scholarly journals Burial and origin of permafrost organic carbon in the Arctic nearshore zone

2020 ◽  
Author(s):  
Michael Fritz ◽  
Hendrik Grotheer ◽  
Vera Meyer ◽  
Thorsten Riedel ◽  
Gregor Pfalz ◽  
...  
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Carbon Cycle ◽  
Coastal Erosion ◽  
Stable Carbon Isotopes ◽  
Carbon Isotopic Composition ◽  
Sediment Traps ◽  
The Arctic ◽  
Nearshore Zone ◽  
Carbon Decomposition

<p>Increasing air and sea surface temperatures at high latitudes lead to accelerated thaw, destabilization, and erosion of perennially frozen soils (i.e., permafrost), which are often rich in organic carbon. Coastal erosion leads to an increased mobilization of organic carbon into the Arctic Ocean that can be converted into greenhouse gases and may therefore contribute to further warming. Carbon decomposition can be limited if organic matter is efficiently deposited on the seafloor, buried in marine sediments and thus removed from the short-term carbon cycle. Basins, canyons and troughs near the coastline can serve as sediment traps and potentially accommodate large quantities of organic carbon along the Arctic coast. Here we use biomarkers (source-specific molecules), stable carbon isotopes (δ<sup>13</sup>C) and radiocarbon (Δ<sup>14</sup>C) to identify the sources of organic carbon in the nearshore zone of the southern Canadian Beaufort Sea. We use an end-member model based on the carbon isotopic composition of bulk organic matter to identify sources of organic carbon. Monte Carlo simulations are applied to quantify the contribution of coastal permafrost erosion to the sedimentary carbon budget. The models suggest that 40% of all carbon released by coastal erosion is efficiently trapped and sequestered in the nearshore zone. We conclude that permafrost coastal erosion releases huge amounts of sediment and organic matter into the nearshore zone. Rapid burial removes large quantities of carbon from the carbon cycle in depositional settings.</p>

scholarly journals Geochemistry of Coastal Permafrost and Erosion-Driven Organic Matter Fluxes to the Beaufort Sea Near Drew Point, Alaska

2021 ◽  
Vol 8 ◽  
Author(s):  
Emily M. Bristol ◽  
Craig T. Connolly ◽  
Thomas D. Lorenson ◽  
Bruce M. Richmond ◽  
Anastasia G. Ilgen ◽  
...  
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Late Pleistocene ◽  
21St Century ◽  
Marine Sediments ◽  
Coastal Erosion ◽  
Beaufort Sea ◽  
The Arctic ◽  
The Holocene ◽  
Kuparuk River

Accelerating erosion of the Alaska Beaufort Sea coast is increasing inputs of organic matter from land to the Arctic Ocean, and improved estimates of organic matter stocks in eroding coastal permafrost are needed to assess their mobilization rates under contemporary conditions. We collected three permafrost cores (4.5–7.5 m long) along a geomorphic gradient near Drew Point, Alaska, where recent erosion rates average 17.2 m year−1. Down-core patterns indicate that organic-rich soils and lacustrine sediments (12–45% total organic carbon; TOC) in the active layer and upper permafrost accumulated during the Holocene. Deeper permafrost (below 3 m elevation) mainly consists of Late Pleistocene marine sediments with lower organic matter content (∼1% TOC), lower C:N ratios, and higher δ13C values. Radiocarbon-based estimates of organic carbon accumulation rates were 11.3 ± 3.6 g TOC m−2 year−1 during the Holocene and 0.5 ± 0.1 g TOC m−2 year−1 during the Late Pleistocene (12–38 kyr BP). Within relict marine sediments, porewater salinities increased with depth. Elevated salinity near sea level (∼20–37 in thawed samples) inhibited freezing despite year-round temperatures below 0°C. We used organic matter stock estimates from the cores in combination with remote sensing time-series data to estimate carbon fluxes for a 9 km stretch of coastline near Drew Point. Erosional fluxes of TOC averaged 1,369 kg C m−1 year−1 during the 21st century (2002–2018), nearly doubling the average flux of the previous half-century (1955–2002). Our estimate of the 21st century erosional TOC flux year−1 from this 9 km coastline (12,318 metric tons C year−1) is similar to the annual TOC flux from the Kuparuk River, which drains a 8,107 km2 area east of Drew Point and ranks as the third largest river on the North Slope of Alaska. Total nitrogen fluxes via coastal erosion at Drew Point were also quantified, and were similar to those from the Kuparuk River. This study emphasizes that coastal erosion represents a significant pathway for carbon and nitrogen trapped in permafrost to enter modern biogeochemical cycles, where it may fuel food webs and greenhouse gas emissions in the marine environment.

Land-to-ocean fluxes and biolability of organic matter eroding along the Beaufort Sea coast near Drew Point, Alaska

2021 ◽  
Author(s):  
Emily Bristol ◽  
Craig Connolly ◽  
Thomas Lorenson ◽  
Bruce Richmond ◽  
Anastasia Ilgen ◽  
...  
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Active Layer ◽  
Late Pleistocene ◽  
Coastal Erosion ◽  
Organic Matter Content ◽  
Beaufort Sea ◽  
The Arctic ◽  
Series Data ◽  
Sea Coast

<p>Coastal erosion rates are increasing along the Alaskan Beaufort Sea coast due to increases in wave action, the increasing length of the ice-free season, and warming permafrost. These eroding permafrost coastlines transport organic matter and inorganic nutrients to the Arctic Ocean, likely fueling biological production and CO<sub>2</sub> emissions. To assess the impacts of Arctic coastal erosion on nearshore carbon and nitrogen cycling, we examined geochemical profiles from eroding coastal bluffs and estimated annual organic matter fluxes from 1955 to 2018 for a 9 km stretch of coastline near Drew Point, Alaska. Additionally, we conducted a laboratory incubation experiment to examine dissolved organic carbon (DOC) leaching and biolability from coastal soils/sediments added to seawater.</p><p>Three permafrost cores (4.5 – 7.5 m long) revealed that two distinct horizons compose eroding bluffs near Drew Point: Holocene age, organic-rich (~12-45% total organic carbon; TOC) terrestrial soils and lacustrine sediments, and below, Late Pleistocene age marine sediments with lower organic matter content (~1% TOC), lower carbon to nitrogen ratios, and higher δ<sup>13</sup>C-TOC values. Organic matter stock estimates from the cores, paired with remote sensing time-series data, show that erosional TOC fluxes from this study coastline averaged 1,369 kg C m<sup>−1</sup> yr<sup>−1</sup> during the 21<sup>st</sup> century, nearly double the average flux of the previous half century. Annual TOC flux from this 9 km coastline is now similar to the annual TOC flux from the Kuparuk River, the third largest river draining the North Slope of Alaska.</p><p>Experimental work demonstrates that there are distinct differences in DOC leaching yields and the fraction of biodegradable DOC across soil/sediment horizons. When core samples were submerged in seawater for 24 hours, the Holocene age organic-rich permafrost leached the most DOC in seawater (~6.3 mg DOC g<sup>-1</sup> TOC), compared to active layer soils and Late-Pleistocene marine-derived permafrost (~2.5 mg DOC g<sup>-1</sup> TOC). Filtered leachates were then incubated aerobically in the dark for 26 and 90 days at 20°C to examine biodegradable DOC (i.e. the proportion of DOC lost due to microbial uptake or remineralization). Of this leached DOC, Late Pleistocene permafrost was the most biolabile over 90 days (31 ± 7%), followed by DOC from active layer soils (24 ± 5%) and Holocene-age permafrost (14% ± 3%). If we scale these results to a typical 4 m tall eroding bluff at Drew Point, we expect that ~341 g DOC m<sup>-2 </sup>will rapidly leach, of which ~25% is biodegradable. These results demonstrate that eroding permafrost bluffs are an increasingly important source of biolabile DOC, likely contributing to greenhouse gas emissions and marine production in the coastal environment.</p>

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.

Characteristics of organic carbon in surface sediments of Laptev Sea shelf

2020 ◽  
Author(s):  
Irina Oberemok ◽  
Elena Gershelis ◽  
Andrey Grin’ko ◽  
Alexey Ruban ◽  
Elizaveta Klevantseva ◽  
...  
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Coastal Erosion ◽  
Surface Sediments ◽  
Oxygen Index ◽  
Outer Shelf ◽  
The Arctic ◽  
Laptev Sea ◽  
Shelf Sediments ◽  
The Laptev Sea

<p>Accelerating coastal erosion and enhancing river sediment discharge are expected to greatly increase the delivery of terrestrial organic carbon (terrOC) to the Arctic Ocean. Remobilized terrOC may be buried in shallow or outer shelf sediments, degraded and translocated to the deeper basins, or remineralized in the water column causing a positive feedback to amplified global warming. The East Siberian Arctic Shelf (ESAS), represented by the Laptev Sea, the East Siberian Sea, and the Russian part of the Chukchi Sea, is the widest and shallowest continental shelf of the World Ocean. In the current study, we investigated surface sediment samples collected across the Laptev Sea shelf (from the coastline to the outer shelf) during the Arctic expedition onboard the Russian <em>R/V Academician M. Keldysh</em> during fall 2018.</p><p>We analyzed 16 samples for bulk (TOC, <em>δ</em>13C) and molecular (distribution and concentration of n-alkanes and PAHs) parameters. We also performed Rock-Eval (RE) analysis in order to compare its results with the signatures provided by traditional geochemical tracers and thereby to gain new insights into the sources of organic matter in modern surface sediments. In addition, a grain-size analysis was carried out to reveal hydrodynamic control on the organic carbon transport across the studied transect. Using a combination of traditional molecular interpretations (performed in this study and published earlier) and RE parameters (Hydrogen index, Oxygen index and T<sub>peak</sub>) we attempted to distinguish riverine input and coastal erosion and disentangle processes of terrOC degradation and its replacement with fresh/marine OC during cross-shelf transport. Overall, a strong decrease of terrigenous contribution to the sedimentary organic carbon was observed on molecular level with increasing distance from the coast. According to the RE data, intensive terrOC degradation takes place in the shallow and mid-shelf sediments which is traced by sharply increasing oxygen index. The clear correlation between OI and the clay content points toward the perception that mineral matrix do not seem to be such good protector as expected, and intensive microbial degradation of the sedimentary organic matter contained in fine particles occurs during repeated resuspension.</p><p>This research is supported by Russian Science Foundation, project # 19-77-00067.</p>

scholarly journals GDGT distributions in the East Siberian Sea: implications for organic carbon export, burial and degradation

2015 ◽  
Vol 12 (1) ◽  
pp. 637-674 ◽  
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 ◽  
Coastal Sediments ◽  
The Arctic ◽  
Rapid Reduction ◽  
Fluvial Erosion ◽  
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 "Yedoma" 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 that OC on the shelf is not only sourced from fluvial erosion, but 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.

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

<p>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 –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 (δ13C-OC) and ammonium. C/N-ratios, δ13C-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 >70% and >50%, respectively. Whereas δ13C-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.</p>

scholarly journals Permafrost-Affected Soils of the Russian Arctic and their Carbon Pools

2014 ◽  
Vol 6 (1) ◽  
pp. 619-655
Author(s):  
S. Zubrzycki ◽  
L. Kutzbach ◽  
E.-M. Pfeiffer
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Soil Organic Carbon ◽  
Carbon Sink ◽  
Global Climate ◽  
Fundamental Property ◽  
Climate System ◽  
The Arctic ◽  
Quaternary Period ◽  
Permafrost Regions

Abstract. Permafrost-affected soils have accumulated enormous pools of organic matter during the Quaternary Period. The area occupied by these soils amounts to more than 8.6 million km2, which is about 27% of all land areas north of 50° N. Therefore, permafrost-affected soils are considered to be one of the most important cryosphere elements within the climate system. Due to the cryopedogenic processes that form these particular soils and the overlying vegetation that is adapted to the arctic climate, organic matter has accumulated to the present extent of up to 1024 Pg (1 Pg = 1015 g = 1 Gt) of soil organic carbon stored within the uppermost three meters of ground. Considering the observed progressive climate change and the projected polar amplification, permafrost-affected soils will undergo fundamental property changes. Higher turnover and mineralization rates of the organic matter are consequences of these changes, which are expected to result in an increased release of climate-relevant trace gases into the atmosphere. As a result, permafrost regions with their distinctive soils are likely to trigger an important tipping point within the global climate system, with additional political and social implications. The controversy of whether permafrost regions continue accumulating carbon or already function as a carbon source remains open until today. An increased focus on this subject matter, especially in underrepresented Siberian regions, could contribute to a more robust estimation of the soil organic carbon pool of permafrost regions and at the same time improve the understanding of the carbon sink and source functions of permafrost-affected soils.

scholarly journals Potential Production of Carbon Gases and Their Responses to Paleoclimate Conditions: An Example From Xiaolongtan Basin, Southeast Tibetan Plateau

2021 ◽  
Vol 9 ◽  
Author(s):  
Gen Wang ◽  
Yongli Wang ◽  
Zhifu Wei ◽  
Zepeng Sun ◽  
Wei He ◽  
...  
Keyword(s):  
Organic Matter ◽  
Tibetan Plateau ◽  
Low Temperature ◽  
Organic Carbon ◽  
Carbon Cycle ◽  
Higher Plants ◽  
The Tibetan Plateau ◽  
Climate Conditions ◽  
Burial Flux ◽  
Carbon Gases

Uplift of the Tibetan Plateau plays a significant and lasting role in the variations of climate conditions and global carbon cycle. However, our knowledge is limited due to the lack of long-sequence records revealing rates of CO2 and CH4 production, hampering our understanding of the relationship between paleoclimatic conditions, carbon cycling and greenhouse gas flux. Here, we present a combination of paleoclimate records and low-temperature thermal simulation results from sediments of the Xiaolongtan Basin at the southeastern margin of the Qinghai-Tibetan Plateau, spanning the late Miocene (14.1 ∼ 11.6 Ma). The n-alkane-derived proxies suggested that the sources of organic matter were obviously different: a mixed source including lower organisms and terrestrial higher plants for the Dongshengqiao Formation from 14.1 to 12.6 Ma, and a predominant contribution from terrestrial higher plants for Xiaolongtan Formation between 12.6 and 11.6 Ma. The paleoclimate was generally warm and humid as reflected by the lipid biomarkers, consistent with previous studies. In addition, the carbon gases (including CO2 and hydrocarbon gases) generated by the low-temperature thermal simulation experiments indicated a production rate of CO2 and CH4 were as high as 88,000 ml/kg rock and 4,000 ml/kg rock, respectively, implying there were certain amounts of carbon gases generated and released into the atmosphere during their shallow burial stage. Besides, the calculated production rate of carbon gases and the estimated burial flux of organic carbon varied in response to the variations of paleoclimate conditions. Based on these observations, we propose that the climate conditions predominantly controlled the formation and accumulation of organic matter, which consequently affected the production of carbon gases and burial flux of organic carbon. The results presented here may provide a significant insight into the carbon cycle in the southeast of the Tibetan Plateau.

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