detected in considerable amounts in all samples, namely various isomers of C16:1, C18:1, C20:1 and C22:1; these are believed to be mainly synthesised by soil bacteria. A significant increase of these compounds in rotation plots leads to an effective microbial consumption of labile organic matter in the surface soil [2]. Regarding FAME, the observed chain lengths ranged from C13 to C32, showing a unimodal distribution maximising at C16 and C18. These compounds are attributed also to microbial products, supporting our findings from the high proportion of the monounsaturated compounds found. In general, and in relation with all compounds, the abundances increased up to 20% compared with the control plots representing the initial content.These results indicate that, only after three years of crop rotation, a considerable contribution of soil organic carbon is inherited from bacterial activity. The combination of extractable lipids has been shown to validate the use of TLE as a proxy for source and other information on vegetation change and soil processes. This work will bring a discussion on the use of these compounds for tracing the impact of crop rotation on carbon storage.Acknowledgement: Ministerio de Ciencia Innovaci&#243;n y Universidades (MICIU) for INTERCARBON project (CGL2016-78937-R). L. San Emeterio also thanks MICIU for funding FPI research grants (BES-2017-07968). Mrs Desir&#233; Monis is acknowledged for technical assistance.[1] M. San-Emeterio, L., Bull, I. D., Holtvoeth, J., and Gonz&#225;lez-P&#233;rez, J. A.: Compound-specific isotopic analysis of fatty acids in three soil profiles to estimate organic matter turnover in agricultural soils., EGU General Assembly 2020, Online, 4&#8211;8 May 2020, EGU2020-18526, https://doi.org/10.5194/egusphere-egu2020-18526, 2020.[2] Tu, T. T. N., Egasse, C., Anquetil, C., Zanetti, F., Zeller, B., Huon, S., & Derenne, S. (2017). Leaf lipid degradation in soils and surface sediments: A litterbag experiment.&#160;Organic Geochemistry,&#160;104, 35-41.

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Evaluating sedimentary DNA for tracing changes in cyanobacteria dynamics from sediments spanning the last 350 years of Lake Tiefer See, NE Germany

Journal of Paleolimnology ◽

10.1007/s10933-021-00206-9 ◽

2021 ◽

Author(s):

Ebuka C. Nwosu ◽

Achim Brauer ◽

Jérôme Kaiser ◽

Fabian Horn ◽

Dirk Wagner ◽

...

Keyword(s):

Lake Sediments ◽

Community Dynamics ◽

Abiotic Factors ◽

Variation Partitioning ◽

Amplicon Sequencing ◽

Cyanobacterial Community ◽

Ne Germany ◽

Lipid Biomarker ◽

Biomarker Analysis ◽

Lake Circulation

AbstractSince the beginning of the Anthropocene, lacustrine biodiversity has been influenced by climate change and human activities. These factors advance the spread of harmful cyanobacteria in lakes around the world, which affects water quality and impairs the aquatic food chain. In this study, we assessed changes in cyanobacterial community dynamics via sedimentary DNA (sedaDNA) from well-dated lake sediments of Lake Tiefer See, which is part of the Klocksin Lake Chain spanning the last 350 years. Our diversity and community analysis revealed that cyanobacterial communities form clusters according to the presence or absence of varves. Based on distance-based redundancy and variation partitioning analyses (dbRDA and VPA) we identified that intensified lake circulation inferred from vegetation openness reconstructions, δ13C data (a proxy for varve preservation) and total nitrogen content were abiotic factors that significantly explained the variation in the reconstructed cyanobacterial community from Lake Tiefer See sediments. Operational taxonomic units (OTUs) assigned to Microcystis sp. and Aphanizomenon sp. were identified as potential eutrophication-driven taxa of growing importance since circa common era (ca. CE) 1920 till present. This result is corroborated by a cyanobacteria lipid biomarker analysis. Furthermore, we suggest that stronger lake circulation as indicated by non-varved sediments favoured the deposition of the non-photosynthetic cyanobacteria sister clade Sericytochromatia, whereas lake bottom anoxia as indicated by subrecent- and recent varves favoured the Melainabacteria in sediments. Our findings highlight the potential of high-resolution amplicon sequencing in investigating the dynamics of past cyanobacterial communities in lake sediments and show that lake circulation, anoxic conditions, and human-induced eutrophication are main factors explaining variations in the cyanobacteria community in Lake Tiefer See during the last 350 years.

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Siberian Arctic inland waters emit mostly contemporary carbon

10.5194/egusphere-egu2020-17416 ◽

2020 ◽

Author(s):

Joshua Dean ◽

Ove Meisel ◽

Melanie Martyn Roscoe ◽

Luca Belelli Marchesini ◽

Mark Garnett ◽

...

Keyword(s):

Organic Carbon ◽

Particulate Organic Carbon ◽

Carbon Emissions ◽

Carbon Sink ◽

Inland Waters ◽

Terrestrial Carbon ◽

Study Region ◽

Inland Water ◽

Radiocarbon Age ◽

Thawing Permafrost

Inland waters (rivers, lakes and ponds) are important conduits for the emission of terrestrial carbon in Arctic permafrost landscapes. These emissions are driven by turnover of contemporary terrestrial carbon and additional &#8220;pre-aged&#8221; (Holocene and late-Pleistocene) carbon released from thawing permafrost soils, but the magnitude of these source contributions to total inland water carbon fluxes remains unknown. Here we present unique simultaneous radiocarbon age measurements of inland water CO2, CH4 and dissolved and particulate organic carbon in northeast Siberia during summer. We show that >80% of total inland water carbon emissions were contemporary in age, but that pre-aged carbon contributed >50% at sites strongly affected by permafrost thaw. CO2 and CH4 were younger than dissolved and particulate organic carbon, suggesting emissions were primarily fuelled by contemporary carbon decomposition. The study region was a net carbon sink (-876.9 &#177; 136.4 Mg C for 25 July to 17 August), but inland waters were a source of contemporary (16.8 Mg C) and pre-aged (3.7 Mg C) emissions that respectively offset 1.9 &#177; 1.2% and 0.4 &#177; 0.3% of CO2 uptake by tundra (&#8209;897 &#177; 115 Mg C). Our findings reveal that inland water carbon emissions from permafrost landscapes may be more sensitive to changes in contemporary carbon turnover than the release of pre-aged carbon from thawing permafrost.

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Organic matter mineralization and trace element post-depositional redistribution in Western Siberia thermokarst lake sediments

Biogeosciences Discussions ◽

10.5194/bgd-8-8845-2011 ◽

2011 ◽

Vol 8 (4) ◽

pp. 8845-8894

Author(s):

S. Audry ◽

O. S. Pokrovsky ◽

L. S. Shirokova ◽

S. N. Kirpotin ◽

B. Dupré

Keyword(s):

Trace Elements ◽

Organic Matter ◽

Organic Carbon ◽

Lake Sediments ◽

Water Column ◽

Western Siberia ◽

Ecosystem Development ◽

Thermokarst Lake ◽

Fe And Mn ◽

The Impact

Abstract. This study reports the very first results on high-resolution sampling of sediments and their porewaters from three thermokarst (thaw) lakes representing different stages of ecosystem development located within the Nadym-Pur interfluve of the Western Siberia plain. Up to present time, the lake sediments of this and other permafrost-affected regions remain unexplored regarding their biogeochemical behavior. The aim of this study was to (i) document the early diagenesic processes in order to assess their impact on the organic carbon stored in the underlying permafrost, and (ii) characterize the post-depositional redistribution of trace elements and their impact on the water column. The estimated organic carbon (OC) stock in thermokarst lake sediments of 14 ± 2 kg m−2 is low compared to that reported for peat soils from the same region and denotes intense organic matter (OM) mineralization. Mineralization of OM in the thermokarst lake sediments proceeds under anoxic conditions in all the three lakes. In the course of the lake development, a shift in mineralization pathways was evidenced from nitrate and sulfate to Fe- and Mn-oxyhydroxides as the main terminal electron acceptors in the early diagenetic reactions. This shift was promoted by the diagenetic consumption of nitrate and sulfate and their gradual depletion in the water column due to progressively decreasing frozen peat lixiviation occurring at the lake's borders. Trace elements were mobilized from host phases (OM and Fe- and Mn-oxyhydroxides) and partly sequestered in the sediment in the form of authigenic Fe-sulfides. Arsenic and Sb cycling was also closely linked to that of OM and Fe- and Mn-oxyhydroxides. Shallow diagenetic enrichment of particulate Sb was observed in the less mature stages. As a result of authigenic sulfide precipitation, the sediments of the early stage of ecosystem development were a sink for water column Cu, Zn, Cd, Pb and Sb. In contrast, at all stages of ecosystem development, the sediments were a source of dissolved Co, Ni and As to the water column. However, the concentrations of these trace elements remained low in the bottom waters, indicating that sorption processes on Fe-bounding particles and/or large-size organo-mineral colloids could mitigate the impact of post-depositional redistribution of toxic elements on the water column.

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Organic matter characteristics of a rapidly eroding permafrost cliff in NE Siberia (Lena Delta, Laptev Sea region)

10.5194/bg-2021-331 ◽

2021 ◽

Author(s):

Charlotte Haugk ◽

Loeka Laura Jongejans ◽

Kai Mangelsdorf ◽

Matthias Fuchs ◽

Olga Ogneva ◽

...

Keyword(s):

Organic Matter ◽

Organic Carbon ◽

The Arctic ◽

Average Chain Length ◽

Organic Carbon Content ◽

Mis 3 ◽

Lipid Biomarker ◽

Isotopic Analyses ◽

High Organic Carbon Content

Abstract. Organic carbon (OC) stored in Arctic permafrost represents one of Earth’s largest and most vulnerable terrestrial carbon pools. Amplified climate warming across the Arctic results in widespread permafrost thaw. Permafrost deposits exposed at river cliffs and coasts are particularly susceptible to thawing processes. Accelerating erosion of terrestrial permafrost along shorelines leads to increased transfer of organic matter (OM) to nearshore waters. However, the amount of terrestrial permafrost carbon and nitrogen as well as the OM quality in these deposits are still poorly quantified. Here, we characterise the sources and the quality of OM supplied to the Lena River at a rapidly eroding permafrost river shoreline cliff in the eastern part of the delta (Sobo-Sise Island). Our multi-proxy approach captures bulk elemental, molecular geochemical and carbon isotopic analyses of late Pleistocene Yedoma permafrost and Holocene cover deposits, discontinuously spanning the last ~52 ka. We show that the ancient permafrost exposed in the Sobo-Sise cliff has a high organic carbon content (mean of about 5 wt%).We found that the OM quality, which we define as the intrinsic potential to further transformation, decomposition, and mineralization, is also high as inferred by the lipid biomarker inventory. The oldest sediments stem from Marine Isotope Stage (MIS) 3 interstadial deposits (dated to 52 to 28 cal kyr BP) and is overlaid by Last Glacial MIS 2 (dated to 28 to 15 cal ka BP) and Holocene MIS 1 (dated to 7–0 cal ka BP) deposits. The relatively high average chain length (ACL) index of n-alkanes along the cliff profile indicates a predominant contribution of vascular plants to the OM composition. The elevated ratio of iso and anteiso-branched FAs relative to long chain (C ≥ 20) n-FAs in the interstadial MIS 3 and the interglacial MIS 1 deposits, suggests stronger microbial activity and consequently higher input of bacterial biomass during these climatically warmer periods. The overall high carbon preference index (CPI) and higher plant fatty acid (HPFA) values as well as high C / N ratios point to a good quality of the preserved OM and thus to a high potential of the OM for decomposition upon thaw. A decrease of HPFA values downwards along the profile probably indicates a relatively stronger OM decomposition in the oldest (MIS 3) deposits of the cliff. The characterisation of OM from eroding permafrost leads to a better assessment of the greenhouse gas potential of the OC released into river and nearshore waters in future, which is important to understand the consequences of a warming climate in Arctic environments on the global carbon cycle.

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