scholarly journals Distinguishing between old and modern permafrost sources in the northeast Siberian land–shelf system with compound-specific <i>δ</i><sup>2</sup>H analysis

2017 ◽  
Vol 11 (4) ◽  
pp. 1879-1895 ◽  
Author(s):  
Jorien E. Vonk ◽  
Tommaso Tesi ◽  
Lisa Bröder ◽  
Henry Holmstrand ◽  
Gustaf Hugelius ◽  
...  
Keyword(s):  
Isotope Composition ◽  
Quantitative Measure ◽  
The Arctic ◽  
Near Surface ◽  
Leaf Wax ◽  
Leaf Waxes ◽  
Shelf Slope ◽  
Siberian Arctic ◽  
Long Chain ◽  
Ice Complex

Abstract. Pleistocene ice complex permafrost deposits contain roughly a quarter of the organic carbon (OC) stored in permafrost (PF) terrain. When permafrost thaws, its OC is remobilized into the (aquatic) environment where it is available for degradation, transport or burial. Aquatic or coastal environments contain sedimentary reservoirs that can serve as archives of past climatic change. As permafrost thaw is increasing throughout the Arctic, these reservoirs are important locations to assess the fate of remobilized permafrost OC.We here present compound-specific deuterium (δ2H) analysis on leaf waxes as a tool to distinguish between OC released from thawing Pleistocene permafrost (ice complex deposits; ICD) and from thawing Holocene permafrost (from near-surface soils). Bulk geochemistry (%OC; δ13C; %total nitrogen, TN) was analyzed as well as the concentrations and δ2H signatures of long-chain n-alkanes (C21 to C33) and mid- to long-chain n-alkanoic acids (C16 to C30) extracted from both ICD-PF samples (n =  9) and modern vegetation and O-horizon (topsoil-PF) samples (n =  9) from across the northeast Siberian Arctic. Results show that these topsoil-PF samples have higher %OC, higher OC ∕ TN values and more depleted δ13C-OC values than ICD-PF samples, suggesting that these former samples trace a fresher soil and/or vegetation source. Whereas the two investigated sources differ on the bulk geochemical level, they are, however, virtually indistinguishable when using leaf wax concentrations and ratios. However, on the molecular isotope level, leaf wax biomarker δ2H values are statistically different between topsoil PF and ICD PF. For example, the mean δ2H value of C29 n-alkane was −246 ± 13 ‰ (mean ± SD) for topsoil PF and −280 ± 12 ‰ for ICD PF. With a dynamic isotopic range (difference between two sources) of 34 to 50 ‰; the isotopic fingerprints of individual, abundant, biomarker molecules from leaf waxes can thus serve as endmembers to distinguish between these two sources. We tested this molecular δ2H tracer along with another source-distinguishing approach, dual-carbon (δ13C–Δ14C) isotope composition of bulk OC, for a surface sediment transect in the Laptev Sea. Results show that general offshore patterns along the shelf-slope transect are similar, but the source apportionment between the approaches vary, which may highlight the advantages of either. This study indicates that the application of δ2H leaf wax values has potential to serve as a complementary quantitative measure of the source and differential fate of OC thawed out from different permafrost compartments.

scholarly journals Distinguishing between old and modern permafrost sources with compound-specific δ<sup>2</sup>H analysis

2017 ◽  
Author(s):  
Jorien E. Vonk ◽  
Tommaso Tesi ◽  
Lisa Bröder ◽  
Henry Holmstrand ◽  
Gustaf Hugelius ◽  
...  
Keyword(s):  
Isotope Composition ◽  
Quantitative Measure ◽  
The Arctic ◽  
Near Surface ◽  
Leaf Wax ◽  
Leaf Waxes ◽  
Shelf Slope ◽  
Alkanoic Acids ◽  
Long Chain ◽  
Ice Complex

Abstract. Pleistocene ice complex permafrost deposits contain roughly a quarter of the organic carbon (OC) stored in permafrost terrain. When permafrost thaws, its OC is remobilized into the (aquatic) environment where it is available for degradation, transport or burial. Aquatic or coastal environments contain sedimentary reservoirs that can serve as archives of past climatic change. As permafrost thaw is increasing throughout the Arctic, these reservoirs are important locations to assess the fate of remobilized permafrost OC. We here present compound-specific deuterium (δ2H) analysis on leaf waxes as a tool to distinguish between OC released from thawing Pleistocene permafrost (Ice Complex Deposits; ICD) and from thawing Holocene permafrost (from near-surface soils). Bulk geochemistry (%OC, δ13C, %total nitrogen; TN) was analyzed as well as the concentrations and δ2H signatures of long-chain n-alkanes (C21 to C33) and mid/long-chain n-alkanoic acids (C16 to C30) extracted from both ICD-PF samples (n = 9) and modern vegetation/O-horizon (Topsoil-PF) samples (n = 9) from across the northeast Siberian Arctic. Results show that these Topsoil-PF samples have higher %OC, higher OC/TN values, and more depleted δ13C-OC values than ICD-PF samples, suggesting that these former samples trace a fresher soil and/or vegetation source. Median concentrations of high-molecular weight n-alkanes (sum of C25-C27-C29-C31) were 210 ± 350 µg/gOC (median ± IQR) for Topsoil-PF and 250 ± 81 µg/gOC for ICD-PF samples. Long-chain n-alkanoic acids (sum of C22-C24-C26-C28) were more abundant than long-chain n-alkanes, both in Topsoil-PF samples (4700 ± 3400 µg/gOC) and in ICD samples (6630 ± 3500 µg/gOC). Whereas the two investigated sources differ on the bulk geochemical level, they are, however, virtually indistinguishable when using leaf wax concentrations and ratios. However, on the molecular-isotope level, leaf wax biomarker δ2H values are statistically different between Topsoil-PF and ICD-PF. The mean δ2H value of C29 n-alkane was −246 ± 13 ‰ (mean ± stdev) for Topsoil-PF and −280 ± 12 ‰ for ICD-PF, whereas the C31 n-alkane was −247 ± 23 ‰ for Topsoil-PF and −297 ± 15 ‰ for ICD-PF. The C28 n-alkanoic acid δ2H value was −220 ± 15 ‰ for Topsoil-PF and −267 ± 16 ‰ for ICD-PF. With a dynamic isotopic range (difference between two sources) of 34 to 50 ‰, the isotopic fingerprints of individual, abundant, biomarker molecules from leaf waxes can thus serve as end-members to distinguish between these two sources. We tested this molecular δ2H tracer along with another source-distinguishing approach, dual-carbon (δ13C-δ14C) isotope composition of bulk OC, for a surface sediment transect in the Laptev Sea. Results show that general offshore patterns along the shelf-slope transect are similar, but the source apportionment between the approaches vary, which may highlight the advantages of either. The δ2H molecular approach has the advantage that it circumvents uncertainties related to a marine end-member, yet the δ13C-δ14C approach has the advantage that it represents the bulk OC fraction thereby avoiding issues related to the molecular-bulk upscaling challenge. This study indicates that the application of δ2H leaf wax values has potential to serve as a complementary quantitative measure of the source and differential fate of OC thawed out from different permafrost compartments.

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

2017 ◽  
Vol 14 (9) ◽  
pp. 2283-2292 ◽  
Author(s):  
Célia J. Sapart ◽  
Natalia Shakhova ◽  
Igor Semiletov ◽  
Joachim Jansen ◽  
Sönke Szidat ◽  
...  
Keyword(s):  
Isotope Composition ◽  
Sediment Cores ◽  
Isotope Analysis ◽  
Age Determination ◽  
Unknown Origin ◽  
Arctic Shelf ◽  
The Arctic ◽  
Small Contribution ◽  
Siberian Arctic ◽  
Subsea Permafrost

Abstract. The Arctic Ocean, especially the East Siberian Arctic Shelf (ESAS), has been proposed as a significant source of methane that might play an increasingly important role in the future. However, the underlying processes of formation, removal and transport associated with such emissions are to date strongly debated. CH4 concentration and triple isotope composition were analyzed on gas extracted from sediment and water sampled at numerous locations on 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 isotope data reveal the predominant occurrence of CH4 that is not of thermogenic origin as it has long been thought, but resultant from microbial CH4 formation. At some locations, meltwater from buried meteoric ice and/or old organic matter preserved in the subsea permafrost were used as substrates. 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 sediment data suggest that at locations where bubble plumes have been observed, CH4 can escape anaerobic oxidation in the surface sediment.

scholarly journals Late Quaternary climate and environmental reconstruction based on leaf wax analyses in the loess sequence of Möhlin, Switzerland

2017 ◽  
Vol 66 (2) ◽  
pp. 91-100
Author(s):  
Lorenz Wüthrich ◽  
Marcel Bliedtner ◽  
Imke Kathrin Schäfer ◽  
Jana Zech ◽  
Fatemeh Shajari ◽  
...  
Keyword(s):  
Radiocarbon Dating ◽  
Late Quaternary ◽  
Marine Isotope Stage ◽  
Environmental Reconstruction ◽  
Moisture Source ◽  
Leaf Wax ◽  
Mis 3 ◽  
Quaternary Climate ◽  
Leaf Waxes ◽  
Long Chain

Abstract. We present the results of leaf wax analyses (long-chain n-alkanes) from the 6.8 m deep loess sequence of Möhlin, Switzerland, spanning the last  ∼  70 kyr. Leaf waxes are well preserved and occur in sufficient amounts only down to 0.4 m and below 1.8 m depth, so no paleoenvironmental reconstructions can be done for marine isotope stage (MIS) 2. Compound-specific δ2Hwax analyses yielded similar values for late MIS 3 compared to the uppermost samples, indicating that various effects (e.g., more negative values due to lower temperatures, more positive values due to an enriched moisture source) cancel each other out. A pronounced  ∼  30 ‰ shift towards more negative values probably reflects more humid conditions before  ∼  32 ka. Radiocarbon dating of the n-alkanes corroborates the stratigraphic integrity of leaf waxes and their potential for dating loess–paleosol sequences (LPS) back to  ∼  30 ka.

Compositions and isotopic differences of iso- and anteiso-alkanes in black mangroves (Avicennia germinans) across a salinity gradient in a subtropical estuary

2016 ◽  
Vol 13 (4) ◽  
pp. 623 ◽  
Author(s):  
Ding He ◽  
Bernd R. T. Simoneit ◽  
Blanca Jara ◽  
Rudolf Jaffé
Keyword(s):  
Environmental Stress ◽  
Salinity Gradient ◽  
Carbon Number ◽  
Dry Weight ◽  
Avicennia Germinans ◽  
Stress Factors ◽  
Chemical Tracers ◽  
Leaf Wax ◽  
Leaf Waxes ◽  
Long Chain

Environmental contextMangroves dominate at the interface between land and sea, especially along tropical and subtropical coasts. To gain a better understanding of how mangroves respond to various environmental stress factors, we investigated the use of monomethylalkanes as potential chemical tracers for black mangroves. The application of these chemical tracers could elucidate how black mangroves respond to environmental stress such as sea level rise in mixed mangrove environments. AbstractA series of iso- and anteiso-monomethylalkanes (MMAs) with carbon numbers from C23 to C35 and C14 to C34 respectively were detected in Avicennia germinans. These compounds were present in varying amounts up to 54.1, 1.0 and 3.4µg g–1 dry weight in the leaves, bark and the crustose lichens attached to the bark of A. germinans respectively. These MMAs were not detected in the leaf waxes of Rhizophora mangle and Laguncularia racemosa, but were detected in significantly lower abundances (2–6% of that in A. germinans leaf wax) in the bark and lichen of R. mangle. Significant odd-carbon number distributions and even-carbon number distributions were observed for long chain (C ≥ 25) iso- (maximising at C31) and anteiso-MMAs (maximising at C32) respectively in A. germinans leaf wax. However, no obvious carbon number preferences were detected for bark and lichen. The long chain (LC) iso- and anteiso-MMAs in A. germinans leaf waxes were found to be enriched in 13C by 0.3–4.3 and 0.7–4.2 per mille (‰) compared to the n-alkanes with the same carbon numbers respectively across the salinity gradient of 19.7–32.0 practical salinity units (psu). In comparison, the LC iso- and anteiso-MMAs were found to be more depleted in D by 6.1–55.1 and 7.3–57.0 ‰ compared to the n-alkanes with same carbon numbers respectively. The results imply that A. germinans could be another important source of iso- and anteiso-alkanes in sediments and soils, and that these compounds could potentially be used as biomarkers for this species in mixed mangrove environments.

scholarly journals Leaf wax <i>n</i>-alkanes in modern plants and topsoils from eastern Georgia (Caucasus) – implications for reconstructing regional paleovegetation

2018 ◽  
Vol 15 (12) ◽  
pp. 3927-3936 ◽  
Author(s):  
Marcel Bliedtner ◽  
Imke K. Schäfer ◽  
Roland Zech ◽  
Hans von Suchodoletz
Keyword(s):  
Regional Scale ◽  
Chemical Degradation ◽  
Terrestrial Plants ◽  
Tropical Regions ◽  
Caucasus Region ◽  
Leaf Wax ◽  
Leaf Waxes ◽  
Southern Caucasus ◽  
Physical And Chemical ◽  
Long Chain

Abstract. Long-chain n-alkanes originate from leaf waxes of higher terrestrial plants, they are relatively resistant against physical and chemical degradation and are preserved in sediment archives for at least millennial timescales. Since their homologue patterns discriminate between vegetation forms, they were increasingly used for paleovegetation reconstructions during the last years. However, before any robust interpretation of the long-chain n-alkane patterns in sediment archives, reference samples from modern vegetation and topsoil material should be investigated at a regional scale. Apart from some temperate and tropical regions, such systematic regional studies on modern plant and topsoil material are still largely lacking.To test the potential of leaf wax-derived n-alkane patterns for paleoenvironmental studies in the semi-humid to semi-arid central southern Caucasus region, we investigated the influence of different vegetation forms on the leaf wax n-alkane signal in modern plants and topsoil material (0–5 cm) from eastern Georgia. We sampled (i) sites with grassland/herbs that included steppe, cultivated grassland and meadows, and (ii) sites that are dominated by deciduous hornbeam forests.The results show that long-chain n-alkanes originate from leaf waxes of higher terrestrial plants and that their homologue pattern allow to discriminate between different vegetation forms: n-Alkanes derived from sites with grassland/herbs are mainly dominated by C31, while n-alkanes derived from sites with deciduous trees/shrubs show high abundances of C29. Thus, long-chain n-alkanes have a great potential when used for regional paleovegetation reconstructions. Moreover, the n-alkane distributions of the topsoils do not show correlations with mean annual temperatures and precipitation along the investigated transect. As degradation of organic matter can affect the leaf wax n-alkane distribution, we further present an updated end-member model that includes our results, accounts for degradation effects and enables semi-quantitative reconstructions of past vegetation changes in the central southern Caucasus region.

scholarly journals A warm jet in a cold ocean

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Jennifer A. MacKinnon ◽  
Harper L. Simmons ◽  
John Hargrove ◽  
Jim Thomson ◽  
Thomas Peacock ◽  
...  
Keyword(s):  
The Arctic ◽  
Bering Strait ◽  
Near Surface ◽  
Ice Melt ◽  
Beaufort Gyre ◽  
The Pacific ◽  
Climate Simulations ◽  
Initial Evolution ◽  
Forecast Models

AbstractUnprecedented quantities of heat are entering the Pacific sector of the Arctic Ocean through Bering Strait, particularly during summer months. Though some heat is lost to the atmosphere during autumn cooling, a significant fraction of the incoming warm, salty water subducts (dives beneath) below a cooler fresher layer of near-surface water, subsequently extending hundreds of kilometers into the Beaufort Gyre. Upward turbulent mixing of these sub-surface pockets of heat is likely accelerating sea ice melt in the region. This Pacific-origin water brings both heat and unique biogeochemical properties, contributing to a changing Arctic ecosystem. However, our ability to understand or forecast the role of this incoming water mass has been hampered by lack of understanding of the physical processes controlling subduction and evolution of this this warm water. Crucially, the processes seen here occur at small horizontal scales not resolved by regional forecast models or climate simulations; new parameterizations must be developed that accurately represent the physics. Here we present novel high resolution observations showing the detailed process of subduction and initial evolution of warm Pacific-origin water in the southern Beaufort Gyre.

Climate and land-use effects on hydrological and vegetation signals during the last three millennia: Evidence from sedimentary leaf waxes in southwestern Morocco

The Holocene ◽  
2021 ◽  
pp. 095968362098805
Author(s):  
Asmae Baqloul ◽  
Enno Schefuß ◽  
Martin Kölling ◽  
Lydie Dupont ◽  
Jeroen Groeneveld ◽  
...  
Keyword(s):  
Land Use ◽  
Carbon Isotope ◽  
Vegetation History ◽  
Isotope Composition ◽  
Stable Carbon Isotope ◽  
Economic Stress ◽  
Published Data ◽  
Leaf Waxes ◽  
Argan Tree ◽  
Precipitation Changes

The southwest of Morocco is considered to be an area of refuge within the Mediterranean region, hosting the endemic tropical Argan tree. This region is presently subject to severe droughts, desertification and land degradation, and likely facing increased climate variability and socio-economic stress in the future. Here, we use the stable hydrogen and carbon isotope composition (δD and δ13C) of plant-waxes in a high-resolution marine sediment core (GeoB8601-3) collected off Cape Ghir in southwestern Morocco, in combination with published data on pollen and XRF element ratios from the same archive. We aim to reconstruct the hydroclimate and vegetation history during the last 3000 years. Stable carbon isotope compositions of leaf waxes (δ13Cwax) show that natural vegetation in southwestern Morocco consists of C3 plants. Minor variations in δ13Cwax were positively correlated to changes in stable hydrogen isotope compositions of leaf waxes (δDwax) before 700 CE. Changes in rainfall amounts and water use efficiency indicate a clear vegetation response to precipitation changes and thus to climate forcing. After 700 CE, δDwax and δ13Cwax became de-coupled suggesting that the plant wax discharge and their isotope signals were no longer solely controlled by climate; the waxes likely mainly originate from the lowlands and carry an enriched (dry) δD signal but a depleted 13C signature. The depletion of δ13Cwax correlates with the increase of Argan pollen concentration in the record. The period between ~700 and 900 CE coincides with the Arabization of Morocco which had an impact on the demographic composition of the country leading to new agricultural habits and, as a result, on the land-use triggering a higher erosion of lowland material by the Souss River.

scholarly journals An Evaluation of Surface Atmospheric Changes over the Arctic Ocean for 2000–09 Using Recent Reanalyses

2015 ◽  
Vol 19 (2) ◽  
pp. 1-18 ◽  
Author(s):  
Ayan H. Chaudhuri ◽  
Rui M. Ponte
Keyword(s):  
Arctic Ocean ◽  
Extreme Event ◽  
Longwave Radiation ◽  
Remotely Sensed ◽  
Surface Radiation ◽  
Shortwave Radiation ◽  
The Arctic ◽  
Near Surface ◽  
The Arctic Ocean ◽  
Ice Retreat

Abstract The authors examine five recent reanalysis products [NCEP Climate Forecast System Reanalysis (CFSR), Modern-Era Retrospective Analysis for Research and Applications (MERRA), Japanese 25-year Reanalysis Project (JRA-25), Interim ECMWF Re-Analysis (ERA-Interim), and Arctic System Reanalysis (ASR)] for 1) trends in near-surface radiation fluxes, air temperature, and humidity, which are important indicators of changes within the Arctic Ocean and also influence sea ice and ocean conditions, and 2) fidelity of these atmospheric fields and effects for an extreme event: namely, the 2007 ice retreat. An analysis of trends over the Arctic for the past decade (2000–09) shows that reanalysis solutions have large spreads, particularly for downwelling shortwave radiation. In many cases, the differences in significant trends between the five reanalysis products are comparable to the estimated trend within a particular product. These discrepancies make it difficult to establish a consensus on likely changes occurring in the Arctic solely based on results from reanalyses fields. Regarding the 2007 ice retreat event, comparisons with remotely sensed estimates of downwelling radiation observations against these reanalysis products present an ambiguity. Remotely sensed observations from a study cited herewith suggest a large increase in downwelling summertime shortwave radiation and decrease in downwelling summertime longwave radiation from 2006 and 2007. On the contrary, the reanalysis products show only small gains in summertime shortwave radiation, if any; however, all the products show increases in downwelling longwave radiation. Thus, agreement within reanalysis fields needs to be further checked against observations to assess possible biases common to all products.

scholarly journals Numerical investigation of the Arctic ice-ocean boundary layer; implications for air-sea gas fluxes

2016 ◽  
Author(s):  
A. Bigdeli ◽  
B. Loose ◽  
S. T. Cole
Keyword(s):  
Sea Ice ◽  
Water Column ◽  
Mixed Layer ◽  
Mixed Layer Depth ◽  
The Arctic ◽  
Layer Depth ◽  
Near Surface ◽  
Resolution Model ◽  
Simplifying Assumptions ◽  
Vertical Spacing

Abstract. In ice-covered regions it can be challenging to determine air-sea exchange – for heat and momentum, but also for gases like carbon dioxide and methane. The harsh environment and relative data scarcity make it difficult to characterize even the physical properties of the ocean surface. Here, we seek a mechanistic interpretation for the rate of air-sea gas exchange (k) derived from radon-deficits. These require an estimate of the water column history extending 30 days prior to sampling. We used coarse resolution (36 km) regional configuration of the MITgcm with fine near surface vertical spacing (2 m) to evaluate the capability of the model to reproduce conditions prior to sampling. The model is used to estimate sea-ice velocity, concentration and mixed-layer depth experienced by the water column. We then compared the model results to existing field data including satellite, moorings and Ice-tethered profilers. We found that model-derived sea-ice coverage is 88 to 98 % accurate averaged over Beaufort Gyre, sea-ice velocities have 78 % correlation which resulted in 2 km/day error in 30 day trajectory of sea-ice. The model demonstrated the capacity to capture the broad trends in the mixed layer although with a bias and model water velocities showed only 29 % correlation with actual data. Overall, we find the course resolution model to be an inadequate surrogate for sparse data, however the simulation results are a slight improvement over several of the simplifying assumptions that are often made when surface ocean geochemistry, including the use of a constant mixed layer depth and a velocity profile that is purely wind-driven.

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