scholarly journals Distribution of methane in the Lena Delta and Buor-Khaya Bay, Russia

2013 ◽  
Vol 10 (7) ◽  
pp. 4641-4652 ◽  
Author(s):  
I. Bussmann
Keyword(s):  
River System ◽  
Methane Flux ◽  
Main Process ◽  
Laptev Sea ◽  
Terrestrial Environment ◽  
Lena River ◽  
Permafrost Soils ◽  
Methane Concentrations ◽  
Lena Delta ◽  
Isotopic Signal

Abstract. The Lena River is one of the largest Russian rivers draining into the Laptev Sea. The permafrost areas surrounding the Lena are predicted to thaw at increasing rates due to global temperature increases. With this thawing, large amounts of carbon – either organic or in the gaseous forms carbon dioxide and methane – will reach the waters of the Lena and the adjacent Buor-Khaya Bay (Laptev Sea). Methane concentrations and the isotopic signal of methane in the waters of the Lena Delta and estuary were monitored from 2008 to 2010. Creeks draining from permafrost soils produced hotspots for methane input into the river system (median concentration 1500 nM) compared with concentrations of 30–85 nM observed in the main channels of the Lena. No microbial methane oxidation could be detected; thus diffusion is the main process of methane removal. We estimated that the riverine diffusive methane flux is 3–10 times higher than the flux from surrounding terrestrial environment. To maintain the observed methane concentrations in the river, additional methane sources are necessary. The methane-rich creeks could be responsible for this input. In the estuary of Buor-Khaya Bay, methane concentrations decreased to 26–33 nM. However, within the bay no consistent temporal and spatial pattern could be observed. The methane-rich waters of the river were not diluted with marine water because of a strong stratification of the water column. Thus, methane is released from the estuary and from the river mainly by diffusion into the atmosphere.

scholarly journals Distribution of methane in the Lena Delta and Buor Khaya Bay, Russia

2012 ◽  
Vol 9 (11) ◽  
pp. 16213-16237
Author(s):  
I. Bussmann
Keyword(s):  
River System ◽  
Oxidation Potential ◽  
Laptev Sea ◽  
Lena River ◽  
Run Off ◽  
Permafrost Soils ◽  
20 Nm ◽  
Methane Concentrations ◽  
Lena Delta

Abstract. The Lena River is one of the largest Russian rivers draining into the Laptev Sea. The permafrost areas surrounding the Lena are predicted to melt at increasing rates due to global temperature increases. With this melting, large amounts of carbon – either organic or as methane – will reach the waters of the Lena and the adjacent Buor Khaya Bay (Laptev Sea). Methane concentrations and the isotopic signal of methane in the waters of the Lena Delta and estuary were monitored from 2008 to 2010. Meltwater run-off of permafrost soils produced hotspots for methane input into the river system (median concentration 1500 nM) compared with concentrations of around 100 nM observed in the main channels of the Lena. Within the river, especially at sites with meltwater input, microbiological experiments indicated strong in situ methane production but a very low methane oxidation potential. In the estuary of Buor Khaya Bay, methane concentrations decreased towards background levels of 20 nM. Here, the strong stratification of the water column permits the dilution of methane with seawater, and methane is released mainly by diffusion into the atmosphere.

scholarly journals Methane distribution and oxidation around the Lena Delta in summer 2013

2017 ◽  
Vol 14 (21) ◽  
pp. 4985-5002 ◽  
Author(s):  
Ingeborg Bussmann ◽  
Steffen Hackbusch ◽  
Patrick Schaal ◽  
Antje Wichels
Keyword(s):  
Methane Oxidation ◽  
Methane Flux ◽  
Methanotrophic Bacteria ◽  
Riverine Water ◽  
Lena River ◽  
Methane Distribution ◽  
Mixed Water ◽  
Methane Concentrations ◽  
Polar Water ◽  
Lena Delta

Abstract. The Lena River is one of the largest Russian rivers draining into the Laptev Sea. The predicted increases in global temperatures are expected to cause the permafrost areas surrounding the Lena Delta to melt at increasing rates. This melting will result in high amounts of methane reaching the waters of the Lena and the adjacent Laptev Sea. The only biological sink that can lower methane concentrations within this system is methane oxidation by methanotrophic bacteria. However, the polar estuary of the Lena River, due to its strong fluctuations in salinity and temperature, is a challenging environment for bacteria. We determined the activity and abundance of aerobic methanotrophic bacteria by a tracer method and by the quantitative polymerase chain reaction. We described the methanotrophic population with a molecular fingerprinting method (monooxygenase intergenic spacer analysis), as well as the methane distribution (via a headspace method) and other abiotic parameters, in the Lena Delta in September 2013. The median methane concentrations were 22 nmol L−1 for riverine water (salinity (S)  < 5), 19 nmol L−1 for mixed water (5 < S < 20) and 28 nmol L−1 for polar water (S > 20). The Lena River was not the source of methane in surface water, and the methane concentrations of the bottom water were mainly influenced by the methane concentration in surface sediments. However, the bacterial populations of the riverine and polar waters showed similar methane oxidation rates (0.419 and 0.400 nmol L−1 d−1), despite a higher relative abundance of methanotrophs and a higher estimated diversity in the riverine water than in the polar water. The methane turnover times ranged from 167 days in mixed water and 91 days in riverine water to only 36 days in polar water. The environmental parameters influencing the methane oxidation rate and the methanotrophic population also differed between the water masses. We postulate the presence of a riverine methanotrophic population that is limited by sub-optimal temperatures and substrate concentrations and a polar methanotrophic population that is well adapted to the cold and methane-poor polar environment but limited by a lack of nitrogen. The diffusive methane flux into the atmosphere ranged from 4 to 163 µmol m2 d−1 (median 24). The diffusive methane flux accounted for a loss of 8 % of the total methane inventory of the investigated area, whereas the methanotrophic bacteria consumed only 1 % of this methane inventory. Our results underscore the importance of measuring the methane oxidation activities in polar estuaries, and they indicate a population-level differentiation between riverine and polar water methanotrophs.

scholarly journals Methane distribution and oxidation around the Lena Delta in summer 2013

2017 ◽  
Author(s):  
Ingeborg Bussmann ◽  
Steffen Hackbusch ◽  
Patrick Schaal ◽  
Antje Wichels
Keyword(s):  
Methane Oxidation ◽  
Methane Flux ◽  
Methanotrophic Bacteria ◽  
Riverine Water ◽  
Lena River ◽  
Methane Distribution ◽  
Methane Oxidation Rate ◽  
Mixed Water ◽  
Polar Water ◽  
Lena Delta

Abstract. The Lena River is one of the biggest Russian rivers draining into the Laptev Sea. Due to predicted increasing temperatures, the permafrost areas surrounding the Lena Delta will melt at increasing rates. With this melting, high amounts of methane will reach the waters of the Lena and the adjacent Laptev Sea. Methane oxidation by methanotrophic bacteria is the only biological way to reduce methane concentrations within the system. However, the polar estuary of the Lena River is a challenging environment for bacteria, with strong fluctuations in salinity and temperature. We determined the activity (tracer method) and the abundance (qPCR) of aerobic methanotrophic bacteria. We described the methanotrophic population with MISA; as well as the methane distribution (head space) and other abiotic parameters in the Lena Delta in September 2013. In riverine water (S < 5) we found a median methane concentration of 22 nM, in mixed water (5 < S < 20) the median methane concentration was 19 nM and in polar water (S > 20) a median 28 nM was observed. The Lena River was not the methane source for surface water, and bottom water methane concentrations were mainly influenced by the concentration in surface sediments. However, the methane oxidation rate in riverine and polar water was very similar (0.419 and 0.400 nM/d), but with a higher relative abundance of methanotrophs and a higher estimated diversity with respect to MISA OTUs in the rivine water as compared to polar water. The turnover times of methane ranged from 167 d in mixed water, 91 d in riverine water and only 36 d in polarwater. Also the environmental parameters influencing the methane oxidation rate and the methanotrophic population differed between the water masses. Thus we postulate a riverine methanotrophic population limited by sub-optimal temperatures and substrate concentrations and a polar methanotrophic population being well adapted to the cold and methane poor environment, but limited by the nitrogen content. The diffusive methane flux into the atmosphere ranged from 4–163 µmol m2 d−1 (median 24). For the total methane inventory of the investigated area, the diffusive methane flux was responsible for 8 % loss, compared to only 1 % of the methane consumed by the methanotrophic bacteria within the system.

Particulate and dissolved organic carbon composition in the Lena River and its Delta, from Yakutsk to the Arctic Ocean.

2021 ◽  
Author(s):  
Olga Ogneva ◽  
Gesine Mollenhauer ◽  
Matthias Fuchs ◽  
Juri Palmtag ◽  
Tina Sanders ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Arctic Ocean ◽  
Main Channel ◽  
The Arctic ◽  
Laptev Sea ◽  
Lena River ◽  
The Arctic Ocean ◽  
The Laptev Sea ◽  
Lena Delta

&lt;p&gt;Rapid climate warming in the Arctic intensifies permafrost thaw, increases active layer depth in summer and enhances riverbank and coastal erosion. All of these cause additional release of organic matter (OM) into streams and rivers. OM will be (1) transformed and modified during transport and subsequently discharged into the Arctic Ocean, or (2) removed from the active cycling by sedimentation. Here, the nearshore zone (which includes deltas, estuaries and coasts) is of great importance, where the major transformation processes of terrestrial material take place. Despite the importance of deltas for the biogeochemical cycle, their functioning is poorly understood. For our study we examined the Lena River nearshore, which represents the world&amp;#8217;s third largest delta and supplies the second highest annual water and sediment discharge into the Arctic Ocean. Running through almost the entirety of East Siberia from Lake Baikal to the Laptev Sea, the Lena River drains an area of &amp;#8764;2,61&amp;#215;10&lt;sup&gt;6&lt;/sup&gt; km&lt;sup&gt;2&lt;/sup&gt;&amp;#160; with approximately 90% underlain by permafrost. Our aims were to investigate the spatial variation of OM concentration and isotopic composition during transit from terrestrial permafrost source to the ocean interface, and to compare riverine and deltaic OM composition. We measured particulate and dissolved organic carbon (POC and DOC) concentrations and their associated &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C and &amp;#8710;&lt;sup&gt;14&lt;/sup&gt;C values in water samples collected along a &amp;#8764;1500 km long Lena River transect from Yakutsk downstream to the river outlet into the Laptev Sea.&lt;/p&gt;&lt;p&gt;We find significant qualitative and quantitative differences between the OM composition in the Lena River main channel and its delta. Further, we found suspended matter and POC concentrations decreased during transit from river to the Arctic Ocean.&amp;#160; DOC concentrations in the Lena delta were almost 50% lower than OM from the main channel. We found that deltaic POC is depleted in &lt;sup&gt;13&lt;/sup&gt;C relative to fluvial POC, and that its &lt;sup&gt;14&lt;/sup&gt;C signature suggests a modern composition indicating phytoplankton origin. This observation likely reflects the difference in hydrological conditions between the delta and the river main channel, caused by lower flow velocity and average water depth. We propose that deltaic environments provide favorable growth conditions for riverine primary producers such as algae and aquatic plants. Deltaic DOC is depleted in &lt;sup&gt;14&lt;/sup&gt;C compared to riverine, especially in samples taken from the water surface, which indicates contributions from an additional old carbon stock source, specific for the Lena Delta. We suggest that this C is released from deltaic bank erosion and partly stays floating on the surface. In conclusion, we found a strong impact of deltaic processes on the fate and dominant signatures of OM discharged into the Arctic Ocean.&lt;/p&gt;

scholarly journals The cryostratigraphy of the Yedoma cliff of Sobo-Sise Island (Lena delta) reveals permafrost dynamics in the central Laptev Sea coastal region during the last 52 kyr

2020 ◽  
Vol 14 (12) ◽  
pp. 4525-4551
Author(s):  
Sebastian Wetterich ◽  
Alexander Kizyakov ◽  
Michael Fritz ◽  
Juliane Wolter ◽  
Gesine Mollenhauer ◽  
...  
Keyword(s):  
Late Pleistocene ◽  
Coastal Region ◽  
The Arctic ◽  
Laptev Sea ◽  
Coarse Silt ◽  
Lena River ◽  
Mis 3 ◽  
D Values ◽  
Δ18o And Δd ◽  
Lena Delta

Abstract. The present study examines the formation history and cryolithological properties of the late-Pleistocene Yedoma Ice Complex (IC) and its Holocene cover in the eastern Lena delta on Sobo-Sise Island. The sedimentary sequence was continuously sampled at 0.5 m resolution at a vertical Yedoma cliff starting from 24.2 m above river level (a.r.l.). The sequence differentiates into three cryostratigraphic units: Unit A, dated from ca. 52 to 28 cal kyr BP; Unit B, dated from ca. 28 to 15 cal kyr BP; Unit C, dated from ca. 7 to 0 cal kyr BP. Three chronologic gaps in the record are striking. The hiatus during the interstadial marine isotope stage (MIS) 3 (36–29 cal kyr BP) as well as during stadial MIS 2 (20–17 cal kyr BP) might be related to fluvial erosion and/or changed discharge patterns of the Lena river caused by repeated outburst floods from the glacial Lake Vitim in southern Siberia along the Lena river valley towards the Arctic Ocean. The hiatus during the MIS 2–1 transition (15–7 cal kyr BP) is a commonly observed feature in permafrost chronologies due to intense thermokarst activity of the deglacial period. The chronologic gaps of the Sobo-Sise Yedoma record are similarly found at two neighbouring Yedoma IC sites on Bykovsky Peninsula and Kurungnakh-Sise Island and are most likely of regional importance. The three cryostratigraphic units of the Sobo-Sise Yedoma exhibit distinct signatures in properties of their clastic, organic, and ice components. Higher permafrost aggradation rates of 1 m kyr−1 with higher organic-matter (OM) stocks (29 ± 15 kg C m−3, 2.2 ± 1.0 kg N m−3; Unit A) and mainly coarse silt are found for the interstadial MIS 3 if compared to the stadial MIS 2 with 0.7 m kyr−1 permafrost aggradation, lower OM stocks (14 ± 8 kg C m−3, 1.4 ± 0.4 kg N m−3; Unit B), and pronounced peaks in the coarse-silt and medium-sand fractions. Geochemical signatures of intra-sedimental ice reflect the differences in summer evaporation and moisture regime by higher ion content and less depleted ratios of stable δ18O and stable δD isotopes but lower deuterium excess (d) values during interstadial MIS 3 if compared to stadial MIS 2. The δ18O and δD composition of MIS 3 and MIS 2 ice wedges shows characteristic well-depleted values and low d values, while MIS 1 ice wedges have elevated mean d values between 11 ‰ and 15 ‰ and surprisingly low δ18O and δD values. Hence, the isotopic difference between late-Pleistocene and Holocene ice wedges is more pronounced in d than in δ values. The present study of the permafrost exposed at the Sobo-Sise Yedoma cliff provides a comprehensive cryostratigraphic inventory, insights into permafrost aggradation, and degradation over the last approximately 52 kyr as well as their climatic and morphodynamic controls on the regional scale of the central Laptev Sea coastal region in NE Siberia.

Features of the Lena River runoff influence on the adjacent Laptev Sea shelf

2021 ◽  
Author(s):  
Vladimir Rogozhin ◽  
Alexander Polukhin ◽  
Evgeniy Yakushev ◽  
Igor Semiletov
Keyword(s):  
Fresh Water ◽  
River Runoff ◽  
Total Alkalinity ◽  
Shelf Zone ◽  
Laptev Sea ◽  
Shirshov Institute ◽  
Riverine Water ◽  
Lena River ◽  
The Laptev Sea ◽  
Lena Delta

&lt;p&gt;The annual runoff of river water into the Laptev Sea is 745 km&lt;sup&gt;3&lt;/sup&gt;, most of the runoff belongs to the Lena River - 525 km&lt;sup&gt;3&lt;/sup&gt;. &amp;#160;Long-term variability in the volume of the Lena River runoff play a significant role in the variability of the scale of distribution of freshwater lenses in the Laptev Sea. The processes that take place in the area of &amp;#8203;&amp;#8203;intense river runoff have an impact both in the shelf zone and in the open part of the sea due to the transfer of large-area lenses of freshened water. The influence of river runoff is considered from the Lena Delta to the continental slope of the Laptev Sea.&lt;/p&gt;&lt;p&gt;The data on physical and chemical properties of the Laptev Sea shelf used in this investigation was obtained during the expeditions of the Shirshov Institute of Oceanology in 2015 and 2017 and the Pacific Oceanological Institute in 2018-2020.&lt;/p&gt;&lt;p&gt;The distribution of hydrochemical parameters in the Lena Delta area in 2019 was typical for the river-sea mixing zone. The distribution of silicate was mixed, i.e. horizontal stratification prevailed in the near-surface layers, and vertical stratification in the bottom layers. The maximum values &amp;#8203;&amp;#8203;were observed in the near-mouth area, reaching indicators over 30 &amp;#181;M / L, which generally coincides with the values &amp;#8203;&amp;#8203;of this indicator in 2015 and more than in 2017.&lt;/p&gt;&lt;p&gt;When considering the distribution of specific alkalinity (total alkalinity-salinity ratio), which serves as a proxie of riverine water, it is worth noting the deepening of the boundary by 0.07 units. In 2019, this border was at depths of 20 to 40 meters, which is an atypical indicator for this water area. Apparently, this has happened owing to an increase in the supply of carbonate ions, which is noticeable from an increase in the values &amp;#8203;&amp;#8203;of carbonate alkalinity in the Lena River waters (Arctic Great Rivers Observatory data).&lt;/p&gt;&lt;p&gt;The calculation of the parts of fresh water, based on salinity data in 2019, showed that the maximum values &amp;#8203;&amp;#8203;were observed near the Lena River delta and amounted to 30-35%. Northward, the part of riverine water was up to 10% only in the surface layer. Comparing with similar calculations performed for the 2015 and 2017 sections, it should be noted that the part of fresh water has decreased. Perhaps this is due to the inflow of continental runoff in 2019 was the lowest over the considered period.&lt;/p&gt;&lt;p&gt;Funding: The work was carried out within the framework of the Shirshov Institute of Oceanology state assignment (theme No. 0149-2019-0008), with funding of the Russian Scientific Foundation (project No. 19-17-00196) and the grant of the President of the Russian Federation MK-860.2020.5.&lt;/p&gt;

scholarly journals Phytoplankton community structure in the Lena Delta (Siberia, Russia) in relation to hydrography

2013 ◽  
Vol 10 (11) ◽  
pp. 7263-7277 ◽  
Author(s):  
A. C. Kraberg ◽  
E. Druzhkova ◽  
B. Heim ◽  
M. J. G. Loeder ◽  
K. H. Wiltshire
Keyword(s):  
Climate Change ◽  
Community Structure ◽  
Phytoplankton Community ◽  
The Arctic ◽  
Laptev Sea ◽  
Phytoplankton Community Structure ◽  
Lena River ◽  
Phytoplankton Communities ◽  
The Laptev Sea ◽  
Lena Delta

Abstract. The Lena Delta in Northern Siberia is one of the largest river deltas in the world. During peak discharge, after the ice melt in spring, it delivers between 60–8000 m3 s−1 of water and sediment into the Arctic Ocean. The Lena Delta and the Laptev Sea coast also constitute a continuous permafrost region. Ongoing climate change, which is particularly pronounced in the Arctic, is leading to increased rates of permafrost thaw. This has already profoundly altered the discharge rates of the Lena River. But the chemistry of the river waters which are discharged into the coastal Laptev Sea have also been hypothesized to undergo considerable compositional changes, e.g. by increasing concentrations of inorganic nutrients such as dissolved organic carbon (DOC) and methane. These physical and chemical changes will also affect the composition of the phytoplankton communities. However, before potential consequences of climate change for coastal arctic phytoplankton communities can be judged, the inherent status of the diversity and food web interactions within the delta have to be established. In 2010, as part of the AWI Lena Delta programme, the phyto- and microzooplankton community in three river channels of the delta (Trofimov, Bykov and Olenek) as well as four coastal transects were investigated to capture the typical river phytoplankton communities and the transitional zone of brackish/marine conditions. Most CTD profiles from 23 coastal stations showed very strong stratification. The only exception to this was a small, shallow and mixed area running from the outflow of Bykov channel in a northerly direction parallel to the shore. Of the five stations in this area, three had a salinity of close to zero. Two further stations had salinities of around 2 and 5 throughout the water column. In the remaining transects, on the other hand, salinities varied between 5 and 30 with depth. Phytoplankton counts from the outflow from the Lena were dominated by diatoms (Aulacoseira species) cyanobacteria (Aphanizomenon, Pseudanabaena) and chlorophytes. In contrast, in the stratified stations the plankton was mostly dominated by dinoflagellates, ciliates and nanoflagellates, with only an insignificant diatom component from the genera Chaetoceros and Thalassiosira (brackish as opposed to freshwater species). Ciliate abundance was significantly coupled with the abundance of total flagellates. A pronounced partitioning in the phytoplankton community was also discernible with depth, with a different community composition and abundance above and below the thermocline in the stratified sites. This work is a first analysis of the phytoplankton community structure in the region where Lena River discharge enters the Laptev Sea.

scholarly journals The cryostratigraphy of the Yedoma cliff of Sobo-Sise Island (Lena Delta) reveals permafrost dynamics in the Central Laptev Sea coastal region during the last about 52 ka

2020 ◽  
Author(s):  
Sebastian Wetterich ◽  
Alexander Kizyakov ◽  
Michael Fritz ◽  
Juliane Wolter ◽  
Gesine Mollenhauer ◽  
...  
Keyword(s):  
Late Pleistocene ◽  
Coastal Region ◽  
The Arctic ◽  
Laptev Sea ◽  
Coarse Silt ◽  
Lena River ◽  
Mis 3 ◽  
D Values ◽  
Δ18o And Δd ◽  
Lena Delta

Abstract. The present study examines the formation history and cryolithological properties of late Pleistocene Yedoma Ice Complex (IC) and its Holocene cover in the eastern Lena Delta on Sobo-Sise Island. The sedimentary sequence was continuously sampled in 0.5 m resolution at a vertical Yedoma cliff starting from 24.2 m above rivel level (arl). The sequence differentiates into three cryostratigraphic units; unit A: dated from ca. 52 to 28 cal ka BP; unit B: dated from ca. 28 to 15 cal ka BP; unit C: dated from ca. 7 to 0 cal ka BP. Three chronologic gaps in the record are striking. The hiatus during the interstadial MIS 3 (36–29 cal ka BP) as well as during stadial MIS 2 (20–17 cal ka BP) might be related to fluvial erosion and/or changed discharge patterns of the Lena River caused by repeated outburst floods from the glacial Lake Vitim in Southern Siberia along the Lena River valley towards the Arctic Ocean. The hiatus during the MIS 2-1 transition (15–7 cal ka BP) is a commonly observed feature in permafrost chronologies due to intense thermokarst activity of the deglacial period. The chronologic gaps of the Sobo-Sise Yedoma record are similarly found at two neighbouring Yedoma IC sites on Bykovsky Peninsula and Kurungnakh-Sise Island, and most likely of regional importance. The three cryostratigraphic units of the Sobo-Sise Yedoma exhibit distinct signatures in properties of their clastic, organic and ice components. Higher permafrost aggradation rates of 1 m ka-1 with higher organic matter (OM) stocks (29±15 kg C m-3, 2.2±1.0 kg N m-3) and mainly coarse silt are found for the interstadial MIS 3 unit A if compared to the stadial MIS 2 unit B with 0.7 m ka-1 permafrost aggradation, lower OM stocks (14±8 kg C m-3, 1.4±0.4 kg N m-3 in unit B) and pronounced peaks in the coarse silt and medium sand fractions. Geochemical signatures of intrasedimental ice reflect the differences in summer evaporation and moisture regime by higher ion contents and less depleted stable δ18O and δD isotope ratios but lower deuterium excess (d) values during interstadial MIS 3 if compared to stadial MIS 2. The δ18O and δD composition of MIS 3 and MIS 2 ice wedges shows characteristic well-depleted values and low d values, while MIS 1 ice wedges have elevated mean d values between 11‰ and 15‰ and surprisingly low δ18O and δD values. Hence, the isotopic difference between late Pleistocene and Holocene ice wedges is more pronounced in d than in δ values. The present study of the permafrost exposed at the Sobo-Sise Yedoma cliff provides a comprehensive cryostratigraphic inventory, insights into permafrost aggradation and degradation over the last about 52 thousand years, and their climatic and morphodynamic controls on the regional scale of the Central Laptev Sea coastal region in NE Siberia.

scholarly journals Composition of Sedimentary Organic Matter across the Laptev Sea Shelf: Evidences from Rock-Eval Parameters and Molecular Indicators

Water ◽  
2020 ◽  
Vol 12 (12) ◽  
pp. 3511
Author(s):  
Elena Gershelis ◽  
Andrey Grinko ◽  
Irina Oberemok ◽  
Elizaveta Klevantseva ◽  
Natalina Poltavskaya ◽  
...  
Keyword(s):  
Organic Matter ◽  
Surface Sediments ◽  
Continental Margins ◽  
Laptev Sea ◽  
Lena River ◽  
Nearshore Sediments ◽  
Rock Eval ◽  
Molecular Indicators ◽  
Sedimentation Regime ◽  
The Laptev Sea

Global warming in high latitudes causes destabilization of vulnerable permafrost deposits followed by massive thaw-release of organic carbon. Permafrost-derived carbon may be buried in the nearshore sediments, transported towards the deeper basins or degraded into the greenhouse gases, potentially initiating a positive feedback to climate change. In the present study, we aim to identify the sources, distribution and degradation state of organic matter (OM) stored in the surface sediments of the Laptev Sea (LS), which receives a large input of terrestrial carbon from both Lena River discharge and intense coastal erosion. We applied a suite of geochemical indicators including the Rock Eval parameters, traditionally used for the matured OM characterization, and terrestrial lipid biomarkers. In addition, we analyzed a comprehensive grain size data in order to assess hydrodynamic sedimentation regime across the LS shelf. Rock-Eval (RE) data characterize LS sedimentary OM with generally low hydrogen index (100–200 mg HC/g TOC) and oxygen index (200 and 300 CO2/g TOC) both increasing off to the continental slope. According to Tpeak values, there is a clear regional distinction between two groups (369–401 °C for the inner and mid shelf; 451–464 °C for the outer shelf). We suggest that permafrost-derived OM is traced across the shallow and mid depths with high Tpeak and slightly elevated HI values if compared to other Arctic continental margins. Molecular-based degradation indicators show a trend to more degraded terrestrial OC with increasing distance from the coast corroborating with RE results. However, we observed much less variation of the degradation markers down to the deeper sampling horizons, which supports the notion that the most active OM degradation in LS land-shelf system takes part during the cross-shelf transport, not while getting buried deeper.

scholarly journals Lena River Delta formation during the Holocene

2014 ◽  
Vol 11 (3) ◽  
pp. 4085-4122 ◽  
Author(s):  
D. Bolshiyanov ◽  
A. Makarov ◽  
L. Savelieva
Keyword(s):  
Sea Water ◽  
River Delta ◽  
The Arctic ◽  
Laptev Sea ◽  
Lena River ◽  
Sea Levels ◽  
Marine Terraces ◽  
Delta Formation ◽  
Carbon Reservoir ◽  
Lena River Delta

Abstract. The Lena River Delta, the largest delta of the Arctic Ocean, differs from other deltas because it consists mainly of organomineral sediments, commonly called peat, that contain a huge organic carbon reservoir. The analysis of Delta sediment radiocarbon ages showed that they could not have formed as peat during floodplain bogging, but accumulated when Laptev Sea water level was high and green mosses and sedges grew and were deposited on the surface of flooded marshes. The Lena River Delta formed as organomineral masses and layered sediments accumulated during transgressive phases when sea level rose. In regressive phases, the islands composed of these sediments and other, more ancient islands were eroded. Each new sea transgression led to further accumulation of layered sediments. As a result of alternating transgressive and regressive phases the first alluvial-marine terrace formed, consisting of geological bodies of different ages. Determining the formation age of different areas of the first terrace and other marine terraces on the coast allowed the periods of increasing (8–6 Ka, 4.5–4 Ka, 2.5–1.5 Ka, 0.4–0.2 Ka) and decreasing (5 Ka, 3 Ka, 0.5 Ka) Laptev Sea levels to be distinguished in the Lena Delta area.

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