| 1. |
- Abbott, Benjamin W., et al.
(författare)
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Biomass offsets little or none of permafrost carbon release from soils, streams, and wildfire : an expert assessment
- 2016
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Ingår i: Environmental Research Letters. - : IOP Publishing. - 1748-9326. ; 11:3
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Tidskriftsartikel (refereegranskat)abstract
- As the permafrost region warms, its large organic carbon pool will be increasingly vulnerable to decomposition, combustion, and hydrologic export. Models predict that some portion of this release will be offset by increased production of Arctic and boreal biomass; however, the lack of robust estimates of net carbon balance increases the risk of further overshooting international emissions targets. Precise empirical or model-based assessments of the critical factors driving carbon balance are unlikely in the near future, so to address this gap, we present estimates from 98 permafrost-region experts of the response of biomass, wildfire, and hydrologic carbon flux to climate change. Results suggest that contrary to model projections, total permafrost-region biomass could decrease due to water stress and disturbance, factors that are not adequately incorporated in current models. Assessments indicate that end-of-the-century organic carbon release from Arctic rivers and collapsing coastlines could increase by 75% while carbon loss via burning could increase four-fold. Experts identified water balance, shifts in vegetation community, and permafrost degradation as the key sources of uncertainty in predicting future system response. In combination with previous findings, results suggest the permafrost region will become a carbon source to the atmosphere by 2100 regardless of warming scenario but that 65%-85% of permafrost carbon release can still be avoided if human emissions are actively reduced.
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| 2. |
- Feng, Xiaojuan, et al.
(författare)
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Differential mobilization of terrestrial carbon pools in Eurasian Arctic river basins
- 2013
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 110:35, s. 14168-14173
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Tidskriftsartikel (refereegranskat)abstract
- Mobilization of Arctic permafrost carbon is expected to increase with warming-induced thawing. However, this effect is challenging to assess due to the diverse processes controlling the release of various organic carbon (OC) pools from heterogeneous Arctic landscapes. Here, by radiocarbon dating various terrestrial OC components in fluvially and coastally integrated estuarine sediments, we present a unique framework for deconvoluting the contrasting mobilization mechanisms of surface vs. deep (permafrost) carbon pools across the climosequence of the Eurasian Arctic. Vascular plant-derived lignin phenol C-14 contents reveal significant inputs of young carbon from surface sources whose delivery is dominantly controlled by river runoff. In contrast, plant wax lipids predominantly trace ancient (permafrost) OC that is preferentially mobilized from discontinuous permafrost regions, where hydrological conduits penetrate deeper into soils and thermokarst erosion occurs more frequently. Because river runoff has significantly increased across the Eurasian Arctic in recent decades, we estimate from an isotopic mixing model that, in tandem with an increased transfer of young surface carbon, the proportion of mobilized terrestrial OC accounted for by ancient carbon has increased by 3-6% between 1985 and 2004. These findings suggest that although partly masked by surface carbon export, climate change-induced mobilization of old permafrost carbon is well underway in the Arctic.
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| 3. |
- Feng, Xiaojuan, et al.
(författare)
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Multimolecular tracers of terrestrial carbon transfer across the pan-Arctic : C-14 characteristics of sedimentary carbon components and their environmental controls
- 2015
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Ingår i: Global Biogeochemical Cycles. - 0886-6236 .- 1944-9224. ; 29:11, s. 1855-1873
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Tidskriftsartikel (refereegranskat)abstract
- Distinguishing the sources, ages, and fate of various terrestrial organic carbon (OC) pools mobilized from heterogeneous Arctic landscapes is key to assessing climatic impacts on the fluvial release of carbon from permafrost. Through molecular C-14 measurements, including novel analyses of suberin- and/or cutin-derived diacids (DAs) and hydroxy fatty acids (FAs), we compared the radiocarbon characteristics of a comprehensive suite of terrestrial markers (including plant wax lipids, cutin, suberin, lignin, and hydroxy phenols) in the sedimentary particles from nine major arctic and subarctic rivers in order to establish a benchmark assessment of the mobilization patterns of terrestrial OC pools across the pan-Arctic. Terrestrial lipids, including suberin-derived longer-chain DAs (C-24,C-26,C-28), plant wax FAs (C(24,26,2)8), and n-alkanes (C-27,C-29,C-31), incorporated significant inputs of aged carbon, presumably from deeper soil horizons. Mobilization and translocation of these old terrestrial carbon components was dependent on nonlinear processes associated with permafrost distributions. By contrast, shorter-chain (C-16,C-18) DAs and lignin phenols (as well as hydroxy phenols in rivers outside eastern Eurasian Arctic) were much more enriched in C-14, suggesting incorporation of relatively young carbon supplied by runoff processes from recent vegetation debris and surface layers. Furthermore, the radiocarbon content of terrestrial markers is heavily influenced by specific OC sources and degradation status. Overall, multitracer molecular C-14 analysis sheds new light on the mobilization of terrestrial OC from arctic watersheds. Our findings of distinct ages for various terrestrial carbon components may aid in elucidating fate of different terrestrial OC pools in the face of increasing arctic permafrost thaw.
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| 4. |
- Wegner, Carolyn, et al.
(författare)
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Variability in transport of terrigenous material on the shelves and the deep Arctic Ocean during the Holocene
- 2015
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Ingår i: Polar Research. - : Norwegian Polar Institute. - 0800-0395 .- 1751-8369. ; 34
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Tidskriftsartikel (refereegranskat)abstract
- Arctic coastal zones serve as a sensitive filter for terrigenous matter input onto the shelves via river discharge and coastal erosion. This material is further distributed across the Arctic by ocean currents and sea ice. The coastal regions are particularly vulnerable to changes related to recent climate change. We compiled a pan-Arctic review that looks into the changing Holocene sources, transport processes and sinks of terrigenous sediment in the Arctic Ocean. Existing palaeoceanographic studies demonstrate how climate warming and the disappearance of ice sheets during the early Holocene initiated eustatic sea-level rise that greatly modified the physiography of the Arctic Ocean. Sedimentation rates over the shelves and slopes were much greater during periods of rapid sea-level rise in the early and middle Holocene, as a result of the relative distance to the terrestrial sediment sources. However, estimates of suspended sediment delivery through major Arctic rivers do not indicate enhanced delivery during this time, which suggests enhanced rates of coastal erosion. The increased supply of terrigenous material to the outer shelves and deep Arctic Ocean in the early and middle Holocene might serve as analogous to forecast changes in the future Arctic.
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| 5. |
- Alling, Vanja, et al.
(författare)
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Non-conservative behavior of dissolved organic carbon across the Laptev and East Siberian Seas
- 2010
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Ingår i: Global Biogeochemical Cycles. - 0886-6236 .- 1944-9224. ; 24, s. GB4033-
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Tidskriftsartikel (refereegranskat)abstract
- Climate change is expected to have a strong effect on the Eastern Siberian Arctic Shelf (ESAS) region, which includes 40% of the Arctic shelves and comprises the Laptev and East Siberian seas. The largest organic carbon pool, the dissolved organic carbon (DOC), may change significantly due to changes in both riverine inputs and transformation rates; however, the present DOC inventories and transformation patterns are poorly understood. Using samples from the International Siberian Shelf Study 2008, this study examines for the first time DOC removal in Arctic shelf waters with residence times that range from months to years. Removals of up to 10%–20% were found in the Lena River estuary, consistent with earlier studies in this area, where surface waters were shown to have a residence time of approximately 2 months. In contrast, the DOC concentrations showed a strong nonconservative pattern in areas with freshwater residence times of several years. The average losses of DOC were estimated to be 30%–50% during mixing along the shelf, corresponding to a first-order removal rate constant of 0.3 yr−1. These data provide the first observational evidence for losses of DOC in the Arctic shelf seas, and the calculated DOC deficit reflects DOC losses that are higher than recent model estimates for the region. Overall, a large proportion of riverine DOC is removed from the surface waters across the Arctic shelves. Such significant losses must be included in models of the carbon cycle for the Arctic Ocean, especially since the breakdown of terrestrial DOC to CO2 in Arctic shelf seas may constitute a positive feedback mechanism for Arctic climate warming. These data also provide a baseline for considering the effects of future changes in carbon fluxes, as the vast northern carbon-rich permafrost areas draining into the Arctic are affected by global warming.
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| 6. |
- Bruhn, Anders Dalhoff, et al.
(författare)
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Terrestrial Dissolved Organic Matter Mobilized From Eroding Permafrost Controls Microbial Community Composition and Growth in Arctic Coastal Zones
- 2021
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Ingår i: Frontiers in Earth Science. - : Frontiers Media SA. - 2296-6463. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Climate warming is accelerating erosion along permafrost-dominated Arctic coasts. This results in the additional supply of organic matter (OM) and nutrients into the coastal zone. In this study we investigate the impact of coastal erosion on the marine microbial community composition and growth rates in the coastal Beaufort Sea. Dissolved organic matter (DOM) derived from three representative glacial deposit types (fluvial, lacustrine, and moraine) along the Yukon coastal plain, Canada, were used as substrate to cultivate marine bacteria using a chemostat setup. Our results show that DOM composition (inferred from UV-Visible spectroscopy) and biodegradability (inferred from DOC concentration, bacterial production and respiration) significantly differ between the three glacial deposit types. DOM derived from fluvial and moraine types show clear terrestrial characteristics with low aromaticity (Sr: 0.63 ± 0.02 and SUVA254: 1.65 ± 0.06 L mg C−1 m−1 & Sr: 0.68 ± 0.01 and SUVA254: 1.17 ± 0.06 L mg C−1 m−1, respectively) compared to the lacustrine soil type (Sr: 0.71 ± 0.02 and SUVA254: 2.15 ± 0.05 L mg C−1 m−1). The difference in composition of DOM leads to the development of three different microbial communities. Whereas Alphaproteobacteria dominate in fluvial and lacustrine deposit types (67 and 87% relative abundance, respectively), Gammaproteobacteria is the most abundant class for moraine deposit type (88% relative abundance). Bacterial growth efficiency (BGE) is 66% for DOM from moraine deposit type, while 13 and 28% for DOM from fluvial and lacustrine deposit types, respectively. The three microbial communities therefore differ strongly in their net effect on DOM utilization depending on the eroded landscape type. The high BGE value for moraine-derived DOM is probably caused by a larger proportion of labile colorless DOM. These results indicate that the substrate controls marine microbial community composition and activities in coastal waters. This suggests that biogeochemical changes in the Arctic coastal zone will depend on the DOM character of adjacent deposit types, which determine the speed and extent of DOM mineralization and thereby carbon channeling into the microbial food web. We conclude that marine microbes strongly respond to the input of terrestrial DOM released by coastal erosion and that the landscape type differently influence marine microbes.
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| 7. |
- Klaminder, Jonatan, et al.
(författare)
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Lead Contamination of Subarctic Lakes and Its Response to Reduced Atmospheric Fallout : Can the Recovery Process Be Counteracted by the Ongoing Climate Change?
- 2010
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 44:7, s. 2335-2340
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Tidskriftsartikel (refereegranskat)abstract
- Can a climate-triggered export of old contaminants from the soil alter the lead (Pb) contaminant burden of subarctic lakes? To address this question, we reconstructed the pollution history of three high latitude lakes situated in a region where a recent climatic shift has occurred. Dated sediment records were used as archives of past Pb inputs to the lakes, where the difference in the Pb-206/Pb-207 ratio between atmospheric contaminants (Pb-206/Pb-207 ratio <1.16) and geogenic Pb in the catchment soil (Pb-206/Pb-207 ratio >1.22) were used to trace fluxes of Pb contaminants. Lead contaminants were found in sediments deposited since Roman times. A significant export of Pb from the soil contaminant pool is indicated in two of the lakes surrounded by near-shore permafrost soils. Here, levels of Pb contaminants and Pb-206/Pb-207 ratios of sediments deposited after the 1970s appear not to have been strongly affected by the >= 90% reduction in atmospheric deposition rates and increasing Pb-206/Pb-207 ratios of atmospheric Pb since the 1990s. We concluded that soil processes stimulated by the ongoing climate change at high latitudes might work counteractive to efforts to reduce contaminant levels in subarctic lakes.
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| 8. |
- Parmentier, Frans Jan W, et al.
(författare)
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A synthesis of the arctic terrestrial and marine carbon cycles under pressure from a dwindling cryosphere
- 2017
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Ingår i: Ambio: a Journal of the Human Environment. - : Springer Science and Business Media LLC. - 0044-7447. ; 46, s. 53-69
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Tidskriftsartikel (refereegranskat)abstract
- The current downturn of the arctic cryosphere, such as the strong loss of sea ice, melting of ice sheets and glaciers, and permafrost thaw, affects the marine and terrestrial carbon cycles in numerous interconnected ways. Nonetheless, processes in the ocean and on land have been too often considered in isolation while it has become increasingly clear that the two environments are strongly connected: Sea ice decline is one of the main causes of the rapid warming of the Arctic, and the flow of carbon from rivers into the Arctic Ocean affects marine processes and the air–sea exchange of CO2. This review, therefore, provides an overview of the current state of knowledge of the arctic terrestrial and marine carbon cycle, connections in between, and how this complex system is affected by climate change and a declining cryosphere. Ultimately, better knowledge of biogeochemical processes combined with improved model representations of ocean–land interactions are essential to accurately predict the development of arctic ecosystems and associated climate feedbacks.
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| 9. |
- Sanchez-Garcia, Laura, et al.
(författare)
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Characterisation of Three Regimes of Collapsing Arctic Ice Complex Deposits on the SE Laptev Sea Coast using Biomarkers and Dual Carbon Isotopes
- 2014
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Ingår i: Permafrost and Periglacial Processes. - : Wiley. - 1045-6740 .- 1099-1530. ; 25:3, s. 172-183
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Tidskriftsartikel (refereegranskat)abstract
- Arctic amplification of climate warming is intensifying the thaw and coastal erosion of the widespread and carbon-rich Siberian Ice Complex Deposits (ICD). Despite the potential for altering long-term carbon dynamics in the Arctic, the susceptibility of organic carbon (OC) to degradation as the ICD thaw is poorly characterised. This study identifies signs of OC degradation in three Siberian ICD regimes of coastal erosion through elemental, isotopic and molecular analyses. The degree of erosion appears to determine the extent of degradation. The moisture-limited and beach-protected ICD bluff near Buor-Khaya Cape, characterised by thermokarst mounds (baydzherakhs), represents a dormant regime with limited ongoing degradation. Conversely, the more exposed ICD scarps on eroding riverbanks (Olenek Channel, Lena Delta) and coastal slopes (Muostakh Island) showed more pronounced signs of ongoing OC decay. Different parameters suggest that degradation can partially explain the shift of the OC signature with C-14 age in the thawing ICD. Exposure time, degree of erosion, slope gradient and moisture conditions appear to be key factors determining the degradation propensity of OC in exposed ICD. These field results document the lability of OC in ICD upon thaw and illustrate the potential for transferring old OC into the rapidly cycling atmosphere-biosphere carbon pools.
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| 10. |
- Sayedi, Sayedeh Sara, et al.
(författare)
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Subsea permafrost carbon stocks and climate change sensitivity estimated by expert assessment
- 2020
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Ingår i: Environmental Research Letters. - : IOP Publishing. - 1748-9326. ; 15:12
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Tidskriftsartikel (refereegranskat)abstract
- The continental shelves of the Arctic Ocean and surrounding seas contain large stocks of organic matter (OM) and methane (CH4), representing a potential ecosystem feedback to climate change not included in international climate agreements. We performed a structured expert assessment with 25 permafrost researchers to combine quantitative estimates of the stocks and sensitivity of organic carbon in the subsea permafrost domain (i.e. unglaciated portions of the continental shelves exposed during the last glacial period). Experts estimated that the subsea permafrost domain contains similar to 560 gigatons carbon (GtC; 170-740, 90% confidence interval) in OM and 45 GtC (10-110) in CH4. Current fluxes of CH4 and carbon dioxide (CO2) to the water column were estimated at 18 (2-34) and 38 (13-110) megatons C yr(-1), respectively. Under Representative Concentration Pathway (RCP) RCP8.5, the subsea permafrost domain could release 43 Gt CO2-equivalent (CO(2)e) by 2100 (14-110) and 190 Gt CO(2)e by 2300 (45-590), with similar to 30% fewer emissions under RCP2.6. The range of uncertainty demonstrates a serious knowledge gap but provides initial estimates of the magnitude and timing of the subsea permafrost climate feedback.
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| 11. |
- Speetjens, Niek Jesse, et al.
(författare)
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Degradation of ice-wedge polygons leads to increased fluxes of water and DOC
- 2024
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Ingår i: Science of the Total Environment. - 0048-9697 .- 1879-1026. ; 920, s. 170931-
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Tidskriftsartikel (refereegranskat)abstract
- Ice-wedge polygon landscapes make up a substantial part of high-latitude permafrost landscapes. The hydrological conditions shape how these landscapes store and release organic carbon. However, their coupled water‑carbon dynamics are poorly understood as field measurements are sparse in smaller catchments and coupled hydrology-dissolved organic carbon (DOC) models are not tailored for these landscapes. Here we present a model that simulates the hydrology and associated DOC export of high-centered and low-centered ice-wedge polygons and apply the model to a small catchment with abundant polygon coverage along the Yukon Coast, Canada. The modeled seasonal pattern of water and carbon fluxes aligns with sparse field data. These modeled seasonal patterns indicate that early-season runoff is mostly surficial and generated by low-centered polygons and snow trapped in troughs of high-centered polygons. High-centered polygons show potential for deeper subsurface flow under future climate conditions. This suggests that high-centered polygons will be responsible for an increasing proportion of annual DOC export compared to low-centered polygons. Warming likely shifts low-centered polygons to high-centered polygons, and our model shows that this shift will cause a deepening of the active layer and a lengthening of the thawing season. This, in turn, intensifies seasonal runoff and DOC flux, mainly through its duration. Our model provides a physical hypothesis that can be used to further quantify and refine our understanding of hydrology and DOC export of arctic ice-wedge polygon terrain.
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| 12. |
- Speetjens, Niek Jesse, et al.
(författare)
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Dissolved organic matter characterization in soils and streams in a small coastal low-Arctic catchment
- 2022
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 19:12, s. 3073-3097
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Tidskriftsartikel (refereegranskat)abstract
- Ongoing climate warming in the western Canadian Arctic is leading to thawing of permafrost soils and subsequent mobilization of its organic matter pool. Part of this mobilized terrestrial organic matter enters the aquatic system as dissolved organic matter (DOM) and is laterally transported from land to sea. Mobilized organic matter is an important source of nutrients for ecosystems, as it is available for microbial breakdown, and thus a source of greenhouse gases. We are beginning to understand spatial controls on the release of DOM as well as the quantities and fate of this material in large Arctic rivers. Yet, these processes remain systematically understudied in small, high-Arctic watersheds, despite the fact that these watersheds experience the strongest warming rates in comparison. Here, we sampled soil (active layer and permafrost) and water (porewater and stream water) from a small ice wedge polygon (IWP) catchment along the Yukon coast, Canada, during the summer of 2018. We assessed the organic carbon (OC) quantity (using dissolved (DOC) and particulate OC (POC) concentrations and soil OC content), quality (δ13C DOC, optical properties and source apportionment) and bioavailability (incubations; optical indices such as slope ratio, Sr; and humification index, HIX) along with stream water properties (temperature, T; pH; electrical conductivity, EC; and water isotopes). We classify and compare different landscape units and their soil horizons that differ in microtopography and hydrological connectivity, giving rise to differences in drainage capacity. Our results show that porewater DOC concentrations and yield reflect drainage patterns and waterlogged conditions in the watershed. DOC yield (in mg DOC g−1 soil OC) generally increases with depth but shows a large variability near the transition zone (around the permafrost table). Active-layer porewater DOC generally is more labile than permafrost DOC, due to various reasons (heterogeneity, presence of a paleo-active-layer and sampling strategies). Despite these differences, the very long transport times of porewater DOC indicate that substantial processing occurs in soils prior to release into streams. Within the stream, DOC strongly dominates over POC, illustrated by DOC/POC ratios around 50, yet storm events decrease that ratio to around 5. Source apportionment of stream DOC suggests a contribution of around 50 % from permafrost/deep-active-layer OC, which contrasts with patterns observed in large Arctic rivers (12 ± 8 %; Wild et al., 2019). Our 10 d monitoring period demonstrated temporal DOC patterns on multiple scales (i.e., diurnal patterns, storm events and longer-term trends), underlining the need for high-resolution long-term monitoring. First estimates of Black Creek annual DOC (8.2 ± 6.4 t DOC yr−1) and POC (0.21 ± 0.20 t yr−1) export allowed us to make a rough upscaling towards the entire Yukon Coastal Plain (34.51 ± 2.7 kt DOC yr−1 and 8.93 ± 8.5 kt POC yr−1). Rising Arctic temperatures, increases in runoff, soil organic matter (OM) leaching, permafrost thawing and primary production are likely to increase the net lateral OC flux. Consequently, altered lateral fluxes may have strong impacts on Arctic aquatic ecosystems and Arctic carbon cycling.
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| 13. |
- Speetjens, Niek Jesse, et al.
(författare)
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The pan-Arctic catchment database (ARCADE)
- 2023
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Ingår i: Earth System Science Data. - : Copernicus GmbH. - 1866-3508 .- 1866-3516. ; 15:2, s. 541-554
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Tidskriftsartikel (refereegranskat)abstract
- The Arctic is rapidly changing. Outside the Arctic, large-sample catchment databases have transformed catchment science from focusing on local case studies to more systematic studies of watershed functioning. Here we present an integrated pan-ARctic CAtchments summary DatabasE (ARCADE) of > 40 000 catchments that drain into the Arctic Ocean and range in size from 1 to 3.1 × 106 km2. These watersheds, delineated at a 90 m resolution, are provided with 103 geospatial, environmental, climatic, and physiographic catchment properties. ARCADE is the first aggregated database of pan-Arctic river catchments that also includes numerous small watersheds at a high resolution. These small catchments are experiencing the greatest climatic warming while also storing large quantities of soil carbon in landscapes that are especially prone to degradation of permafrost (i.e., ice wedge polygon terrain) and associated hydrological regime shifts. ARCADE is a key step toward monitoring the pan-Arctic across scales and is publicly available: https://doi.org/10.34894/U9HSPV (Speetjens et al., 2022).
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| 14. |
- Tesi, Tommaso, et al.
(författare)
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Carbon geochemistry of plankton-dominated samples in the Laptev and East Siberian shelves : contrasts in suspended particle composition
- 2017
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Ingår i: Ocean Science. - : Copernicus GmbH. - 1812-0784 .- 1812-0792. ; 13:5, s. 735-748
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Tidskriftsartikel (refereegranskat)abstract
- Recent Arctic studies suggest that sea ice decline and permafrost thawing will affect phytoplankton dynamics and stimulate heterotrophic communities. However, in what way the plankton composition will change as the warming proceeds remains elusive. Here we investigate the chemical signature of the plankton-dominated fraction of particulate organic matter (POM) collected along the Siberian Shelf. POM (>10 mu m) samples were analysed using molecular biomarkers (CuO oxidation and IP25 ) and dual-carbon isotopes (delta C-13 and Delta C-14). In addition, surface water chemical properties were integrated with the POM (>10 mu m) dataset to understand the link between plankton composition and environmental conditions. delta C-13 and Delta C-14 exhibited a large variability in the POM (> 10 mu m) distribution while the content of terrestrial biomarkers in the POM was negligible. In the Laptev Sea (LS), delta C-13 and Delta C-14 of POM (> 10 mu m) suggested a heterotrophic environment in which dissolved organic carbon (DOC) from the Lena River was the primary source of metabolisable carbon. Within the Lena plume, terrestrial DOC probably became part of the food web via bacteria uptake and subsequently transferred to relatively other heterotrophic communities (e.g. dinoflagellates). Moving eastwards toward the sea-ice-dominated East Siberian Sea (ESS), the system became progressively more autotrophic. Comparison between delta C-13 of POM (> 10 mu m) samples and CO(2)aq concentrations revealed that the carbon isotope fractionation increased moving towards the easternmost and most productive stations. In a warming scenario characterised by enhanced terrestrial DOC release (thawing permafrost) and progressive sea ice decline, heterotrophic conditions might persist in the LS while the nutrient-rich Pacific inflow will likely stimulate greater primary productivity in the ESS. The contrasting trophic conditions will result in a sharp gradient in delta C-13 between the LS and ESS, similar to what is documented in our semi-synoptic study.
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| 15. |
- Vonk, Jorien E., et al.
(författare)
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Distinguishing between old and modern permafrost sources in the northeast Siberian land-shelf system with compound-specific delta H-2 analysis
- 2017
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Ingår i: The Cryosphere. - : Copernicus GmbH. - 1994-0416 .- 1994-0424. ; 11:4, s. 1879-1895
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Tidskriftsartikel (refereegranskat)abstract
- Pleistocene ice complex permafrost deposits contain roughly a quarter of the organic carbon (OC) stored in permafrost (PF) terrain. When permafrost thaws, its OC is remobilized into the (aquatic) environment where it is available for degradation, transport or burial. Aquatic or coastal environments contain sedimentary reservoirs that can serve as archives of past climatic change. As permafrost thaw is increasing throughout the Arctic, these reservoirs are important locations to assess the fate of remobilized permafrost OC. We here present compound-specific deuterium (delta H-2) analysis on leaf waxes as a tool to distinguish between OC released from thawing Pleistocene permafrost (ice complex deposits; ICD) and from thawing Holocene permafrost (from near-surface soils). Bulk geochemistry (%OC; delta C-13; % total nitrogen, TN) was analyzed as well as the concentrations and delta H-2 signatures of long-chain n-alkanes (C-21 to C-33) and midto long-chain n-alkanoic acids (C-16 to C-30) extracted from both ICD-PF samples (n = 9) and modern vegetation and Ohorizon (topsoil-PF) samples (n = 9) from across the northeast Siberian Arctic. Results show that these topsoil-PF samples have higher %OC, higher OC/TN values and more depleted delta(COC)-C-13 values than ICD-PF samples, suggesting that these former samples trace a fresher soil and/or vegetation source. Whereas the two investigated sources differ on the bulk geochemical level, they are, however, virtually indistinguishable when using leaf wax concentrations and ratios. However, on the molecular isotope level, leaf wax biomarker delta H-2 values are statistically different between topsoil PF and ICD PF. For example, the mean delta H-2 value of C-29 n-alkane was -246 +/- 13% (mean +/- SD) for topsoil PF and -280 +/- 12 parts per thousand for ICD PF. With a dynamic isotopic range (difference between two sources) of 34 to 50 parts per thousand; the isotopic fingerprints of individual, abundant, biomarker molecules from leaf waxes can thus serve as endmembers to distinguish between these two sources. We tested this molecular delta H-2 tracer along with another source-distinguishing approach, dual-carbon (delta C-13-Delta C-14) isotope composition of bulk OC, for a surface sediment transect in the Laptev Sea. Results show that general offshore patterns along the shelfslope transect are similar, but the source apportionment between the approaches vary, which may highlight the advan-tages of either. This study indicates that the application of delta H-2 leaf wax values has potential to serve as a complementary quantitative measure of the source and differential fate of OC thawed out from different permafrost compartments.
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| 16. |
- Vonk, Jorien E., et al.
(författare)
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Molecular and radiocarbon constraints on sources and degradation of terrestrial organic carbon along the Kolyma paleoriver transect, East Siberian Sea
- 2010
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 7:10, s. 3153-3166
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Tidskriftsartikel (refereegranskat)abstract
- Climate warming in northeastern Siberia may induce thaw-mobilization of the organic carbon (OC) now held in permafrost. This study investigated the composition of terrestrial OC exported to Arctic coastal waters to both obtain a natural integration of terrestrial permafrost OC release and to further understand the fate of released carbon in the extensive Siberian Shelf Seas. Application of a variety of elemental, molecular and isotopic (delta C-13 and Delta C-14) analyses of both surface water suspended particulate matter and underlying surface sediments along a 500 km transect from Kolyma River mouth to the mid-shelf of the East Siberian Sea yielded information on the sources, degradation status and transport processes of thaw-mobilized soil OC. A three end-member dual-carbon-isotopic mixing model was applied to deduce the relative contributions from riverine, coastal erosion and marine sources. The mixing model was solved numerically using Monte Carlo simulations to obtain a fair representation of the uncertainties of both end-member composition and the end results. Riverine OC contributions to sediment OC decrease with increasing distance offshore (35 +/- 15 to 13 +/- 9%), whereas coastal erosion OC exhibits a constantly high contribution (51 +/- 11 to 60 +/- 12%) and marine OC increases offshore (9 +/- 7 to 36 +/- 10%). We attribute the remarkably strong imprint of OC from coastal erosion, extending up to similar to 500 km from the coast, to efficient offshoreward transport in these shallow waters presumably through both the benthic boundary layer and ice-rafting. There are also indications of simultaneous selective preservation of erosion OC compared to riverine OC. Molecular degradation proxies and radiocarbon contents indicated a degraded but young (Delta C-14 ca. -60% or ca. 500 C-14 years) terrestrial OC pool in surface water particulate matter, underlain by a less degraded but old (Delta C-14 ca. -500% or ca. 5500 C-14 years) terrestrial OC pool in bottom sediments. We suggest that the terrestrial OC fraction in surface water particulate matter is mainly derived from surface soil and recent vegetation fluvially released as buoyant organic-rich aggregates (e. g., humics), which are subjected to extensive processing during coastal transport. In contrast, terrestrial OC in the underlying sediments is postulated to originate predominantly from erosion of mineral-rich Pleistocene coasts (i.e., yedoma) and inland mineral soils. Sorptive association of this organic matter with mineral particles protects the OC from remineralization and also promotes rapid settling (ballasting) of the OC. Our findings corroborate recent studies by indicating that different Arctic surface soil OC pools exhibit distinguishing susceptibilities to degradation in coastal waters. Consequently, the general postulation of a positive feedback to global warming from degradation of permafrost carbon may be both attenuated (by reburial of one portion) and geographically displaced (degradation of released terrestrial permafrost OC far out over the Arctic shelf seas).
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| 17. |
- Vonk, Jorien E., et al.
(författare)
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Preferential burial of permafrost-derived organic carbon in Siberian-Arctic shelf waters
- 2014
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Ingår i: Journal of Geophysical Research Oceans. - 2169-9275. ; 119:12, s. 8410-8421
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Tidskriftsartikel (refereegranskat)abstract
- The rapidly changing East Siberian Arctic Shelf (ESAS) receives large amounts of terrestrial organic carbon (OC) from coastal erosion and Russian-Arctic rivers. Climate warming increases thawing of coastal Ice Complex Deposits (ICD) and can change both the amount of released OC, as well as its propensity to be converted to greenhouse gases (fueling further global warming) or to be buried in coastal sediments. This study aimed to unravel the susceptibility to degradation, and transport and dispersal patterns of OC delivered to the ESAS. Bulk and molecular radiocarbon analyses on surface particulate matter (PM), sinking PM and underlying surface sediments illustrate the active release of old OC from coastal permafrost. Molecular tracers for recalcitrant soil OC showed ages of 3.4-13 C-14-ky in surface PM and 5.5-18 C-14-ky in surface sediments. The age difference of these markers between surface PM and surface sediments is larger (i) in regions with low OC accumulation rates, suggesting a weaker exchange between water column and sediments, and (ii) with increasing distance from the Lena River, suggesting preferential settling of fluvially derived old OC nearshore. A dual-carbon end-member mixing model showed that (i) contemporary terrestrial OC is dispersed mainly by horizontal transport while being subject to active degradation, (ii) marine OC is most affected by vertical transport and also actively degraded in the water column, and (iii) OC from ICD settles rapidly and dominates surface sediments. Preferential burial of ICD-OC released into ESAS coastal waters might therefore lower the suggested carbon cycle climate feedback from thawing ICD permafrost.
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| 18. |
- Vonk, Jorien Elisabeth, et al.
(författare)
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Selective preservation of old organic carbon fluvially released from sub-arctic soils
- 2010
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 37, s. L11605-
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 19. |
- Vonk, Jorien E., et al.
(författare)
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Temporal deconvolution of vascular plant-derived fatty acids exported from terrestrial watersheds
- 2019
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Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier BV. - 0016-7037 .- 1872-9533. ; 244, s. 502-521
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Tidskriftsartikel (refereegranskat)abstract
- Relatively little is known about the amount of time that lapses between the photosynthetic fixation of carbon by vascular land plants and its incorporation into the marine sedimentary record, yet the dynamics of terrestrial carbon sequestration have important implications for the carbon cycle. Vascular plant carbon may encounter multiple potential intermediate storage pools and transport trajectories, and the age of vascular plant carbon accumulating in marine sediments will reflect these different pre-depositional histories. Here, we examine down-core C-14 profiles of higher plant leaf wax-derived fatty acids isolated from high fidelity sedimentary sequences spanning the so-called bomb-spike, and encompassing a ca. 60-degree latitudinal gradient from tropical (Cariaco Basin), temperate (Saanich Inlet), and polar (Mackenzie Delta) watersheds to constrain integrated vascular plant carbon storage/transport times (residence times). Using a modeling framework, we find that, in addition to a young (conditionally defined as < 50 y) carbon pool, an old pool of compounds comprises 49 to 78 % of the fractional contribution of organic carbon (OC) and exhibits variable ages reflective of the environmental setting. For the Mackenzie Delta sediments, we find a mean age of the old pool of 28 ky (+/- 9.4, standard deviation), indicating extensive pre-aging in permafrost soils, whereas the old pools in Saanich Inlet and Cariaco Basin sediments are younger, 7.9 (+/- 5.0) and 2.4 (+/- 0.50) to 3.2 (+/- 0.54) ky, respectively, indicating less protracted storage in terrestrial reservoirs. The young pool showed clear annual contributions for Saanich Inlet and Mackenzie Delta sediments (comprising 24% and 16% of this pool, respectively), likely reflecting episodic transport of OC from steep hillside slopes surrounding Saanich Inlet and annual spring flood deposition in the Mackenzie Delta, respectively. Contributions of 5-10 year old OC to the Cariaco Basin show a short delay of OC inflow, potentially related to transport time to the offshore basin. Modeling results also indicate that the Mackenzie Delta has an influx of young but decadal material (20-30 years of age), pointing to the presence of an intermediate reservoir. Overall, these results show that a significant fraction of vascular plant C undergoes pre-aging in terrestrial reservoirs prior to accumulation in deltaic and marine sediments. The age distribution, reflecting both storage and transport times, likely depends on landscape-specific factors such as local topography, hydrographic characteristics, and mean annual temperature of the catchment, all of which affect the degree of soil buildup and preservation. We show that catchment-specific carbon residence times across landscapes can vary by an order of magnitude, with important implications both for carbon cycle studies and for the interpretation of molecular terrestrial paleoclimate records preserved in sedimentary sequences.
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| 20. |
- Wagner, Julia, et al.
(författare)
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High resolution mapping shows differences in soil carbon and nitrogen stocks in areas of varying landscape history in Canadian lowland tundra
- 2023
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Ingår i: Geoderma. - 0016-7061 .- 1872-6259. ; 438
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Tidskriftsartikel (refereegranskat)abstract
- Soil organic carbon (SOC) in Arctic coastal polygonal tundra is vulnerable to climate change, especially in soils with occurrence of large amounts of ground ice. Pan-arctic studies of mapping SOC exist, yet they fail to describe the high spatial variability of SOC storage in permafrost landscapes. An important factor is the landscape history which determines landform development and consequently the spatial variability of SOC. Our aim was to map SOC stocks, and which environmental variables that determine SOC, in two adjacent coastal areas along Canadian Beaufort Sea coast with different glacial history. We used the machine learning technique random forest and environmental variables to map the spatial distribution of SOC stocks down to 1 m depth at a spatial resolution of 2 m for depth increments of 0-5, 5-15, 15-30, 30-60 and 60-100 cm. The results show that the two study areas had large differences in SOC stocks in the depth 60-100 cm due to high amounts of ground ice in one of the study areas. There are also differences in variable importance of the explanatory variables between the two areas. The area low in ground ice content had with 66.6 kg C/m(-2) more stored SOC than the area rich in ground ice content with 40.0 kg C/m(-2). However, this SOC stock could be potentially more vulnerable to climate change if ground ice melts and the ground subsides. The average N stock of the area low in ground ice is 3.77 kg m(-2) and of the area rich in ground ice is 3.83 kg m(-2). These findings support that there is a strong correlation between ground ice and SOC, with less SOC in ice-rich layers on a small scale. In addition to small scale studies of SOC mapping, detailed maps of ground ice content and distribution are needed for a validation of large-scale quantifications of SOC stocks and transferability of models.
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