scholarly journals Carbonaceous material export from Siberian permafrost tracked across the Arctic Shelf using Raman spectroscopy

2018 ◽  
Vol 12 (10) ◽  
pp. 3293-3309 ◽  
Author(s):  
Robert B. Sparkes ◽  
Melissa Maher ◽  
Jerome Blewett ◽  
Ayça Doğrul Selver ◽  
Örjan Gustafsson ◽  
...  
Keyword(s):  
Raman Spectroscopy ◽  
Organic Matter ◽  
Deep Ocean ◽  
Carbonaceous Material ◽  
Arctic Shelf ◽  
The Arctic ◽  
Organic Load ◽  
Terrestrial Organic Matter ◽  
Labile Organic Matter ◽  
Thawing Permafrost

Abstract. Warming-induced erosion of permafrost from Eastern Siberia mobilises large amounts of organic carbon and delivers it to the East Siberian Arctic Shelf (ESAS). In this study Raman spectroscopy of carbonaceous material (CM) was used to characterise, identify and track the most recalcitrant fraction of the organic load: 1463 spectra were obtained from surface sediments collected across the ESAS and automatically analysed for their Raman peaks. Spectra were classified by their peak areas and widths into disordered, intermediate, mildly graphitised and highly graphitised groups and the distribution of these classes was investigated across the shelf. Disordered CM was most prevalent in a permafrost core from Kurungnakh Island and from areas known to have high rates of coastal erosion. Sediments from outflows of the Indigirka and Kolyma rivers were generally enriched in intermediate CM. These different sediment sources were identified and distinguished along an E–W transect using their Raman spectra, showing that sediment is not homogenised on the ESAS. Distal samples, from the ESAS slope, contained greater amounts of highly graphitised CM compared to the rest of the shelf, attributable to degradation or, more likely, winnowing processes offshore. The presence of all four spectral classes in distal sediments demonstrates that CM degrades much more slowly than lipid biomarkers and other traditional tracers of terrestrial organic matter and shows that alongside degradation of the more labile organic matter component there is also conservative transport of carbon across the shelf toward the deep ocean. Thus, carbon cycle calculations must consider the nature as well as the amount of carbon liberated from thawing permafrost and other erosional settings.

scholarly journals Carbonaceous material export from Siberian permafrost tracked across the Arctic Shelf using Raman spectroscopy

2018 ◽  
Author(s):  
Robert B. Sparkes ◽  
Melissa Maher ◽  
Jerome Blewett ◽  
Ayca Dogrul Selver ◽  
Örjan Gustafsson ◽  
...  
Keyword(s):  
Raman Spectroscopy ◽  
Organic Matter ◽  
Deep Ocean ◽  
Carbonaceous Material ◽  
Arctic Shelf ◽  
The Arctic ◽  
Organic Load ◽  
Terrestrial Organic Matter ◽  
Labile Organic Matter ◽  
Thawing Permafrost

Abstract. Warming-induced erosion of permafrost from Eastern Siberia mobilises large amounts of organic carbon and delivers it to the East Siberian Arctic Shelf (ESAS). In this study Raman spectroscopy of Carbonaceous Material (CM) was used to characterise, identify and track the most recalcitrant fraction of the organic load. 1463 spectra were obtained from surface sediments collected across the ESAS and automatically analysed for their Raman peaks. Spectra were classified by their peak areas and widths into Disordered, Intermediate, Mildly Graphitised and Highly Graphitised groups, and the distribution of these classes was investigated across the shelf. Disordered CM was most prevalent in a permafrost core from Kurungnakh Island, and from areas known to have high rates of coastal erosion. Sediments from outflows of the Indigirka and Kolyma rivers were generally enriched in Intermediate CM. These different sediment sources were identified and distinguished along an E-W transect using their Raman spectra, showing that sediment is not homogenised on the ESAS. Distal samples, from the ESAS slope, contained greater amounts of Highly Graphitised CM compared to the rest of the shelf, attributable to degradation or, more likely, winnowing processes offshore. The presence of all four spectral classes in distal sediments demonstrates that CM degrades much slower than lipid biomarkers and other traditional tracers of terrestrial organic matter, and shows that alongside degradation of the more labile organic matter component there is also conservative transport of carbon across the shelf toward the deep ocean. Thus, carbon cycle calculations must consider the nature as well as the amount of carbon liberated from thawing permafrost and other erosional settings.

scholarly journals Macromolecular composition of terrestrial and marine organic matter in sediments across the East Siberian Arctic Shelf

2016 ◽  
Vol 10 (5) ◽  
pp. 2485-2500 ◽  
Author(s):  
Robert B. Sparkes ◽  
Ayça Doğrul Selver ◽  
Örjan Gustafsson ◽  
Igor P. Semiletov ◽  
Negar Haghipour ◽  
...  
Keyword(s):  
Organic Matter ◽  
Coastal Erosion ◽  
Principal Component ◽  
Arctic Shelf ◽  
The Arctic ◽  
Gas Chromatography Mass Spectrometry ◽  
Terrestrial Organic Matter ◽  
Pyrolysis Gas ◽  
Siberian Arctic ◽  
Extractable Organic Matter

Abstract. Mobilisation of terrestrial organic carbon (terrOC) from permafrost environments in eastern Siberia has the potential to deliver significant amounts of carbon to the Arctic Ocean, via both fluvial and coastal erosion. Eroded terrOC can be degraded during offshore transport or deposited across the wide East Siberian Arctic Shelf (ESAS). Most studies of terrOC on the ESAS have concentrated on solvent-extractable organic matter, but this represents only a small proportion of the total terrOC load. In this study we have used pyrolysis–gas chromatography–mass spectrometry (py-GCMS) to study all major groups of macromolecular components of the terrOC; this is the first time that this technique has been applied to the ESAS. This has shown that there is a strong offshore trend from terrestrial phenols, aromatics and cyclopentenones to marine pyridines. There is good agreement between proportion phenols measured using py-GCMS and independent quantification of lignin phenol concentrations (r2 = 0.67, p < 0.01, n = 24). Furfurals, thought to represent carbohydrates, show no offshore trend and are likely found in both marine and terrestrial organic matter. We have also collected new radiocarbon data for bulk OC (14COC) which, when coupled with previous measurements, allows us to produce the most comprehensive 14COC map of the ESAS to date. Combining the 14COC and py-GCMS data suggests that the aromatics group of compounds is likely sourced from old, aged terrOC, in contrast to the phenols group, which is likely sourced from modern woody material. We propose that an index of the relative proportions of phenols and pyridines can be used as a novel terrestrial vs. marine proxy measurement for macromolecular organic matter. Principal component analysis found that various terrestrial vs. marine proxies show different patterns across the ESAS, and it shows that multiple river–ocean transects of surface sediments transition from river-dominated to coastal-erosion-dominated to marine-dominated signatures.

scholarly journals Retrogressive thaw slumps along permafrost coasts transform organic matter before release into the Arctic Ocean

2020 ◽  
Author(s):  
George Tanski ◽  
Hugues Lantuit ◽  
Dirk Wagner ◽  
Christian Knoblauch ◽  
Saskia Ruttor ◽  
...  
Keyword(s):  
Organic Matter ◽  
Stable Carbon Isotopes ◽  
Dry Weight ◽  
The Arctic ◽  
Nearshore Zone ◽  
Terrestrial Organic Matter ◽  
Annual Carbon ◽  
Thawing Permafrost ◽  
Retrogressive Thaw Slump ◽  
Carbon Dioxide Co2

&lt;p&gt;Changing environmental conditions in the Arctic have profound impacts on permafrost coasts, which erode at great pace. Although numbers exist on annual carbon and sediment fluxes from coastal erosion, little is known on how terrestrial organic matter (OM) is transformed by thermokarst and &amp;#8211;erosional processes on transit from land to sea. Here, we investigated a retrogressive thaw slump (RTS) on Qikiqtaruk - Herschel Island in the western Canadian Arctic. The RTS was classified into an undisturbed, disturbed and nearshore zone and systematically sampled along transects. Collected sediments were analyzed for organic carbon (OC), nitrogen (N), stable carbon isotopes (&amp;#948;13C-OC) and ammonium. C/N-ratios, &amp;#948;13C-signatures and ammonium concentrations were used as general indicator for OM degradation. Permafrost sediments from the RTS headwall and mud lobe sediments from the thaw stream outlet were incubated to further assess OM degradation and potential greenhouse gas formation during slumping and upon release into the nearshore zone. Our results show that OM concentrations significantly decrease upon slumping in the disturbed zone with OC and N decreasing by &gt;70% and &gt;50%, respectively. Whereas &amp;#948;13C-signatures remain fairly stable, C/N-ratios decrease significantly and ammonium concentrations increase slightly in fresh slumping material. Nearshore sediments have low OM contents and a terrestrial signature comparable to disturbed sites on land. The incubations show that carbon dioxide (CO2) forms quickly from thawing permafrost deposits and mud debris with ~2-3 mg CO2 per gram dry weight being cumulatively produced within two months. We suggest that the initial strong decrease in OM concentration after slumping is caused by a combination of OC degradation, dilution with melted massive ice and immediate offshore transport via the thaw stream. After stabilization in the slump floor, recolonizing vegetation takes up N from the disturbed sediment. Upon release into the nearshore zone, larger portions of OM are directly deposited in marine sediments, where they further degrade or being buried. The incubations indicate that CO2 is rapidly produced upon slumping and potentially continues to form within the nearshore zone that receives eroded material. We conclude that coastal RTS systems profoundly change the characteristic of modern and ancient permafrost terrestrial OM during transit from land to sea - a process which is likely linked to the production of greenhouse gases. Our study provides valuable information on the potential fate of terrestrial OM along eroding permafrost coasts under the trajectory of a warming Arctic.&lt;/p&gt;

scholarly journals Macromolecular composition of terrestrial and marine organic matter in sediments across the East Siberian Arctic Shelf

2016 ◽  
Author(s):  
Robert B. Sparkes ◽  
Ayça Dogrul Selver ◽  
Örjan Gustafsson ◽  
Igor P. Semiletov ◽  
Negar Haghipour ◽  
...  
Keyword(s):  
Organic Matter ◽  
Coastal Erosion ◽  
Principal Component ◽  
Arctic Shelf ◽  
The Arctic ◽  
Gas Chromatography Mass Spectrometry ◽  
Terrestrial Organic Matter ◽  
Pyrolysis Gas ◽  
Siberian Arctic ◽  
Extractable Organic Matter

Abstract. Mobilisation of terrestrial organic carbon (terrOC) from permafrost environments in Eastern Siberia has the potential to deliver significant amounts of carbon to the Arctic Ocean, via both fluvial and coastal erosion. Eroded terrOC can be degraded during offshore transport, or deposited across the wide East Siberian Arctic Shelf (ESAS). Most studies of terrOC on the ESAS have concentrated on solvent-extractable organic matter, but this represents only a small proportion of the total terrOC load. In this study we have used pyrolysis gas chromatography mass spectrometry (py-GCMS) to study all major groups of macromolecular components of the terrOC; this is the first time that this technique has been applied to the ESAS. This has shown that there is a strong offshore trend from terrestrial Phenols, Aromatics, Cyclopentenones to marine Pyridines. There is good agreement between proportion Phenols measured using py-GCMS and independent quantification of lignin phenol concentrations (r2 = 0.67, p < 0.01, n = 24). Furfurals, thought to represent carbohydrates, show no offshore trend and are likely found in both marine and terrestrial organic matter. We have also collected new radiocarbon data for bulk OC (14COC) which, when coupled with previous measurements, allows us to produce the most comprehensive 14COC map of the ESAS to date. Combining the 14COC and py-GCMS data suggests that the Aromatics group of compounds is likely sourced from old, aged terrOC in contrast to the Phenols group, which is likely sourced from modern woody material. We propose that an index of the relative proportions of Phenols and Pyridines can be used as a novel terrestrial vs. marine proxy measurement for macromolecular organic matter. Principal component analysis found that various terrestrial vs. marine proxies show different patterns across the ESAS, and shows that multiple river-ocean transects of surface sediments transition from river-dominated to coastal erosion-dominated to marine-dominated signatures.

scholarly journals Genomic evidence for the degradation of terrestrial organic matter by pelagic Arctic Ocean Chloroflexi bacteria

2018 ◽  
Author(s):  
David Colatriano ◽  
Patricia Tran ◽  
Celine Guéguen ◽  
Williams J. William ◽  
Connie Lovejoy ◽  
...  
Keyword(s):  
Organic Matter ◽  
Carbon Cycle ◽  
Arctic Ocean ◽  
Hydrological Cycle ◽  
The Arctic ◽  
Terrestrial Organic Matter ◽  
Aromatic Compound Degradation ◽  
The Arctic Ocean ◽  
Western Arctic ◽  
Thawing Permafrost

AbstractThe Arctic Ocean currently receives a large supply of global river discharge and terrestrial dissolved organic matter. Moreover, an increase in freshwater runoff and riverine transport of organic matter to the Arctic Ocean is a predicted consequence of thawing permafrost and increased precipitation. The fate of the terrestrial humic-rich organic material and its impact on the marine carbon cycle are largely unknown. Here, the first metagenomic survey of the Canada Basin in the Western Arctic Ocean showed that pelagic Chloroflexi from the Arctic Ocean are replete with aromatic compound degradation genes, acquired in part by lateral transfer from terrestrial bacteria. Our results imply marine Chloroflexi have the capacity to use terrestrial organic matter and that their role in the carbon cycle may increase with the changing hydrological cycle.

Impacts of riverine terrestrial organic matter on the lower trophic levels of an Arctic shelf ecosystem

2021 ◽  
Author(s):  
Michael Bedington ◽  
Ricardo Torres ◽  
Luca Polimene ◽  
Phillip Wallhead ◽  
Bennett Juhls ◽  
...  
Keyword(s):  
Organic Matter ◽  
Future Climate ◽  
Trophic Levels ◽  
The Arctic ◽  
Nutrient Concentrations ◽  
Climate Scenarios ◽  
Arctic Ecosystems ◽  
Terrestrial Organic Matter ◽  
Biogeochemical Models ◽  
Near Shore

&lt;p&gt;The Arctic ocean receives 11% of the entire global river discharge via several great Arctic rivers that drain vast catchments underlain with carbon-rich permafrost. Arctic marginal shelf seas are therefore heavily influenced by terrestrial dissolved organic matter (tDOM) supply, influencing coastal biogeochemical processes and food-webs, as well as physio-chemical properties (e.g. stratification or nutrient concentrations).&lt;/p&gt;&lt;p&gt;Whilst carbon and associated macronutrients supplied by tDOM may enhance the nutrient and carbon substrates for lower trophic levels (phytoplankton/zooplankton), promoting increased local and regional productivity, it can also have opposing effects through a series of indirect processes (e.g. increased light absorption limiting light penetration through the water column). Understanding the relative importance and timing of these processes, and how they vary spatially, is necessary to identify how land-ocean interfaces currently operate.&lt;/p&gt;&lt;p&gt;Future climate scenarios indicate increased quantities of riverine tDOM delivered to the near-shore, with increased freshwater runoff and greater terrestrial permafrost thaw and erosion. This is likely to be exacerbated by the disappearance of seasonal sea ice cover and increased coastal erosion rates. We can therefore expect changes in planktonic phenology and productivity, with concomitant changes in bacterial and higher trophic level success. Understanding how these factors interact and may change under future climate scenarios is therefore critical to predict the future impact on shelf sea Arctic ecosystems and the ecosystem services they provide.&lt;/p&gt;&lt;p&gt;In the Changing Arctic Carbon cycle in the cOastal Ocean Near-shore (CACOON) project (UK-Germany collaboration) we are using coupled hydrodynamic-biogeochemical models in the extensive shallow shelf of the Laptev sea to explore the relationship between these factors. The ecosystem model ERSEM has been adapted to explicitly include a tDOM component. This coupled model system allows us to investigate both the role of present day tDOM in an Arctic coastal ecosystem and to project the potential impacts of increased tDOM input in future.&lt;/p&gt;

Mercury and methylmercury along a transect from the Lena river estuary across the Laptev Sea Shelf

2020 ◽  
Author(s):  
Van Liem Nguyen ◽  
Birgit Wild ◽  
Örjan Gustafsson ◽  
Igor Semiletov ◽  
Oleg Dudarev ◽  
...  
Keyword(s):  
Organic Matter ◽  
Continental Shelf ◽  
Arctic Ocean ◽  
River Delta ◽  
The Arctic ◽  
Laptev Sea ◽  
Terrestrial Organic Matter ◽  
Lena River ◽  
The Arctic Ocean ◽  
The Laptev Sea

&lt;p&gt;Widespread accelerated permafrost thawing is predicted for this century and beyond. This threatens to remobilize the large amounts of Mercury (Hg) currently &amp;#8216;locked&amp;#8217; in Arctic permafrost soils to the Arctic Ocean and thus potentially lead to severe consequences for human and wildlife health. Future risks of Arctic Hg in a warmer climate are, however, poorly understood. One crucial knowledge gap to fill is the fate of Hg once it enters the marine environment on the continental shelves. Arctic rivers are already today suggested to be the main source of Hg into the Arctic Ocean, with dissolved and particulate organic matter (DOM and POM, respectively) identified as important vectors for the land to sea transport.&lt;/p&gt;&lt;p&gt;In this study, we have investigated total Hg (HgT) and monomethylmercury (MeHg) concentrations in surface sediments from the East Siberian Arctic Shelf (ESAS) along a transect from the Lena river delta to the Laptev Sea continental slope. The ESAS is the world&amp;#8217;s largest continental shelf and receives large amounts of organic carbon by the great Arctic Russian rivers (e.g., Lena, Indigirka and Kolyma), remobilized from continuous and discontinuous permafrost regions in the river catchments, and from coastal erosion. Data on HgT and MeHg levels in ESAS sediments is however limited. Here, we observed concentrations of Hg ranging from 30 to 96 ng Hg g&lt;sup&gt;-1&lt;/sup&gt; d.w. of HgT, and 0.03 to 9.5 ng Hg g&lt;sup&gt;-1&lt;/sup&gt; d.w. of MeHg. Similar concentrations of HgT were observed close to the river delta (54 &amp;#177; 19 ng Hg g&lt;sup&gt;-1&lt;/sup&gt; d.w.), where &gt;95 % of the organic matter is of terrestrial origin, and the other section of the transect (42 &amp;#177; 7 ng Hg g&lt;sup&gt;-1&lt;/sup&gt; d.w.) where the terrestrial organic matter is diluted with carbon from marine sources. In contrast, we observed higher concentrations of MeHg close to the river delta (0.72 &amp;#177; 0.71 ng Hg g&lt;sup&gt;-1&lt;/sup&gt; d.w. as MeHg) than further out on the continental shelf (0.031 &amp;#177; 0.71 ng Hg g&lt;sup&gt;-1&lt;/sup&gt; d.w. as MeHg). We also observed a positive correlation between the MeHg:Hg ratio and previously characterized molecular markers of terrestrial organic matter (Br&amp;#246;der et al. Biogeosciences (2016) &amp; Nature Com. (2018)). We thus suggest riverine inputs, rather than in situ MeHg formation, to explain observed MeHg trends.&lt;/p&gt;

scholarly journals The impact of land-fast ice on the distribution of terrestrial dissolved organic matter in the Siberian Arctic shelf seas

2021 ◽  
Author(s):  
Jens A. Hölemann ◽  
Bennet Juhls ◽  
Dorothea Bauch ◽  
Markus Janout ◽  
Boris P. Koch ◽  
...  
Keyword(s):  
Organic Matter ◽  
Dissolved Organic Matter ◽  
River Water ◽  
Arctic Shelf ◽  
The Arctic ◽  
Permafrost Degradation ◽  
Surface Mixed Layer ◽  
Siberian Arctic ◽  
Shelf Seas ◽  
Fast Ice

Abstract. Remobilization of soil carbon as a result of permafrost degradation in the drainage basin of the major Siberian rivers combined with higher precipitation in a warming climate potentially increase the flux of terrestrial derived dissolved organic matter (tDOM) into the Arctic Ocean. The Laptev (LS) and East Siberian Seas (ESS) receive enormous amounts of tDOM-rich river water, which undergoes at least one freeze-melt cycle in the Siberian Arctic shelf seas. To better understand how freezing and melting affect the tDOM dynamics in the LS and ESS, we sampled sea ice, river and seawater for their dissolved organic carbon (DOC) concentration and the colored fraction of dissolved organic matter. The sampling took place in different seasons over a period of 9 years (2010–2019). Our results suggest that the main factor regulating the tDOM distribution in the LS and ESS is the mixing of marine waters with freshwater sources carrying different tDOM concentrations. Of particular importance in this context are the 211 km3 of meltwater from land-fast ice from the LS, containing ~ 0.3 Tg DOC, which in spring mixes with 245 km3 of river water from the peak spring discharge of the Lena River, carrying ~ 2.4 Tg DOC into the LS. During the ice-free season, tDOM transport on the shelves takes place in the surface mixed layer, with the direction of transport depending on the prevailing wind direction. In winter, about 1.2 Tg of brine-related DOC, which was expelled from the growing land-fast ice in the LS, is transported in the near-surface water layer into the Transpolar Drift Stream that flows from the Siberian Shelf toward Greenland. The actual water depth in which the tDOM-rich brines are transported, depends mainly on the density stratification of the LS and ESS in the preceding summer and the amount of ice produced in winter. We suspect that climate change in the Arctic will fundamentally alter the dynamics of tDOM transport in the Arctic marginal seas, which will also have consequences for the Arctic carbon cycle.

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