scholarly journals Carbon cycling on the East Siberian Arctic Shelf – a change in air-sea CO<sub>2</sub> flux induced by mineralization of terrestrial organic carbon

2017 ◽  
Author(s):  
Erik Gustafsson ◽  
Christoph Humborg ◽  
Göran Björk ◽  
Christian Stranne ◽  
Leif G. Anderson ◽  
...  
Keyword(s):  
Stable Isotope ◽  
Organic Carbon ◽  
Carbon Cycling ◽  
Dissolved Inorganic Carbon ◽  
Carbon Sources ◽  
Atmospheric Co2 ◽  
Arctic Shelf ◽  
The Arctic ◽  
Biogeochemical Model ◽  
Siberian Arctic

Abstract. Measurements from the SWERUS-C3 and ISSS-08 Arctic expeditions were used to calibrate and validate a new physical-biogeochemical model developed to quantify key carbon cycling processes on the East Siberian Arctic Shelf (ESAS). The model was used in a series of experimental simulations with the specific aim to investigate the pathways of terrestrial dissolved and particulate organic carbon (DOCter and POCter) supplied to the shelf. Rivers supply on average 8.5 Tg C yr−1 dissolved inorganic carbon (DIC), and further 8.5 and 1.1 Tg C yr−1 DOCter and POCter respectively. Based on observed and simulated DOC concentrations and stable isotope values (δ13CDOC) in shelf waters, we estimate that only some 20 % of the riverine DOCter is labile. According to our model results, an additional supply of approximately 14 Tg C yr−1 eroded labile POCter is however required to describe the observed stable isotope values of DIC (δ13CDIC). Degradation of riverine DOCter and POCter results in a 1.8 Tg C yr−1 reduction in the uptake of atmospheric CO2, while degradation of eroded POCter results in an additional 10 Tg C yr−1 reduction. Our calculations indicate nevertheless that the ESAS is an overall small net sink for atmospheric CO2 (1.7 Tg C yr−1). The external carbon sources are largely compensated by a net export from the shelf to the Arctic Ocean (31 Tg C yr−1), and to a smaller degree by a permanent burial in the sediments (2.7 Tg C yr−1).

scholarly journals Organic matter across subsea permafrost thaw horizons on the East Siberian Arctic Shelf

2018 ◽  
Author(s):  
Birgit Wild ◽  
Natalia Shakhova ◽  
Oleg Dudarev ◽  
Alexey Ruban ◽  
Denis Kosmach ◽  
...  
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Luminescence Dating ◽  
Arctic Shelf ◽  
The Arctic ◽  
Organic Carbon Content ◽  
Study Region ◽  
Permafrost Thaw ◽  
Siberian Arctic ◽  
Subsea Permafrost

Abstract. Thaw of subsea permafrost across the Arctic Ocean shelves might promote the degradation of organic matter to CO2 and CH4, but also create conduits for transfer of deeper CH4 pools to the atmosphere and thereby amplify global warming. In this study, we describe sedimentary characteristics of three subsea permafrost cores of 21–56 m length drilled near the current delta of the Lena River in the Buor–Khaya Bay on the East Siberian Arctic Shelf, including content, origin and degradation state of organic matter around the current thaw front. Grain size distribution and optically stimulated luminescence dating suggest the alternating deposition of aeolian silt and fluvial sand over the past 160 000 years. Organic matter in 3 m sections across the current permafrost table was characterized by low organic carbon contents (average 0.7 ± 0.2 %) as well as enriched δ13C values and low concentrations of the terrestrial plant biomarker lignin compared to other recent and Pleistocene deposits in the study region. The lignin phenol composition further suggests contribution of both tundra and boreal forest vegetation, at least the latter likely deposited by rivers. Our findings indicate high variability in organic matter composition of subsea permafrost even within a small study area, reflecting its development in a heterogeneous and dynamic landscape. Even with this relatively low organic carbon content, the high rates of observed subsea permafrost thaw in this area yield a thaw-out of 1.6 kg OC m−2 year−1, emphasizing the need to constrain the fate of the poorly described and thawing subsea permafrost organic carbon pool.

scholarly journals GDGT distributions on the East Siberian Arctic Shelf: implications for organic carbon export, burial and degradation

2015 ◽  
Vol 12 (12) ◽  
pp. 3753-3768 ◽  
Author(s):  
R. B. Sparkes ◽  
A. Doğrul Selver ◽  
J. Bischoff ◽  
H. M. Talbot ◽  
Ö. Gustafsson ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Carbon Cycle ◽  
Arctic Ocean ◽  
Coastal Erosion ◽  
Stable Carbon Isotope ◽  
Arctic Shelf ◽  
The Arctic ◽  
Fluvial Erosion ◽  
Siberian Arctic ◽  
The Arctic Ocean

Abstract. Siberian permafrost contains a globally significant pool of organic carbon (OC) that is vulnerable to enhanced warming and subsequent release into the contemporary carbon cycle. OC release by both fluvial and coastal erosion has been reported in the region, but the behaviour of this material in the Arctic Ocean is insufficiently understood. The balance between OC deposition and degradation on the East Siberian Arctic Shelf (ESAS) influences the climate–carbon cycle feedback in this area. In this study we couple measurements of glycerol dialkyl glycerol tetraethers (GDGTs) with bulk geochemical observations to improve knowledge of the sources of OC to the ESAS, the behaviour of specific biomarkers on the shelf and the balance between delivery and removal of different carbon pools. Branched GDGT (brGDGT) concentrations were highest close to river mouths, yet low in "ice complex" permafrost deposits, supporting recent observations that brGDGTs are mostly delivered by fluvial erosion, and may be a tracer for this in complex sedimentary environments. BrGDGT concentrations and the branched and isoprenoidal tetraether (BIT) index reduced quickly offshore, demonstrating a rapid reduction in river influence. Stable carbon isotope ratios changed at a different rate to the BIT index, suggesting not only that OC on the shelf is sourced from fluvial erosion but also that erosion of coastal sediments delivers substantial quantities of OC to the Arctic Ocean. A model of OC export from fluvial, coastal and marine sources is able to recreate the biomarker and bulk observations and provide estimates for the influence of fluvial and coastal OC across the whole shelf. The model shows that coastal erosion delivers 43 % of the OC and 87 % of the mineral sediment to the ESAS, but that rivers deliver 72 % of brGDGTs, indicating that brGDGTs can be used as a proxy for river-derived sediment.

The vulnerability of Arctic shelf sediments to climate change

2015 ◽  
Vol 23 (4) ◽  
pp. 461-479 ◽  
Author(s):  
Robie W. Macdonald ◽  
Zou Zou A. Kuzyk ◽  
Sophia C. Johannessen
Keyword(s):  
Organic Carbon ◽  
Carbon Sources ◽  
The Arctic ◽  
Sedimentary Environments ◽  
Carbon Supply ◽  
Shelf Sediment ◽  
Wide Range ◽  
Metabolic Conditions ◽  
Shelf Sediments ◽  
Ocean Ecosystem

The sediments of the pan-Arctic shelves contribute an important component to the Arctic Ocean ecosystem by providing a habitat for biota (benthos), a repository for organic and inorganic non-conservative substances entering or produced within the ocean, a reactor and source of transformed substances back to the water column, and a mechanism of burial. Sediments interact with ice, ocean, and the surrounding land over a wide range of space and time scales. We discuss the vulnerability of shelf sediment to changes in (i) organic carbon sources, (ii) pathways of sediment and organic carbon supply, and (iii) physical and biogeochemical alteration (diagenesis). Sedimentary environments of the shelves and basins are likely to exhibit a wide variance in their response to global change because of their wide variation in sediment sources, processes, and metabolic conditions. In particular, the Chukchi and Barents shelves are dominated by inflowing waters from oceans to the south, whereas the interior shelves are more closely tied to terrigenous sources due to river inflow and coastal erosion.

scholarly journals Air-sea CO<sub>2</sub> fluxes and the controls on ocean surface <i>p</i>CO<sub>2</sub> seasonal variability in the coastal and open-ocean southwestern Atlantic Ocean: a modeling study

2015 ◽  
Vol 12 (19) ◽  
pp. 5793-5809 ◽  
Author(s):  
R. Arruda ◽  
P. H. R. Calil ◽  
A. A. Bianchi ◽  
S. C. Doney ◽  
N. Gruber ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Seasonal Variability ◽  
Dissolved Inorganic Carbon ◽  
Open Ocean ◽  
Atmospheric Co2 ◽  
Biogeochemical Model ◽  
Southwestern Atlantic ◽  
Biological Production ◽  
The North ◽  
Southwestern Atlantic Ocean

Abstract. We use an eddy-resolving, regional ocean biogeochemical model to investigate the main variables and processes responsible for the climatological spatio-temporal variability of pCO2 and the air-sea CO2 fluxes in the southwestern Atlantic Ocean. Overall, the region acts as a sink of atmospheric CO2 south of 30° S, and is close to equilibrium with the atmospheric CO2 to the north. On the shelves, the ocean acts as a weak source of CO2, except for the mid/outer shelves of Patagonia, which act as sinks. In contrast, the inner shelves and the low latitude open ocean of the southwestern Atlantic represent source regions. Observed nearshore-to-offshore and meridional pCO2 gradients are well represented by our simulation. A sensitivity analysis shows the importance of the counteracting effects of temperature and dissolved inorganic carbon (DIC) in controlling the seasonal variability of pCO2. Biological production and solubility are the main processes regulating pCO2, with biological production being particularly important on the shelves. The role of mixing/stratification in modulating DIC, and therefore surface pCO2, is shown in a vertical profile at the location of the Ocean Observatories Initiative (OOI) site in the Argentine Basin (42° S, 42° W).

scholarly journals The East Siberian Arctic Shelf: towards further assessment of permafrost-related methane fluxes and role of sea ice

2015 ◽  
Vol 373 (2052) ◽  
pp. 20140451 ◽  
Author(s):  
Natalia Shakhova ◽  
Igor Semiletov ◽  
Valentin Sergienko ◽  
Leopold Lobkovsky ◽  
Vladimir Yusupov ◽  
...  
Keyword(s):  
Arctic Shelf ◽  
The Arctic ◽  
Permafrost Degradation ◽  
Run Off ◽  
Heating Effects ◽  
Siberian Arctic ◽  
Methane Fluxes ◽  
Near Shore ◽  
Permafrost Thawing ◽  
Subsea Permafrost

Sustained release of methane (CH 4 ) to the atmosphere from thawing Arctic permafrost may be a positive and significant feedback to climate warming. Atmospheric venting of CH 4 from the East Siberian Arctic Shelf (ESAS) was recently reported to be on par with flux from the Arctic tundra; however, the future scale of these releases remains unclear. Here, based on results of our latest observations, we show that CH 4 emissions from this shelf are likely to be determined by the state of subsea permafrost degradation. We observed CH 4 emissions from two previously understudied areas of the ESAS: the outer shelf, where subsea permafrost is predicted to be discontinuous or mostly degraded due to long submergence by seawater, and the near shore area, where deep/open taliks presumably form due to combined heating effects of seawater, river run-off, geothermal flux and pre-existing thermokarst. CH 4 emissions from these areas emerge from largely thawed sediments via strong flare-like ebullition, producing fluxes that are orders of magnitude greater than fluxes observed in background areas underlain by largely frozen sediments. We suggest that progression of subsea permafrost thawing and decrease in ice extent could result in a significant increase in CH 4 emissions from the ESAS.

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 The origin of methane in the East Siberian Arctic Shelf unraveled with triple isotope analysis

2016 ◽  
Author(s):  
Célia J. Sapart ◽  
Natalia Shakhova ◽  
Igor Semiletov ◽  
Joachim Jansen ◽  
Sönke Szidat ◽  
...  
Keyword(s):  
Water Column ◽  
Large Scale ◽  
Age Determination ◽  
Arctic Shelf ◽  
Climate Feedback ◽  
The Arctic ◽  
Small Contribution ◽  
Isotope Data ◽  
Siberian Arctic ◽  
Subsea Permafrost

Abstract. Methane (CH4) is a strong greenhouse gas emitted by human activity and natural processes that are highly sensitive to climate change. The Arctic Ocean, especially the East Siberian Arctic Shelf (ESAS) overlays large areas of subsea permafrost that is degrading. The release of large amount of CH4 originally stored or formed there could create a strong positive climate feedback. Large scale CH4 super-saturation has been observed in the ESAS waters, pointing to leakages of CH4 through the sea floor and possibly to the atmosphere, but the origin of this gas is still debated. Here, we present CH4 concentration and triple isotope data analyzed on gas extracted from sediment and water sampled over the shallow ESAS from 2007 to 2013. We find high concentrations (up to 500 μM) of CH4 in the pore water of the partially thawed subsea permafrost of this region. For all sediment cores, both hydrogen and carbon CH4 isotope data reveal the predominant presence of CH4 that is not of thermogenic/natural gas origin as it has long been thought, but resultant from microbial CH4 formation using as primary substrate glacial water and old organic matter preserved in the subsea permafrost or below. Radiocarbon data demonstrate that the CH4 present in the ESAS sediment is of Pleistocene age or older, but a small contribution of highly 14C-enriched CH4, from unknown origin, prohibits precise age determination for one sediment core and in the water column. Our data suggest that at locations where bubble plumes have been observed, CH4 can escape anaerobic oxidation in the surface sediment. CH4 will then rapidly migrate through the very shallow water column of the ESAS to escape to the atmosphere generating a positive radiative feedback.

scholarly journals Migration and transformation of dissolved carbon during accumulated cyanobacteria decomposition in shallow eutrophic lakes: a simulated microcosm study

PeerJ ◽  
2018 ◽  
Vol 6 ◽  
pp. e5922 ◽  
Author(s):  
Zhichun Li ◽  
Yanping Zhao ◽  
Xiaoguang Xu ◽  
Ruiming Han ◽  
Mingyue Wang ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Carbon Cycling ◽  
Dissolved Inorganic Carbon ◽  
Eutrophic Lakes ◽  
Overlying Water ◽  
Dissolved Carbon ◽  
Laboratory Microcosm ◽  
Transformation Mechanisms ◽  
Diffusive Fluxes ◽  
Sediment Interface

The decomposition processes of accumulated cyanobacteria can release large amounts of organic carbon and affect the carbon cycling in shallow eutrophic lakes. However, the migration and transformation mechanisms of dissolved carbon (DC) require further study and discussion. In this study, a 73-day laboratory microcosm experiment using suction samplers (Rhizon and syringe) was conducted to understand the migration and transformation of DC during the cyanobacteria decomposition. The decomposition of cyanobacteria biomass caused anoxic and reduction conditions, and changed the acid-base environment in the water column. During the early incubation (days 0–18), a large amount of cyanobacteria-derived particulate organic matter (POM) was decomposed into dissolved organic carbon (DOC) in the overlying water, reaching the highest peak value of 1.82 g L−1 in the treatment added the high cyanobacteria biomass (470 g). After 18 days of incubation, the mineralization of increased DOC to dissolved inorganic carbon (DIC) maintained a high DIC level of overlying water in treatments added cyanobacteria biomass. The treatment added the medium cyanobacteria biomass (235 g) presented the lower DOC/total dissolved carbon ratio than the high cyanobacteria biomass associated with the lower mineralization from DOC to DIC. Due to the concentration differences of DIC at water-sediment interface, the main migration of DIC from pore water to overlying water occurred in the treatment without added cyanobacteria biomass. However, the treatments added the cyanobacteria biomass presented the obvious diffusion of DOC and the low migration of DIC at the water-sediment interface. The diffusive fluxes of DOC at the water-sediment interface increased with the cyanobacteria biomass added, reaching the maximum value of 411.01 mg/(m2·d) in the treatment added the high cyanobacteria biomass. In the overlying water, the group added the sediment and medium cyanobacteria biomass presented a faster degradation of cyanobacteria-derived POM to DOC and a higher mineralization level of DOC to DIC than added the medium cyanobacteria biomass without sediment. Therefore, during accumulated cyanobacteria decomposition, the biomass of accumulated cyanobacteria and sediment property can influence the migration and transformation of DC, playing an important role in carbon cycling in shallow eutrophic lakes.

First experimental estimation of the methane ebullition fraction in water column from the bottom to the surface: application for the East Siberian Arctic Shelf

2021 ◽  
Author(s):  
Denis Chernykh ◽  
Denis Kosmach ◽  
Anton Konstantinov ◽  
Aleksander Salomatin ◽  
Vladimir Yusupov ◽  
...  
Keyword(s):  
Water Column ◽  
Thermal State ◽  
Terrestrial Ecosystems ◽  
Arctic Shelf ◽  
The Arctic ◽  
Arctic Ecosystems ◽  
Russian Scientific ◽  
Siberian Arctic ◽  
Methane Ebullition ◽  
Subsea Permafrost

&lt;p&gt;The key area of the Arctic ocean for atmospheric venting of CH&lt;sub&gt;4&lt;/sub&gt; is the East Siberian Arctic Shelf (ESAS). The ESAS covers &gt;2 million square kilometers (equal to the areas of Germany, France, Great Britain, Italy, and Japan combined). This vast yet shallow region has recently been shown to be a significant modern source of atmospheric CH&lt;sub&gt;4&lt;/sub&gt;, contributing annually no less than terrestrial Arctic ecosystems; but unlike terrestrial ecosystems, the ESAS emits CH&lt;sub&gt;4 &lt;/sub&gt;year-round due to its partial openness during the winter when terrestrial ecosystems are dormant. Emissions are determined by and dependent on the current thermal state of the subsea permafrost and environmental factors controlling permafrost dynamics. Releases could potentially increase by 3-5 orders of magnitude, considering the sheer amount of CH&lt;sub&gt;4&lt;/sub&gt; preserved within the shallow ESAS seabed deposits and the documented thawing rates of subsea permafrost reported recently.&lt;/p&gt;&lt;p&gt;The purpose of this work is to determine the methane ebullition fraction in water column: from the bottom to the surface, which is a key to evaluate quantitively methane release from the ESAS bottom through the water column into the atmosphere. A series of 351 experiments was carried out at to determine the quantity of methane (and other greenhouse gases) delivered by bubbles of various sizes through a water column into the atmosphere. It has been shown for depth up to 22 m (about 30% of the ESAS) that pure methane bubbles, depending on their diameter and water salinity, transported to the surface from 60.9% to 85.3% of gaseous methane.&lt;/p&gt;&lt;p&gt;This work was supported in part by grants from Russian Scientific Foundation (&amp;#8470; 18-77-10004 to DCh, DK, AK, &amp;#8470; 19-77-00067 to EG), the Ministry of Science and Higher Education of the Russian Federation (grant ID: 075-15-2020-978 to IS). The work was carried out as a part of Federal[&amp;#1055;W1]&amp;#160; assignment &amp;#8470; &amp;#1040;&amp;#1040;&amp;#1040;&amp;#1040;-&amp;#1040;17-117030110031-6 to AS.&lt;/p&gt;

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